physicsworld--2020-11-24--MRS combines Spring and Fall meetings into virtual event

For nearly 50 years , researchers from around the world have converged in Boston for the Fall Meeting of the Materials Research Society .
This year , however , as a result of the Covid-19 pandemic , the meeting will be convened as a fully digital event in combination with the Spring Meeting , which was due to take place in Pheonix , Arizona , back in April .
The joint 2020 MRS Spring/Fall Meeting & Exhibit , scheduled for 27 November ̶ 4 December , will include the scientific programmes from both meetings , with a combination of live @ @ @ @ @ @ @ Northwestern University will give a plenary lecture on functional materials that enable small electronic devices to be integrated into the body , while a range of networking , Q & A sessions and professional development events are available to access before and after the meeting .
A virtual exhibit will enable attendees to interact directly with equipment vendors , with extended “ booth hours ” where delegates can chat with company representatives .
It is also an ideal opportunity to up to date with the latest technology developments – a few of which @ @ @ @ @ @ @ measurement platform from Lake Shore Cryotronics makes it quicker and more convenient to acquire high-precision Hall measurements .
Ideal for anyone studying semiconductor materials , the MeasureReady FastHall Station incorporates Lake Shore ’ s M91 FastHall controller into a tabletop system that enables simplified Hall measurements and reduces the time needed for experimental setup .
Along with the M91 measurement controller , the all-in-one station includes a Windows-based computer , a 1 T permanent magnet , a high-precision sample holder , and all the necessary software and cabling to provide a comprehensive range @ @ @ @ @ @ @ detect sample resistances up to 1 GΩ and mobilities as low as 0.01 cm2/V s –making it ideal for research into low-mobility materials .
Lake Shore ’ s patented FastHall method speeds up measurement times , while easy-to-use spring pin and solder sample holder cards accommodate up to 10 mm × 10 mm van der Pauw and Hall bar type samples .
The station also features an electronically shielded , low-noise sample space with guarded contacts , making it quicker and easier to derive accurate measurements of the carrier type , carrier concentration @ @ @ @ @ @ @ The system ’ s MeasureLINK-MCS software collects all the data , and provides standard sequences , charts , and test scripts that can be customized by the user .
In addition to performing complete Hall analyses and outputting all measured and derived values , detailed reports can be generated that include all the supporting intermediate data , so a researcher can readily confirm the integrity of the results .
Optional extras include a gate-bias instrument plus a liquid-nitrogen add-on to convert the standard room-temperature station to a cryogenically cooled sample space maintained at @ @ @ @ @ @ @ ) has become a crucial tool in both research and industry for studying the properties and structure of many different materials and devices .
In an online presentation that is now available to view on demand , Dr Vladimir Korolkov , a senior application scientist at AFM manufacturer Park Systems , highlights the use of AFMs to study the structure of polymer materials .
In the presentation , Korolkov explains how to exploit an AFM to resolve individual polymer chains in real space , which is particularly important because the properties of polymer @ @ @ @ @ @ @ and conformation of individual macromolecules as well as their monomer composition .
He also shows how an AFM can be used to acquire ultrahigh-resolution images of individual PTFE molecules on the semi-crystalline surface of a commercial Teflon tape .
Using these real-world polymer samples , Korolkov highlights the capabilities of Park Systems ’ NX20 AFM for high-speed acquisition of high-resolution images .
The NX20 is designed to study large samples and conduct multi-sample analyses , and comes with an automated interface that makes it easy for non-experts to acquire high-quality data .
The @ @ @ @ @ @ @ mode of Park ’ s SmartScan software , while automatic operation of the cantilever brings it safely into contact with the surface within just 10 seconds .
The NX20 also controls the scan speed based on the peaks and valleys of the sample surface , minimizing the scanning time while also acquiring a high-quality image .
When moving to a neighbouring location or zooming into a target , the system automatically applies a new optimal condition .
A unique atomic force microscope ( AFM ) from Quantum Design can easily be integrated into @ @ @ @ @ @ @ electron or scanning ion microscope ( SEM/FIB ) .
The AFSEM® Nano enables simultaneous operation of SEM , FIB , and AFM inside the vacuum chamber , allowing these complementary techniques to be combined without needing to transfer the sample or break the vacuum .
The AFSEM Nano directly correlates AFM functionality to SEM or FIB information at the same location on the sample .
This correlated functionality allows users to , for example , measure the real 3D-topography of their sample with ( sub ) -nanometer resolution inside their SEM or FIB @ @ @ @ @ @ @ of interest with the SEM and then use the AFM to measure the physical , electrical , or magnetic properties at the same location .
Combining the different techniques makes it easy to analyse samples with very different shapes or sizes .
Users can also obtain in-situ correlation of chemical ( EDX ) and crystallographic ( EBSD ) information , and achieve 3D subtractive tomography by combining FIB slicing with the mapping of nanomechanical properties using the AFM .
The AFSEM Nano is a laser-free AFM that exploits a self-sensing cantilever technology to @ @ @ @ @ @ @ the vacuum chamber .
Its open design allows for easy integration with other optional add-ons , such as tensile stages , nano-indentors or nano-manipulators .
2D layered perovskites have attracted huge research interest for their unique optoelectronic properties , helped enormously by the discovery that the most promising structures – usually hybrid organic–inorganic lead halides – can be prepared easily and cheaply using solution processing techniques .
Photoluminescent 2D perovskites have a direct bandgap with a narrow emission peak that can be tuned by changing the layer thickness and the material composition , @ @ @ @ @ @ @ in light-emitting diodes , phototransistors , lasers , and solar cells .
Materials company MilliporeSigma offers a range of fully synthesized layered 2D perovskites , including some of the most popular organolead halides .
Also available is a comprehensive portfolio of precursor materials , including lead halides , organohalides , and halide acids , as well as other key materials needed to fabricate 2D layered perovskites .

This year the Materials Research Society will replace its traditional Boston-based Fall Meeting with a virtual conference and exhibition
Virtual exhibit: this year’s Spring and Fall Meetings of the Materials Research Society will be combined into one online event. (Courtesy: Shutterstock/Ambelrip)
For nearly 50 years, researchers from around the world have converged in Boston for the Fall Meeting of the Materials Research Society. This year, however, as a result of the Covid-19 pandemic, the meeting will be convened as a fully digital event in combination with the Spring Meeting, which was due to take place in Pheonix, Arizona, back in April.
The joint 2020 MRS Spring/Fall Meeting & Exhibit, scheduled for 27 November ̶ 4 December, will include the scientific programmes from both meetings, with a combination of live and on-demand presentations. John Rogers of Northwestern University will give a plenary lecture on functional materials that enable small electronic devices to be integrated into the body, while a range of networking, Q&A sessions and professional development events are available to access before and after the meeting.
A virtual exhibit will enable attendees to interact directly with equipment vendors, with extended “booth hours” where delegates can chat with company representatives. It is also an ideal opportunity to up to date with the latest technology developments – a few of which are highlighted below.
Turnkey system delivers fast and precise Hall measurements
A fully integrated measurement platform from Lake Shore Cryotronics makes it quicker and more convenient to acquire high-precision Hall measurements. Ideal for anyone studying semiconductor materials, the MeasureReady FastHall Station incorporates Lake Shore’s M91 FastHall controller into a tabletop system that enables simplified Hall measurements and reduces the time needed for experimental setup.
Along with the M91 measurement controller, the all-in-one station includes a Windows-based computer, a 1 T permanent magnet, a high-precision sample holder, and all the necessary software and cabling to provide a comprehensive range of Hall measurements. The system can detect sample resistances up to 1 GΩ and mobilities as low as 0.01 cm2/V s –making it ideal for research into low-mobility materials.
The MeasureReady FastHall Station for Lake Shore Cryotronics provides an integrated solution for quick and easy Hall measurements. (Courtesy: Lake Shore Cryotronics)
Lake Shore’s patented FastHall method speeds up measurement times, while easy-to-use spring pin and solder sample holder cards accommodate up to 10 mm × 10 mm van der Pauw and Hall bar type samples. The station also features an electronically shielded, low-noise sample space with guarded contacts, making it quicker and easier to derive accurate measurements of the carrier type, carrier concentration, mobility, and Hall coefficient.
The system’s MeasureLINK-MCS software collects all the data, and provides standard sequences, charts, and test scripts that can be customized by the user. In addition to performing complete Hall analyses and outputting all measured and derived values, detailed reports can be generated that include all the supporting intermediate data, so a researcher can readily confirm the integrity of the results. Optional extras include a gate-bias instrument plus a liquid-nitrogen add-on to convert the standard room-temperature station to a cryogenically cooled sample space maintained at 77 K.
Large-sample AFM pinpoints polymer properties
Atomic force microscopy (AFM) has become a crucial tool in both research and industry for studying the properties and structure of many different materials and devices. In an online presentation that is now available to view on demand, Dr Vladimir Korolkov, a senior application scientist at AFM manufacturer Park Systems, highlights the use of AFMs to study the structure of polymer materials.
In the presentation, Korolkov explains how to exploit an AFM to resolve individual polymer chains in real space, which is particularly important because the properties of polymer materials are strongly influenced by the packing and conformation of individual macromolecules as well as their monomer composition. He also shows how an AFM can be used to acquire ultrahigh-resolution images of individual PTFE molecules on the semi-crystalline surface of a commercial Teflon tape.
The NX20 AFM from Park Systems is designed for failure analysis and large sample research. (Courtesy: Park Systems)
Using these real-world polymer samples, Korolkov highlights the capabilities of Park Systems’ NX20 AFM for high-speed acquisition of high-resolution images. The NX20 is designed to study large samples and conduct multi-sample analyses, and comes with an automated interface that makes it easy for non-experts to acquire high-quality data. The instrument supports single-click imaging through the auto mode of Park’s SmartScan software, while automatic operation of the cantilever brings it safely into contact with the surface within just 10 seconds.
The NX20 also controls the scan speed based on the peaks and valleys of the sample surface, minimizing the scanning time while also acquiring a high-quality image. When moving to a neighbouring location or zooming into a target, the system automatically applies a new optimal condition.
Single instrument combines AFM with scanning microscopy
A unique atomic force microscope (AFM) from Quantum Design can easily be integrated into the high-vacuum environment of almost any scanning electron or scanning ion microscope (SEM/FIB). The AFSEM® Nano enables simultaneous operation of SEM, FIB, and AFM inside the vacuum chamber, allowing these complementary techniques to be combined without needing to transfer the sample or break the vacuum.
The AFSEM Nano directly correlates AFM functionality to SEM or FIB information at the same location on the sample. This correlated functionality allows users to, for example, measure the real 3D-topography of their sample with (sub)-nanometer resolution inside their SEM or FIB system, or easily identify the region of interest with the SEM and then use the AFM to measure the physical, electrical, or magnetic properties at the same location.
Best of both worlds: the AFSEM Nano from Quantum Design can be integrated into the vacuum chamber of almost any scanning microscope. (Courtesy: Quantum Design)
Combining the different techniques makes it easy to analyse samples with very different shapes or sizes. Users can also obtain in-situ correlation of chemical (EDX) and crystallographic (EBSD) information, and achieve 3D subtractive tomography by combining FIB slicing with the mapping of nanomechanical properties using the AFM.
The AFSEM Nano is a laser-free AFM that exploits a self-sensing cantilever technology to avoid the need for optical alignment inside the vacuum chamber. Its open design allows for easy integration with other optional add-ons, such as tensile stages, nano-indentors or nano-manipulators.
Materials matter for 2D layered perovskite research
2D layered perovskites have attracted huge research interest for their unique optoelectronic properties, helped enormously by the discovery that the most promising structures – usually hybrid organic–inorganic lead halides – can be prepared easily and cheaply using solution processing techniques. Photoluminescent 2D perovskites have a direct bandgap with a narrow emission peak that can be tuned by changing the layer thickness and the material composition, and have been widely studied for applications in light-emitting diodes, phototransistors, lasers, and solar cells.
MilliporeSigma supplies the precursor materials needed to create 2D layered perovskites with different compositions and properties. (Courtesy: MilliporeSigma)
Materials company MilliporeSigma offers a range of fully synthesized layered 2D perovskites, including some of the most popular organolead halides. Also available is a comprehensive portfolio of precursor materials, including lead halides, organohalides, and halide acids, as well as other key materials needed to fabricate 2D layered perovskites.


