physicsworld--2020-09-07--Self-assembled peptides exhibit surprisingly strong diamagnetism - Physics World

Peptides exhibit surprisingly strong diamagnetism when they join together to form microfibres , say researchers in China .
Haijun Yang , at the Chinese Academy of Sciences ( CAS ) in Shanghai , and colleagues measured the force exerted by peptide-containing liquids placed in a static magnetic field .
They found that samples in which the peptides had been allowed to self-assemble had a diamagnetic mass susceptibility 11 times higher than samples in which the peptides were dissolved , and 175 times that of pure water .
The unexpected result , reported in Chinese Physics Letters , helps to explain @ @ @ @ @ @ @ and could have applications in magnetically controlled microfabrication , medical imaging and brain–computer interfaces .
A diverse range of biological structures – from entire cells down to DNA and other subcellular polymers – are known to change their orientation in response to magnetic fields .
This effect is behind the ability of some animals to navigate using the Earth ’ s magnetic field .
However , many of the biological structures that respond to such fields apparently contain too little iron for the phenomenon to be explained by either ferromagnetism or ferrimagnetism .
@ @ @ @ @ @ @ these structures is instead due to more subtle magnetic effects .
In an amino-acid chain called a peptide , for example , an external magnetic field induces a weak secondary field with the opposite direction , which pushes the peptide away .
This effect , known as diamagnetism , has been attributed to the alignment of electrons in the peptide bonds between amino acids , or to electron currents flowing around cyclic structures called aromatic rings .
To investigate this phenomenon , Yang and colleagues prepared three different samples of a pentapeptide with @ @ @ @ @ @ @ a polymer consisting specifically of five amino acid units – in this case , one unit of alanine ( A ) , one of tyrosine ( Y ) and three of phenylalanine ( F ) .
In the first sample , the researchers dissolved the peptide in the organic solvent dimethyl sulfoxide ( DMSO ) .
In the second sample , they dispersed the powdered peptide in water .
In the third sample , they also dispersed the powdered peptide in water , but then left it to stand for 16 hours .
@ @ @ @ @ @ @ self-assembled into fibres more than 10 µm long .
The researchers weighed the samples , and then repeated the measurement in the presence of a magnetic field , which they applied by placing a permanent magnet above the apparatus .
They assumed that any difference between measurements with and without the magnet was due to the diamagnetic interaction between the external magnetic field and the magnetic fields induced within the sample .
They found that the peptide dissolved in DMSO exhibited the weakest diamagnetic response , while the sample in which the peptide @ @ @ @ @ @ @ strongest .
The strength of diamagnetism in the water-dispersed sample was somewhere between the two , which the researchers put down to the occurrence of a limited degree of self-assembly .
When the team performed the same experiment using a different pentapeptide – IIIGK , comprising isoleucine ( I ) , glycine ( G ) and lysine ( K ) – they found only a weak diamagnetic response , even for the sample that had been left to self-assemble into fibril structures .
Whereas tyrosine and phenylalanine in the AYFFF sequence incorporate aromatic @ @ @ @ @ @ @ not the case for any of the components of the IIIGK peptide .
Yang and colleagues therefore interpret their results as confirmation that the electron dynamics of the aromatic rings , rather than the peptide bonds , are responsible for strong diamagnetism in peptides .
Although the role of aromatic ring currents was not unexpected in itself , the researchers were surprised by how strong the diamagnetism was in the self-assembled peptide samples .
They are still investigating the physics underlying the effect , but they do already have an idea of how @ @ @ @ @ @ @ “ Each peptide molecule has an induced magnetic moment in the presence of an applied magnetic field , ” says Haiping Fang , of the CAS and East China University of Science and Technology in Shanghai , who led the research .
“ Thermal forces randomize the orientation of these magnetic moments , weakening the diamagnetism .
A group of aromatic peptides in the assembled state – with interactions between them – might reduce the effect of these thermal fluctuations , resulting in the strong diamagnetism.
” Whatever its origin , the researchers @ @ @ @ @ @ @ .
“ Peptides with various sequences could be easily assembled into different nanostructures under magnetic fields , widening fabrication strategies , ” says Feng Zhang , a collaborator from Guangzhou Medical University .
“ Assembled peptides modified with biomarkers could also be used as biological tracers , enhancing the contrast between normal and abnormal tissues in magnetic resonance imaging .
Or , in novel brain–computer interfaces , the assembled peptides ’ strong diamagnetism could be used as a non-invasive sensor to detect weak variations in magnetic signals from brain activity .
”

Average magnetic forces per unit mass of the AYFFF aromatic peptide and a control non-aromatic peptide, IIIGK, in dissolved, dispersed and assembled states. (Courtesy: Haijun Yang, Feng Zhang and Haiping Fang)
Peptides exhibit surprisingly strong diamagnetism when they join together to form microfibres, say researchers in China. Haijun Yang, at the Chinese Academy of Sciences (CAS) in Shanghai, and colleagues measured the force exerted by peptide-containing liquids placed in a static magnetic field. They found that samples in which the peptides had been allowed to self-assemble had a diamagnetic mass susceptibility 11 times higher than samples in which the peptides were dissolved, and 175 times that of pure water. The unexpected result, reported in Chinese Physics Letters, helps to explain the origin of magnetism in biomolecules, and could have applications in magnetically controlled microfabrication, medical imaging and brain–computer interfaces.
A diverse range of biological structures – from entire cells down to DNA and other subcellular polymers – are known to change their orientation in response to magnetic fields. This effect is behind the ability of some animals to navigate using the Earth’s magnetic field. However, many of the biological structures that respond to such fields apparently contain too little iron for the phenomenon to be explained by either ferromagnetism or ferrimagnetism. This suggests that the magnetic sensitivity of these structures is instead due to more subtle magnetic effects.
In an amino-acid chain called a peptide, for example, an external magnetic field induces a weak secondary field with the opposite direction, which pushes the peptide away. This effect, known as diamagnetism, has been attributed to the alignment of electrons in the peptide bonds between amino acids, or to electron currents flowing around cyclic structures called aromatic rings.
To investigate this phenomenon, Yang and colleagues prepared three different samples of a pentapeptide with the sequence AYFFF. A pentapeptide is a polymer consisting specifically of five amino acid units – in this case, one unit of alanine (A), one of tyrosine (Y) and three of phenylalanine (F).
In the first sample, the researchers dissolved the peptide in the organic solvent dimethyl sulfoxide (DMSO). In the second sample, they dispersed the powdered peptide in water. In the third sample, they also dispersed the powdered peptide in water, but then left it to stand for 16 hours. Over this 16-hour period, the peptides self-assembled into fibres more than 10 µm long.
AFM images of the self-assembled fibres of AYFFF aromatic peptides (left) and fibres of a control non-aromatic peptide IIIGK (right). (Courtesy: Haijun Yang, Feng Zhang and Haiping Fang)
The researchers weighed the samples, and then repeated the measurement in the presence of a magnetic field, which they applied by placing a permanent magnet above the apparatus. They assumed that any difference between measurements with and without the magnet was due to the diamagnetic interaction between the external magnetic field and the magnetic fields induced within the sample.
They found that the peptide dissolved in DMSO exhibited the weakest diamagnetic response, while the sample in which the peptide had been allowed to self-assemble exhibited the strongest. The strength of diamagnetism in the water-dispersed sample was somewhere between the two, which the researchers put down to the occurrence of a limited degree of self-assembly.
When the team performed the same experiment using a different pentapeptide – IIIGK, comprising isoleucine (I), glycine (G) and lysine (K) – they found only a weak diamagnetic response, even for the sample that had been left to self-assemble into fibril structures. Whereas tyrosine and phenylalanine in the AYFFF sequence incorporate aromatic rings in their structures, this is not the case for any of the components of the IIIGK peptide. Yang and colleagues therefore interpret their results as confirmation that the electron dynamics of the aromatic rings, rather than the peptide bonds, are responsible for strong diamagnetism in peptides.
Although the role of aromatic ring currents was not unexpected in itself, the researchers were surprised by how strong the diamagnetism was in the self-assembled peptide samples. They are still investigating the physics underlying the effect, but they do already have an idea of how such anomalously strong diamagnetism might arise.
“Each peptide molecule has an induced magnetic moment in the presence of an applied magnetic field,” says Haiping Fang, of the CAS and East China University of Science and Technology in Shanghai, who led the research. “Thermal forces randomize the orientation of these magnetic moments, weakening the diamagnetism. A group of aromatic peptides in the assembled state – with interactions between them – might reduce the effect of these thermal fluctuations, resulting in the strong diamagnetism.”
Whatever its origin, the researchers foresee several possible applications for the effect. “Peptides with various sequences could be easily assembled into different nanostructures under magnetic fields, widening fabrication strategies,” says Feng Zhang, a collaborator from Guangzhou Medical University. “Assembled peptides modified with biomarkers could also be used as biological tracers, enhancing the contrast between normal and abnormal tissues in magnetic resonance imaging. Or, in novel brain–computer interfaces, the assembled peptides’ strong diamagnetism could be used as a non-invasive sensor to detect weak variations in magnetic signals from brain activity.”


