physicsworld--2020-10-10--Physicists place fresh limits on gravity’s role in wavefunction collapse - Physics World

Our everyday experience shows that the macroscopic world is different from the quantum one .
Unlike quantum particles , the objects in our daily existence do not , for example , exist in a superposition of different states .
Traditionally , physicists explain the transition between the two worlds by saying that the quantum superposition principle , which is the building block of quantum theory , breaks down when measurements are performed .
The wavefunction of this system is then said to “ collapse ” with the measurement .
Why such a collapse should happen is still unclear , but @ @ @ @ @ @ @ physicist Roger Penrose , and drawing on earlier work by Lajos Diósi – suggests that gravity might play a role .
Researchers in Italy , Germany and Hungary have now set important constraints on this so-called Diósi-Penrose model , in a work that could shed fresh light on a long-standing puzzle in quantum theory : why don ’ t the inherent properties of microscopic systems carry over to macroscopic ones ?
In 1996 , Penrose suggested that the collapse of quantum superpositions might be caused by the curvature of space-time – that is @ @ @ @ @ @ @ gravitation , he reasoned , are negligible at the level of atoms , but increase dramatically at the level of macroscopic objects .
Penrose also provided a formula to compute the decay of the superposition , using methods that were similar to Diósi ’ s earlier work .
In this Diósi-Penrose ( DP ) model , the gravity-related wavefunction collapse , which depends on the effective size of the mass density of particles in the superposition , induces a random motion of the particles .
When the particles are charged ( like protons @ @ @ @ @ @ @ ” produces a characteristic and very faint emission of electromagnetic radiation .
A team of researchers led by Angelo Bassi of the University of Trieste has now computed the rate at which this radiation is emitted by solving the main equation of the DP model .
They did this by calculating the number of photons emitted per unit time and unit frequency integrated over all spatial directions in the wavelength range λ of 10−5 to 10−1 nm , which corresponds to energies E of 10–105 keV .
In a further development , a @ @ @ @ @ @ @ and Matthias Laubenstein from the INFN and Kristian Piscicchia from the Enrico Fermi Research Center , both in Italy , went on to measure this calculated radiation rate in an experiment at the INFN-LNGS Gran Sasso underground laboratory in Assergi .
According to study lead author Sandro Donadi of the Frankfurt Institute for Advanced Studies , the experiment was designed to be sensitive to the faint X- and gamma-ray radiation that the DP model predicts .
To this end , the researchers used a high-purity germanium detector to measure the radiation spectrum at @ @ @ @ @ @ @ should be enhanced .
They also constructed their whole setup using materials with very low radioactivity and enveloped it in a complex system of shielding .
Finally , they carried out their experiments in an underground facility specially built to have low background radioactivity .
“ All this effort was intended to minimize background noise sources that can mimic the collapse-related radiation that we are looking for , ” Donadi says .
In addition to these measures , the researchers carefully characterized the background spectrum produced by known natural contamination sources that can @ @ @ @ @ @ @ experimental precautions with refined theoretical and statistical analyses of their data , they were able to set a lower bound on the effective size of the nuclei ’ s mass density .
This lower bound is equivalent to about 1 Å , or approximately three orders of magnitude larger than previously reported bounds .
Not ruled out yet “ Our result suggests that more work needs to be done to relate gravity to wavefunction collapse , since it excludes the most natural ( ‘ parameter-free ’ ) version of the DP model , @ @ @ @ @ @ @ However , it would be premature to dismiss gravity ’ s role at this stage.
” Donadi adds that Diósi and Penrose put forward good reasons for believing that there is a tension between the quantum superposition principle and general relativity .
“ We now intend to investigate possible solutions to this by developing refined wavefunction collapse models based on our recent findings , ” he says .
In the short term , the researchers plan to apply a similar type of analysis to other collapse theories , such as the GRW model @ @ @ @ @ @ @ Rimini and Tullio Weber , and another model known as Continuous Spontaneous Localization ( CSL ) .
These other models are more difficult to falsify , Donadi explains , because of the different mathematical relationships between the models ’ parameters and the expected radiation emission rate .
“ These studies will ultimately push us in the direction of realizing new , more sensitive experimental setups based on new vanguard radiation detectors , data acquisition systems and analyses methods , ” Curceanu adds .
The work is detailed in Nature Physics .

The INFN Gran Sasso National Laboratory (LNGS). Courtesy: INFN-LNGS
Our everyday experience shows that the macroscopic world is different from the quantum one. Unlike quantum particles, the objects in our daily existence do not, for example, exist in a superposition of different states. Traditionally, physicists explain the transition between the two worlds by saying that the quantum superposition principle, which is the building block of quantum theory, breaks down when measurements are performed. The wavefunction of this system is then said to “collapse” with the measurement.
Why such a collapse should happen is still unclear, but one model – developed by the mathematical physicist Roger Penrose, and drawing on earlier work by Lajos Diósi – suggests that gravity might play a role. Researchers in Italy, Germany and Hungary have now set important constraints on this so-called Diósi–Penrose model, in a work that could shed fresh light on a long-standing puzzle in quantum theory: why don’t the inherent properties of microscopic systems carry over to macroscopic ones?
Gravity-related wavefunction collapse
In 1996, Penrose suggested that the collapse of quantum superpositions might be caused by the curvature of space–time – that is, by gravity. The effects of gravitation, he reasoned, are negligible at the level of atoms, but increase dramatically at the level of macroscopic objects. Penrose also provided a formula to compute the decay of the superposition, using methods that were similar to Diósi’s earlier work.
In this Diósi–Penrose (DP) model, the gravity-related wavefunction collapse, which depends on the effective size of the mass density of particles in the superposition, induces a random motion of the particles. When the particles are charged (like protons and electrons), this “jitter” produces a characteristic and very faint emission of electromagnetic radiation.
A team of researchers led by Angelo Bassi of the University of Trieste has now computed the rate at which this radiation is emitted by solving the main equation of the DP model. They did this by calculating the number of photons emitted per unit time and unit frequency integrated over all spatial directions in the wavelength range λ ∈ of 10−5 to 10−1 nm, which corresponds to energies E ∈ of 10–105 keV. In a further development, a team of experimentalists led by Catalina Curceanu and Matthias Laubenstein from the INFN and Kristian Piscicchia from the Enrico Fermi Research Center, both in Italy, went on to measure this calculated radiation rate in an experiment at the INFN-LNGS Gran Sasso underground laboratory in Assergi.
Dedicated underground experiment
According to study lead author Sandro Donadi of the Frankfurt Institute for Advanced Studies, the experiment was designed to be sensitive to the faint X- and gamma-ray radiation that the DP model predicts. To this end, the researchers used a high-purity germanium detector to measure the radiation spectrum at the point at which theory predicts it should be enhanced. They also constructed their whole setup using materials with very low radioactivity and enveloped it in a complex system of shielding. Finally, they carried out their experiments in an underground facility specially built to have low background radioactivity. “All this effort was intended to minimize background noise sources that can mimic the collapse-related radiation that we are looking for,” Donadi says.
In addition to these measures, the researchers carefully characterized the background spectrum produced by known natural contamination sources that cannot be eliminated. By combining these experimental precautions with refined theoretical and statistical analyses of their data, they were able to set a lower bound on the effective size of the nuclei’s mass density. This lower bound is equivalent to about 1 Å, or approximately three orders of magnitude larger than previously reported bounds.
Not ruled out yet
“Our result suggests that more work needs to be done to relate gravity to wavefunction collapse, since it excludes the most natural (‘parameter-free’) version of the DP model,” Donadi tells Physics World. “However, it would be premature to dismiss gravity’s role at this stage.”
Donadi adds that Diósi and Penrose put forward good reasons for believing that there is a tension between the quantum superposition principle and general relativity. “We now intend to investigate possible solutions to this by developing refined wavefunction collapse models based on our recent findings,” he says.
In the short term, the researchers plan to apply a similar type of analysis to other collapse theories, such as the GRW model put forward by Giancarlo Ghirardi, Alberto Rimini and Tullio Weber, and another model known as Continuous Spontaneous Localization (CSL). These other models are more difficult to falsify, Donadi explains, because of the different mathematical relationships between the models’ parameters and the expected radiation emission rate.
“These studies will ultimately push us in the direction of realizing new, more sensitive experimental setups based on new vanguard radiation detectors, data acquisition systems and analyses methods,” Curceanu adds.
The work is detailed in Nature Physics.


physicsworld--2020-10-12--Nanocrystals could drive explosive volcanic eruptions - Physics World