physicsworld--2020-11-24--China launches sample-return mission to the Moon

China has successfully launched a mission to bring back rocks from the Moon– the first attempt to do so for nearly 45 years .
Chang ’ e-5 was launched at 4:30 a.m. local time today by a Long March 5 rocket from Wenchang Satellite Launch Center .
Once it lands on the Moon it is expected to grab up to two kilograms of soil from an area not previously sampled to better understand the evolution history of our closest neighbour .
Chang ’ e-5 , weighing 8.2 tonnes , consists of four parts : an ascender , lander , returner @ @ @ @ @ @ @ ’ s orbit , the ascender and lander will separate and touch down in the Mons Rümker region — a volcanic mound in the northwestern part of the Moon ’ s near side .
The lander will use a panoramic camera , spectrometer and ground-penetrating radar among other payloads to document the landing site .
It will also use a robotic arm to scoop up small rocks from the surface and drill up to 2 m into the ground .
Once the sampling is done and before the lunar night falls , the @ @ @ @ @ @ @ of the lander and dock with the returner-orbiter in orbit .
The sample container is then transferred to the returner , which will head back to the Earth .
Using a technology called ballistic re-entry , the returner will safely travel through the Earth ’ s atmosphere towards a planned landing site in Inner Mongolia , north China .
It is expected that most of the returned samples will be stored at the National Astronomical Observatories of China , Chinese Academy of Science , in Beijing with possible access by foreign scientists through @ @ @ @ @ @ @ that part of Mons Rümker might have formed 1-2 billion years ago , being much younger than the sites visited by US and Soviet sample-return missions that were over three billion years old .
Back in the 1960s and 1970s , six US Apollo crewed landings brought back 382 kg of rocks from the Moon while three Soviet Luna robotic missions returned 0.326 kg .
The samples from the Chinese mission will help scientists improve their model to estimate the age of surfaces in the solar system , from rocky planets such as @ @ @ @ @ @ @ ages are roughly defined by crater densities : more craters , older surfaces .
If the age of Chang ’ e-5 samples are confirmed to be 1-2 billion years , it may challenge our current theory on the formation of the Moon , which should have cooled off by that time due to its small size and limited “ heat budget ” .
Scientists would need to find out what had fuelled those volcanic eruptions .
“ [ Chang ’ e-5 ] can lead to a whole new understanding of recent volcanisms on @ @ @ @ @ @ @ from the University of Notre Dame in the US .
“ The new samples from Chang ’ e-5 will give us a way to quantify the younger end of the crater-counting curve.
” As China ’ s most complex and ambitious lunar mission so far , Chang ’ e-5 could go wrong in many ways .
“ Safe return is the most important thing for a first attempt , ” adds Neal .
Brett Denevi from the Applied Physics Laboratory , Johns Hopkins University , who has analyzed Apollo lunar samples , notes @ @ @ @ @ @ @ the best places to go ” for a lunar sample-return mission .
“ That ’ s why this mission has attracted broad , international interests , ” she adds , cautioning that 2 kg is an ambitious target .
“ Two grams can already teach us a lot , ” she says .
China is also working on multiple follow-up lunar missions that will eventually lead to a human mission in the 2030s .
These include Chang ’ e-6 , which will return samples from the south pole , as well as Chang @ @ @ @ @ @ @ survey of the south polar region .
With renewed interest in lunar exploration and the advances in sampling and analytic capabilities , space-policy expert John Logsdon from George Washington University says that Chang ’ e-5 could “ set a new standard ” for robotic lunar exploration .
“ Chang ’ e-5 is an important step in the plan , ” says Logsdon .
“ One that deserves close attention .
”

Lift-off: Chang’e-5 will attempt to bring back 2 kg of lunar material to study the evolution history of our closest neighbour (Courtesy: CNSA)
China has successfully launched a mission to bring back rocks from the Moon– the first attempt to do so for nearly 45 years. Chang’e-5 was launched at 4:30 a.m. local time today by a Long March 5 rocket from Wenchang Satellite Launch Center. Once it lands on the Moon it is expected to grab up to two kilograms of soil from an area not previously sampled to better understand the evolution history of our closest neighbour.
Chang’e-5, weighing 8.2 tonnes, consists of four parts: an ascender, lander, returner and orbiter. Upon entering the Moon’s orbit, the ascender and lander will separate and touch down in the Mons Rümker region — a volcanic mound in the northwestern part of the Moon’s near side. The lander will use a panoramic camera, spectrometer and ground-penetrating radar among other payloads to document the landing site. It will also use a robotic arm to scoop up small rocks from the surface and drill up to 2 m into the ground.
Chang’e-5 is an important step in the plan. One that deserves close attention John Logsdon
Once the sampling is done and before the lunar night falls, the ascender will lift off from the top of the lander and dock with the returner-orbiter in orbit. The sample container is then transferred to the returner, which will head back to the Earth. Using a technology called ballistic re-entry, the returner will safely travel through the Earth’s atmosphere towards a planned landing site in Inner Mongolia, north China. It is expected that most of the returned samples will be stored at the National Astronomical Observatories of China, Chinese Academy of Science, in Beijing with possible access by foreign scientists through collaboration with Chinese colleagues.
Rock collector
Scientists believe that part of Mons Rümker might have formed 1-2 billion years ago, being much younger than the sites visited by US and Soviet sample-return missions that were over three billion years old. Back in the 1960s and 1970s, six US Apollo crewed landings brought back 382 kg of rocks from the Moon while three Soviet Luna robotic missions returned 0.326 kg. The samples from the Chinese mission will help scientists improve their model to estimate the age of surfaces in the solar system, from rocky planets such as Mars and Mercury to asteroids. Surface ages are roughly defined by crater densities: more craters, older surfaces.
If the age of Chang’e-5 samples are confirmed to be 1-2 billion years, it may challenge our current theory on the formation of the Moon, which should have cooled off by that time due to its small size and limited “heat budget”. Scientists would need to find out what had fuelled those volcanic eruptions. “[Chang’e-5] can lead to a whole new understanding of recent volcanisms on the Moon,” says Clive Neal from the University of Notre Dame in the US. “The new samples from Chang’e-5 will give us a way to quantify the younger end of the crater-counting curve.”
As China’s most complex and ambitious lunar mission so far, Chang’e-5 could go wrong in many ways. “Safe return is the most important thing for a first attempt,” adds Neal. Brett Denevi from the Applied Physics Laboratory, Johns Hopkins University, who has analyzed Apollo lunar samples, notes that China has picked “one of the best places to go” for a lunar sample-return mission. “That’s why this mission has attracted broad, international interests,” she adds, cautioning that 2 kg is an ambitious target. “Two grams can already teach us a lot,” she says. Read more Exploring the far side
China is also working on multiple follow-up lunar missions that will eventually lead to a human mission in the 2030s. These include Chang’e-6, which will return samples from the south pole, as well as Chang’e-7 that will perform a detailed survey of the south polar region. With renewed interest in lunar exploration and the advances in sampling and analytic capabilities, space-policy expert John Logsdon from George Washington University says that Chang’e-5 could “set a new standard” for robotic lunar exploration. “Chang’e-5 is an important step in the plan,” says Logsdon. “One that deserves close attention.”