physicsworld--2020-09-07--Flat bands appear in buckled graphene superlattices - Physics World

An international team led by researchers at Rutgers University in the US has found a way to create “ flat ” electronic bands – that is , electron states in which there is no relationship between the electrons ’ energy and velocity – in graphene simply by causing the material to buckle .
This new strategy could be used to produce so-called “ superlattice ” systems that serve as platforms for exploring the collective behaviour of electrons in strongly-interacting quantum systems .
Such behaviour is known to be linked to high-temperature superconductivity , but a complete understanding is still lacking @ @ @ @ @ @ @ physicists because electrons become “ dispersionless ” in these bands – that is , their kinetic energy is suppressed .
As the electrons slow down almost to a halt , their effective mass approaches infinity , leading to exotic topological phenomena as well as strongly-correlated states of matter associated with high-temperature superconductivity , magnetism and other quantum properties of solids .
Flat bands are , however , difficult to engineer , and researchers have only observed them in a handful of physical systems .
An example is twisted bilayer graphene , which is @ @ @ @ @ @ @ on top of each other and slightly misaligning them .
Under these conditions , the atoms in the graphene sheets form a quasi-periodic moiré pattern with a period that is determined by the relative twist between the sheets ’ crystallographic axes , rather than the spacing between individual atoms .
The result is a “ superlattice ” in which the material ’ s unit cell ( that is , the simple repetition of carbon atoms in its crystal structure ) expands to a huge extent – as if the 2D crystal were being @ @ @ @ @ @ @ This stretching dramatically changes the material ’ s interactions and properties .
Notably , it undergoes a transition from an insulator to a superconductor at a “ magic ” twist angle of 1.1° and a temperature of 1.7 K. “ Magic angle ” graphene has been studied extensively since its discovery in 2018 .
However , because the “ magic ” effect disappears at slightly larger or smaller twists , very accurate fine-tuning of the material is required to achieve the desired electronic band structure .
A team led by Eva Andrei of @ @ @ @ @ @ @ Rutgers has now developed an alternative means of producing flat electronic bands .
She and her colleagues began by placing graphene on an atomically flat substrate of niobium diselenide or hexagonal boron nitride .
Using scanning tunnelling microscope topography and computer simulations , they found that the graphene sheet buckled when cooled to 4 degrees above absolute zero .
This buckling is driven by compressive strain within the graphene sample , which develops when ridges that formed during the sample ’ s fabrication collapse as it cools .
As the graphene buckles , @ @ @ @ @ @ @ forms that electrons in the material experience as pseudo-magnetic fields .
“ These fields are an electronic illusion , but they act as real magnetic fields , ” Andrei explains .
The result , she says , is a dramatic change in the material ’ s electronic properties – including the emergence of flat bands .
Unlike earlier realizations of a pseudo-magnetic fields that were mostly local in their extent , the buckling transition observed in this work produces a global change in the electronic structure of graphene , with a sequence of @ @ @ @ @ @ @ According to the team , the new technique could thus become a general strategy for creating other superlattice systems and using them to explore interaction phenomena characteristic of flat bands .
The researchers , who report their work in Nature , say they would now like to develop ways of engineering buckled 2D materials with novel electronic and mechanical properties for use in applications such as nanorobotics and quantum computing .

Simulated mountain and valley landscape created by buckling in graphene. Credit: Yuhang Jiang
An international team led by researchers at Rutgers University in the US has found a way to create “flat” electronic bands – that is, electron states in which there is no relationship between the electrons’ energy and velocity – in graphene simply by causing the material to buckle. This new strategy could be used to produce so-called “superlattice” systems that serve as platforms for exploring the collective behaviour of electrons in strongly interacting quantum systems. Such behaviour is known to be linked to high-temperature superconductivity, but a complete understanding is still lacking.
Flat bands are especially interesting for physicists because electrons become “dispersionless” in these bands – that is, their kinetic energy is suppressed. As the electrons slow down almost to a halt, their effective mass approaches infinity, leading to exotic topological phenomena as well as strongly correlated states of matter associated with high-temperature superconductivity, magnetism and other quantum properties of solids.
A fine-tuning challenge
Flat bands are, however, difficult to engineer, and researchers have only observed them in a handful of physical systems. An example is twisted bilayer graphene, which is created by placing two sheets of graphene on top of each other and slightly misaligning them. Under these conditions, the atoms in the graphene sheets form a quasi-periodic moiré pattern with a period that is determined by the relative twist between the sheets’ crystallographic axes, rather than the spacing between individual atoms.
The result is a “superlattice” in which the material’s unit cell (that is, the simple repetition of carbon atoms in its crystal structure) expands to a huge extent – as if the 2D crystal were being stretched 100 times in all directions. This stretching dramatically changes the material’s interactions and properties. Notably, it undergoes a transition from an insulator to a superconductor at a “magic” twist angle of 1.1° and a temperature of 1.7 K.
“Magic angle” graphene has been studied extensively since its discovery in 2018. However, because the “magic” effect disappears at slightly larger or smaller twists, very accurate fine-tuning of the material is required to achieve the desired electronic band structure.
Pseudo-magnetic fields
A team led by Eva Andrei of the Department of Physics and Astronomy at Rutgers has now developed an alternative means of producing flat electronic bands. She and her colleagues began by placing graphene on an atomically flat substrate of niobium diselenide or hexagonal boron nitride. Using scanning tunnelling microscope topography and computer simulations, they found that the graphene sheet buckled when cooled to 4 degrees above absolute zero. This buckling is driven by compressive strain within the graphene sample, which develops when ridges that formed during the sample’s fabrication collapse as it cools.
As the graphene buckles, a “mountain and valley” landscape forms that electrons in the material experience as pseudo-magnetic fields. “These fields are an electronic illusion, but they act as real magnetic fields,” Andrei explains. The result, she says, is a dramatic change in the material’s electronic properties – including the emergence of flat bands.
Unlike earlier realizations of a pseudo-magnetic fields that were mostly local in their extent, the buckling transition observed in this work produces a global change in the electronic structure of graphene, with a sequence of flat bands spread throughout the material.
According to the team, the new technique could thus become a general strategy for creating other superlattice systems and using them to explore interaction phenomena characteristic of flat bands.
The researchers, who report their work in Nature, say they would now like to develop ways of engineering buckled 2D materials with novel electronic and mechanical properties for use in applications such as nanorobotics and quantum computing.


physicsworld--2020-09-07--Inverted buoyancy makes tiny boat appear to defy gravity - Physics World

Physicists in France have made small objects float upside-down on the underside of a layer of viscous liquid levitating in air .
Although their apparently gravity-defying demonstration breaks no laws of physics , they say it could shed new light on the interaction between air and liquids .
Archimedes ’ principle says that an object fully or partially immersed in a liquid experiences the upward force of buoyancy , which is equal to the weight of liquid it displaces .
By opposing the force of gravity due to the object ’ s own weight , buoyancy will cause an object @ @ @ @ @ @ @ ( overall ) than the liquid – while denser objects will sink .
This is a very familiar phenomenon in our everyday world in which water and other liquids naturally exist at a lower gravitational potential than less dense gases .
People on a boat travel through the air , with the sea below them .
What the latest research shows is that the same principle would hold for people in an upside-down world – one in which , in effect , the sky lies beneath the sea .
The secret to bringing @ @ @ @ @ @ @ Since the 1950s , scientists have demonstrated a range of counter-intuitive effects by vibrating fluids at high frequencies .
Gas bubbles , for example , can be made to sink , while heavier particles rise .
On a larger scale , whole layers of fluid can levitate in air .
This is because more dense fluids tend to drip under the action of gravity , eventually displacing the air beneath them .
By preventing the formation of drops , vibration keeps the fluid ’ s lower surface flat and allows it to hover @ @ @ @ @ @ @ Fort and colleagues at the PSL University in Paris fixed a plexiglass container to a vibrating platform and then filled the container with either silicon oil or glycerol .
These viscous liquids have surfaces that remain stable even at high accelerations .
After turning the shaker on , the researchers used a syringe with a long needle to inject air towards the bottom of the liquid .
With the resulting bubble sinking and growing , it eventually created a layer of air across the bottom of the container – causing the viscous liquid @ @ @ @ @ @ @ nothing new , but what Fort and co-workers then did was to place objects upside-down on the lower interface between the liquid and the air .
As they explain in a paper in Nature , this buoyancy is governed by the same basic physics that would be at work on the upper interface .
The object ’ s gravity tending to pull it down while the disturbance its downward motion creates in the liquid tends to pull it up .
There is an important difference between the normal and inverted flotation , however @ @ @ @ @ @ @ is in stable equilibrium because any attempt to move it up or down will be met by a restoring force .
When pushed down it displaces a greater amount of liquid and so experiences more buoyancy , while any force pushing it out of the liquid will be opposed by gravity .
But in the upside-down case , any slight displacement from equilibrium will see the object accelerate away – thanks to gravity below and the mass of liquid above .
Fort and colleagues found that the vibrations needed to invert the air @ @ @ @ @ @ @ exotic buoyancy – at least for objects up to a certain density .
They vibrated the container at 100 Hz and showed they could pin a series of small plastic spheres to the lower liquid-air interface , with the spheres remaining in place even when they poked them .
To make the demonstration more eye-catching they repeated the feat with a little plastic boat , while floating an identical boat on the upper interface ( see figure ) .
The researchers then found that 2.5 cm-diameter plastic spheres weighing no more than about @ @ @ @ @ @ @ of the chamber once they had reduced the amplitude of the vibrations to the point where the liquid layer itself succumbed to gravity .
Heavier spheres , in contrast , fell first .
This behaviour , they say , is consistent with a simple theoretical model that they developed to explain the inverted buoyancy .
Only when the spheres ’ density approached that of the liquid – meaning a mass of about 8 g – did significant discrepancies occur .
In that case , they add , other more complex effects play a @ @ @ @ @ @ @ on the concept of time-averaged forces , which tend to stabilize the equilibrium states .
As they point out , this is the same basic idea underlying what is known as a Stephenson–Kapitza pendulum .
In that case , vibrations allow a pendulum fixed from below to oscillate back and forth in a small arc – when otherwise it would fall to the ground .
Writing a commentary piece in Nature , Vladislav Sorokin of the University of Auckland in New Zealand and Iliya Blekhman of the Russian Academy of Science in St @ @ @ @ @ @ @ assumptions – such as a linear relationship between the pressure and height of the air layer – “ somewhat limit the accuracy ” of the French group ’ s model .
But they reckon that the work might nevertheless lead to practical applications – pointing out that gravity-defying effects in fluids have previously been used to improve chemical reactions and aid mineral processing – and that it suggests other “ remarkable phenomena ” remain to be discovered in vibrating mechanical systems .