The formation of nanometre-sized crystals can – even in low concentrations – temporarily change the viscosity of magma and lead to violent volcanic eruptions .
That is the conclusion of geophysicists in the UK , Germany and France , who say that their research helps to explain how otherwise calm and predictable volcanoes can turn unexpectedly explosive .
There are essentially two types of volcanic eruption : explosive and effusive .
In the former , viscous molten rock with a high silica content tends to trap volcanic gases more readily .
This increases the pressure on the magma column such @ @ @ @ @ @ @ explosion .
Basaltic magmas , meanwhile , have a low silica content and tend to be runnier .
This usually allow gas to escape gently , leading to effusive eruptions that produce lava domes and flows of the kind seen on Hawaii .
This distinction is not clear cut , however , and basaltic magmas can sometimes unexpectedly produce explosive events .
This happened at New Zealand ’ s Mount Tarawera in June 1886 , which destroyed ten Māori settlements and killed around 120 people .
A common explanation for this unexpected explosivity @ @ @ @ @ @ @ microlites , which are small crystals ranging in size from 1–100 micron .
In sufficient volumes , these can lock up magma flow , leading to explosive fragmentation .
This occurs when magma flow switches from being a continuous liquid body containing gas and crystals to a turbulent flow dominated by gases that contain fragments of molten rock .
There is one problem with this theory , however , in that many such unexpected explosions ( including Indonesia ’ s Mount Tambora in 1815 – the most powerful eruption in human history ) @ @ @ @ @ @ @ seemingly not at a sufficiently high level of around 30 % total volume .
In a new study , volcanologist Danilo Di Genova of the University of Bristol and colleagues considered the effects of nanolites , which are smaller crystals that are the precursors of microlites .
Using scanning electron transmission microscopy and Raman spectroscopy , the team revealed the presence of previously-unidentified nanolites ( 20–50 nm in size ) in ash samples from three low-viscosity eruptions : Italy ’ s Mount Etna ( 122 BC ) ; the Colli Albani volcano ( @ @ @ @ @ @ @ Mount Tambora .
The team then created their own nanolites in the lab by melting and then cooling volcanic rock samples .
Synchrotron-based X-ray spectroscopy revealed how nanolites grow under rapid cooling regimes of around 10–20 degrees per second .
This cooling is typical of that experienced by magma that is ascending quickly at metres-per-second speeds .
Further experiments with a synthetic magma , alongside modelling , suggest that the after-effect of so-called undercooling ( where a magma , unable to solidify thanks to its dissolved water content , rapidly crystallizes once it @ @ @ @ @ @ @ nanolite growth .
Furthermore , the team found that even in low nanolite concentrations of 5 % by volume , the spacing between each nanolite can be very small .
“ It is already accepted that even a low viscosity melt struggles to flow if it becomes locked by a network of crystals , but this usually requires a fraction of well over 30 % , ” Di Genova explained .
“ Nanolites also have a propensity to agglomerate together and form new and larger solid objects .
During this process , volcanic @ @ @ @ @ @ @ effectively increase the fraction of solids in the magma.
” Together , he explained , these processes account for how nanolites can increase magma viscosity for a short time as they form – leading to the previously inexplicable “ sudden switch in behaviour , ” that can cause calm volcanoes “ to occasionally present us with a deadly surprise ” .
“ Nanoparticles suspended in a very low viscosity fluid appear to have a great effect increasing the bulk viscosity of the suspension even at low concentrations – a factor which could , @ @ @ @ @ @ @ explosivity during eruptions , ” comments Francisco Cáceres , an experimental volcanologist from the Ludwig-Maximilians-University of Munich .
He adds , “ This work opens a window to new research that needs to be performed on natural magma , in order to test this claim ” .
University of Cambridge volcanologist Marie Edmonds adds , “ This work will have very important implications for our understanding of basaltic explosive eruptions but also more broadly for magma rheology , nucleation and growth of crystals and bubbles ; and the strength of magma under shear @ @ @ @ @ @ @ future to understand whether wet magmas – those containing lots of water , such as in subduction zones – behave in the same way as those in the experiments , which were dry.
” With their initial study complete , the researchers are moving to model the explosive impact of nanolites on real-life low-silica volcanic settings .
When travel restrictions lift after the pandemic , they will be hunting for more examples of nanolites in volcanic rock from across the globe .
The research is described in the Science Advances .

Effusive volcano: lava flowing down the slopes of Mount Mayon in the Philippines. (Courtesy: Top1963/CC BY-SA 3.0)
The formation of nanometre-sized crystals can – even in low concentrations – temporarily change the viscosity of magma and lead to violent volcanic eruptions. That is the conclusion of geophysicists in the UK, Germany and France, who say that their research helps to explain how otherwise calm and predictable volcanoes can turn unexpectedly explosive.
There are essentially two types of volcanic eruption: explosive and effusive. In the former, viscous molten rock with a high silica content tends to trap volcanic gases more readily. This increases the pressure on the magma column such that it can ultimately lead to an explosion. Basaltic magmas, meanwhile, have a low silica content and tend to be runnier. This usually allow gas to escape gently, leading to effusive eruptions that produce lava domes and flows of the kind seen on Hawaii.
This distinction is not clear cut, however, and basaltic magmas can sometimes unexpectedly produce explosive events. This happened at New Zealand’s Mount Tarawera in June 1886, which destroyed ten Māori settlements and killed around 120 people.
Explosive fragmentation
A common explanation for this unexpected explosivity is the growth in molten rock of microlites, which are small crystals ranging in size from 1–100 micron. In sufficient volumes, these can lock up magma flow, leading to explosive fragmentation. This occurs when magma flow switches from being a continuous liquid body containing gas and crystals to a turbulent flow dominated by gases that contain fragments of molten rock.
There is one problem with this theory, however, in that many such unexpected explosions (including Indonesia’s Mount Tambora in 1815 – the most powerful eruption in human history) occurred even though their microlite concentrations were seemingly not at a sufficiently high level of around 30% total volume.
In a new study, volcanologist Danilo Di Genova of the University of Bristol and colleagues considered the effects of nanolites, which are smaller crystals that are the precursors of microlites. Using scanning electron transmission microscopy and Raman spectroscopy, the team revealed the presence of previously-unidentified nanolites (20–50 nm in size) in ash samples from three low-viscosity eruptions: Italy’s Mount Etna (122 BC); the Colli Albani volcano (about 37,000 years ago); and Mount Tambora.
Rapid cooling
The team then created their own nanolites in the lab by melting and then cooling volcanic rock samples. Synchrotron-based X-ray spectroscopy revealed how nanolites grow under rapid cooling regimes of around 10–20 degrees per second. This cooling is typical of that experienced by magma that is ascending quickly at metres-per-second speeds. Further experiments with a synthetic magma, alongside modelling, suggest that the after-effect of so-called undercooling (where a magma, unable to solidify thanks to its dissolved water content, rapidly crystallizes once it degasses) provides the ideal scenario for nanolite growth.
Furthermore, the team found that even in low nanolite concentrations of 5% by volume, the spacing between each nanolite can be very small. “It is already accepted that even a low viscosity melt struggles to flow if it becomes locked by a network of crystals, but this usually requires a fraction of well over 30%,” Di Genova explained. “Nanolites also have a propensity to agglomerate together and form new and larger solid objects. During this process, volcanic liquid remains trapped inside these agglomerates to effectively increase the fraction of solids in the magma.”
Together, he explained, these processes account for how nanolites can increase magma viscosity for a short time as they form – leading to the previously inexplicable “sudden switch in behaviour,” that can cause calm volcanoes “to occasionally present us with a deadly surprise”.
“Nanoparticles suspended in a very low viscosity fluid appear to have a great effect increasing the bulk viscosity of the suspension even at low concentrations – a factor which could, if confirmed for magma viscosity, enhance explosivity during eruptions,” comments Francisco Cáceres, an experimental volcanologist from the Ludwig-Maximilians-University of Munich. He adds, “This work opens a window to new research that needs to be performed on natural magma, in order to test this claim”.
University of Cambridge volcanologist Marie Edmonds adds, “This work will have very important implications for our understanding of basaltic explosive eruptions but also more broadly for magma rheology, nucleation and growth of crystals and bubbles; and the strength of magma under shear. It will be important in the future to understand whether wet magmas – those containing lots of water, such as in subduction zones – behave in the same way as those in the experiments, which were dry.”
With their initial study complete, the researchers are moving to model the explosive impact of nanolites on real-life low-silica volcanic settings. When travel restrictions lift after the pandemic, they will be hunting for more examples of nanolites in volcanic rock from across the globe.
The research is described in the Science Advances.


physicsworld--2020-10-13--Black metal hydrogen emerges at high pressures - Physics World

At pressures of millions of atmospheres , hydrogen – normally an excellent insulator thanks to the tightly-bound electrons in the H molecule – becomes an electrical conductor .
Its exact transition point is , however , the subject of much debate , with the results of several recent experiments seemingly contradicting each other .
Researchers in Italy , Spain and France now say they have resolved the discrepancy by using an advanced computing technique that takes the quantum fluctuations of protons into account when simulating the behaviour of hydrogen at high pressures .
The group ’ s simulations also reveal @ @ @ @ @ @ @ very little light , and would thus appear pitch-black to anyone who observed it – further proof , says study lead author Lorenzo Monacelli , that metallic hydrogen is a very peculiar substance indeed .
Solid hydrogen at high pressures boasts a rich phase diagram , with five insulating molecular phases labelled I to V. The idea that it might become metallic at high pressures can be traced back to a theoretical proposal made by the Hungarian-born physicist Eugene Wigner and his American colleague Hillard Bell Huntington in 1935 .
Since then , @ @ @ @ @ @ @ in the core of gas-giant planets like Jupiter and Saturn .
It has also been suggested that metallic hydrogen could be a room-temperature superconductor .
Difficult to stabilize and challenging to characterize Such predictions are hard to confirm , however , because metallic hydrogen is extremely difficult to stabilize in the laboratory .
It is also challenging to characterize , since it does not interact with X-rays and techniques that rely on neutron scattering can not be used at high pressures .
Scientists must therefore infer its structure indirectly , using vibrational spectroscopy @ @ @ @ @ @ @ optical approaches that measure light transmittance and reflectivity from a sample .
These intense experimental difficulties may well explain why different research groups have obtained apparently contradictory results about the behaviour of hydrogen at low temperatures and high pressures .
Optical reflectivity measurements suggest that metallization takes place in atomic hydrogen at 495 GPa , when the element transforms from a black lower-pressure phase to a shiny higher-pressure one .
Electrical conductivity measurements , meanwhile , imply that hydrogen in phase III – a molecular phase in which the strength of the hydrogen-hydrogen @ @ @ @ @ @ @ that protons can jump between different molecules – exhibits semi-metallic behaviour at pressures above 360 GPa .
Infrared light transmission experiments , for their part , suggest that phase III hydrogen becomes metallic at 420 GPa .
According to researchers led by Francesco Mauri of the University Sapienza in Rome , these results are not , in fact , contradictory .
The team came to this conclusion by simulating the properties of phase III hydrogen under pressures of between 150 GPa and 450 GPa .
In their simulations , they used a technique @ @ @ @ @ @ @ ) to account for quantum effects on the hydrogen nuclei .
Simply put , this technique simulates the wavefunction of the hydrogen nuclei ( protons ) by sampling their probability cloud – that is , the collection of locations where nuclei are likely to be found .
The researchers then solved the electrons ’ quantum equations for each configuration of nuclei .
This approach means that nuclei are not treated as static “ balls ” frozen in position , as is the case in most simulations .
Instead , the nuclei have delocalized @ @ @ @ @ @ @ the probability of where they might be located at a given time .
Based on these simulations , the researchers found that phase III hydrogen starts conducting electricity at 370 GPa – a result that Monacelli says is “ in very close agreement with previous experimental findings ” – while reflecting very little light even at the highest pressures .
They also found that factoring in quantum effects on nuclei has a dramatic impact on hydrogen ’ s physical properties .
This impact was expected , since the nucleus of hydrogen ( the @ @ @ @ @ @ @ quantum fluctuations , but Monacelli says that the difference was still impressive .
“ We found that the bond length of the H molecules increases by 6 % ( which is huge in terms of the energy involved ) if quantum effects are considered , ” he explains .
“ The [ simulated ] Raman and infrared spectra completely change when these effects are taken into account , with signal peaks shifting by more than 25 % and their energy profile broadening a lot.
” Such simulations of vibrational spectra are important , @ @ @ @ @ @ @ the only way we can understand the crystalline structure of high-pressure hydrogen ” .
Encouragingly , he adds that the team ’ s calculated results exhibited “ a remarkable agreement ” with results from experimental studies of infrared absorption .
Based on these results ( which are detailed in Nature Physics ) , Monacelli says that if the data from the optical reflectivity experiments are correct , then the high measured reflectivities observed in those experiments are not consistent with hydrogen existing in a molecular phase .
Instead , they imply that hydrogen @ @ @ @ @ @ @ We have proven that molecular metallic hydrogen is very peculiar , ” he tells Physics World .
“ It is conductive , black , and transparent in the infrared .
This is almost unique for a metal.
” The calculations of Mauri , Monacelli and colleagues also led them to make a new prediction : deuterium – hydrogen ’ s heavier isotope , with a neutron as well as a proton in its nucleus – should start to conduct electricity at pressures 70 GPa higher than ordinary hydrogen .
“ This prediction could @ @ @ @ @ @ @ further support or contradict our results , ” Monacelli says .