physicsworld--2020-11-24--Perovskites could be platforms for exciton condensates

Organic–inorganic perovskite materials are usually studied in the context of making solar cells and other photovoltaic devices .
Now researchers from the Institute of Semiconductors at the Chinese Academy of Sciences in Beijing have shown that these hybrid halide materials could also be ideal platforms for realizing Bose–Einstein condensates of excitons ( electron–hole pairs ) .
Such condensates , which appear as vortex patterns , could be produced at liquid nitrogen temperatures – positively balmy , by the standard of the field – thanks to the long lifetimes of the excitons in the materials and their huge binding energies .
@ @ @ @ @ @ @ all the bosonic atoms or particles in a gas collapse into the same quantum ground state and can therefore be described by the same wavefunction .
Such collapses are triggered by cooling the gas until the de Broglie wavelength of its constituent atoms or particles is comparable to the distance between them .
Once in this state , the atoms or particles behave as a superfluid , flowing without friction .
Researchers made the first BEC in 1995 from rubidium atoms .
Since then , condensates have been observed in various other types @ @ @ @ @ @ @ and magnons as well as other species of atoms and molecules .
In all cases , however , the phenomenon has only appeared at ultralow temperatures of no more than a few Kelvin above absolute zero .
To make BECs easier to study – and perhaps also to put their amazing properties to practical use – researchers have long sought to increase the temperature at which they form .
One way of doing this might be to make a BEC using excitons , which are bosons composed of the bound states of two @ @ @ @ @ @ @ a positively charged hole , or electron vacancy .
These fermions are bound together via weak Coulomb interactions that cause them to form dipoles .
Since these bound states are much lighter than atoms , they can be packed together with higher density – meaning that they ought to Bose condense at much higher temperatures .
That , at least , is the theory .
Unfortunately , previous attempts to make such excitonic BECs – for example in semiconductor wells and graphene – have succeeded only at disappointingly low temperatures of around 1 @ @ @ @ @ @ @ binding energy in these material systems .
In their new work , researchers led by Kai Chang studied a 2D hybrid perovskite with the chemical formula ( PEA ) PbI .
Perovskites in general are promising thin-film solar-cell materials thanks to the fact that they can absorb light over a broad range of solar spectrum wavelengths .
Electrons and holes have a long lifetime in these materials too ( that is , they can diffuse through the material over long lengths ) and this is the property that Chang and colleagues focused on @ @ @ @ @ @ @ has a stable layered structure comprising layers of [ PbI ] 4− octahedra and long-chain organic molecules with the formula C H C H NH + ( abbreviated PEA+ ) .
The inorganic PbI layers are sandwiched between two organic layers and have effective potential barriers with energies of 8.1 eV .
These barriers make ( PEA ) PbI behave like stacked quantum wells confined by “ hard-wall ” energy potentials , the researchers explain .
Using first-principles calculations and a theoretical framework known as the Keldysh model , the researchers calculated a @ @ @ @ @ @ @ for the excitons in monolayer ( PEA ) PbI , a value that agrees with that obtained in laboratory experiments .
“ The Keldysh model is a standard treatment for describing 2D excitons with ‘ unscreened ’ Coulomb interactions and the large exciton binding energy we calculated means that the critical temperature of the exciton BEC could approach the liquid nitrogen regime ( 77 K ) , ” team member Dong Zhang tells Physics World .
The researchers studied their flakes of ( PEA ) PbI further by applying an electric field perpendicular @ @ @ @ @ @ @ found that the applied field slightly changed the material ’ s binding energy , while also causing all the electron–hole dipoles to line up in the same direction .
In this situation , the interaction between the dipoles becomes repulsive .
When the researchers then “ pumped ” the flakes of the ( PEA ) PbI using pulses from a laser , they found that the repulsive dipole–dipole interaction created by the perpendicular electric field can drive the laterally confined excitons into various vortex patterns .
The time it takes for these vortices @ @ @ @ @ @ @ the lifetime of the exciton itself and the result is a stable pattern with a certain number of vortices rotating at the centre .
Members of the team , who report their work in Chinese Physics Letters , say they now plan to study exciton BEC in few-layered hybrid perovskites as opposed to just monolayer ones .
“ We will also be looking at how to manipulate exciton vortices and make vortex-based information-storage porotype devices , ” Zhang says .

Laser pumping applied on a perovskite monolayer and the emerging exciton vortices. Courtesy: D Zhang
Organic–inorganic perovskite materials are usually studied in the context of making solar cells and other photovoltaic devices. Now researchers from the Institute of Semiconductors at the Chinese Academy of Sciences in Beijing have shown that these hybrid halide materials could also be ideal platforms for realizing Bose–Einstein condensates of excitons (electron–hole pairs). Such condensates, which appear as vortex patterns, could be produced at liquid nitrogen temperatures – positively balmy, by the standard of the field – thanks to the long lifetimes of the excitons in the materials and their huge binding energies.
Bose–Einstein condensation (BEC) occurs when all the bosonic atoms or particles in a gas collapse into the same quantum ground state and can therefore be described by the same wavefunction. Such collapses are triggered by cooling the gas until the de Broglie wavelength of its constituent atoms or particles is comparable to the distance between them. Once in this state, the atoms or particles behave as a superfluid, flowing without friction.
Exciton BECs
Researchers made the first BEC in 1995 from rubidium atoms. Since then, condensates have been observed in various other types of particles, including polaritons, photons and magnons as well as other species of atoms and molecules. In all cases, however, the phenomenon has only appeared at ultralow temperatures of no more than a few Kelvin above absolute zero.
To make BECs easier to study – and perhaps also to put their amazing properties to practical use – researchers have long sought to increase the temperature at which they form. One way of doing this might be to make a BEC using excitons, which are bosons composed of the bound states of two fermions: a negatively charged electron and a positively charged hole, or electron vacancy. These fermions are bound together via weak Coulomb interactions that cause them to form dipoles. Since these bound states are much lighter than atoms, they can be packed together with higher density – meaning that they ought to Bose condense at much higher temperatures.
That, at least, is the theory. Unfortunately, previous attempts to make such excitonic BECs – for example in semiconductor wells and graphene – have succeeded only at disappointingly low temperatures of around 1 K, due to the small exciton binding energy in these material systems.
Calculating the exciton binding energy
In their new work, researchers led by Kai Chang studied a 2D hybrid perovskite with the chemical formula (PEA) 2 PbI 4 . Perovskites in general are promising thin-film solar-cell materials thanks to the fact that they can absorb light over a broad range of solar spectrum wavelengths. Electrons and holes have a long lifetime in these materials too (that is, they can diffuse through the material over long lengths) and this is the property that Chang and colleagues focused on.
The team’s chosen perovskite has a stable layered structure comprising layers of [PbI 6 ]4− octahedra and long-chain organic molecules with the formula C 6 H 5 C 2 H 4 NH 3 + (abbreviated PEA+). The inorganic PbI 4 layers are sandwiched between two organic layers and have effective potential barriers with energies of 8.1 eV. These barriers make (PEA) 2 PbI 4 behave like stacked quantum wells confined by “hard-wall” energy potentials, the researchers explain.
Using first-principles calculations and a theoretical framework known as the Keldysh model, the researchers calculated a binding energy as high as 238.5 meV for the excitons in monolayer (PEA) 2 PbI 4 , a value that agrees with that obtained in laboratory experiments. “The Keldysh model is a standard treatment for describing 2D excitons with ‘unscreened’ Coulomb interactions and the large exciton binding energy we calculated means that the critical temperature of the exciton BEC could approach the liquid nitrogen regime (77 K),” team member Dong Zhang tells Physics World.
Vortex patterns
The researchers studied their flakes of (PEA) 2 PbI 4 further by applying an electric field perpendicular to them. From this, they found that the applied field slightly changed the material’s binding energy, while also causing all the electron–hole dipoles to line up in the same direction. In this situation, the interaction between the dipoles becomes repulsive.
When the researchers then “pumped” the flakes of the (PEA) 2 PbI 4 using pulses from a laser, they found that the repulsive dipole–dipole interaction created by the perpendicular electric field can drive the laterally confined excitons into various vortex patterns. The time it takes for these vortices to evolve is on a par with the lifetime of the exciton itself and the result is a stable pattern with a certain number of vortices rotating at the centre.
Members of the team, who report their work in Chinese Physics Letters, say they now plan to study exciton BEC in few-layered hybrid perovskites as opposed to just monolayer ones. “We will also be looking at how to manipulate exciton vortices and make vortex-based information-storage porotype devices,” Zhang says.


physicsworld--2020-11-24--Carbon ions team up with immunotherapy to tackle advanced tumours