Topsy-turvy: plastic boats floating above and below a levitated liquid layer. (Courtesy: Benjamin Apffel et al./Nature)
Physicists in France have made small objects float upside-down on the underside of a layer of viscous liquid levitating in air. Although their apparently gravity-defying demonstration breaks no laws of physics, they say it could shed new light on the interaction between air and liquids.
Archimedes’ principle says that an object fully or partially immersed in a liquid experiences the upward force of buoyancy, which is equal to the weight of liquid it displaces. By opposing the force of gravity due to the object’s own weight, buoyancy will cause an object to float if it is less dense (overall) than the liquid – while denser objects will sink.
This is a very familiar phenomenon in our everyday world in which water and other liquids naturally exist at a lower gravitational potential than less dense gases. People on a boat travel through the air, with the sea below them. What the latest research shows is that the same principle would hold for people in an upside-down world – one in which, in effect, the sky lies beneath the sea.
Counter-intuitive effects
The secret to bringing about this topsy-turvy floating is vibration. Since the 1950s, scientists have demonstrated a range of counter-intuitive effects by vibrating fluids at high frequencies. Gas bubbles, for example, can be made to sink, while heavier particles rise. On a larger scale, whole layers of fluid can levitate in air. This is because more dense fluids tend to drip under the action of gravity, eventually displacing the air beneath them. By preventing the formation of drops, vibration keeps the fluid’s lower surface flat and allows it to hover.
In the new experiment, Emmanuel Fort and colleagues at the PSL University in Paris fixed a plexiglass container to a vibrating platform and then filled the container with either silicon oil or glycerol. These viscous liquids have surfaces that remain stable even at high accelerations. After turning the shaker on, the researchers used a syringe with a long needle to inject air towards the bottom of the liquid. With the resulting bubble sinking and growing, it eventually created a layer of air across the bottom of the container – causing the viscous liquid to levitate.
This fluid levitation is nothing new, but what Fort and co-workers then did was to place objects upside-down on the lower interface between the liquid and the air. As they explain in a paper in Nature, this buoyancy is governed by the same basic physics that would be at work on the upper interface. The object’s gravity tending to pull it down while the disturbance its downward motion creates in the liquid tends to pull it up.
Slight displacement from equilibrium
There is an important difference between the normal and inverted flotation, however. In the former, an object is in stable equilibrium because any attempt to move it up or down will be met by a restoring force. When pushed down it displaces a greater amount of liquid and so experiences more buoyancy, while any force pushing it out of the liquid will be opposed by gravity. But in the upside-down case, any slight displacement from equilibrium will see the object accelerate away – thanks to gravity below and the mass of liquid above.
Fort and colleagues found that the vibrations needed to invert the air and liquid also in fact stabilized the exotic buoyancy – at least for objects up to a certain density. They vibrated the container at 100 Hz and showed they could pin a series of small plastic spheres to the lower liquid-air interface, with the spheres remaining in place even when they poked them. To make the demonstration more eye-catching they repeated the feat with a little plastic boat, while floating an identical boat on the upper interface (see figure).
The researchers then found that 2.5 cm-diameter plastic spheres weighing no more than about 6 g only fell to the bottom of the chamber once they had reduced the amplitude of the vibrations to the point where the liquid layer itself succumbed to gravity. Heavier spheres, in contrast, fell first. This behaviour, they say, is consistent with a simple theoretical model that they developed to explain the inverted buoyancy. Only when the spheres’ density approached that of the liquid – meaning a mass of about 8 g – did significant discrepancies occur. In that case, they add, other more complex effects play a role.
The team based its model on the concept of time-averaged forces, which tend to stabilize the equilibrium states. As they point out, this is the same basic idea underlying what is known as a Stephenson–Kapitza pendulum. In that case, vibrations allow a pendulum fixed from below to oscillate back and forth in a small arc – when otherwise it would fall to the ground.
Writing a commentary piece in Nature, Vladislav Sorokin of the University of Auckland in New Zealand and Iliya Blekhman of the Russian Academy of Science in St Petersburg, Russia, argue that several assumptions – such as a linear relationship between the pressure and height of the air layer – “somewhat limit the accuracy” of the French group’s model. But they reckon that the work might nevertheless lead to practical applications – pointing out that gravity-defying effects in fluids have previously been used to improve chemical reactions and aid mineral processing – and that it suggests other “remarkable phenomena” remain to be discovered in vibrating mechanical systems.


physicsworld--2020-09-08--The Physics World China Briefing  is now out - Physics World

This year has been dominated by one event : the SARS-CoV-2 coronavirus , which was first reported in Wuhan , China , before quickly spreading throughout the world .
The severe impact of COVID-19 , the disease caused by the coronavirus , has been felt by all and physicists are no exception .
Universities and research facilities all shut their doors earlier this year as scientists headed home under lockdown .
In this year ’ s Physics World China Briefing , we report how universities in China – the first to be affected – are now beginning to cautiously reopen @ @ @ @ @ @ @ the country , which seem to have been contained , things appear to be getting back on track .
Without a vaccine on the immediate horizon , however , progress will remain slow and cautious and with international travel limited , collaborations will likely remain online-only for the foreseeable future .
Indeed , the impact of COVID-19 has already hit many scientific conferences , some of which have had to switch at short notice to online platforms .
One example is Quantum 2020 – a major international conference in quantum technology organized by @ @ @ @ @ @ @ in partnership with the Chinese Physical Society and the University of Science and Technology of China .
Due to be held in Shanghai , it will now take place entirely online on 19–22 October .
For this year ’ s briefing , which is free to read , we talk to USTC physicist Chaoyang Lu about managing this virtual shift as well as the future of quantum technologies .
Let us know what you think about the publication on Twitter , Facebook or by e-mailing us at pwld @ ioppublishing.org .

This year has been dominated by one event: the SARS-CoV-2 coronavirus, which was first reported in Wuhan, China, before quickly spreading throughout the world. The severe impact of COVID-19, the disease caused by the coronavirus, has been felt by all and physicists are no exception. Universities and research facilities all shut their doors earlier this year as scientists headed home under lockdown.
In this year’s Physics World China Briefing, we report how universities in China – the first to be affected – are now beginning to cautiously reopen. Despite a few localized outbreaks in the country, which seem to have been contained, things appear to be getting back on track. Without a vaccine on the immediate horizon, however, progress will remain slow and cautious and with international travel limited, collaborations will likely remain online-only for the foreseeable future.
Indeed, the impact of COVID-19 has already hit many scientific conferences, some of which have had to switch at short notice to online platforms. One example is Quantum 2020 – a major international conference in quantum technology organized by the Institute of Physics and IOP Publishing in partnership with the Chinese Physical Society and the University of Science and Technology of China. Due to be held in Shanghai, it will now take place entirely online on 19–22 October. For this year’s briefing, which is free to read, we talk to USTC physicist Chaoyang Lu about managing this virtual shift as well as the future of quantum technologies.
Let us know what you think about the publication on Twitter, Facebook or by e-mailing us at pwld@ioppublishing.org.


physicsworld--2020-09-08--Multi-user communication network paves the way towards the quantum internet - Physics World