The phases of hydrogen. Courtesy: Source: I F Silvera/Harvard University
At pressures of millions of atmospheres, hydrogen – normally an excellent insulator thanks to the tightly-bound electrons in the H 2 molecule – becomes an electrical conductor. Its exact transition point is, however, the subject of much debate, with the results of several recent experiments seemingly contradicting each other. Researchers in Italy, Spain and France now say they have resolved the discrepancy by using an advanced computing technique that takes the quantum fluctuations of protons into account when simulating the behaviour of hydrogen at high pressures. The group’s simulations also reveal that hydrogen in this metal-like phase reflects very little light, and would thus appear pitch-black to anyone who observed it – further proof, says study lead author Lorenzo Monacelli, that metallic hydrogen is a very peculiar substance indeed.
Solid hydrogen at high pressures boasts a rich phase diagram, with five insulating molecular phases labelled I to V. The idea that it might become metallic at high pressures can be traced back to a theoretical proposal made by the Hungarian-born physicist Eugene Wigner and his American colleague Hillard Bell Huntington in 1935. Since then, metallic hydrogen has been predicted to exist in the core of gas-giant planets like Jupiter and Saturn. It has also been suggested that metallic hydrogen could be a room-temperature superconductor.
Difficult to stabilize and challenging to characterize
Such predictions are hard to confirm, however, because metallic hydrogen is extremely difficult to stabilize in the laboratory. It is also challenging to characterize, since it does not interact with X-rays and techniques that rely on neutron scattering cannot be used at high pressures. Scientists must therefore infer its structure indirectly, using vibrational spectroscopy techniques like Raman and infrared spectroscopy or optical approaches that measure light transmittance and reflectivity from a sample.
These intense experimental difficulties may well explain why different research groups have obtained apparently contradictory results about the behaviour of hydrogen at low temperatures and high pressures. Optical reflectivity measurements suggest that metallization takes place in atomic hydrogen at 495 GPa, when the element transforms from a black lower-pressure phase to a shiny higher-pressure one. Electrical conductivity measurements, meanwhile, imply that hydrogen in phase III – a molecular phase in which the strength of the hydrogen-hydrogen bonds is thought to become so weak that protons can jump between different molecules – exhibits semi-metallic behaviour at pressures above 360 GPa. Infrared light transmission experiments, for their part, suggest that phase III hydrogen becomes metallic at 420 GPa.
Not contradictory
According to researchers led by Francesco Mauri of the University Sapienza in Rome, these results are not, in fact, contradictory. The team came to this conclusion by simulating the properties of phase III hydrogen under pressures of between 150 GPa and 450 GPa. In their simulations, they used a technique called the Self-Consistent Harmonic Approximation (SCHA) to account for quantum effects on the hydrogen nuclei. Simply put, this technique simulates the wavefunction of the hydrogen nuclei (protons) by sampling their probability cloud – that is, the collection of locations where nuclei are likely to be found. The researchers then solved the electrons’ quantum equations for each configuration of nuclei.
This approach means that nuclei are not treated as static “balls” frozen in position, as is the case in most simulations. Instead, the nuclei have delocalized wavefunctions, the square of which describe the probability of where they might be located at a given time.
Based on these simulations, the researchers found that phase III hydrogen starts conducting electricity at 370 GPa – a result that Monacelli says is “in very close agreement with previous experimental findings” – while reflecting very little light even at the highest pressures. They also found that factoring in quantum effects on nuclei has a dramatic impact on hydrogen’s physical properties. This impact was expected, since the nucleus of hydrogen (the lightest element) is subject to large quantum fluctuations, but Monacelli says that the difference was still impressive.
“We found that the bond length of the H 2 molecules increases by 6% (which is huge in terms of the energy involved) if quantum effects are considered,” he explains. “The [simulated] Raman and infrared spectra completely change when these effects are taken into account, with signal peaks shifting by more than 25% and their energy profile broadening a lot.” Such simulations of vibrational spectra are important, he says, because they are “the only way we can understand the crystalline structure of high-pressure hydrogen”. Encouragingly, he adds that the team’s calculated results exhibited “a remarkable agreement” with results from experimental studies of infrared absorption.
Very peculiar
Based on these results (which are detailed in Nature Physics), Monacelli says that if the data from the optical reflectivity experiments are correct, then the high measured reflectivities observed in those experiments are not consistent with hydrogen existing in a molecular phase. Instead, they imply that hydrogen is in its atomic form. “We have proven that molecular metallic hydrogen is very peculiar,” he tells Physics World. “It is conductive, black, and transparent in the infrared. This is almost unique for a metal.”
The calculations of Mauri, Monacelli and colleagues also led them to make a new prediction: deuterium – hydrogen’s heavier isotope, with a neutron as well as a proton in its nucleus – should start to conduct electricity at pressures 70 GPa higher than ordinary hydrogen. “This prediction could be confirmed in the coming months to further support or contradict our results,” Monacelli says.


physicsworld--2020-10-13--Fluttering polymer ribbons harvest electrical energy - Physics World

A new low-cost nanogenerator that can efficiently harvest electrical energy from ambient wind has been created by Ya Yang at the Beijing Institute of Nanoenergy and Nanosystems of the Chinese Academy of Sciences and colleagues .
The team reports that the device achieves high electrical conversion efficiencies for breezes of 4–8 m/s ( 14–28 km/h ) and say that it could be used to generate electricity in everyday situations , where conventional wind turbines are not practical .
As the drive to develop renewable sources of energy intensifies , there is growing interest in harvesting ambient energy in everyday environments @ @ @ @ @ @ @ to the airflows created as we walk , the mechanical energy contained in ambient wind is abundant .
The challenge is to harvest this every in an efficient and practical way .
This has proven difficult using existing technologies such as piezoelectric films , which operate at very low power outputs .
Yang ’ s team based their new design around two well-known phenomena in physics .
The first is the Bernoulli effect , which causes the fluttering of two adjacent flags to couple .
If separated by a very small gap , @ @ @ @ @ @ @ at slightly larger separations , they flap out-of-phase , and symmetrically about a central plane .
The second is the triboelectric effect – the familiar phenomenon behind the “ static electricity ” that is created when different objects are rubbed together and then separated – resulting in opposite electrical charges on the objects and a voltage between the two .
Using two polymer ribbons ; one coated with a silver electrode , and the other with the polymer FEP , Yang and colleagues combined these phenomena to create a “ Bernoulli effect-dominated triboelectric @ @ @ @ @ @ @ subjected to a parallel airflow , the out-of-phase fluttering of the ribbons causes them to touch and separate periodically ; resulting in a build-up of charge which could be used to generate an output voltage .
The researchers showed that their 3×8 cm device created usable electrical energy for wind speeds as low as 1.6 m/s , with conversion efficiencies exceeding 3.2 % for speeds between 4–8 m/s .
The device ’ s practicality was demonstrated by using it to illuminating 100 LEDs in a series circuit ; integrating it into a self-powering @ @ @ @ @ @ @ a 100 µF capacitor to 3 V in 3 min .
Together , these elements were incorporated into a self-powered pressure sensor for a pipeline , using lightweight and extremely low-cost materials .
Yang ’ s team now hope to improve the B-TENG ’ s efficiency to make it even more compact – potentially enabling its integration with everyday devices .
At the same time , they also hope to scale-up the device to create kilowatt-scale generators , which could compete with traditional wind turbines .
If successful , the B-TENG could be @ @ @ @ @ @ @ , which can be charged by the airflow generated by walking ; to clean power generation in biodiverse areas , where spinning turbines can be harmful to wildlife .
B-TENG is described in Cell Reports Physical Science .