Immunotherapy using checkpoint inhibitors is an emerging cancer treatment that has recently had great success in treating metastatic cancer .
The technique works by blocking checkpoint proteins ( such as CTLA-4 or PD-1 ) that stop the patient ’ s immune system from attacking cancer cells , and reactivating the immune system to fight cancer .
Unfortunately , however , only a fraction of patients respond to such immunotherapy and only certain tumour types can be treated .
To increase its potential pool of patients and cancers , immunotherapy can be combined with radiation therapy , which under certain conditions @ @ @ @ @ @ @ has also been proposed that charged particles – such as the carbon-ion beams already used clinically to treat certain cancers – could prove more effective than X-rays in this combination .
To investigate this idea further , an international research team headed up at the GSI Helmholtz Centre for Heavy Ion Research has compared the efficacy of carbon-ion radiotherapy and conventional X-ray radiotherapy in combination with checkpoint inhibitors in a mouse bone tumour model .
The researchers report their findings in the International Journal of Radiation Oncology , Biology , Physics .
“ @ @ @ @ @ @ @ carbon ions and immunotherapy are a good match , ” explains lead author Alexander Helm .
“ The most prominent is actually the peculiar pattern of cell death that is induced by carbon ions compared with conventional radiotherapy .
It is hypothesized that this very cell death is more immunogenic , which will eventually lead to a more efficient activation of the immune response and a better elimination of metastases .
These effects , nonetheless , depend on the combination with immunotherapy to boost such immune responses.
” The researchers , also from @ @ @ @ @ @ @ in Japan , conducted their experiments at the accelerator in Chiba , Japan .
They inoculated mice in both hind legs with osteosarcoma cells , a bone tumour that is generally considered radioresistant .
They then treated each mouse with a 10 Gy dose of either carbon ions or X-rays , in combination with two immune checkpoint inhibitors : anti-PD-1 and anti-CTLA-4 .
Tumours on the animals ’ left legs ( representing primary tumours ) were irradiated , while those on the right legs ( abscopal tumours ) were kept out of the @ @ @ @ @ @ @ irradiated , with either carbon ions or X-rays , demonstrated reduced growth compared with untreated mice .
Tumour growth was better controlled in mice that received irradiation plus immunotherapy than in animals treated with radiotherapy alone , suggesting a synergistic effect likely based on the additional immune response boost by the checkpoint inhibitors .
In mice receiving the combination treatments , growth of the unirradiated abscopal tumours also decreased .
This reduced growth was most pronounced when the animals received a combination of carbon ions plus checkpoint inhibitors .
The team also examined @ @ @ @ @ @ @ lung metastases , which form spontaneously from the bone tumours in the mice .
When combined with immunotherapy , both radiation types essentially suppressed the metastases .
As found previously , the combination of carbon ions plus checkpoint inhibitors had the greatest effect , resulting in the least number of metastases .
Carbon-ion irradiation alone also significantly reduced the number of lung metastases compared with the control group , comparable with results in animals that received only checkpoint inhibitors .
This was not the case for mice treated with X-rays .
The team @ @ @ @ @ @ @ radiotherapy and checkpoint inhibitors has the highest potential to control distal metastases in this mouse model and could provide a potential clinical option for treatment of advanced tumours .
Corresponding author Marco Durante , director of the department of biophysics at GSI , has previously demonstrated that carbon ions and protons have physical advantages over X-rays that enable drastically improved sparing of healthy tissue during radiotherapy .
In fact , charged particles spare circulating immune cells in the blood much more than X-rays , which is necessary for an efficient immune response .
@ @ @ @ @ @ @ the mechanisms underlying these immune responses .
Understanding these mechanisms should allow them to tailor radiation treatments to increase immune response activation .
“ For example , the radiotherapy fractionation scheme has been shown to have a crucial role on the immunogenicity of the induced cell death , ” explains Helm .
“ Hypofractionation , in which higher doses are applied in a shorter time span ( than with conventional radiotherapy ) , has been reported as beneficial – and carbon ions are a perfect match for hypofractionation .
”

Lead author Alexander Helm from GSI’s department of biophysics working with cell cultures on the GSI/FAIR campus. (Courtesy: Adrian Rodríguez Rodríguez/GSI)
Immunotherapy using checkpoint inhibitors is an emerging cancer treatment that has recently had great success in treating metastatic cancer. The technique works by blocking checkpoint proteins (such as CTLA-4 or PD-1) that stop the patient’s immune system from attacking cancer cells, and reactivating the immune system to fight cancer. Unfortunately, however, only a fraction of patients respond to such immunotherapy and only certain tumour types can be treated.
To increase its potential pool of patients and cancers, immunotherapy can be combined with radiation therapy, which under certain conditions also triggers an immune response. It has also been proposed that charged particles – such as the carbon-ion beams already used clinically to treat certain cancers – could prove more effective than X-rays in this combination.
To investigate this idea further, an international research team headed up at the GSI Helmholtz Centre for Heavy Ion Research has compared the efficacy of carbon-ion radiotherapy and conventional X-ray radiotherapy in combination with checkpoint inhibitors in a mouse bone tumour model. The researchers report their findings in the International Journal of Radiation Oncology, Biology, Physics.
“There are several explanations as to why carbon ions and immunotherapy are a good match,” explains lead author Alexander Helm. “The most prominent is actually the peculiar pattern of cell death that is induced by carbon ions compared with conventional radiotherapy. It is hypothesized that this very cell death is more immunogenic, which will eventually lead to a more efficient activation of the immune response and a better elimination of metastases. These effects, nonetheless, depend on the combination with immunotherapy to boost such immune responses.”
Radiation comparisons
The researchers, also from the Parthenope University of Naples and NIRS-QST in Japan, conducted their experiments at the accelerator in Chiba, Japan. They inoculated mice in both hind legs with osteosarcoma cells, a bone tumour that is generally considered radioresistant. They then treated each mouse with a 10 Gy dose of either carbon ions or X-rays, in combination with two immune checkpoint inhibitors: anti-PD-1 and anti-CTLA-4. Tumours on the animals’ left legs (representing primary tumours) were irradiated, while those on the right legs (abscopal tumours) were kept out of the radiation field.
Tumours that were directly irradiated, with either carbon ions or X-rays, demonstrated reduced growth compared with untreated mice. Tumour growth was better controlled in mice that received irradiation plus immunotherapy than in animals treated with radiotherapy alone, suggesting a synergistic effect likely based on the additional immune response boost by the checkpoint inhibitors.
In mice receiving the combination treatments, growth of the unirradiated abscopal tumours also decreased. This reduced growth was most pronounced when the animals received a combination of carbon ions plus checkpoint inhibitors.
The team also examined the effects of the various treatments on lung metastases, which form spontaneously from the bone tumours in the mice. When combined with immunotherapy, both radiation types essentially suppressed the metastases. As found previously, the combination of carbon ions plus checkpoint inhibitors had the greatest effect, resulting in the least number of metastases.
Carbon-ion irradiation alone also significantly reduced the number of lung metastases compared with the control group, comparable with results in animals that received only checkpoint inhibitors. This was not the case for mice treated with X-rays.
The team concludes that a combination of high-energy carbon-ion radiotherapy and checkpoint inhibitors has the highest potential to control distal metastases in this mouse model and could provide a potential clinical option for treatment of advanced tumours. Corresponding author Marco Durante, director of the department of biophysics at GSI, has previously demonstrated that carbon ions and protons have physical advantages over X-rays that enable drastically improved sparing of healthy tissue during radiotherapy. In fact, charged particles spare circulating immune cells in the blood much more than X-rays, which is necessary for an efficient immune response.
The researchers are now working to discover the mechanisms underlying these immune responses. Understanding these mechanisms should allow them to tailor radiation treatments to increase immune response activation.
“For example, the radiotherapy fractionation scheme has been shown to have a crucial role on the immunogenicity of the induced cell death,” explains Helm. “Hypofractionation, in which higher doses are applied in a shorter time span (than with conventional radiotherapy), has been reported as beneficial – and carbon ions are a perfect match for hypofractionation.”


physicsworld--2020-11-23--Entangled erbium qubits are addressed individually in a crystal

The spin states of entangled erbium ions in a solid crystal can be controlled and read out individually using a new technique developed by Jeff Thompson and colleagues at Princeton University in the US .
In doing so , the team has overcome the important challenge of making measurements on closely spaced ions in a crystal .
Their technique could lead to the creation of new quantum devices that could be integrated with existing optical telecommunications technology .
Some atomic-scale impurities in solid-state crystals have spins states that endure for long periods of time and can therefore be used as @ @ @ @ @ @ @ .
If the impurities are located close enough together in a crystal , their spins will become entangled with each other .
This entanglement can be exploited to create quantum logic gates for quantum computers .
However , the nanoscale separation required for entanglement is typically well below the diffraction limit of visible light .
This means that the optical lasers used to control and read out spin states can not normally distinguish between the spins of individual impurities .
One promising way around this problem is to use the rare-earth ions of @ @ @ @ @ @ @ retain quantum information over long periods of time and they interact with light at wavelengths used for optical telecommunications .
But most importantly , each erbium-ion impurity in a crystal experiences a random static shift in its optical transition energies .
This means that even if the positions of multiple ions can not be resolved spatially , their spin states can be controlled and read-out using the distinct wavelengths of the light they absorb and emit when illuminated by a laser .
To exploit this property , Thompson ’ s team doped a @ @ @ @ @ @ @ They then coupled the system to a photonic silicon cavity , which enhances the emission of light from the ions and makes it easier to read out the spins .
Out of hundreds of erbium ions in the sample , the researchers focused on six ions in a sub-micron region , tuning the wavelength of a laser to match each of the ions .
This approach allowed them to easily control and read out the spin states of individual ions with high fidelity .
Thompson and colleagues now hope that their approach can @ @ @ @ @ @ @ of rare earth ions with arbitrarily small separations – making them suitable for multiple-qubit systems .
Crucially , they point out that the technology could be easily integrated into existing communications infrastructures : transmitting encoded signals in telecommunications frequency bands using present-day silicon devices and optical fibres .
If achieved , this could soon allow erbium ion defects to provide a solid basis for future quantum computers , as well as ultra-secure quantum communication networks .
The research is described in Science .