The concept of quantum communication , with security guaranteed by the laws of physics , took the world by storm when first unveiled in 1984 .
The traditional protocol , however , allows only two people to communicate securely .
Attempts to extend this to “ quantum networking ” have usually proved either insecure or impracticably complex .
Now , however , researchers in the UK and Austria have demonstrated secure information exchange between eight users spaced all around a city .
The canonical quantum communication protocol relies on two parties generating a secure key by exchanging polarized photons .
@ @ @ @ @ @ @ by the fact a third party can not make a measurement of their state without disturbing them and being detected .
Though remarkable , this approach is fundamentally limited to pairwise communication : it does not provide a blueprint for the multi-dimensional quantum network , or “ quantum internet ” that some researchers have dreamed of , in which multiple users connected together can all communicate simultaneously and securely with any other member of the network .
One obvious way to extend the scheme beyond two people is for the second person to @ @ @ @ @ @ @ chain , repeating the procedure and communicating securely with a third person , who in turn passes the message on until the message reaches its ultimate destination .
Quantum networking schemes based on such “ trusted nodes ” have been developed .
The security of such schemes is no longer absolute , however , because a trusted node may not be totally secure .
Schemes that avoid trusted nodes have generally proved unfeasibly complex and hardware-intensive or have suffered other problems , such as restricting which users can communicate at any one time @ @ @ @ @ @ @ Institute for Quantum Optics and Quantum Information in Vienna led by Rupert Ursin demonstrated a scheme in which four users received pairs of entangled photons from a single , laser-pumped crystal source .
“ I generate these two-by-two , but I generate several such two-by-two pairs in a tiny amount of time , ” explains project leader Siddarth Koduru Joshi .
This constant stream of entangled photon pairs from a single , central source allowed each of the four parties to become pairwise entangled with each of the other three parties .
“ @ @ @ @ @ @ @ , I look at stream one , if I ’ m talking to somebody else , I look at stream two , and so on , ” says Joshi , now at the University of Bristol .
The researchers believed that this scheme provided a simpler , more scalable architecture for secure , trusted-node free information exchange between multiple parties .
In the new work , researchers at the University of Bristol , in collaboration with the Austrian scientists , have confirmed that the technique works , demonstrating simultaneous and secure exchange of @ @ @ @ @ @ @ 12.6 km away from the central source around the city of Bristol .
“ This time , we actually demonstrated quantum communication , and we did this through deployed fibres across the city to show compatibility with existing infrastructure , ” says Joshi .
Moreover , the researchers added additional multiplexing to simplify the hardware required by each user and make the protocol even more scalable : whereas their original protocol would have required 56 wavelength channels to fully interconnect eight users , their improved version required only 16 .
The researchers believe @ @ @ @ @ @ @ quantum network to date .
Quantum and computer engineer Wolfgang Tittel of QuTech at Delft University of Technology in the Netherlands describes the paper as “ nice and important work ” and is especially impressed by the absence of trusted nodes .
An important next step , he says , is the scheme ’ s integration with quantum repeater technology , which to mitigates photon loss and decoherence and allows entanglement distribution over long distances .
This , he says , could “ extend the network beyond metropolitan size ” .
The research @ @ @ @ @ @

The quantum physics experiment demonstrated an important step towards quantum cryptography between many users, an essential requirement for a secure quantum internet. (Courtesy: © ÖAW/Klaus Pichler)
The concept of quantum communication, with security guaranteed by the laws of physics, took the world by storm when first unveiled in 1984. The traditional protocol, however, allows only two people to communicate securely. Attempts to extend this to “quantum networking” have usually proved either insecure or impracticably complex. Now, however, researchers in the UK and Austria have demonstrated secure information exchange between eight users spaced all around a city.
The canonical quantum communication protocol relies on two parties generating a secure key by exchanging polarized photons. The security of the link is guaranteed by the fact a third party cannot make a measurement of their state without disturbing them and being detected. Though remarkable, this approach is fundamentally limited to pairwise communication: it does not provide a blueprint for the multi-dimensional quantum network, or “quantum internet” that some researchers have dreamed of, in which multiple users connected together can all communicate simultaneously and securely with any other member of the network.
One obvious way to extend the scheme beyond two people is for the second person to simply act as a link in the chain, repeating the procedure and communicating securely with a third person, who in turn passes the message on until the message reaches its ultimate destination. Quantum networking schemes based on such “trusted nodes” have been developed. The security of such schemes is no longer absolute, however, because a trusted node may not be totally secure. Schemes that avoid trusted nodes have generally proved unfeasibly complex and hardware-intensive or have suffered other problems, such as restricting which users can communicate at any one time.
In 2018, researchers at the Institute for Quantum Optics and Quantum Information in Vienna led by Rupert Ursin demonstrated a scheme in which four users received pairs of entangled photons from a single, laser-pumped crystal source. “I generate these two-by-two, but I generate several such two-by-two pairs in a tiny amount of time,” explains project leader Siddarth Koduru Joshi.
Project leader Siddarth Joshi optimizes the central quantum network hub. Instead of making a physical connection between each and every user, the researchers created a scheme where every user only has a single glass fibre connected to a source of quantum entanglement. (Courtesy: Soeren Wengerowsky)
This constant stream of entangled photon pairs from a single, central source allowed each of the four parties to become pairwise entangled with each of the other three parties. “If I’m talking to you, I look at stream one, if I’m talking to somebody else, I look at stream two, and so on,” says Joshi, now at the University of Bristol. The researchers believed that this scheme provided a simpler, more scalable architecture for secure, trusted-node free information exchange between multiple parties.
In the new work, researchers at the University of Bristol, in collaboration with the Austrian scientists, have confirmed that the technique works, demonstrating simultaneous and secure exchange of information between eight users spaced up to 12.6 km away from the central source around the city of Bristol. “This time, we actually demonstrated quantum communication, and we did this through deployed fibres across the city to show compatibility with existing infrastructure,” says Joshi.
Moreover, the researchers added additional multiplexing to simplify the hardware required by each user and make the protocol even more scalable: whereas their original protocol would have required 56 wavelength channels to fully interconnect eight users, their improved version required only 16. The researchers believe their network is the largest trusted-node free quantum network to date.
Quantum and computer engineer Wolfgang Tittel of QuTech at Delft University of Technology in the Netherlands describes the paper as “nice and important work” and is especially impressed by the absence of trusted nodes. An important next step, he says, is the scheme’s integration with quantum repeater technology, which to mitigates photon loss and decoherence and allows entanglement distribution over long distances. This, he says, could “extend the network beyond metropolitan size”.
The research is published in Science Advances.


physicsworld--2020-09-08--Using particle physics to foster medical innovation - Physics World

What are your main areas of research at the Institute of High Energy Physics ( IHEP ) , Chinese Academy of Sciences ?
My interest focuses on radiation imaging and its applications in medical physics and industry .
This includes the design of X-ray and gamma-ray detectors , imaging algorithms as well as systems development .
How did you get into medical imaging ?
For my PhD , I worked on IHEP ’ s Beijing Electron Positron Collider , which gave me experience in radiation measurements of positron annihilation .
When I graduated in 2006 , I began research on @ @ @ @ @ @ @ ( PET ) , single-photon emission computed tomography ( SPECT ) and computerized tomography ( CT ) .
Since 2008 research into radiation-imaging technology that has been carried out at IHEP ’ s division of nuclear technology and applications has achieved a number of breakthroughs in PET and SPECT detector development .
Such work has especially benefited from the development of electronics and detection technology during the construction of big-science facilities at IHEP .
Do you have an example ?
With the rapid development of the Chinese medical-imaging market , our team has @ @ @ @ @ @ @ as a dedicated breast-PET ( PEMi ) scanners .
We have now completed more than 500 clinical test runs and in 2015 received certification from the China Food and Drug Administration .
Now it is being used for early breast cancer diagnosis in clinical settings – an important addition to improving breast cancer survival rates .
How important is technology transfer at IHEP ?
It is very important .
In IHEP ’ s strategic outlook , technology transfer is as critical as the construction of big-science facilities and basic scientific research .
Most @ @ @ @ @ @ @ in technology transfer to some degree , with IHEP also setting up a dedicated technology-transfer office and a spin-out company .
What are some of the technologies that IHEP has spun out of its research ?
The main technologies that have been successfully transferred are accelerator and medical-imaging technologies , such as the PEMi scanner .
As IHEP makes large accelerators and their core components , we have also developed high-power electronic irradiation accelerators that are being used for the sterilization of food and medical equipment .
These accelerators have already been installed @ @ @ @ @ @ @ other regions around China .
Many of the technologies at IHEP seem suited for medical applications .
Why is this ?
The dominant technologies of IHEP are accelerator , nuclear detection and nuclear electronics technologies , which are exactly the type of technologies that are needed in nuclear medicine , radiotherapy and medical diagnosis .
National funding projects give support for these areas of medical physics and there are many companies in this area that we collaborate with .
What kind of innovations do you see in the future ?
Given advanced detector @ @ @ @ @ @ @ such as high resolution – i.e .
less than 100 picoseconds – time-of-flight PET technology that can increase the resolution of images and reduce the radiation dose to patients .
Another aspect in medical applications is “ static spectral ” CT scanners , which will also allow for high-resolution imaging .
In addition , the integration of diagnosis and treatment , especially in precision-particle therapy is another development I see in the future .
Do you collaborate on technology transfer with other countries ?
Not yet , but international cooperation is an aspect @ @ @ @ @ @ @ The Physics World China Briefing is now out With China designing a 100 km collider , do you envisage a similar emphasis on technology transfer when planning that project ?
Each of IHEP ’ s big-science facilities has led to the development of multiple disciplines and technologies .
Pixel-detector technology , for example , is involved in almost every scientific project , so we will accumulate more technical knowledge in this field as we advance .
Combining the emphasis on detector development with medical-imaging equipment , we plan to focus on pixel-type semiconductor-detector @ @ @ @ @ @ @ and utilizing it in the next generation of CT and SPECT scanners .
COVID-19 has not really had any effect on our lab and we have continued to carry on with our research during the pandemic .