Gentle breeze: illustration of the B-TENG triboelectric nanogenerator, which harvests electricity that is generated by fluttering polymer strips. (Courtesy: Xin Chen/Xiaojing Mu/Ya Yang)
A new low-cost nanogenerator that can efficiently harvest electrical energy from ambient wind has been created by Ya Yang at the Beijing Institute of Nanoenergy and Nanosystems of the Chinese Academy of Sciences and colleagues. The team reports that the device achieves high electrical conversion efficiencies for breezes of 4–8 m/s (14–28 km/h) and say that it could be used to generate electricity in everyday situations, where conventional wind turbines are not practical.
As the drive to develop renewable sources of energy intensifies, there is growing interest in harvesting ambient energy in everyday environments. From breezes along city streets, to the airflows created as we walk, the mechanical energy contained in ambient wind is abundant. The challenge is to harvest this every in an efficient and practical way. This has proven difficult using existing technologies such as piezoelectric films, which operate at very low power outputs.
Yang’s team based their new design around two well-known phenomena in physics. The first is the Bernoulli effect, which causes the fluttering of two adjacent flags to couple. If separated by a very small gap, the flags will flutter in-phase, while at slightly larger separations, they flap out-of-phase, and symmetrically about a central plane. The second is the triboelectric effect – the familiar phenomenon behind the “static electricity” that is created when different objects are rubbed together and then separated – resulting in opposite electrical charges on the objects and a voltage between the two.
Two polymer ribbons
Using two polymer ribbons; one coated with a silver electrode, and the other with the polymer FEP, Yang and colleagues combined these phenomena to create a “Bernoulli effect-dominated triboelectric nanogenerator”, or B-TENG. When subjected to a parallel airflow, the out-of-phase fluttering of the ribbons causes them to touch and separate periodically; resulting in a build-up of charge which could be used to generate an output voltage.
The researchers showed that their 3×8 cm device created usable electrical energy for wind speeds as low as 1.6 m/s, with conversion efficiencies exceeding 3.2% for speeds between 4–8 m/s. The device’s practicality was demonstrated by using it to illuminating 100 LEDs in a series circuit; integrating it into a self-powering thermometer; and using it to charge a 100 µF capacitor to 3 V in 3 min. Together, these elements were incorporated into a self-powered pressure sensor for a pipeline, using lightweight and extremely low-cost materials.
Yang’s team now hope to improve the B-TENG’s efficiency to make it even more compact – potentially enabling its integration with everyday devices. At the same time, they also hope to scale-up the device to create kilowatt-scale generators, which could compete with traditional wind turbines. If successful, the B-TENG could be used in applications ranging from wearable electronics, which can be charged by the airflow generated by walking; to clean power generation in biodiverse areas, where spinning turbines can be harmful to wildlife.
B-TENG is described in Cell Reports Physical Science.


physicsworld--2020-10-13--Positronium formed during PET scans could detect hypoxic tumours - Physics World

A variation on positron emission tomography ( PET ) offers a new way to diagnose hypoxia in tumours .
Researchers at the University of Tokyo and Japan ’ s National Institute of Radiological Sciences demonstrated that positronium , which forms in tissues due to positron emission from a radiopharmaceutical agent , decays differently depending upon its chemical environment , and is especially sensitive to local oxygen saturation .
This means that signs of tumour hypoxia could be spotted among the gamma rays collected routinely during PET imaging , providing clinicians with an additional source of information to guide treatment decisions @ @ @ @ @ @ @ scan are annihilated almost as soon as they are emitted : they lose energy through interactions with nearby molecules , then collide with electrons in those molecules to produce pairs of 511 keV photons .
Some positrons hang around a little longer , however , and instead of annihilating the electrons that they encounter , they capture them , forming metastable positronium atoms .
When this happens , the positronium is created in one of two distinct configurations .
The least stable is para-positronium ( p-Ps ) , in which the spins of @ @ @ @ @ @ @ directions .
p-Ps atoms have a mean lifetime of only 125 ps , after which they decay into a pair of 511 keV photons .
This process therefore adds to the near-immediate gamma signal produced by annihilation of those positrons that never form a positronium atom .
The other configuration is ortho-positronium ( o-Ps ) , in which the spins of the electron and positron are parallel .
Left alone , o-Ps would decay into three photons ( with energies ranging from 0 to 511 keV ) after a mean lifetime of 142 @ @ @ @ @ @ @ that o-Ps atoms have more time to interact with their surroundings before they decay .
One of the routes open to o-Ps atoms is an interaction called spin exchange .
In this process , the positronium ’ s electron switches with an electron of opposite spin in a nearby molecule .
This converts the positronium atom into the less stable p-Ps form , hastening its decay .
The likelihood of spin exchange occurring depends on the availability of unpaired electrons in the vicinity of the o-Ps atoms .
In tissues , such unpaired @ @ @ @ @ @ @ .
This means that in oxygen-poor environments such as hypoxic tumours , more o-Ps atoms survive long enough to decay via the three-photon route .
Measuring the timing and spectrum of the gamma rays emitted during the PET procedure should , therefore , yield information about the oxygen saturation .
As they report in Communications Physics , Kengo Shibuya and colleagues tested this principle by preparing samples of water saturated with either air , nitrogen or oxygen .
Each sample also contained the unstable sodium isotope 22Na .
When 22Na undergoes beta decay @ @ @ @ @ @ @ ray at 1.27 MeV .
The researchers used this signal as the starter pistol for each measurement .
In instances where the positron emission resulted in a positronium atom , the end of the measurement was marked by the detection of sub-511-keV photons announcing the positronium ’ s final decay .
By comparing the timing and energy of the photons emitted during millions of measurement intervals for the three samples , the team derived a linear relationship between oxygen saturation and positronium decay rate .
They calculated that , in a clinical PET @ @ @ @ @ @ @ 30 min would yield enough measurements to distinguish a hypoxic tumour from normally oxygenated healthy tissue .
In terms of detector hardware , current PET devices are already suited to this task , although the researchers say that they will need new timer systems and software .
“ The performance required by the new timers is comparable to those already used in conventional PET , ” says Shibuya .
“ Therefore , I think it will not be difficult for medical device manufacturers to install them.
” Finding the right radiopharmaceutical agent might @ @ @ @ @ @ @ PET imaging techniques employ pure positron emitters , positronium imaging can only work if , like 22Na , the radioisotope emits a gamma photon and a positron simultaneously .
Unfortunately , the 2.6-year half-life of 22Na makes it unsuitable for the clinic , for which sources with half-lives on the order of hours or days are required .

Researchers in Japan aim to use PET scans to detect oxygen concentration in tumours, which may lead to more effective cancer treatment. From left: Taiga Yamaya, Miwako Takahashi, Fumihiko Nishikido and Kengo Shibuya. (Courtesy: Taiga Yamaya, CC BY 4.0)
A variation on positron emission tomography (PET) offers a new way to diagnose hypoxia in tumours. Researchers at the University of Tokyo and Japan’s National Institute of Radiological Sciences demonstrated that positronium, which forms in tissues due to positron emission from a radiopharmaceutical agent, decays differently depending upon its chemical environment, and is especially sensitive to local oxygen saturation. This means that signs of tumour hypoxia could be spotted among the gamma rays collected routinely during PET imaging, providing clinicians with an additional source of information to guide treatment decisions.
Most positrons created during a PET scan are annihilated almost as soon as they are emitted: they lose energy through interactions with nearby molecules, then collide with electrons in those molecules to produce pairs of 511 keV photons. Some positrons hang around a little longer, however, and instead of annihilating the electrons that they encounter, they capture them, forming metastable positronium atoms.
When this happens, the positronium is created in one of two distinct configurations. The least stable is para-positronium (p-Ps), in which the spins of the electron and positron point in opposite directions. p-Ps atoms have a mean lifetime of only 125 ps, after which they decay into a pair of 511 keV photons. This process therefore adds to the near-immediate gamma signal produced by annihilation of those positrons that never form a positronium atom.
The other configuration is ortho-positronium (o-Ps), in which the spins of the electron and positron are parallel. Left alone, o-Ps would decay into three photons (with energies ranging from 0 to 511 keV) after a mean lifetime of 142 ns. This much longer period means that o-Ps atoms have more time to interact with their surroundings before they decay.
One of the routes open to o-Ps atoms is an interaction called spin exchange. In this process, the positronium’s electron switches with an electron of opposite spin in a nearby molecule. This converts the positronium atom into the less stable p-Ps form, hastening its decay.
The likelihood of spin exchange occurring depends on the availability of unpaired electrons in the vicinity of the o-Ps atoms. In tissues, such unpaired electrons are present primarily in oxygen molecules. This means that in oxygen-poor environments such as hypoxic tumours, more o-Ps atoms survive long enough to decay via the three-photon route. Measuring the timing and spectrum of the gamma rays emitted during the PET procedure should, therefore, yield information about the oxygen saturation.
As they report in Communications Physics, Kengo Shibuya and colleagues tested this principle by preparing samples of water saturated with either air, nitrogen or oxygen. Each sample also contained the unstable sodium isotope 22Na.
When 22Na undergoes beta decay, it simultaneously emits a high-energy gamma ray at 1.27 MeV. The researchers used this signal as the starter pistol for each measurement. In instances where the positron emission resulted in a positronium atom, the end of the measurement was marked by the detection of sub-511-keV photons announcing the positronium’s final decay.
By comparing the timing and energy of the photons emitted during millions of measurement intervals for the three samples, the team derived a linear relationship between oxygen saturation and positronium decay rate. They calculated that, in a clinical PET scanner, an acquisition time of around 30 min would yield enough measurements to distinguish a hypoxic tumour from normally oxygenated healthy tissue.
In terms of detector hardware, current PET devices are already suited to this task, although the researchers say that they will need new timer systems and software.
“The performance required by the new timers is comparable to those already used in conventional PET,” says Shibuya. “Therefore, I think it will not be difficult for medical device manufacturers to install them.”
Finding the right radiopharmaceutical agent might be more challenging, however. Whereas PET imaging techniques employ pure positron emitters, positronium imaging can only work if, like 22Na, the radioisotope emits a gamma photon and a positron simultaneously. Unfortunately, the 2.6-year half-life of 22Na makes it unsuitable for the clinic, for which sources with half-lives on the order of hours or days are required.