Random wavelengths: artist's impression of a method for measuring and controlling quantum spins developed at Princeton University. (Courtesy: Rachel Davidowitz)
The spin states of entangled erbium ions in a solid crystal can be controlled and read out individually using a new technique developed by Jeff Thompson and colleagues at Princeton University in the US. In doing so, the team has overcome the important challenge of making measurements on closely spaced ions in a crystal. Their technique could lead to the creation of new quantum devices that could be integrated with existing optical telecommunications technology.
Some atomic-scale impurities in solid-state crystals have spins states that endure for long periods of time and can therefore be used as quantum bits (qubits) of information. If the impurities are located close enough together in a crystal, their spins will become entangled with each other. This entanglement can be exploited to create quantum logic gates for quantum computers.
However, the nanoscale separation required for entanglement is typically well below the diffraction limit of visible light. This means that the optical lasers used to control and read out spin states cannot normally distinguish between the spins of individual impurities.
Random shift
One promising way around this problem is to use the rare-earth ions of erbium as impurities. Their spins can retain quantum information over long periods of time and they interact with light at wavelengths used for optical telecommunications. But most importantly, each erbium-ion impurity in a crystal experiences a random static shift in its optical transition energies. This means that even if the positions of multiple ions cannot be resolved spatially, their spin states can be controlled and read-out using the distinct wavelengths of the light they absorb and emit when illuminated by a laser.
To exploit this property, Thompson’s team doped a yttrium orthosilicate crystal with erbium ions. They then coupled the system to a photonic silicon cavity, which enhances the emission of light from the ions and makes it easier to read out the spins. Out of hundreds of erbium ions in the sample, the researchers focused on six ions in a sub-micron region, tuning the wavelength of a laser to match each of the ions. This approach allowed them to easily control and read out the spin states of individual ions with high fidelity.
Thompson and colleagues now hope that their approach can be scaled up to accommodate large numbers of rare earth ions with arbitrarily small separations – making them suitable for multiple-qubit systems. Crucially, they point out that the technology could be easily integrated into existing communications infrastructures: transmitting encoded signals in telecommunications frequency bands using present-day silicon devices and optical fibres. If achieved, this could soon allow erbium ion defects to provide a solid basis for future quantum computers, as well as ultra-secure quantum communication networks.
The research is described in Science.


physicsworld--2020-11-23--Imaging spectrometer slims down

Imaging spectrometer slims down

A new , slimline imaging spectrometer developed by researchers at the Massachusetts Institute of Technology ( MIT ) in the US boasts the same performance as the most advanced devices of its kind while being much more compact .
Thanks to its reduced size , the instrument could perform remote terrestrial sensing from airborne vehicles such as drones or satellites and might even become a component of future space missions .
Imaging spectrometers that operate in the visible , near and short-wave infrared ( VNIR/SWIR ) regions of the electromagnetic spectrum are routinely deployed in studies of atmospheric science , @ @ @ @ @ @ @ .
They work by recording a series of monochromatic images , the spectrum of which is then analysed over a given imaging area .
One of their advantages over traditional cameras is that they are very good at controlling the chromatic aberrations ( blurring or distortion ) that arise because of light being spread out over a region of space rather than focused to a point .
They also have high signal-to-noise ratios .
The snag , however , is that current devices are relatively bulky , which means they can ’ t @ @ @ @ @ @ @ .
Researchers led by Ronald Lockwood have now developed a miniaturized spectrometer with a volume of just 350 cm3 – less than one-tenth the size of standard instruments .
One version of the new device , which is known as a “ Chrisp ” compact VNIR/SWIR imaging spectrometer ( CCVIS ) , measures just 8.3 cm in diameter and 7 cm long .
To downsize their device , Lockwood and colleagues used an optical component called a catadioptric lens that consists of a concave meniscus with a reflective coating on the back .
@ @ @ @ @ @ @ that corrects the spectrometer ’ s Petzval field curvature ( that is , the optical aberration that prevents an object from being properly brought into focus ) .
Because it combines reflective and refractive elements into a single component , the lens makes it possible for the spectrometer to control optical aberrations efficiently in a smaller volume .
In another miniaturizing move , the researchers used a special flat reflection grating that they immersed in a refractive medium , rather than in air as is usually the case .
The flat grating takes @ @ @ @ @ @ @ or concave grating , but has the same spatial resolution , and Lockwood notes that it is also easier to make than a curved grating .
While a flat grating can be made using a greyscale photolithographic microfabrication technique that only requires a one-time exposure , curved gratings require labour-intensive electron-beam processing , he explains .
The researchers tested their new device on an aquatic remote sensing system made up of several CCVISs ( each with a spectral range of 380 to 1050 nm ) stacked behind a freeform telescope .
The entire @ @ @ @ @ @ @ satellite ( smallsat ) platform , and the miniaturized nature of the spectrometry modules means that they could be stacked in even greater numbers to further increase the field of view , Lockwood says .
The spectrometers ’ compactness also makes it easier to keep them at a stable temperature , thus ensuring consistent performance .
Lockwood tells Physics World that devices of this type could be deployed on a low Earth orbit satellite platform to map , monitor and track changes in coastal and inland aquatic systems ecosystems from an altitude of @ @ @ @ @ @ @ in useful for projects like the US National Research Council ’ s Decadal Survey , which aims to assess the characteristics and health of terrestrial vegetation and aquatic ecosystems , he explains .
Surveys like these are important for understanding key consequences such as crop yields , carbon uptake and biodiversity .
“ Laboratory and field experiments , even when coupled with numerical models , are unable to quantify ecosystem processes with sufficient temporal spatial and spectral resolution , ” he says .
“ Measuring habitat extent and spatial distribution and observing changes @ @ @ @ @ @ @ however , by detecting the spectral signatures of ‘ foundation ’ species ( such as sea grass meadows , coral reefs , emergent and terrestrial vegetation ) , their structures and their environment using a compact spectrometer like ours.
” The researchers , who report their work in Applied Optics , are now planning to seek funding from NASA to develop a full prototype that they could test on a real airborne vehicle .
“ This is always a challenge since NASA receives many meritorious proposals , but our CCVIS is certainly applicable @ @ @ @ @ @ @ ” Lockwood says .

Compact imaging spectrometer combines a catadioptric lens and a special flat immersion reflection grating. (Courtesy: Ronald B. Lockwood, MIT Lincoln Laboratory)
A new, slimline imaging spectrometer developed by researchers at the Massachusetts Institute of Technology (MIT) in the US boasts the same performance as the most advanced devices of its kind while being much more compact. Thanks to its reduced size, the instrument could perform remote terrestrial sensing from airborne vehicles such as drones or satellites and might even become a component of future space missions.
Imaging spectrometers that operate in the visible, near and short-wave infrared (VNIR/SWIR) regions of the electromagnetic spectrum are routinely deployed in studies of atmospheric science, ecology, geology, agriculture and forestry. They work by recording a series of monochromatic images, the spectrum of which is then analysed over a given imaging area. One of their advantages over traditional cameras is that they are very good at controlling the chromatic aberrations (blurring or distortion) that arise because of light being spread out over a region of space rather than focused to a point. They also have high signal-to-noise ratios. The snag, however, is that current devices are relatively bulky, which means they can’t be deployed on small satellites or drones.
11 times smaller in volume
Researchers led by Ronald Lockwood have now developed a miniaturized spectrometer with a volume of just 350 cm3 – less than one-tenth the size of standard instruments. One version of the new device, which is known as a “Chrisp” compact VNIR/SWIR imaging spectrometer (CCVIS), measures just 8.3 cm in diameter and 7 cm long.
To downsize their device, Lockwood and colleagues used an optical component called a catadioptric lens that consists of a concave meniscus with a reflective coating on the back. The lens acts as a concave mirror that corrects the spectrometer’s Petzval field curvature (that is, the optical aberration that prevents an object from being properly brought into focus). Because it combines reflective and refractive elements into a single component, the lens makes it possible for the spectrometer to control optical aberrations efficiently in a smaller volume.
In another miniaturizing move, the researchers used a special flat reflection grating that they immersed in a refractive medium, rather than in air as is usually the case. The flat grating takes up less space than a conventional convex or concave grating, but has the same spatial resolution, and Lockwood notes that it is also easier to make than a curved grating. While a flat grating can be made using a greyscale photolithographic microfabrication technique that only requires a one-time exposure, curved gratings require labour-intensive electron-beam processing, he explains.
New design fits on a smallsat
The researchers tested their new device on an aquatic remote sensing system made up of several CCVISs (each with a spectral range of 380 to 1050 nm) stacked behind a freeform telescope. The entire ensemble would easily fit onto a small satellite (smallsat) platform, and the miniaturized nature of the spectrometry modules means that they could be stacked in even greater numbers to further increase the field of view, Lockwood says. The spectrometers’ compactness also makes it easier to keep them at a stable temperature, thus ensuring consistent performance.
Lockwood tells Physics World that devices of this type could be deployed on a low Earth orbit satellite platform to map, monitor and track changes in coastal and inland aquatic systems ecosystems from an altitude of 500 km. Such measurements would come in useful for projects like the US National Research Council’s Decadal Survey, which aims to assess the characteristics and health of terrestrial vegetation and aquatic ecosystems, he explains. Surveys like these are important for understanding key consequences such as crop yields, carbon uptake and biodiversity.
“Laboratory and field experiments, even when coupled with numerical models, are unable to quantify ecosystem processes with sufficient temporal spatial and spectral resolution,” he says. “Measuring habitat extent and spatial distribution and observing changes in these quantities can be achieved, however, by detecting the spectral signatures of ‘foundation’ species (such as sea grass meadows, coral reefs, emergent and terrestrial vegetation), their structures and their environment using a compact spectrometer like ours.”
The researchers, who report their work in Applied Optics, are now planning to seek funding from NASA to develop a full prototype that they could test on a real airborne vehicle. “This is always a challenge since NASA receives many meritorious proposals, but our CCVIS is certainly applicable to both terrestrial and planetary missions,” Lockwood says.