Physics World China Briefing. You can enjoy the full issue Taken from the September 2020. You can enjoy the full issue via the Physics World app
Cunfeng Wei, head of nuclear technology and applications at the Institute of High Energy Physics in Beijing, talks to Michael Banks about the close links between particle physics and medical applications
Knowledge transfer Physicist Cunfeng Wei has been at the Institute of High Energy Physics in Beijing since he began his PhD in 2002. (Courtesy: IHEP)
What are your main areas of research at the Institute of High Energy Physics (IHEP), Chinese Academy of Sciences?
My interest focuses on radiation imaging and its applications in medical physics and industry. This includes the design of X-ray and gamma-ray detectors, imaging algorithms as well as systems development.
How did you get into medical imaging?
For my PhD, I worked on IHEP’s Beijing Electron Positron Collider, which gave me experience in radiation measurements of positron annihilation. When I graduated in 2006, I began research on radiation-imaging technologies such as positron emission tomography (PET), single-photon emission computed tomography (SPECT) and computerized tomography (CT). Since 2008 research into radiation-imaging technology that has been carried out at IHEP’s division of nuclear technology and applications has achieved a number of breakthroughs in PET and SPECT detector development. Such work has especially benefited from the development of electronics and detection technology during the construction of big-science facilities at IHEP.
Do you have an example?
With the rapid development of the Chinese medical-imaging market, our team has co-operated with companies to develop devices such as a dedicated breast-PET (PEMi) scanners. We have now completed more than 500 clinical test runs and in 2015 received certification from the China Food and Drug Administration. Now it is being used for early breast cancer diagnosis in clinical settings – an important addition to improving breast cancer survival rates.
How important is technology transfer at IHEP?
It is very important. In IHEP’s strategic outlook, technology transfer is as critical as the construction of big-science facilities and basic scientific research. Most research centres in IHEP have been involved in technology transfer to some degree, with IHEP also setting up a dedicated technology-transfer office and a spin-out company.
Each of IHEP’s big-science facilities has led to the development of multiple disciplines and technologies.
What are some of the technologies that IHEP has spun out of its research?
The main technologies that have been successfully transferred are accelerator and medical-imaging technologies, such as the PEMi scanner. As IHEP makes large accelerators and their core components, we have also developed high-power electronic irradiation accelerators that are being used for the sterilization of food and medical equipment. These accelerators have already been installed in Yantai, Wuhan, Tianjin and other regions around China.
Many of the technologies at IHEP seem suited for medical applications. Why is this?
The dominant technologies of IHEP are accelerator, nuclear detection and nuclear electronics technologies, which are exactly the type of technologies that are needed in nuclear medicine, radiotherapy and medical diagnosis. National funding projects give support for these areas of medical physics and there are many companies in this area that we collaborate with.
What kind of innovations do you see in the future?
Given advanced detector and electronics technology, we see developments such as high resolution – i.e. less than 100 picoseconds – time-of-flight PET technology that can increase the resolution of images and reduce the radiation dose to patients. Another aspect in medical applications is “static spectral” CT scanners, which will also allow for high-resolution imaging. In addition, the integration of diagnosis and treatment, especially in precision-particle therapy is another development I see in the future.
Do you collaborate on technology transfer with other countries?
Not yet, but international co-operation is an aspect that we are interested to grow. Read more The Physics World China Briefing is now out
With China designing a 100 km collider, do you envisage a similar emphasis on technology transfer when planning that project?
Each of IHEP’s big-science facilities has led to the development of multiple disciplines and technologies. Pixel-detector technology, for example, is involved in almost every scientific project, so we will accumulate more technical knowledge in this field as we advance. Combining the emphasis on detector development with medical-imaging equipment, we plan to focus on pixel-type semiconductor-detector technology by developing an advanced sensing chip and utilizing it in the next generation of CT and SPECT scanners.
Has COVID-19 affected your research?
COVID-19 has not really had any effect on our lab and we have continued to carry on with our research during the pandemic.


physicsworld--2020-09-08--Contact-free 3D display responds to tiny changes in ambient humidity - Physics World

Researchers in Korea have developed a new 3D display with a touchless interface that responds to the water vapour in a user ’ s hovering finger .
The display , which relies on structural colour ( that is , colour produced by light-scattering nanostructures ) rather than reflections from coloured pigments , changes its hue depending on how far the user ’ s finger is from the screen .
The technology might find use in wearable electronics and electronic skins that mimic how human skin can sense pressure , temperature and humidity .
Structural colours are often found in nature @ @ @ @ @ @ @ of some butterfly species .
Because they arise from a physical structure ( such as photonic crystals or arrays of nanofibers that reflect certain wavelengths of light ) , they are more durable than chemical pigments , which inevitably fade over time .
Structural colours can also be changed by altering the molecular configuration of their surfaces .
Both properties are attractive for novel “ smart ” materials used in interactive displays , and to this end researchers have long searched for ways to mimic the structural colours of the biological world .
@ @ @ @ @ @ @ to external stimuli by varying the intensity of light they emit , rather than changing colour .
The display made by Cheolmin Park and Won-Gun Koh and colleagues of Yonsei University in Seoul is different in that it is based on the multi-order reflection of structural colours in a thin , solid-state block copolymer ( BCP ) photonic crystal .
This material spontaneously develops a layered 1D periodic microstructural film as it forms .
The nanostructured surface of the photonic crystal has a refractive index that varies with a period that is close @ @ @ @ @ @ @ This variation produces a photonic “ band gap ” that affects how photons propagate through the material , much as a periodic potential in semiconductors affects the flow of electrons by defining allowed and forbidden energy bands .
In the case of photonic crystals , light in the wavelength range that corresponds to the photonic band gap gets reflected , while light at other wavelengths is transmitted .
To achieve full-visible-range structural colours , the researchers used a BCP photonic crystal made from alternating layers , including a layer containing a chemically cross-linked @ @ @ @ @ @ @ of this network are filled with a non-volatile ionic liquid ( which alters the photonic crystal ’ s electronic properties ) , the subtle changes in water vapour levels that occur when a human finger is brought to within 1 to 15 mm from its surface are enough to shift the configuration of the surface structures to produce blue , green and orange colours .
These colour changes occur thanks to a phenomenon known as reflective colour mixing .
When light hits the material ’ s surface , it couples with surface plasmons @ @ @ @ @ @ @ plasmons then become trapped in the surface , creating regions in which the dielectric constant of the structure is nearly zero , separated by areas of high refractive index .
The presence of the non-volatile ionic liquid changes these dynamics and increases the reflection of different wavelengths of light thanks to two-colour mixing of pairs of reflections .
The researchers also found that they could easily transfer their photonic crystal-based film from a silicon substrate onto another support ( in this case a printed one-dollar bill ) .
This means that the technology @ @ @ @ @ @ @ displays , they say .
The touchless sensing display is detailed in Science Advances .

Photographs of the block copolymer photonic crystal display material transferred onto a glass bottle (left) and onto a PET substrate (right). (Courtesy: Han Sol Kang/Yonsei University)
Researchers in Korea have developed a new 3D display with a touchless interface that responds to the water vapour in a user’s hovering finger. The display, which relies on structural colour (that is, colour produced by light-scattering nanostructures) rather than reflections from coloured pigments, changes its hue depending on how far the user’s finger is from the screen. The technology might find use in wearable electronics and electronic skins that mimic how human skin can sense pressure, temperature and humidity.
Structural colours are often found in nature – for example, in the wings of some butterfly species. Because they arise from a physical structure (such as photonic crystals or arrays of nanofibers that reflect certain wavelengths of light), they are more durable than chemical pigments, which inevitably fade over time. Structural colours can also be changed by altering the molecular configuration of their surfaces. Both properties are attractive for novel “smart” materials used in interactive displays, and to this end researchers have long searched for ways to mimic the structural colours of the biological world.
Photonic crystal display
Most interactive displays made to date respond to external stimuli by varying the intensity of light they emit, rather than changing colour. The display made by Cheolmin Park and Won-Gun Koh and colleagues of Yonsei University in Seoul is different in that it is based on the multi-order reflection of structural colours in a thin, solid-state block copolymer (BCP) photonic crystal. This material spontaneously develops a layered 1D periodic microstructural film as it forms.
The nanostructured surface of the photonic crystal has a refractive index that varies with a period that is close to the wavelength of visible light. This variation produces a photonic “band gap” that affects how photons propagate through the material, much as a periodic potential in semiconductors affects the flow of electrons by defining allowed and forbidden energy bands. In the case of photonic crystals, light in the wavelength range that corresponds to the photonic band gap gets reflected, while light at other wavelengths is transmitted.
To achieve full-visible-range structural colours, the researchers used a BCP photonic crystal made from alternating layers, including a layer containing a chemically cross-linked interpenetrating hydrogel network. When the domains of this network are filled with a non-volatile ionic liquid (which alters the photonic crystal’s electronic properties), the subtle changes in water vapour levels that occur when a human finger is brought to within 1 to 15 mm from its surface are enough to shift the configuration of the surface structures to produce blue, green and orange colours.
Reflective colour mixing
These colour changes occur thanks to a phenomenon known as reflective colour mixing. When light hits the material’s surface, it couples with surface plasmons – collective excitations of electrons. These plasmons then become trapped in the surface, creating regions in which the dielectric constant of the structure is nearly zero, separated by areas of high refractive index. The presence of the non-volatile ionic liquid changes these dynamics and increases the reflection of different wavelengths of light thanks to two-colour mixing of pairs of reflections.
The researchers also found that they could easily transfer their photonic crystal-based film from a silicon substrate onto another support (in this case a printed one-dollar bill). This means that the technology could be used in printable and rewritable displays, they say.
The touchless sensing display is detailed in Science Advances.