physicsworld--2020-10-14--Radiologists and space experts to develop imaging tools for space missions - Physics World

The French Society of Radiology ( SFR ) and the country ’ s national centre for space exploration ( CNES ) have signed a partnership , details of which were streamed live at the Journées Francophones de Radiologie ( JFR ) congress on 4 October .
The aim is to develop imaging solutions to be sent on space flights and to collaborate on image collection and optimization , teleradiology and training of astronauts .
France has the largest space program in Europe and the third oldest institutional space programme in history , along with Russia and the US .
CNES @ @ @ @ @ @ @ in space exploration , recognizes the great potential of diagnostic imaging for monitoring astronauts ’ health while on missions , according to general director Lionel Suchet .
The plan is to create a “ two-way street ” in which radiologists and space experts will collaborate on innovative projects to make further progress , JFR delegates heard online at the plenary Antoine Béclère lecture .
A SFR–CNES working group will now define the research themes and establish a schedule of tasks ahead by December .
Discussing the deal , SFR president Jean-François Meder noted @ @ @ @ @ @ @ the interest of space exploration for imaging and the role of medicine in space .
“ We share the same interests : the support of innovation , and research .
Today SFR and its members have needs , the first is to be able to discuss and collaborate with real professionals .
Your [ astronaut ] teams have become true imaging professionals , ” he said .
“ The second is the need to dream .
This partnership between the SFR and the CNES will allow our radiologists to dream.
” Suchet pointed @ @ @ @ @ @ @ in good health after a mission , noting that the priority of the partnership is developing operational medicine on board the space station .
The second aspect is to harness imaging in the longer term for research .
“ Microgravity present in space stations makes them not only science laboratories but also tools for medical research to explore its effect on the human body , ” he said .
CNES hopes that working with SFR will allow researchers to better explore health issues associated with this microgravity effect , such as cardiovascular problems @ @ @ @ @ @ @ certain model of accelerated ageing .
For the SFR , the partnership will be a means to benefit from knowledge gained by astronauts .
Discoveries from monitoring the process of accelerated ageing in astronauts , for example , could be applied to patients on Earth , helping radiologists understand the evolution of muscle mass loss , or osteoporosis , markers of patient fragility when they are exposed to cancer treatment , for example .
In a special film broadcast during the JFR session , Claudie Haigneré ( rheumatologist , astronaut and counsellor for @ @ @ @ @ @ @ imaging can demonstrate the impact of microgravity – not only on the heart but also on other organs , such as the brain and the eyes .
If such transformations can be imaged and followed , they can also be predicted .
Furthermore , after returning to Earth , astronauts undergo a complete reversal of the phenomenon , providing a platform for experimentation to better understand and treat associated symptoms .
Such a model of the process of accelerated ageing and of the correction of these anomalies , would contribute to making predictive @ @ @ @ @ @ @ future missions will be essential elements , but any progress will necessitate innovation and creativity and will also be very important for issues on Earth .
“ Together we have to work and perfect the imaging tools that will accompany us .
Space exploration is an international co-operative venture , whether this is with the SFR or European industrial bodies which will contribute new imaging methodology , Europe must make its voice heard … because it ’ s a beautiful adventure , the adventure of tomorrow , ” Haigneré elaborated .
With the @ @ @ @ @ @ @ , communication from the ground with teleultrasound specialists in real-time is feasible .
However for longer missions , communication may take from 20 to 40 minutes for information transferral .
In this respect , crews will have to be even more autonomous than they are now for medical matters .
Therefore the SFR has pledged as part of the partnership to contribute to astronaut training to improve diagnostics in real time .
Such education will cover interpretation of radiological images , methods of image compression and training in interventional radiology .
“ It @ @ @ @ @ @ @ and therapy , will become a major aspect , notably on long missions .
Should therapy be needed , minimally invasive interventional radiology will be key , ” noted JFR 2020 president Alain Luciani at the session .
Generally , astronauts are selected for their underlying good health .
Only one case of venal thrombosis has ever been diagnosed via ultrasound and was treated on the space station , according to Suchet .
Nevertheless diagnosis is paramount should the need arise .
At present , astronauts use ultrasound for different organs including the @ @ @ @ @ @ @ for potential ocular problems related to microgravity .
Imaging in space would need to move beyond just ultrasound , noted Luciani .
Interventional radiology will need to be made compatible with a long-distance mission and safe for the astronauts and would need to be as small as possible .
Telemedicine will be another convergent theme between the SFR and CNES .
In a later stage of the partnership , techniques for noise reduction from the research team at CNES could be applied to radiology , the presenters noted .
There will also be @ @ @ @ @ @ @ using artificial intelligence ( AI ) .
CNES uses AI analysis of satellite images of the Earth to understand phenomena linked to climate change .
Techniques based on AI algorithms and data processing to mine the useful data from the mass of information and are very similar to those needed for advanced medical image analysis , according to Suchet , pointing to this other fruitful area of collaboration , where the partners could enrich and help each other .
• This article was originally published on AuntMinnieEurope.com ©2020 by AuntMinnieEurope.com .
Any copying @ @ @ @ @ @ @ is expressly prohibited without the prior written consent of AuntMinnieEurope.com .

The French Society of Radiology (SFR) and the country’s national centre for space exploration (CNES) have signed a partnership, details of which were streamed live at the Journées Francophones de Radiologie (JFR) congress on 4 October. The aim is to develop imaging solutions to be sent on space flights and to collaborate on image collection and optimization, teleradiology and training of astronauts.
France has the largest space program in Europe and the third oldest institutional space programme in history, along with Russia and the US. CNES, which has a long track record in space exploration, recognizes the great potential of diagnostic imaging for monitoring astronauts’ health while on missions, according to general director Lionel Suchet.
The plan is to create a “two-way street” in which radiologists and space experts will collaborate on innovative projects to make further progress, JFR delegates heard online at the plenary Antoine Béclère lecture. A SFR–CNES working group will now define the research themes and establish a schedule of tasks ahead by December.
Imaging plays a vital role in monitoring astronauts’ health. (Courtesy: CNES, SFR and partners)
Shared interests
Discussing the deal, SFR president Jean-François Meder noted how the collaboration would shed light on the interest of space exploration for imaging and the role of medicine in space.
“We share the same interests: the support of innovation, and research. Today SFR and its members have needs, the first is to be able to discuss and collaborate with real professionals. Your [astronaut] teams have become true imaging professionals,” he said. “The second is the need to dream. This partnership between the SFR and the CNES will allow our radiologists to dream.”
Suchet pointed to the priority of getting crews back in good health after a mission, noting that the priority of the partnership is developing operational medicine on board the space station. The second aspect is to harness imaging in the longer term for research.
Astronauts have had to become true imaging professionals, and now the SFR will help them to carry out their own exams even better. (Courtesy: CNES, SFR and partners)
“Microgravity present in space stations makes them not only science laboratories but also tools for medical research to explore its effect on the human body,” he said.
CNES hopes that working with SFR will allow researchers to better explore health issues associated with this microgravity effect, such as cardiovascular problems, muscle loss, osteoporosis and a certain model of accelerated ageing.
For the SFR, the partnership will be a means to benefit from knowledge gained by astronauts. Discoveries from monitoring the process of accelerated ageing in astronauts, for example, could be applied to patients on Earth, helping radiologists understand the evolution of muscle mass loss, or osteoporosis, markers of patient fragility when they are exposed to cancer treatment, for example.
Beautiful adventure
In a special film broadcast during the JFR session, Claudie Haigneré (rheumatologist, astronaut and counsellor for the European Space Agency) explained how imaging can demonstrate the impact of microgravity – not only on the heart but also on other organs, such as the brain and the eyes. If such transformations can be imaged and followed, they can also be predicted.
Furthermore, after returning to Earth, astronauts undergo a complete reversal of the phenomenon, providing a platform for experimentation to better understand and treat associated symptoms. Such a model of the process of accelerated ageing and of the correction of these anomalies, would contribute to making predictive models of recuperation.
Imaging tools for future missions will be essential elements, but any progress will necessitate innovation and creativity and will also be very important for issues on Earth.
“Together we have to work and perfect the imaging tools that will accompany us. Space exploration is an international co-operative venture, whether this is with the SFR or European industrial bodies which will contribute new imaging methodology, Europe must make its voice heard … because it’s a beautiful adventure, the adventure of tomorrow,” Haigneré elaborated.
Interventional training
With the space station 400 km above the planet, communication from the ground with teleultrasound specialists in real-time is feasible. However for longer missions, communication may take from 20 to 40 minutes for information transferral. In this respect, crews will have to be even more autonomous than they are now for medical matters. Therefore the SFR has pledged as part of the partnership to contribute to astronaut training to improve diagnostics in real time. Such education will cover interpretation of radiological images, methods of image compression and training in interventional radiology.
“It seems to us that interventional radiology, and therapy, will become a major aspect, notably on long missions. Should therapy be needed, minimally invasive interventional radiology will be key,” noted JFR 2020 president Alain Luciani at the session.
Generally, astronauts are selected for their underlying good health. Only one case of venal thrombosis has ever been diagnosed via ultrasound and was treated on the space station, according to Suchet. Nevertheless diagnosis is paramount should the need arise.
Teleradiology lies at the heart of the new collaboration. (Courtesy: CNES, SFR and partners)
At present, astronauts use ultrasound for different organs including the heart and brain, and eye tomography for potential ocular problems related to microgravity. Imaging in space would need to move beyond just ultrasound, noted Luciani. Interventional radiology will need to be made compatible with a long-distance mission and safe for the astronauts and would need to be as small as possible. Telemedicine will be another convergent theme between the SFR and CNES.
Ahead to the future
In a later stage of the partnership, techniques for noise reduction from the research team at CNES could be applied to radiology, the presenters noted.
There will also be a chance for collaboration on image analysis using artificial intelligence (AI). CNES uses AI analysis of satellite images of the Earth to understand phenomena linked to climate change. Techniques based on AI algorithms and data processing to mine the useful data from the mass of information and are very similar to those needed for advanced medical image analysis, according to Suchet, pointing to this other fruitful area of collaboration, where the partners could enrich and help each other.
This article was originally published on AuntMinnieEurope.com ©2020 by AuntMinnieEurope.com. Any copying, republication or redistribution of AuntMinnieEurope.com content is expressly prohibited without the prior written consent of AuntMinnieEurope.com.