physicsworld--2020-11-23--Molecular spins show promise as quantum bits

The states of molecular spins in a crystal can be detected optically using the polarization of the photons they emit , researchers in the US have shown .
This allowed the team to prepare and precisely read out spin states within molecules – a capability that could be used to engineer quantum bits ( qubits ) with greater flexibility and control than possible using other platforms .
So far , the most successful platforms for quantum computing have proved to be trapped-ion qubits and superconducting qubits .
However , both technologies have significant drawbacks .
Ion qubits require high vacuum @ @ @ @ @ @ @ must be made from identical quantum circuits , which are extremely difficult to produce with the required consistency .
One possible alternative is the diamond nitrogen-vacancy ( NV ) centre , which occurs when two adjacent carbon atoms in a diamond lattice are replaced by a single nitrogen atom .
Unlike the rest of the carbon lattice , an NV centre has a spin that can be readily manipulated and read out with laser light .
Unfortunately , the process for creating NV centres involves irradiating diamonds before exposing them to nitrogen gas @ @ @ @ @ @ @ “ One of the major challenges to building scaleable solid state quantum systems is being able to place the quantum bit where you like at the atomic scale over the length of a wafer , ” explains condensed matter physicist David Awschalom at the University of Chicago .
Awschalom ’ s group has collaborated with researchers led by chemist Danna Freedman of Northwestern University to focus on a “ bottom-up ” approach to creating a crystal with appropriate spin centres , Instead of implanting the spin centres into an existing crystal , they @ @ @ @ @ @ @ and crystallize it .
“ You take it for granted that every molecule in a tablet of aspirin is identical , ” explains Freedman .
However , the technological challenge is that that nobody had successfully produced a molecular crystal containing spins that could be manipulated and read by a laser beam .
Now , Awschalom , Freedman and colleagues synthesized three different compounds comprising chromium ( IV ) ions coordinated to aryl ligands .
The resulting samples of organometallic molecules each behaved much like NV centres — albeit at different laser frequencies @ @ @ @ @ @ @ into a state that rapidly relaxes into a metastable state and then emits a photon , ” says Awschalom , “ From our perspective , the single pulse of light ultimately initializes the system into a state from which it can emit one photon whose polarization reflects the spin of the system .
That ’ s the qubit spin-photon interface.
” This entire process effectively creates a molecular single qubit .
At present , the researchers are working with coherent ensembles of qubits , but they are working to achieve single molecule sensitivity @ @ @ @ @ @ @ longer coherence times .
The team hopes that , by connecting the output of one qubit into the input of another , it may be possible to build optical quantum gates and then quantum circuits using their system .
In the short term , says Awschalom , they plan to make interfaces between their qubits using integrated photonics .
A more ambitious , long-term possibility may be to craft photonic highways by chemical self-assembly .
“ This opens up a new frontier for what my students like to call designer qubits , ” @ @ @ @ @ @ @ imagine so many things that would have been very challenging with other techniques , where you ’ re limited by the material family…But here , because you ’ re literally cooking [ the material ] , you can imagine incorporating memories , systems that are designed so that they ’ re heavily entangled .
I think the sky ’ s the limit here for both computing and sensing.
” Freedman adds , “ Broadly speaking , quantum information science is a multi-decade challenge .
There are a whole host of areas that will @ @ @ @ @ @ @ so there ’ s both a whole lot of work to do and a whole lot of fun to have.
” Commenting on the work , Stephen Hill of the National High Field Magnet Laboratory at Florida State University says , “ Molecular materials are very promising as potential qubits for quantum computing but that area lags behind some of the more mature areas partly because some of the key properties have not been demonstrated .
This [ work ] demonstrates one of those key properties .
I think the result itself is @ @ @ @ @ @ @ ’ s exciting for the field that it has taken that big jump in actually demonstrating this.
” The research is described in Science .

Spin doctors Berk Kovos, Sam Bayliss and Peter Mintun (left to right) work on qubit technology at the University of Chicago. (Courtesy: Pratiti Deb/University of Chicago)
The states of molecular spins in a crystal can be detected optically using the polarization of the photons they emit, researchers in the US have shown. This allowed the team to prepare and precisely read out spin states within molecules – a capability that could be used to engineer quantum bits (qubits) with greater flexibility and control than possible using other platforms.
So far, the most successful platforms for quantum computing have proved to be trapped-ion qubits and superconducting qubits. However, both technologies have significant drawbacks. Ion qubits require high vacuum and electromagnetic traps, whereas superconducting qubits must be made from identical quantum circuits, which are extremely difficult to produce with the required consistency. One possible alternative is the diamond nitrogen-vacancy (NV) centre, which occurs when two adjacent carbon atoms in a diamond lattice are replaced by a single nitrogen atom. Unlike the rest of the carbon lattice, an NV centre has a spin that can be readily manipulated and read out with laser light.
Unfortunately, the process for creating NV centres involves irradiating diamonds before exposing them to nitrogen gas and is difficult to execute precisely. “One of the major challenges to building scaleable solid state quantum systems is being able to place the quantum bit where you like at the atomic scale over the length of a wafer,” explains condensed matter physicist David Awschalom at the University of Chicago.
“Bottom-up” approach
Awschalom’s group has collaborated with researchers led by chemist Danna Freedman of Northwestern University to focus on a “bottom-up” approach to creating a crystal with appropriate spin centres, Instead of implanting the spin centres into an existing crystal, they take a molecule that contains spin centres and crystallize it. “You take it for granted that every molecule in a tablet of aspirin is identical,” explains Freedman. However, the technological challenge is that that nobody had successfully produced a molecular crystal containing spins that could be manipulated and read by a laser beam.
Now, Awschalom, Freedman and colleagues synthesized three different compounds comprising chromium (IV) ions coordinated to aryl ligands. The resulting samples of organometallic molecules each behaved much like NV centres — albeit at different laser frequencies. “You optically excite the qubit into a state that rapidly relaxes into a metastable state and then emits a photon,” says Awschalom, “From our perspective, the single pulse of light ultimately initializes the system into a state from which it can emit one photon whose polarization reflects the spin of the system. That’s the qubit spin-photon interface.”
This entire process effectively creates a molecular single qubit. At present, the researchers are working with coherent ensembles of qubits, but they are working to achieve single molecule sensitivity becasue single molecular quantum states would have longer coherence times.
Optical quantum gates
The team hopes that, by connecting the output of one qubit into the input of another, it may be possible to build optical quantum gates and then quantum circuits using their system. In the short term, says Awschalom, they plan to make interfaces between their qubits using integrated photonics. A more ambitious, long-term possibility may be to craft photonic highways by chemical self-assembly.
“This opens up a new frontier for what my students like to call designer qubits,” he says, “Now you can imagine so many things that would have been very challenging with other techniques, where you’re limited by the material family…But here, because you’re literally cooking [the material], you can imagine incorporating memories, systems that are designed so that they’re heavily entangled. I think the sky’s the limit here for both computing and sensing.”
Freedman adds, “Broadly speaking, quantum information science is a multi-decade challenge. There are a whole host of areas that will be impacted by new materials discoveries, so there’s both a whole lot of work to do and a whole lot of fun to have.”
Commenting on the work, Stephen Hill of the National High Field Magnet Laboratory at Florida State University says, “Molecular materials are very promising as potential qubits for quantum computing but that area lags behind some of the more mature areas partly because some of the key properties have not been demonstrated. This [work] demonstrates one of those key properties. I think the result itself is not a huge surprise – but it’s exciting for the field that it has taken that big jump in actually demonstrating this.”
The research is described in Science.