physicsworld--2020-09-08--Entangled light is unscrambled using entanglement itself - Physics World

Natalia Herrera-Valencia and colleagues have successfully unscrambled entangled light after it has passed through a 2 m long multimode fibre .
Led by Mehul Malik , the team at the Heriot-Watt University in Edinburgh tackled the challenge using entanglement itself .
The research was done in collaboration with a colleague at the University of Glasgow and is described in a recent paper in Nature Physics .
Light passing through a disordered ( or “ complex ” ) medium like atmospheric fog or a multimode fibre gets scattered , albeit in a known manner .
As a result , the information @ @ @ @ @ @ @ is preserved , and extra steps are needed to access it .
This gets especially tricky for the transport of entangled states of light because the medium muddles up the quantum correlations .
The states get “ scrambled ” and “ unscrambling ” becomes necessary to retrieve the original entangled states .
To understand a complex medium , physicists use a transmission matrix , which is a 2D array of complex numbers that predicts the fate of any input going through the medium .
The transmission matrix theory , along with some key @ @ @ @ @ @ @ enabled propagation of classical light through complex media .
In this work , the Edinburgh team has extended the idea of the transmission matrix to quantum photonics .
A property called the “ channel-state duality ” allows the researchers to use just a single quantum entangled state – a pair of photons that are correlated in their properties – as a probe to extract the entire transmission matrix of the medium .
This is different from the classical way of constructing the matrix , where multiple light probes must be sent in through @ @ @ @ @ @ @ .
Once they know how the medium scrambles information , Herrera-Valencia and colleagues could undo its effects using the same matrix .
Here again , entanglement offers a neat trick : instead of unscrambling light going through the fibre , the researchers can instead scramble its “ entangled twin ” , that does not go through the medium , to get the exact same results .
They scramble light using a device called the spatial light modulator ( SLM ) which shapes the light field profile .
Compared to 2D qubits , higher @ @ @ @ @ @ @ they can carry more information and are more robust to noise .
But such states are also much more susceptible to changes by the environment .
Reporting the preservation of six-dimensional entanglement in space , the research tackles a significant challenge in quantum photonics .
“ Qubit entanglement already has the technology and deals with degrees of freedom [ like polarization ] that are not affected by the channel .
When it comes to high-dimensional states , there are many issues with spatial mode encoding ” , Malik explains .
Something as simple @ @ @ @ @ @ @ .
To create and measure high-dimensional entangled states , physicists often use the spatial degree of freedom .
In this work , the group uses a spatial “ pixel ” basis .
They divide the continuous position space into discrete regions , or pixels , so if a photon is detected at the first pixel for one arm , its entangled twin will be detected at the same pixel in the other arm .
The number of pixels determines the maximum dimension of entanglement that is possible in the system .
The pixel @ @ @ @ @ @ @ , speed and dimensionality , more so because the SLM enables a precise and lossless control .
In addition to increasing dimensionality of states and addressing issues like dispersion in longer fibres , the team is exploring how the idea that a complex channel is equivalent to a quantum state can simplify measurement of quantum states carrying a lot of information .
In their paper , the team also mentions that the technique can be used to transport high-dimensional entanglement even through dynamic media like biological tissues .
Entangled light can also be @ @ @ @ @ @ @ manipulating any channel would affect the whole state , hence the other channel as well .
They write , “ Such an ability could be useful in quantum network scenarios or for non-invasive biological imaging , where access to all parts of the complex system may be limited ” .

Chaotic speckle: a pattern resulting from light being scrambled by a complex medium such as a multimode optical fibre. (Courtesy: M Malik and S Goel)
Natalia Herrera-Valencia and colleagues have successfully unscrambled entangled light after it has passed through a 2 m long multimode fibre. Led by Mehul Malik, the team at the Heriot-Watt University in Edinburgh tackled the challenge using entanglement itself. The research was done in collaboration with a colleague at the University of Glasgow and is described in a recent paper in Nature Physics.
Light passing through a disordered (or “complex”) medium like atmospheric fog or a multimode fibre gets scattered, albeit in a known manner. As a result, the information carried by the light gets distorted but is preserved, and extra steps are needed to access it. This gets especially tricky for the transport of entangled states of light because the medium muddles up the quantum correlations. The states get “scrambled” and “unscrambling” becomes necessary to retrieve the original entangled states.
Entanglement rescues entanglement
To understand a complex medium, physicists use a transmission matrix, which is a 2D array of complex numbers that predicts the fate of any input going through the medium. The transmission matrix theory, along with some key developments in technology, has only recently enabled propagation of classical light through complex media. In this work, the Edinburgh team has extended the idea of the transmission matrix to quantum photonics.
A property called the “channel-state duality” allows the researchers to use just a single quantum entangled state – a pair of photons that are correlated in their properties – as a probe to extract the entire transmission matrix of the medium. This is different from the classical way of constructing the matrix, where multiple light probes must be sent in through the medium to get the full matrix.
Once they know how the medium scrambles information, Herrera-Valencia and colleagues could undo its effects using the same matrix. Here again, entanglement offers a neat trick: instead of unscrambling light going through the fibre, the researchers can instead scramble its “entangled twin”, that does not go through the medium, to get the exact same results. They scramble light using a device called the spatial light modulator (SLM) which shapes the light field profile.
Dealing with higher dimensions
Compared to 2D qubits, higher dimensional entangled states have great potential because they can carry more information and are more robust to noise. But such states are also much more susceptible to changes by the environment.
Reporting the preservation of six-dimensional entanglement in space, the research tackles a significant challenge in quantum photonics. “Qubit entanglement already has the technology and deals with degrees of freedom [like polarization] that are not affected by the channel. When it comes to high-dimensional states, there are many issues with spatial mode encoding”, Malik explains. Something as simple as wavefront distortion could scramble the information.
To create and measure high-dimensional entangled states, physicists often use the spatial degree of freedom. In this work, the group uses a spatial “pixel” basis. They divide the continuous position space into discrete regions, or pixels, so if a photon is detected at the first pixel for one arm, its entangled twin will be detected at the same pixel in the other arm. The number of pixels determines the maximum dimension of entanglement that is possible in the system. The pixel basis works great in terms of quality, speed and dimensionality, more so because the SLM enables a precise and lossless control.
Implications for quantum technologies
In addition to increasing dimensionality of states and addressing issues like dispersion in longer fibres, the team is exploring how the idea that a complex channel is equivalent to a quantum state can simplify measurement of quantum states carrying a lot of information.
In their paper, the team also mentions that the technique can be used to transport high-dimensional entanglement even through dynamic media like biological tissues. Entangled light can also be sent through two independent channels, where manipulating any channel would affect the whole state, hence the other channel as well. They write, “Such an ability could be useful in quantum network scenarios or for non-invasive biological imaging, where access to all parts of the complex system may be limited”.


physicsworld--2020-09-09--New photocatalyst makes liquid fuel with few unwanted byproducts - Physics World