physicsworld--2020-10-14--How capable are today’s quantum computers? - Physics World

Media coverage of quantum computing often focusses on the long term potential for these devices to leave classical computing in the dust .
But what about the rudimentary quantum systems that are already being developed and tested by technology companies ?
What are the latest advances in the field ?
And what might these systems realistically be able to achieve in the short to medium term ?
Andrew Glester investigates these questions in the latest episode of the Physics World Stories podcast .
The episode previews Quantum 2020 , a free online event running 19–22 October hosted by IOP Publishing @ @ @ @ @ @ @ .
Tim Smith , associate director for journals product development , describes how the conference will cover the latest developments across quantum science and technology .
While Claire Weber , associate director for content and engagement marketing , explains how you can participate in the event .
Glester then catches up with one of the speakers at Quantum 2020 – Ryan Babbush , head of quantum algorithms at Google .
In 2019 Google made headlines after asserting that its Sycamore quantum processor was the first to achieve “ quantum supremacy , ” whereby @ @ @ @ @ @ @ a significantly shorter time than a conventional computer .
Although the specifics of that claim have been disputed , it was still celebrated as a key breakthrough in the field .
Babbush describes some of the key goals for Google ’ s first generation of practical quantum computers .
One of them is to realise Richard Feynman ’ s idea of using quantum devices to simulate physical systems that behave according to the laws of quantum physics .
Such a system could be used to solve the fiendishly complex chemistry equations required to @ @ @ @ @ @ @ Another key goal is quantum cryptography , which could offer secure communication systems .

Media coverage of quantum computing often focuses on the long term potential for these devices to leave classical computing in the dust. But what about the rudimentary quantum systems that are already being developed and tested by technology companies? What are the latest advances in the field? And what might these systems realistically be able to achieve in the short to medium term? Andrew Glester investigates these questions in the latest episode of the Physics World Stories podcast.
The episode previews Quantum 2020, a free online event running 19–22 October hosted by IOP Publishing (which also published Physics World). Tim Smith, associate director for journals product development, describes how the conference will cover the latest developments across quantum science and technology. While Claire Webber, associate director for content and engagement marketing, explains how you can participate in the event.
Glester then catches up with one of the speakers at Quantum 2020 – Ryan Babbush, head of quantum algorithms at Google. In 2019 Google made headlines after asserting that its Sycamore quantum processor was the first to achieve “quantum supremacy”, whereby a quantum computer solves a problem in a significantly shorter time than a conventional computer. Although the specifics of that claim have been disputed, it was still celebrated as a key breakthrough in the field.
Babbush describes some of the key goals for Google’s first generation of practical quantum computers. One of them is to realize Richard Feynman’s idea of using quantum devices to simulate physical systems that behave according to the laws of quantum physics. Such a system could be used to solve the fiendishly complex chemistry equations required to predict the properties of new materials. Another key goal is quantum cryptography, which could offer secure communication systems.


physicsworld--2020-10-14--Combining elemental/chemical analysis: when micro-XRF meets Raman microscopy - Physics World

Combining elemental and molecular characterization enables better and faster research in many real-world applications .
Applications such as pharmaceuticals , environment , or geochemistry can benefit from this complementarity of techniques .
Micro-XRF provides elemental distribution on a large area without any compromise on sample preparation , while Raman microscopy can depict molecular heterogeneity in the same conditions .
In this webinar , Thibault Brulé and Jocelyne Marciano will demonstrate how the combination of these two unique techniques can fully characterize the organic and inorganic layout over samples such as tablets , rocks or pollutant particles on filter .
Thibault @ @ @ @ @ @ @ France , working in the Demonstration Centre at the HORIBA Laboratory in Palaiseau .
He is responsible for providing Raman spectroscopy applications support to key customers from various industries , as well as contributing to HORIBA ’ s application strategies .
Prior to joining HORIBA in 2017 , he conducted research on proteins in blood characterization based on dynamic surface enhanced Raman spectroscopy .
He then applied this technique to cell-secretion monitoring .
Thibault holds a MSc from the University of Technologies of Troyes , completed his PhD at the University of Burgundy @ @ @ @ @ @ @ at the University of Montreal .
Jocelyne Marciano is application scientist at HORIBA France , working in the Demonstration Centre at the HORIBA Laboratory in Palaiseau .
She is responsible for testing and demonstrating different types of elemental analysers ( EMIA-EMGA , SLFA , MESA and XGT ) that are part of the HORIBA Japan product portfolio .
Prior to joining HORIBA in 2008 , Jocelyne spent 17 years working for Saint-Gobain as a key specialist for glass products analysis .
She has in-depth experience in X-ray fluorescence and gas analysers as well @ @ @ @ @ @ @ .

Available to watch now, HORIBA Scientific explores how elemental and molecular characterizations combined can help solve issues across many applications
Want to learn more on this subject? Watch now
Combining elemental and molecular characterization enables better and faster research in many real-world applications. Applications such as pharmaceuticals, environment, or geochemistry can benefit from this complementarity of techniques. Micro-XRF provides elemental distribution on a large area without any compromise on sample preparation, while Raman microscopy can depict molecular heterogeneity in the same conditions.
In this webinar, Thibault Brulé and Jocelyne Marciano will demonstrate how the combination of these two unique techniques can fully characterize the organic and inorganic layout over samples such as tablets, rocks or pollutant particles on filter.
Want to learn more on this subject? Watch now
Thibault Brulé is Raman application scientist at HORIBA France, working in the Demonstration Centre at the HORIBA Laboratory in Palaiseau. He is responsible for providing Raman spectroscopy applications support to key customers from various industries, as well as contributing to HORIBA’s application strategies. Prior to joining HORIBA in 2017, he conducted research on proteins in blood characterization based on dynamic surface enhanced Raman spectroscopy. He then applied this technique to cell-secretion monitoring. Thibault holds a MSc from the University of Technologies of Troyes, completed his PhD at the University of Burgundy and followed on with a postdoc fellowship at the University of Montreal.
Jocelyne Marciano is application scientist at HORIBA France, working in the Demonstration Centre at the HORIBA Laboratory in Palaiseau. She is responsible for testing and demonstrating different types of elemental analysers (EMIA-EMGA, SLFA, MESA and XGT) that are part of the HORIBA Japan product portfolio. Prior to joining HORIBA in 2008, Jocelyne spent 17 years working for Saint-Gobain as a key specialist for glass products analysis. She has in-depth experience in X-ray fluorescence and gas analysers as well as in XPS, SEM-EDX and µ-probe.


physicsworld--2020-10-14--Proton-coupled electron transfer in electrochemistry - Physics World

Proton-coupled electron transfer ( PCET ) reactions play a vital role in a wide range of electrochemical processes .
This talk will focus on theoretical studies of molecular and heterogeneous electrocatalysis , highlighting the interplay between theory and experiment .
A general theory of PCET that enables the calculation of rate constants , current densities , Tafel slopes , and kinetic isotope effects has been developed .
The application of this PCET theory to molecular electrocatalysts designed for water splitting illustrates the use of multi-proton relays to transport protons over hydrogen-bonded networks , as well as the ability to tune @ @ @ @ @ @ @ molecular design strategies .
The application of this PCET theory to proton discharge on a gold electrode provides insight into the fundamental principles underlying this process in acidic and alkaline aqueous solution as well as acetonitrile , and explains experimentally observed potential dependent kinetic isotope effects .
Recent periodic density functional theory calculations of electric fields at electrochemical interfaces and PCET at graphite-conjugated acids elucidate the impact of the applied potential on the electronic structure and interfacial fields .
The insights from these theoretical studies are useful for the design of both molecular @ @ @ @ @ @ @ and coupling of electrons and protons for energy-conversion processes .
Sharon Hammes-Schiffer received her BA in chemistry from Princeton University in 1988 and her PhD in chemistry from Stanford University in 1993 , followed by two years at AT & T Bell Laboratories .
She was the Clare Boothe Luce Assistant Professor at the University of Notre Dame from 1995–2000 .
She then became the Eberly Professor of Biotechnology at The Pennsylvania State University until 2012 , when she became the Swanlund Professor of Chemistry at the University of Illinois Urbana-Champaign .
Since @ @ @ @ @ @ @ Gamble Kirkwood Professor of Chemistry at Yale University .
Her research centres on the investigation of charge transfer reactions , proton-coupled electron transfer , nonadiabatic dynamics , and quantum mechanical effects in chemical , biological , and interfacial processes .
Her work encompasses the development of analytical theories and computational methods and applications to experimentally relevant systems .
She is a Fellow of the American Physical Society , American Chemical Society , American Association for the Advancement of Science , and the Biophysical Society .
She is a member of the American Academy @ @ @ @ @ @ @ National Academy of Sciences , and the International Academy of Quantum Molecular Science .
She has received the American Chemical Society Award in Theoretical Chemistry , the Royal Society of Chemistry Bourke Award , and the Joseph O Hirschfelder Prize in Theoretical Chemistry .
She was the deputy editor of The Journal of Physical Chemistry B and is currently the editor-in-chief of Chemical Reviews .
She is on the Board of Reviewing Editors for Science and has served as Chair of the Physical Division and the Theoretical Subdivision of the American Chemical Society @ @ @ @ @ @ @ , is co-author of a textbook entitled Physical Chemistry for the Biological Sciences , and has given more than 415 invited lectures , including 24 named lectureships .