physicsworld--2020-11-23--Building a flexible future

Building a flexible future

The most famous 2D material is graphene , but the focus of your research has shifted to other substances .
Why is that ?
We are still working on graphene , it ’ s just that we have expanded to investigate other 2D materials as well .
The value of these other 2D materials and the motivation for investigating them is that they have properties that graphene does not have .
Graphene is unique in its material properties , but other 2D materials are also unique from an electronic , optical or magnetic point of view , so they are @ @ @ @ @ @ @ s like if you have a sports car .
It has value if you want to speed down a fast road .
But if you want to carry cargo during transportation , you need a truck .
These other 2D materials complement what graphene has to offer in a unique way .
A few years ago you used one of those other 2D materials , molybdenum disulphide ( MoS ) , to make a flexible transistor .
What did that project involve ?
That was a very multidisciplinary project , which was challenging @ @ @ @ @ @ @ ’ m an electrical engineer and an applied physicist , but that project also involved quite a bit of materials science in terms of materials synthesis .
We had to do things from the bottom up , starting with growing the materials ourselves , then putting it on a flexible substrate like plastic kapton tape and creating devices on this non-electronic substance .
And then , after fabricating the devices , we had to characterize them and do measurements to ensure they were of good quality .
So it was a very complex @ @ @ @ @ @ @ chemistry , applied physics and electronic measurements .
What are some applications of flexible electronic devices ?
I ’ ll give you some examples that we have worked on and that are still a matter of very active investigation .
One of the applications is transparent conductive films like the ones used in mobile phone screens .
Because these materials are thinner than what is currently used in most phones , they are much more transparent .
That translates into screens that are brighter or more efficient in their battery use .
Flexible @ @ @ @ @ @ @ whole devices .
For example , we ’ ve demonstrated a flexible radio , where you have a piece of plastic , you have a speaker on that piece of plastic , and that piece of plastic can receive signals – let ’ s say music signals – wirelessly and play them .
So you can imagine having a foldable , flexible radio that you can take with you and unfold when you go to the beach .
Another application is graphene tattoos , where you put the tattoo on the skin , @ @ @ @ @ @ @ , and then convey that information to an app on a mobile phone .
A system like that can record your pulse , your heartbeat , your blood pressure and other information for health .
We ’ re working on a system for continuous monitoring of blood pressure , which is very important for many diagnostic reasons in medicine .
You mentioned making a radio from flexible electronic components .
More recently , you ’ ve been developing flexible memory components called atomristors .
Could you explain what they are ?
Of all @ @ @ @ @ @ @ today , memory or information storage components are the most important .
These are the components that store information in binary code – ones and zeros – and those ones and zeros can represent any kind of data , from videos to images and so on .
That ’ s why , when you buy a smartphone , if you get 512 gigabytes instead of 256 gigabytes of memory , it ’ s going to cost you significantly more money .
Because memory is so important , we knew that if we wanted @ @ @ @ @ @ @ electronics , we needed to have a flexible memory , too .
And in order to make a flexible memory , you need materials that are themselves flexible , which implies that they must be very thin .
In this sense , 2D materials are the best class of flexible materials because they are the thinnest materials that exist in nature .
Our atomristors are atomically thin , less than one nanometre thick , and you can make them from molybdenum disulfide , which is a common 2D material .
And that can @ @ @ @ @ @ @ that discovery a few years ago and we continue to advance it today .
Your most recent work is an extension of that project , but it involves a different 2D material , hexagonal boron nitride ( hBN ) .
Can you tell us more about that ?
We were challenged by some of our sponsors to consider what other applications , in addition to information storage , could be served by our new memory technology .
That led us to explore hexagonal boron nitride , which has the distinction of being the @ @ @ @ @ @ @ out that , not only is it good as a memory , but it can also be used as a radio-frequency ( RF ) switch .
At the most basic level , a switch is a component that toggles between states , such as the different bands of communication we have on our mobile networks .
For example , for 5G there are many , many bands : LTE , 4G , 3G , 2G , Bluetooth and so on .
That means that RF switches need to be able to toggle rapidly @ @ @ @ @ @ @ they need to do that without consuming significant energy .
Our present switching technologies are based on transistors , but transistor switches consume a lot of energy .
Even when they ’ re not toggling or switching , the standby energy to keep them operational is substantial .
A memory switch like the kind we have been working on and developing is different , because its standby consumption of energy is zero .
That would extend the battery life on your device significantly , and switches of this type are also much faster @ @ @ @ @ @ @ data but even 6G , which is 100 GB per second .
For streaming applications , those speeds are unheard-of with current technologies .
There was a lot of hype about graphene when it was first isolated .
Why has it taken so long to exploit its electronic properties in a commercial device ?
If you look at the history of technology , normally it takes 20 to 30 years to take an idea all the way from concept to product .
Graphene has really only been in development for 10 years , @ @ @ @ @ @ @ a few years less than that .
The technology is still at a nascent stage .
Nonetheless , several applications ( including some that we have worked on ) are on the market today .
I mentioned graphene-based transparent conductive films earlier , and these are a real technology – you can buy them on certain smartphones in Asia , and the manufacturers have sold those phones in a reasonable volume .
Some of our esteemed colleagues have also commercialized graphene sensor technology ; I know there ’ s a start-up company in @ @ @ @ @ @ @ Bio that sells monolayer graphene biosensors .
There are also many other applications for graphene composites .
An example is the packaging of smartphones , where composites help spread the heat around the back of the phone .
And there are some consumer applications too , like using graphene to reinforce sportswear and the frames of bicycles so they are lighter and stronger .
What do you think the future holds for electronic devices made from 2D materials ?
I think the future is brighter than it was a few years ago .
@ @ @ @ @ @ @ several major semiconductor firms – including TSMC , Intel and some European companies – have invested a huge amount in terms of infrastructure , talent and R & D funds to try to integrate these materials into silicon-based semiconductor technology .
Based on these trends from well-known , leading companies , I think we ’ ll see more 2D materials in electronic devices in the future .
However , as an addendum to that , when you consider the 2D materials that we ’ ve been working on , and many others across @ @ @ @ @ @ @ dollars in R & D funding , there ’ s a huge number of possibilities out there .
It ’ s not one or two or five or a dozen materials .
We ’ re talking about a thousand materials , and there ’ s a lot in this landscape that is undiscovered from a basic physics and science point of view .
So even though there ’ s a lot of pressure for development and applications , there ’ s still a lot of basic science that we don ’ t know @ @ @ @ @ @ @ materials to investigate .

Physics World Materials Briefing. You can enjoy the full issue Taken from the 2020. You can enjoy the full issue via the Physics World app
Deji Akinwande is an applied physicist and electrical engineer who develops flexible electronic devices based on 2D materials. He spoke to Margaret Harris about the challenges of working in this interdisciplinary field
Collaborative effort Deji Akinwande (right) and students in his research group. (Courtesy: Deji Akinwande)
The most famous 2D material is graphene, but the focus of your research has shifted to other substances. Why is that?
We are still working on graphene, it’s just that we have expanded to investigate other 2D materials as well. The value of these other 2D materials and the motivation for investigating them is that they have properties that graphene does not have.
Graphene is unique in its material properties, but other 2D materials are also unique from an electronic, optical or magnetic point of view, so they are very worthy of consideration. It’s like if you have a sports car. It has value if you want to speed down a fast road. But if you want to carry cargo during transportation, you need a truck. These other 2D materials complement what graphene has to offer in a unique way.
A few years ago you used one of those other 2D materials, molybdenum disulphide (MoS 2 ), to make a flexible transistor. What did that project involve?
That was a very multidisciplinary project, which was challenging for us at that time. I’m an electrical engineer and an applied physicist, but that project also involved quite a bit of materials science in terms of materials synthesis. We had to do things from the bottom up, starting with growing the materials ourselves, then putting it on a flexible substrate like plastic kapton tape and creating devices on this non-electronic substance. And then, after fabricating the devices, we had to characterize them and do measurements to ensure they were of good quality. So it was a very complex project, spanning materials science, materials chemistry, applied physics and electronic measurements.
What are some applications of flexible electronic devices?
I’ll give you some examples that we have worked on and that are still a matter of very active investigation. One of the applications is transparent conductive films like the ones used in mobile phone screens. Because these materials are thinner than what is currently used in most phones, they are much more transparent. That translates into screens that are brighter or more efficient in their battery use.
Flexible electronics can also be used to make whole devices. For example, we’ve demonstrated a flexible radio, where you have a piece of plastic, you have a speaker on that piece of plastic, and that piece of plastic can receive signals – let’s say music signals – wirelessly and play them. So you can imagine having a foldable, flexible radio that you can take with you and unfold when you go to the beach.
Another application is graphene tattoos, where you put the tattoo on the skin, use it to record your vital signals, and then convey that information to an app on a mobile phone. A system like that can record your pulse, your heartbeat, your blood pressure and other information for health. We’re working on a system for continuous monitoring of blood pressure, which is very important for many diagnostic reasons in medicine.
You mentioned making a radio from flexible electronic components. More recently, you’ve been developing flexible memory components called atomristors. Could you explain what they are?
Of all the vast array of electronic components available today, memory or information storage components are the most important. These are the components that store information in binary code – ones and zeros – and those ones and zeros can represent any kind of data, from videos to images and so on. That’s why, when you buy a smartphone, if you get 512 gigabytes instead of 256 gigabytes of memory, it’s going to cost you significantly more money.
Because memory is so important, we knew that if we wanted to make a complete system of flexible electronics, we needed to have a flexible memory, too. And in order to make a flexible memory, you need materials that are themselves flexible, which implies that they must be very thin.
In this sense, 2D materials are the best class of flexible materials because they are the thinnest materials that exist in nature. Our atomristors are atomically thin, less than one nanometre thick, and you can make them from molybdenum disulfide, which is a common 2D material. And that can lead to flexible memories. We made that discovery a few years ago and we continue to advance it today.
Your most recent work is an extension of that project, but it involves a different 2D material, hexagonal boron nitride (hBN). Can you tell us more about that?
We were challenged by some of our sponsors to consider what other applications, in addition to information storage, could be served by our new memory technology. That led us to explore hexagonal boron nitride, which has the distinction of being the thinnest insulator on earth. We found out that, not only is it good as a memory, but it can also be used as a radio-frequency (RF) switch.
At the most basic level, a switch is a component that toggles between states, such as the different bands of communication we have on our mobile networks. For example, for 5G there are many, many bands: LTE, 4G, 3G, 2G, Bluetooth and so on. That means that RF switches need to be able to toggle rapidly between these bands, and ideally, they need to do that without consuming significant energy.
Our present switching technologies are based on transistors, but transistor switches consume a lot of energy. Even when they’re not toggling or switching, the standby energy to keep them operational is substantial. A memory switch like the kind we have been working on and developing is different, because its standby consumption of energy is zero. That would extend the battery life on your device significantly, and switches of this type are also much faster – they can handle not only 5G data but even 6G, which is 100 GB per second. For streaming applications, those speeds are unheard-of with current technologies.
Imagine having a foldable, flexible radio that you can take with you and unfold when you go to the beach
There was a lot of hype about graphene when it was first isolated. Why has it taken so long to exploit its electronic properties in a commercial device?
If you look at the history of technology, normally it takes 20 to 30 years to take an idea all the way from concept to product. Graphene has really only been in development for 10 years, and 2D materials, in general, a few years less than that. The technology is still at a nascent stage.
Nonetheless, several applications (including some that we have worked on) are on the market today. I mentioned graphene-based transparent conductive films earlier, and these are a real technology – you can buy them on certain smartphones in Asia, and the manufacturers have sold those phones in a reasonable volume. Some of our esteemed colleagues have also commercialized graphene sensor technology; I know there’s a start-up company in San Diego, California, called Cardea Bio that sells monolayer graphene biosensors.
There are also many other applications for graphene composites. An example is the packaging of smartphones, where composites help spread the heat around the back of the phone. And there are some consumer applications too, like using graphene to reinforce sportswear and the frames of bicycles so they are lighter and stronger.
What do you think the future holds for electronic devices made from 2D materials?
I think the future is brighter than it was a few years ago. The reason I say that is because several major semiconductor firms – including TSMC, Intel and some European companies – have invested a huge amount in terms of infrastructure, talent and R&D funds to try to integrate these materials into silicon-based semiconductor technology. Based on these trends from well-known, leading companies, I think we’ll see more 2D materials in electronic devices in the future.
However, as an addendum to that, when you consider the 2D materials that we’ve been working on, and many others across the world that have enjoyed billions of dollars in R&D funding, there’s a huge number of possibilities out there. It’s not one or two or five or a dozen materials. We’re talking about a thousand materials, and there’s a lot in this landscape that is undiscovered from a basic physics and science point of view. So even though there’s a lot of pressure for development and applications, there’s still a lot of basic science that we don’t know because there’s just so many materials to investigate.


physicsworld--2020-11-23--Physics and LEGO: an enduring love affair

An unlimited world of structures built from precision-engineered unit parts – it is easy to see why LEGO appeals to many physicists .
But in addition to the pure enjoyment , this plastic construction toy is also a great teaching tool , and it has even featured in serious science experiments .
In the November episode of Physics World Stories , Andrew Glester meets physicists who have used LEGO in fun and creative ways to communicate physics .
The first guest is Lewis Matherson aka @ LegoPhysicsGuy , a former physics teacher who now makes physics videos aimed at students @ @ @ @ @ @ @ LEGO to illustrate core physics concepts in GCSEs and A levels – exams typically sat by 16- and 18-year-olds in the UK .
Next up is Joshua Chawner , a low-temperature-physics researcher at Lancaster University , UK .
Chawner captured the imagination by subjecting LEGO pieces to the coldest temperatures on Earth , placing them inside his group ’ s dilution refrigerator , as documented in an award-winning video ( below ) .
Despite reaching 1.6 millidegrees above absolute zero ( 2000 times colder than deep space ) the bricks proved to be @ @ @ @ @ @ @ result described in Scientific Reports .
Last but not least is Maria Parappilly , a physics education expert at Flinders University , Australia .
One of Parappilly ’ s successful initiatives was to create a LEGO race cars exercise for an introductory physics course that previously seen high drop-out rates .
Parappilly is also the founder of the STEM Women Branching Out at Flinders University , designed to make science and other technical subjects more inclusive .