A new photocatalyst sheet that uses light to convert carbon dioxide and water into a useful chemical fuel has been developed by Erwin Reisner and colleagues at the University of Cambridge .
The device produces formic acid – a liquid fuel – with very few unwanted byproducts .
With improvements to its conversion efficiency , the system could soon make an important contribution towards large-scale , carbon-neutral fuel production .
For billions of years , photosynthesis has provided living cells with an efficient way of using sunlight to convert carbon dioxide and water into chemical fuel .
Recently , researchers @ @ @ @ @ @ @ exploit this process to generate carbon-neutral fuels .
So far , however , these devices have often required sacrificial reagents to catalyse the oxidation of water – a key part of the photosynthesis process .
This produces unwanted byproducts that need to be separated from the useful fuel , limiting the sustainability of the technology .
In their study , Reisner ’ s team developed a more sophisticated device that integrates two doped , light-absorbing semiconductor powders that are fixed onto a conductive layer of gold .
In addition , a molecular , @ @ @ @ @ @ @ .
When sunlight illuminates the sheet , electron-hole pairs are generated in both semiconductors .
One of the semiconductors transfers electrons to the other via the gold layer , leaving behind an excess of positively charged holes .
These holes can then be filled by electrons donated by water via an oxidation reaction that was enabled by the photocatalyst .
Meanwhile , the excess of electrons in the other semiconductor causes carbon dioxide to undergo a reduction reaction to produce formate .
This is a negative ion that can be used to make @ @ @ @ @ @ @ as a liquid .
The powders and catalyst comprising the device are easy and inexpensive to produce in large quantities and the role of water as an electron donor eliminates the need for wasteful oxidation-triggering reagents , significantly boosting the sustainability of the process .
Although the team ’ s initial experiments yielded a low solar-to-formate conversion efficiency of just 0.08 % , they demonstrated an extremely high formate selectivity of 97±3 % , with very few unwanted by-products .
Reisner and colleagues achieved these results with a sheet area of 20 cm2 @ @ @ @ @ @ @ easy to scale it up to several square metres – making it suitable for use on commercial solar farms .
Since formate is a stable liquid fuel , it can easily be stored and transported , or converted into gaseous hydrogen fuel if necessary .
Furthermore , the device is completely wireless and requires no external power , enhancing its sustainability even further .
The researchers will now aim to boost the conversion efficiency of their device to levels suitable for commercialization , by experimenting with a range of different photocatalysts .
Through @ @ @ @ @ @ @ soon become suitable for practical , large-scale solar fuel production , which actively reduces levels of atmospheric carbon dioxide .
The research is described in Nature Energy .

Energy converter: the device converts sunlight, carbon dioxide and water into oxygen and formic acid. (Courtesy: University of Cambridge)
A new photocatalyst sheet that uses light to convert carbon dioxide and water into a useful chemical fuel has been developed by Erwin Reisner and colleagues at the University of Cambridge. The device produces formic acid – a liquid fuel – with very few unwanted byproducts. With improvements to its conversion efficiency, the system could soon make an important contribution towards large-scale, carbon-neutral fuel production.
For billions of years, photosynthesis has provided living cells with an efficient way of using sunlight to convert carbon dioxide and water into chemical fuel. Recently, researchers have made strides towards practical technologies that exploit this process to generate carbon-neutral fuels. So far, however, these devices have often required sacrificial reagents to catalyse the oxidation of water – a key part of the photosynthesis process. This produces unwanted byproducts that need to be separated from the useful fuel, limiting the sustainability of the technology.
In their study, Reisner’s team developed a more sophisticated device that integrates two doped, light-absorbing semiconductor powders that are fixed onto a conductive layer of gold. In addition, a molecular, cobalt-based photocatalyst is embedded into the sheet.
Excess of electrons
When sunlight illuminates the sheet, electron-hole pairs are generated in both semiconductors. One of the semiconductors transfers electrons to the other via the gold layer, leaving behind an excess of positively charged holes. These holes can then be filled by electrons donated by water via an oxidation reaction that was enabled by the photocatalyst. Meanwhile, the excess of electrons in the other semiconductor causes carbon dioxide to undergo a reduction reaction to produce formate. This is a negative ion that can be used to make formic acid, which can be stored as a liquid.
The powders and catalyst comprising the device are easy and inexpensive to produce in large quantities and the role of water as an electron donor eliminates the need for wasteful oxidation-triggering reagents, significantly boosting the sustainability of the process. Although the team’s initial experiments yielded a low solar-to-formate conversion efficiency of just 0.08%, they demonstrated an extremely high formate selectivity of 97±3%, with very few unwanted by-products.
Reisner and colleagues achieved these results with a sheet area of 20 cm2, but believe it should be relatively easy to scale it up to several square metres – making it suitable for use on commercial solar farms. Since formate is a stable liquid fuel, it can easily be stored and transported, or converted into gaseous hydrogen fuel if necessary. Furthermore, the device is completely wireless and requires no external power, enhancing its sustainability even further.
The researchers will now aim to boost the conversion efficiency of their device to levels suitable for commercialization, by experimenting with a range of different photocatalysts. Through these improvements, the photocatalyst sheet could soon become suitable for practical, large-scale solar fuel production, which actively reduces levels of atmospheric carbon dioxide.
The research is described in Nature Energy.


physicsworld--2020-09-09--Ultrafast detectors line up for proton beam energy measurements - Physics World

Beam energy is a key parameter in particle therapy , defining the depth inside the patient at which the therapeutic radiation is deposited .
Any deviations in energy will change the particle range , which could lead to tumour underdosage or overdose to normal structures , particularly for the increasingly prevalent pencil-beam scanning treatments .
A detector that can rapidly measure particle beam energy could prove invaluable .
Such a device could be used for regular quality assurance ( QA ) , to check beam energy during irradiation , or even to implement future adaptive dose delivery schemes employing fast @ @ @ @ @ @ @ , researchers in Italy have developed a prototype detector that measures the time-of-flight ( ToF ) of protons to determine the beam energy .
To measure the energy , and thus the range , of a clinical proton beam , a detector must match the clinically acceptable range uncertainty , which is typically less than 1 mm at therapeutic proton energies .
This corresponds to measurement accuracies ranging from about 0.5 MeV for 230 MeV protons to 1 MeV for 60 MeV protons .
To achieve this , the researchers – from the @ @ @ @ @ @ @ a detector from two thin ultrafast silicon detector ( UFSD ) sensors placed a specific distance apart along the beam direction .
“ The main advantages of ultrafast silicon detectors over traditional silicon ones are excellent time resolution , reduced thickness , good signal-to-noise ratio and short signal duration , ” explains first author Anna Vignati .
“ These features allow identification of single protons , even in beams of high intensity and irregular time structure .
Thus , the number of protons needed to measure the beam energy with the required accuracy @ @ @ @ @ @ @ ( a few seconds ) for QA checks in a proton therapy facility.
” Vignati and colleagues tested the prototype device on a clinical proton beam at the CNAO facility and reported their findings in Physics in Medicine & Biology .
They performed ToF measurements at five clinical beam energies ( 58.9 , 77.6 , 103.5 , 148.5 and 226.1 MeV , corresponding to water equivalent depths of between 30 and 320 mm ) .
They measured each beam energy with the sensors positioned at four distances , from few centimetres up to @ @ @ @ @ @ @ calculated the ToF from the mean time difference between the coincident signals generated when a single proton crosses both sensors , minus a constant time offset related to signal routing .
To determine the beam energy from these ToF measurements , they developed a model that accounts for energy loss in the sensors and in air , benchmarking it against Monte Carlo simulations .
The main error sources for this setup are the uncertainties in the distance between the sensors and the time offset .
To minimize these uncertainties , the team developed @ @ @ @ @ @ @ ToF measurements ( excluding those at 103.5 MeV , which were used to test the calibration ) and assuming the nominal energies at the isocentre as known quantities .
Comparing the measured energies with nominal beam energies revealed that , at the two largest sensor spacings ( 67 and 97 cm ) , deviations were less than 0.5 MeV for all five proton energies – compatible with the clinically acceptable measurement accuracy .
The detector also demonstrated short acquisition times .
For a test with 97 cm detector spacing and a beam energy @ @ @ @ @ @ @ that 6 s of irradiation at an intensity of 5×108 protons/s was sufficient to remain below the maximum acceptable ToF error ( 4 ps for sensors 1 m apart ) .
From a clinical stance , the most significant parameter is the corresponding range deviation in water .
At 67 and 97 cm sensor spacing , the range discrepancies between measured and nominal beam energies were within 0.5 mm at lower energies and within 1 mm for the maximum energy , in compliance with clinical requirements .
The researchers conclude that UFSD silicon @ @ @ @ @ @ @ clinical proton beam in a few seconds , with good accuracy and minimal beam perturbation .
They note that their detector could find immediate application for daily QA .
“ With further improvements , our detector will be even compatible with use during treatment , ” Vignati tells Physics World .
“ Indeed , properly exploiting the extremely reduced thickness of these sensors would minimize the beam perturbation , while reducing the acquisition dead time would allow measurements of similar sensitivity in a few milliseconds.
” To further improve the collection of coincident @ @ @ @ @ @ @ dedicated sensor with appropriate segmentation of the active area .
They have also developed a mechanical system that varies the distance between sensors with high accuracy , enabling a self-calibration process that no longer requires knowledge of the beam energy used for calibration .
“ This ensures that the same precision and sensitivity will be achieved in any clinical facility where the device will be used , ” says Vignati .