Available to watch now, The Electrochemical Society, in partnership with ACS Chemical Reviews and Gamry Instruments, explores the theoretical studies of molecular and heterogeneous electrocatalysis
Want to learn more on this subject? Watch now
Proton-coupled electron transfer (PCET) reactions play a vital role in a wide range of electrochemical processes. This talk will focus on theoretical studies of molecular and heterogeneous electrocatalysis, highlighting the interplay between theory and experiment. A general theory of PCET that enables the calculation of rate constants, current densities, Tafel slopes, and kinetic isotope effects has been developed.
The application of this PCET theory to molecular electrocatalysts designed for water splitting illustrates the use of multi-proton relays to transport protons over hydrogen-bonded networks, as well as the ability to tune the redox potentials through substituents and other molecular design strategies.
The application of this PCET theory to proton discharge on a gold electrode provides insight into the fundamental principles underlying this process in acidic and alkaline aqueous solution as well as acetonitrile, and explains experimentally observed potential dependent kinetic isotope effects.
Recent periodic density functional theory calculations of electric fields at electrochemical interfaces and PCET at graphite-conjugated acids elucidate the impact of the applied potential on the electronic structure and interfacial fields.
The insights from these theoretical studies are useful for the design of both molecular and heterogeneous electrocatalysts to control the movement and coupling of electrons and protons for energy-conversion processes.
Want to learn more on this subject? Watch now
Sharon Hammes-Schiffer received her BA in chemistry from Princeton University in 1988 and her PhD in chemistry from Stanford University in 1993, followed by two years at AT&T Bell Laboratories. She was the Clare Boothe Luce Assistant Professor at the University of Notre Dame from 1995–2000. She then became the Eberly Professor of Biotechnology at The Pennsylvania State University until 2012, when she became the Swanlund Professor of Chemistry at the University of Illinois Urbana-Champaign. Since 2018, she has been the John Gamble Kirkwood Professor of Chemistry at Yale University.
Her research centres on the investigation of charge transfer reactions, proton-coupled electron transfer, nonadiabatic dynamics, and quantum mechanical effects in chemical, biological, and interfacial processes. Her work encompasses the development of analytical theories and computational methods and applications to experimentally relevant systems. She is a Fellow of the American Physical Society, American Chemical Society, American Association for the Advancement of Science, and the Biophysical Society. She is a member of the American Academy of Arts and Sciences, the US National Academy of Sciences, and the International Academy of Quantum Molecular Science. She has received the American Chemical Society Award in Theoretical Chemistry, the Royal Society of Chemistry Bourke Award, and the Joseph O Hirschfelder Prize in Theoretical Chemistry.
She was the deputy editor of The Journal of Physical Chemistry B and is currently the editor-in-chief of Chemical Reviews. She is on the Board of Reviewing Editors for Science and has served as Chair of the Physical Division and the Theoretical Subdivision of the American Chemical Society. She has more than 285 publications, is co-author of a textbook entitled Physical Chemistry for the Biological Sciences, and has given more than 415 invited lectures, including 24 named lectureships.


physicsworld--2020-10-14--Superconductivity endures to 15 °C in high-pressure material - Physics World

Superconductivity has been observed at temperatures up to 15 °C in a hydrogen-rich material under immense pressure – shattering the previous high-temperature record by about 35 degrees .
The carbonaceous sulphur hydride material was made and studied by Ranga Dias and colleagues at the University of Rochester and the University of Nevada Las Vegas in the US , who say that it may be possible to reduce the pressure required to achieve room-temperature superconductivity by changing the chemistry of the material .
Superconductors carry electrical current with no electrical resistance and have a range of applications from the high-field magnets @ @ @ @ @ @ @ to the quantum bits used in quantum computers .
Today , practical devices based on superconductors must be chilled to very cold temperatures , which is costly and can involve the use of helium – which is a limited natural resource .
Therefore , a long-standing goal of condensed-matter physicists has been to develop a material that is a superconductor at room temperature .
In 2015 , Mikhail Eremets and colleagues at the Max Planck Institute for Chemistry and the Johannes Gutenberg University Mainz , both in Germany , made a huge breakthrough @ @ @ @ @ @ @ ( -70 °C ) in a sample of hydrogen sulphide at about 1.5 million times atmospheric pressure .
This new record was a huge leap forward in the quest for a room-temperature superconductor and reinforced theoretical predictions that hydrogen-rich materials could offer a way forward .
Indeed , the metallic state of hydrogen – which is expected to occur at extremely high pressures and has yet to be fully characterized – is expected to be a superconductor at room temperature .
In early 2019 Eremets ’ team and a group led by Russell @ @ @ @ @ @ @ US reported superconductivity at temperatures up to about -20 °C – a typical winter temperature across vast swathes of Russia and Canada .
Now Dias and colleagues have boosted this temperature to 15 °C , which coincidentally is the average surface temperature of the Earth .
They did this by adding carbon to hydrogen sulphide – which was done by mixing methane and hydrogen sulphide together in a photochemical process .
Dias told Physics World that part of his team ’ s success can be attributed to the precision of their synthesis technique @ @ @ @ @ @ @ pressure .
“ [ The photochemical process ] is critical in introducing methane and hydrogen sulphide into the starting material , that allows just the ‘ right ’ amount of hydrogen needed for such remarkable properties , ” he explains .
The team placed their samples in the jaws of a diamond anvil and squeezed them to pressures between about 1.4-2.7 million atmospheres .
They found a sharp upturn in the superconducting transition temperature at about 2.2 million atmospheres with the maximum temperature of 15 °C occurring at about 2.6 million atmospheres .
@ @ @ @ @ @ @ able to make three measurements to confirm that the material is indeed a superconductor .
The resistance of the sample was measured using two-probe and four-probe techniques to ensure that it was indeed zero .
The team also measured the transition temperature as a function of applied magnetic field and found that the temperature dropped as the field increased – which is a hallmark of a superconductor .
Finally , they observed that the material expelled magnetic field lines , which is another characteristic of a supercomputer .
One shortcoming of the research @ @ @ @ @ @ @ opportunity : the team does not know the structure and exact stoichiometry ( ratios of carbon , sulphur and hydrogen atoms ) of the material at very high pressure .
Dias says that the team has “ some idea [ of the stoichiometry ] but don ’ t know the exact answer ” .
Determining the structure is difficult because the constituent atoms are too light so see using X-ray diffraction .
“ We have been developing a new set of tools to solve this problem , ” says Dias .
Once the @ @ @ @ @ @ @ structure and stoichiometry they hope to be able to chemically tune the material to be a room-temperature superconductor at lower pressures .
Commenting on the significance of this latest result , Mikhail Eremets told Physics World , “ We should keep in mind that truly room-temperature superconductor should be at ambient pressure , which will allow applications ” .
He adds that the high-pressure studies that began with his hydrogen sulphide work in 2015 provide important information in the search for an ambient-pressure room-temperature superconductor – which he says will be likely a @ @ @ @ @ @ @ this latest temperature record will not stand for long , pointing out that “ there are predictions of SC even above 400 K at high pressures ” .
The research is described in Nature .

Hot stuff: inside the lab at Rochester where the superconductor was discovered. (Courtesy: Adam Fenster)
This article reports on research described in a paper in Nature. This paper has since been retracted by the journal.
Superconductivity has been observed at temperatures up to 15 °C in a hydrogen-rich material under immense pressure – shattering the previous high-temperature record by about 35 degrees. The carbonaceous sulphur hydride material was made and studied by Ranga Dias and colleagues at the University of Rochester and the University of Nevada Las Vegas in the US, who say that it may be possible to reduce the pressure required to achieve room-temperature superconductivity by changing the chemistry of the material.
Superconductors carry electrical current with no electrical resistance and have a range of applications from the high-field magnets used in MRI scanners and particle accelerators to the quantum bits used in quantum computers. Today, practical devices based on superconductors must be chilled to very cold temperatures, which is costly and can involve the use of helium – which is a limited natural resource. Therefore, a long-standing goal of condensed-matter physicists has been to develop a material that is a superconductor at room temperature.
In 2015 Mikhail Eremets and colleagues at the Max Planck Institute for Chemistry and the Johannes Gutenberg University Mainz, both in Germany, made a huge breakthrough when they observed superconductivity at 203 K (–70 °C) in a sample of hydrogen sulphide at about 1.5 million times atmospheric pressure. This new record was a huge leap forward in the quest for a room-temperature superconductor and reinforced theoretical predictions that hydrogen-rich materials could offer a way forward. Indeed, the metallic state of hydrogen – which is expected to occur at extremely high pressures and has yet to be fully characterized – is expected to be a superconductor at room temperature.
Winter’s day in Siberia
In early 2019 Eremets’ team and a group led by Russell Hemley at George Washington University in the US reported superconductivity at temperatures up to about –20 °C – a typical winter temperature across vast swathes of Russia and Canada.
Now Dias and colleagues have boosted this temperature to 15 °C, which coincidentally is the average surface temperature of the Earth. They did this by adding carbon to hydrogen sulphide – which was done by mixing methane and hydrogen sulphide together in a photochemical process. Dias told Physics World that part of his team’s success can be attributed to the precision of their synthesis technique, which is done at relatively low pressure. “[The photochemical process] is critical in introducing methane and hydrogen sulphide into the starting material, that allows just the ‘right’ amount of hydrogen needed for such remarkable properties,” he explains.
The team placed their samples in the jaws of a diamond anvil and squeezed them to pressures between about 1.4 and 2.7 million atmospheres. They found a sharp upturn in the superconducting transition temperature at about 2.2 million atmospheres with the maximum temperature of 15 °C occurring at about 2.6 million atmospheres.
Hallmarks of superconductivity
According to Dias, the team was able to make three measurements to confirm that the material is indeed a superconductor. The resistance of the sample was measured using two-probe and four-probe techniques to ensure that it was indeed zero. The researchers also measured the transition temperature as a function of applied magnetic field and found that the temperature dropped as the field increased – which is a hallmark of a superconductor. Finally, they observed that the material expelled magnetic field lines, which is another characteristic of a superconductor.
One shortcoming of the research may turn out to be an important opportunity: the team does not know the structure and exact stoichiometry (ratios of carbon, sulphur and hydrogen atoms) of the material at very high pressure. Dias says that the researchers have “some idea [of the stoichiometry] but don’t know the exact answer”. Determining the structure is difficult because the constituent atoms are too light so see using X-ray diffraction. “We have been developing a new set of tools to solve this problem,” says Dias. Once the team has a better understanding of the structure and stoichiometry they hope to be able to chemically tune the material to be a room-temperature superconductor at lower pressures.
Commenting on the significance of this latest result, Mikhail Eremets told Physics World, “We should keep in mind that truly room-temperature superconductor should be at ambient pressure, which will allow applications.” He adds that the high-pressure studies that began with his hydrogen sulphide work in 2015 provide important information in the search for an ambient-pressure room-temperature superconductor – which he says will be likely a ternary compound. Eremets also believes that this latest temperature record will not stand for long, pointing out that “there are predictions of [superconductivity] even above 400 K at high pressures”.
The research is described in Nature.