An unlimited world of structures built from precision-engineered unit parts – it is easy to see why LEGO appeals to many physicists. But in addition to the pure enjoyment, this plastic construction toy is also a great teaching tool, and it has even featured in serious science experiments. In the November episode of Physics World Stories, Andrew Glester meets physicists who have used LEGO in fun and creative ways to communicate physics.
The first guest is Lewis Matherson aka @LegoPhysicsGuy, a former physics teacher who now makes physics videos aimed at students and teachers. These videos regularly incorporate LEGO to illustrate core physics concepts in GCSEs and A levels – exams typically sat by 16- and 18-year-olds in the UK.
Next up is Joshua Chawner, a low-temperature-physics researcher at Lancaster University, UK. Chawner captured the imagination by subjecting LEGO pieces to the coldest temperatures on Earth, placing them inside his group’s dilution refrigerator, as documented in an award-winning video (below). Despite reaching 1.6 millidegrees above absolute zero (2000 times colder than deep space) the bricks proved to be extremely good thermal insulators, a surprising result described in Scientific Reports.
Last but not least is Maria Parappilly, a physics education expert at Flinders University, Australia. One of Parappilly’s successful initiatives was to create a LEGO race cars exercise for an introductory physics course that previously seen high drop-out rates. Parappilly is also the founder of the STEM Women Branching Out at Flinders University, designed to make science and other technical subjects more inclusive.


physicsworld--2020-11-21--Fish save energy by swimming in schools

Fish save energy by swimming in schools

Swimming in schools helps fish avoid predators , but it also allows them to conserve energy .
This is the finding of researchers in Germany , China and Hungary who used fish-like robots to investigate how real fish might gain from the watery vortices that other fish generate as they swim .
The phenomenon they observed is known as vortex phase matching , and the researchers say that understanding how it works could inspire the development of more efficient fish-like underwater vehicles .
While scientists have long suspected that swimming fish might exploit the swirling hydrodynamic flows created by their @ @ @ @ @ @ @ individual fish coordinated their movements to benefit from these vortices .
Researchers led by Iain Couzin at the Max Planck Institute of Animal Behavior and the University of Konstanz studied this question by constructing fish-like robots and measuring how much energy they consume when swimming in pairs ( the most common swimming configuration in natural fish populations ) compared to when they swim alone .
Such measurements would , they say , be impossible to perform on real animals .
The researchers ’ robotic fish are 45 cm long with a mass of @ @ @ @ @ @ @ servo-motors that are connected to joints covered in a soft , waterproof , rubber skin , and controlled using a “ central pattern generator ” that enables the robot to mimic the undulations of real fish .
Over the course of 10 080 trials ( representing 120 hours of swimming time ) , the researchers monitored how their “ robofish ” behaved when placed at different distances from a “ lead ” robofish .
They found that paired-up fish consume much less energy than loners because the followers adjust their tailbeats to match @ @ @ @ @ @ @ by the leader .
The matching takes place with a time lag that varies with distance : when the follower fish is beside the leader , the tailbeats are synchronized , but when the follower falls behind , its tailbeats go out of sync , with a delay that increases the further away it gets .
This vortex phase matching allows the follower fish to exploit the “ Kármán vortices ” – chains of swirling vortices shed by a blunt object as it travels through a liquid – that the leader fish leaves @ @ @ @ @ @ @ a reduction in the follower ’ s energy consumption , but team member Máté Nagy of the Hungarian Academy of Sciences and Eötvös University notes that it ’ s not just about saving energy .
“ By changing the way they synchronize , followers can also use the vortices shed by other fish to generate thrust and help them accelerate , ” he explains .
To find out whether real fish use vortex phase matching too , Couzin and colleagues made observations on 32 freely-swimming pairs of goldfish .
While the real fish @ @ @ @ @ @ @ , the researchers observed that they nonetheless adopted a type of hydrodynamic interaction that could be described by a simple mathematical model that incorporates swim speed and the amplitude and frequency of the leader ’ s tailbeats .
This model , Couzin tells Physics World , was then used to predict how real fish would behave if they were using vortex phase matching , and tested using artificial-intelligence-assisted analysis of the body posture of goldfish as they swim together .
The results indicate that real fish do indeed exploit vortex phase matching .
@ @ @ @ @ @ @ “ may be a result of preflex or proprioceptive responses to neighbour-generated hydrodynamic cues ” , since neither the fishes ’ visual nor their lateral-line systems are required for them to behave this way .
This leaves fish free to process other important information from their environment , including flows created by creatures other than their school mates – such as predators .
The team , which reports its work in Nature Communications , concludes that real fish use vortex phase matching “ at least in part ” to save energy .
This @ @ @ @ @ @ @ be applied to improve the collective swimming efficiency of fish-like underwater vehicles , the researchers say .
Members of the team , which also includes scientists from Peking University , now plan to develop more advanced robots and to study “ hybrid swarms ” composed of real and robotic fish .
In doing so , they hope to uncover further collective benefits of schooling .

Robot-like fish provide insight into how fish can save energy by swimming in schools. Credit: Liang Li, Max Planck Institute of Animal Behavior (MPI-AB)
Swimming in schools helps fish avoid predators, but it also allows them to conserve energy. This is the finding of researchers in Germany, China and Hungary who used fish-like robots to investigate how real fish might gain from the watery vortices that other fish generate as they swim. The phenomenon they observed is known as vortex phase matching, and the researchers say that understanding how it works could inspire the development of more efficient fish-like underwater vehicles.
While scientists have long suspected that swimming fish might exploit the swirling hydrodynamic flows created by their neighbours, it was not clear how individual fish coordinated their movements to benefit from these vortices. Researchers led by Iain Couzin at the Max Planck Institute of Animal Behavior and the University of Konstanz studied this question by constructing fish-like robots and measuring how much energy they consume when swimming in pairs (the most common swimming configuration in natural fish populations) compared to when they swim alone. Such measurements would, they say, be impossible to perform on real animals.
“Robofish”
The researchers’ robotic fish are 45 cm long with a mass of 0.8 kg. Each boasts three sequential servo-motors that are connected to joints covered in a soft, waterproof, rubber skin, and controlled using a “central pattern generator” that enables the robot to mimic the undulations of real fish.
Over the course of 10 080 trials (representing 120 hours of swimming time), the researchers monitored how their “robofish” behaved when placed at different distances from a “lead” robofish. They found that paired-up fish consume much less energy than loners because the followers adjust their tailbeats to match the induced flow of the vortices shed by the leader. The matching takes place with a time lag that varies with distance: when the follower fish is beside the leader, the tailbeats are synchronized, but when the follower falls behind, its tailbeats go out of sync, with a delay that increases the further away it gets.
This vortex phase matching allows the follower fish to exploit the “Kármán vortices” – chains of swirling vortices shed by a blunt object as it travels through a liquid – that the leader fish leaves in its wake. The result is a reduction in the follower’s energy consumption, but team member Máté Nagy of the Hungarian Academy of Sciences and Eötvös University notes that it’s not just about saving energy. “By changing the way they synchronize, followers can also use the vortices shed by other fish to generate thrust and help them accelerate,” he explains.
Comparison to real fish
To find out whether real fish use vortex phase matching too, Couzin and colleagues made observations on 32 freely-swimming pairs of goldfish. While the real fish constantly changed positions relative to each other, the researchers observed that they nonetheless adopted a type of hydrodynamic interaction that could be described by a simple mathematical model that incorporates swim speed and the amplitude and frequency of the leader’s tailbeats. This model, Couzin tells Physics World, was then used to predict how real fish would behave if they were using vortex phase matching, and tested using artificial-intelligence-assisted analysis of the body posture of goldfish as they swim together.
The results indicate that real fish do indeed exploit vortex phase matching. According to the researchers, this strategy “may be a result of preflex or proprioceptive responses to neighbour-generated hydrodynamic cues”, since neither the fishes’ visual nor their lateral-line systems are required for them to behave this way. This leaves fish free to process other important information from their environment, including flows created by creatures other than their school mates – such as predators.
The team, which reports its work in Nature Communications, concludes that real fish use vortex phase matching “at least in part” to save energy. This simple and robust natural strategy might now be applied to improve the collective swimming efficiency of fish-like underwater vehicles, the researchers say.
Members of the team, which also includes scientists from Peking University, now plan to develop more advanced robots and to study “hybrid swarms” composed of real and robotic fish. In doing so, they hope to uncover further collective benefits of schooling.