Experimental setup showing the two ultrafast silicon detectors used to determine the energy of clinical proton beams. (Courtesy: Anna Vignati)
Beam energy is a key parameter in particle therapy, defining the depth inside the patient at which the therapeutic radiation is deposited. Any deviations in energy will change the particle range, which could lead to tumour underdosage or overdose to normal structures, particularly for the increasingly prevalent pencil-beam scanning treatments.
A detector that can rapidly measure particle beam energy could prove invaluable. Such a device could be used for regular quality assurance (QA), to check beam energy during irradiation, or even to implement future adaptive dose delivery schemes employing fast energy modulation. With this in mind, researchers in Italy have developed a prototype detector that measures the time-of-flight (ToF) of protons to determine the beam energy.
To measure the energy, and thus the range, of a clinical proton beam, a detector must match the clinically acceptable range uncertainty, which is typically less than 1 mm at therapeutic proton energies. This corresponds to measurement accuracies ranging from about 0.5 MeV for 230 MeV protons to 1 MeV for 60 MeV protons. To achieve this, the researchers – from the University of Turin and INFN – created a detector from two thin ultrafast silicon detector (UFSD) sensors placed a specific distance apart along the beam direction.
“The main advantages of ultrafast silicon detectors over traditional silicon ones are excellent time resolution, reduced thickness, good signal-to-noise ratio and short signal duration,” explains first author Anna Vignati. “These features allow identification of single protons, even in beams of high intensity and irregular time structure. Thus, the number of protons needed to measure the beam energy with the required accuracy could be collected in a favourable timeframe (a few seconds) for QA checks in a proton therapy facility.”
Vignati and colleagues tested the prototype device on a clinical proton beam at the CNAO facility and reported their findings in Physics in Medicine & Biology. They performed ToF measurements at five clinical beam energies (58.9, 77.6, 103.5, 148.5 and 226.1 MeV, corresponding to water equivalent depths of between 30 and 320 mm). They measured each beam energy with the sensors positioned at four distances, from few centimetres up to roughly 1 m apart.
Anna Vignati (bottom left) and colleagues. (Courtesy: Anna Vignati)
The researchers calculated the ToF from the mean time difference between the coincident signals generated when a single proton crosses both sensors, minus a constant time offset related to signal routing. To determine the beam energy from these ToF measurements, they developed a model that accounts for energy loss in the sensors and in air, benchmarking it against Monte Carlo simulations.
The main error sources for this setup are the uncertainties in the distance between the sensors and the time offset. To minimize these uncertainties, the team developed a calibration method using 16 of the ToF measurements (excluding those at 103.5 MeV, which were used to test the calibration) and assuming the nominal energies at the isocentre as known quantities.
Comparing the measured energies with nominal beam energies revealed that, at the two largest sensor spacings (67 and 97 cm), deviations were less than 0.5 MeV for all five proton energies – compatible with the clinically acceptable measurement accuracy.
The detector also demonstrated short acquisition times. For a test with 97 cm detector spacing and a beam energy of 226.1 MeV, the researchers found that 6 s of irradiation at an intensity of 5×108 protons/s was sufficient to remain below the maximum acceptable ToF error (4 ps for sensors 1 m apart).
From a clinical stance, the most significant parameter is the corresponding range deviation in water. At 67 and 97 cm sensor spacing, the range discrepancies between measured and nominal beam energies were within 0.5 mm at lower energies and within 1 mm for the maximum energy, in compliance with clinical requirements.
The researchers conclude that UFSD silicon sensors can measure the energy of a clinical proton beam in a few seconds, with good accuracy and minimal beam perturbation. They note that their detector could find immediate application for daily QA. “With further improvements, our detector will be even compatible with use during treatment,” Vignati tells Physics World. “Indeed, properly exploiting the extremely reduced thickness of these sensors would minimize the beam perturbation, while reducing the acquisition dead time would allow measurements of similar sensitivity in a few milliseconds.”
To further improve the collection of coincident protons, the researchers have produced a dedicated sensor with appropriate segmentation of the active area. They have also developed a mechanical system that varies the distance between sensors with high accuracy, enabling a self-calibration process that no longer requires knowledge of the beam energy used for calibration. “This ensures that the same precision and sensitivity will be achieved in any clinical facility where the device will be used,” says Vignati.


physicsworld--2020-09-09--IOP Publishing pledges to implement double-blind peer review - Physics World

IOP Publishing , which publishes Physics World , has announced it will introduce double-blind peer review on all of its wholly-owned journals by the end of 2021 .
The publisher says the rollout will be phased , with some journals shifting to double blind by the end of 2020 followed by the full portfolio of IOP Publishing-owned journals by the end of 2021 .
Journal publishing has traditionally operated using single-blind peer review , in which the reviewers of the paper know who has written the paper , but the authors do not know who has reviewed their paper .
@ @ @ @ @ @ @ hand , is when both the reviewers and authors do not know who each other are .
IOP publishes 96 journals , around half of which are published jointly with or on behalf of partner societies .
Since 2017 , the publisher has offered double-blind peer review as an option for authors on two of its journals : Materials Research Express and Biomedical Physics & Engineering Express .
After a year , author uptake of the double-blind review option was around 20 % on each journal with many authors being positive about the @ @ @ @ @ @ @ single-blind peer review .
Since then three more IOP Publishing journals – New Journal of Physics , Plasma Research Express and Engineering Research Express — have begun offering authors a choice of double-blind peer review with uptake as high as 35 % .
IOP Publishing says that the move to apply double blind across all of its wholly-owed journals is part of the publisher ’ s “ dedication to tackle the significant gender , racial and geographical under-representation in the scholarly publishing process ” .
It adds that double-blind peer review “ has @ @ @ @ @ @ @ to gender , race , country of origin or affiliation which should lead to a more equitable system ” .
Double blind will be the default option when submitting a paper , but authors have the option to remain under the single blind model .
“ We believe that keeping both the author and the reviewers anonymous will mean the research is judged more fairly , giving authors a better chance of impartial evaluation ” says Kim Eggleton , integrity and inclusion manager at IOP Publishing .
“ We believe that double-blind peer @ @ @ @ @ @ @ right direction – but it is by no means a panacea .
There is a lot more work to be done.
” Indeed , Eggleton adds that publishers have an “ influential role ” to play in making academia more inclusive .
“ By doing our best to ensure peer review is objective , we can increase the proportions of under-represented groups that get published , ” she adds .
“ That links to funding , to promotions , to participation on editorial boards – all of which bring about more diverse role @ @ @ @ @ @ @ researchers.
” Penny Gowland from the University of Nottingham in the UK , who is an advocate for double blind says she is “ absolutely delighted ” by the move and for the IOPP “ for listening and leading on this ” .
She adds that this is a “ great day for the integrity of the scientific method and it provides natural justice for all scientists ” .
• IOP Publishing recenty carried out a survey to understand what motivates researchers to carry our peer reivew .
You can read the full @ @ @

IOP Publishing aims to implement double-blind peer review on all of its journals by the end of 2021. (Courtesy: Shutterstock/PolyPloiid)
IOP Publishing, which publishes Physics World, has announced it will introduce double-blind peer review on all of its wholly owned journals by the end of 2021. The publisher says the rollout will be phased, with some journals shifting to double blind by the end of 2020, followed by the full portfolio of IOP Publishing-owned journals by the end of 2021.
Journal publishing has traditionally operated using single-blind peer review, in which the reviewers of the paper know who has written the paper, but the authors do not know who has reviewed their paper. Double-blind peer review, on the other hand, is when both the reviewers and authors do not know who each other are.
We believe that double-blind peer review is a significant step in the right direction Kim Eggleton
IOP publishes 96 journals, around half of which are published jointly with or on behalf of partner societies. Since 2017 the publisher has offered double-blind peer review as an option for authors on two of its journals: Materials Research Express and Biomedical Physics & Engineering Express. After a year, author uptake of the double-blind review option was around 20% on each journal, with many authors being positive about the move, noting it to be fairer than single-blind peer review. Since then three more IOP Publishing journals – New Journal of Physics, Plasma Research Express and Engineering Research Express – have begun offering authors a choice of double-blind peer review, with uptake as high as 35%.
“Impartial evaluation”
IOP Publishing says that the move to apply double blind across all of its wholly owned journals is part of the publisher’s “dedication to tackle the significant gender, racial and geographical under-representation in the scholarly publishing process”. It adds that double-blind peer review “has the potential to reduce bias with respect to gender, race, country of origin or affiliation which should lead to a more equitable system”. Double-blind will be the default option when submitting a paper, but authors have the option to remain under the single-blind model.
“We believe that keeping both the author and the reviewers anonymous will mean the research is judged more fairly, giving authors a better chance of impartial evaluation,” says Kim Eggleton, integrity and inclusion manager at IOP Publishing. “We believe that double-blind peer review is a significant step in the right direction – but it is by no means a panacea. There is a lot more work to be done.”
Indeed, Eggleton adds that publishers have an “influential role” to play in making academia more inclusive. “By doing our best to ensure peer review is objective, we can increase the proportions of under-represented groups that get published,” she adds. “That links to funding, to promotions, to participation on editorial boards – all of which bring about more diverse role models to inspire the next generation of researchers.”
Penny Gowland from the University of Nottingham in the UK, who is an advocate for double-blind, says she is “absolutely delighted” by the move and by IOP Publishing “for listening and leading on this”. She adds that this is a “great day for the integrity of the scientific method and it provides natural justice for all scientists”.
IOP Publishing recently carried out a survey to understand what motivates researchers to carry our peer review. You can read the full report here.