physicsworld--2020-10-15--Quantum spin liquid candidate becomes a superconductor under pressure - Physics World

Researchers in China report that they have observed both superconductivity and an insulator-to-metal transition in sodium ytterbium ( III ) selenide ( NaYbSe ) simply by applying pressure to it .
This inorganic substance , which is also a quantum spin liquid ( QSL ) candidate , could therefore become a new platform for investigating superconductivity in compounds that have electrons in their f orbitals , and for exploring the mechanisms of unconventional superconductivity in these materials .
Quantum spin liquids ( QSLs ) are solid magnetic materials that can not arrange their magnetic moments ( or spins ) into @ @ @ @ @ @ @ behaviour contrasts with that of ordinary ferromagnets , in which all the spins point in the same direction , or antiferromagnets , in which the spins point in alternating directions .
Instead , the spins in a QSL constantly change direction in a fluid-like way – even at ultracold temperatures near absolute zero – and are thus said to be “ frustrated ” .
The late physicist and Nobel laureate Philip W Anderson proposed the existence of QSLs in the early 1970s , when he was studying the ground state of antiferromagnetically interacting @ @ @ @ @ @ @ Although Anderson did not follow up the idea at the time , he returned to it in 1986 after the discovery of high-temperature superconductivity in copper oxides ( cuprates ) .
A year later , his work bore fruit when he uncovered a potentially crucial link between QSL theory and “ unconventional ” high-temperature superconductivity .
He described this link in the so-called resonant valence bond theory .
Today , QSLs are thought to be the “ parent state ” for high-temperature unconventional superconductivity in cuprates .
This class of superconductors could have @ @ @ @ @ @ @ grids , levitating transport and even quantum computing , but the physics underlying them is still not very well understood .
Studying QSLs is thus important for condensed-matter physicists if these applications are to see the light of day .
A team of researchers jointly led by Run-Ze Yu and Chang-Qing Jin of the Institute of Physics at the Chinese Academy of Sciences , and He-chang Lei of Renmin University of China in Beijing , used a diamond anvil cell to measure the electronic conductivity of NaYbSe under varying high pressures ( up @ @ @ @ @ @ @ magnetic field .
This crystalline material features a triangular lattice of 4f-orbital Yb3+ions bonded to six equivalent Se2- atoms to form YbSe octahedra .
These YbSe octrahedra share corners with six equivalent NaSe octahedra , while sharing edges with six equivalent YbSe octahedra .
The researchers found that their sample acts as a paramagnetic insulator ( a material with a permanent magnetic dipole moment ) at applied pressures below 8 GPa .
As the pressure increases from 8 GPa to 50 GPa , the material remains an insulator , but its resistance decreases @ @ @ @ @ @ @ A metallic phase is eventually observed at about 60 GPa and further increases in pressure lead to the emergence of a superconducting state at 103 GPa , with a superconducting transition temperature of 8 K. This transition from insulator to conductor is known as a Mott transition .
Because the material contains exotic spin excitations carrying fractional quantum numbers at low energies , its metallic state behaves like a non-Fermi liquid – meaning that its electrical conductivity depends linearly on temperature .
“ The origin of the superconductivity should therefore be exotic , @ @ @ @ @ @ @ that the relationship to the resonant valence bond theory proposed by Anderson for copper oxide superconductors needs to further investigated in experiments.
” The fact that the researchers observed such a transition by simply applying pressure means that it is an intrinsic , physical property of the material , free from chemical transformations that are usually introduced by doping .
And since Yb3+ ions contain f-electrons , Yu adds that the NaYbSe system provides a new platform to investigate unconventional superconductivity mechanisms in such compounds .
“ The work will certainly help researchers @ @ @ @ @ @ @ between the QSL and unconventional superconductivity , ” he tells Physics World .
Members of the team , who report their work in Chinese Physics Letters , say they will now study the nature of the insulator-to-metal transition in NaYbSe in-depth , as well as the intrinsic physical properties of superconductivity in this QSL .
“ We will also be focusing on the possibility of ‘ heavy fermion ’ phenomena in this compound , ” Yu adds .
Such phenomena , he explains , arise when the conduction electrons , which are fermions @ @ @ @ @ @ @ of times more massive than electrons in conventional metals , like copper .
This large “ effective mass ” comes about thanks to strong electron-electron interactions , which are also thought to play an important role in high-temperature superconductors .

Pressure-temperature (P-T) phase diagram of a NaYbSe2 single crystal. Courtesy: Run-Ze Yu
Researchers in China report that they have observed both superconductivity and an insulator-to-metal transition in sodium ytterbium (III) selenide (NaYbSe 2 ) simply by applying pressure to it. This inorganic substance, which is also a quantum spin liquid (QSL) candidate, could therefore become a new platform for investigating superconductivity in compounds that have electrons in their f orbitals, and for exploring the mechanisms of unconventional superconductivity in these materials.
Quantum spin liquids (QSLs) are solid magnetic materials that cannot arrange their magnetic moments (or spins) into a regular and stable pattern. This behaviour contrasts with that of ordinary ferromagnets, in which all the spins point in the same direction, or antiferromagnets, in which the spins point in alternating directions. Instead, the spins in a QSL constantly change direction in a fluid-like way – even at ultracold temperatures near absolute zero – and are thus said to be “frustrated”.
The late physicist and Nobel laureate Philip W Anderson proposed the existence of QSLs in the early 1970s, when he was studying the ground state of antiferromagnetically interacting spins on a triangular crystal lattice. Although Anderson did not follow up the idea at the time, he returned to it in 1986 after the discovery of high-temperature superconductivity in copper oxides (cuprates). A year later, his work bore fruit when he uncovered a potentially crucial link between QSL theory and “unconventional” high-temperature superconductivity. He described this link in the so-called resonant valence bond theory.
“Parent states”
Today, QSLs are thought to be the “parent state” for high-temperature unconventional superconductivity in cuprates. This class of superconductors could have applications in many areas, including energy grids, levitating transport and even quantum computing, but the physics underlying them is still not very well understood. Studying QSLs is thus important for condensed-matter physicists if these applications are to see the light of day.
A team of researchers jointly led by Run-Ze Yu and Chang-Qing Jin of the Institute of Physics at the Chinese Academy of Sciences, and He-chang Lei of Renmin University of China in Beijing, used a diamond anvil cell to measure the electronic conductivity of NaYbSe 2 under varying high pressures (up to 126 GPa) and a high magnetic field. This crystalline material features a triangular lattice of 4f-orbital Yb3+ions bonded to six equivalent Se2- atoms to form YbSe 6 octahedra. These YbSe 6 octrahedra share corners with six equivalent NaSe 6 octahedra, while sharing edges with six equivalent YbSe 6 octahedra.
The researchers found that their sample acts as a paramagnetic insulator (a material with a permanent magnetic dipole moment) at applied pressures below 8 GPa. As the pressure increases from 8 GPa to 50 GPa, the material remains an insulator, but its resistance decreases by nearly eight orders of magnitude. A metallic phase is eventually observed at about 60 GPa and further increases in pressure lead to the emergence of a superconducting state at 103 GPa, with a superconducting transition temperature of 8 K.
Mott transition
This transition from insulator to conductor is known as a Mott transition. Because the material contains exotic spin excitations carrying fractional quantum numbers at low energies, its metallic state behaves like a non-Fermi liquid – meaning that its electrical conductivity depends linearly on temperature. “The origin of the superconductivity should therefore be exotic,” Yu explains. “This implies that the relationship to the resonant valence bond theory proposed by Anderson for copper oxide superconductors needs to further investigated in experiments.”
The fact that the researchers observed such a transition by simply applying pressure means that it is an intrinsic, physical property of the material, free from chemical transformations that are usually introduced by doping. And since Yb3+ ions contain f-electrons, Yu adds that the NaYbSe 2 system provides a new platform to investigate unconventional superconductivity mechanisms in such compounds. “The work will certainly help researchers gain a deeper understanding of the interplay between the QSL and unconventional superconductivity,” he tells Physics World.
Members of the team, who report their work in Chinese Physics Letters, say they will now study the nature of the insulator-to-metal transition in NaYbSe 2 in-depth, as well as the intrinsic physical properties of superconductivity in this QSL. “We will also be focusing on the possibility of ‘heavy fermion’ phenomena in this compound,” Yu adds. Such phenomena, he explains, arise when the conduction electrons, which are fermions, move as if they were hundreds of times more massive than electrons in conventional metals, like copper. This large “effective mass” comes about thanks to strong electron-electron interactions, which are also thought to play an important role in high-temperature superconductors.


physicsworld--2020-10-15--Comprehensive machine targeting and image quality QA with the QUASAR™ Penta-Guide system - Physics W

Comprehensive machine targeting and image quality QA with the QUASAR™ Penta-Guide system - Physics World

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