physicsworld--2020-10-02--Conjuring solitons in optical moiré lattices - Physics World

Moiré lattices — wherever they form – are full of surprises .
Superimpose two or more 2D periodic patterns on top of each other with a slight twist , and exotic properties will emerge .
A single sheet of graphene is a decent electrical conductor , but when two graphene sheets are stacked into a moiré lattice , the bilayer morphs into a superconductor , a Mott insulator , or a magnet ; depending on the twist angle .
Analogously , when two light beams “ patterned ” by masks interact , the resulting moiré lattice can transform the signal @ @ @ @ @ @ @ single localized spot .
Recently , a group of researchers led by Fangwei Ye at Shanghai Jiao Tong University , China discovered that optical moiré lattices can also produce solitons – self-trapped solitary waves – at extremely low power levels .
Light tends to disperse as it propagates .
For example , a ray of light from a torch gradually spreads out .
Earlier this year , Ye ’ s team discovered a way to stop the spreading and localize a laser into a tight spot using moiré lattices .
Now , the @ @ @ @ @ @ @ step further by exciting the light in moiré lattices into self-sustaining pulses known as solitons .
Solitons retain their shape as they propagate over long distances , so they are important in telecommunications as steadfast information carriers .
The enemy of light localization is diffraction .
Ye ’ s optical solitons fend off diffraction by relying on the nonlinear effect , a self-reinforcing phenomenon whereby the medium through which light shines modifies the light ’ s behavior .
Ye ’ s medium is a photorefractive strontium barium niobite crystal with nonlinear holographic properties @ @ @ @ @ @ @ onto the crystal by shining a light beam stenciled by two twisted lattice masks .
Then , the researchers shone a second light beam and observed how the beam profile evolved while they changed the masks ’ twist angle and the laser powers .
The researchers discovered that their moiré lattices can produce solitons above a certain laser power threshold , depending on the twist angles in the patterning masks .
Nonlinearity is a weak phenomenon that usually only manifests at high laser powers .
But Ye and his team found that their @ @ @ @ @ @ @ nanowatts of power is required – a million times weaker than a laser pointer .
“ Our work is the first observation of solitons in moiré lattices , ” says Ye .
“ It turns out , it ’ s quite easy to create solitons this way.
” The key to the low power requirement is the flat energy band in the moiré lattice .
The photons in optical moiré lattices are squeezed into a narrow range of energies at certain twist angles .
This energy range only supports certain self-trapped modes of @ @ @ @ @ @ @ much weaker in such flat energy bands , so only a small nonlinear effect is necessary to generate solitons .
“ Thanks to the almost flat bands in moiré lattices , ” says Ye , “ this experiment brings the power threshold down to an extremely low level , representing a big step in soliton research ” .
Optical moiré lattices present a rich playground to look for other elusive nonlinear phenomena , such as four-wave mixing and second harmonic generation .
According to Ye , solitons may be just the beginning .

New twist: a smeared out signal can transform into a soliton, depending on the laser powers and the twist angle of the optical moiré lattice. (Courtesy: Fangwei Ye)
Moiré lattices — wherever they form – are full of surprises. Superimpose two or more 2D periodic patterns on top of each other with a slight twist, and exotic properties will emerge.
A single sheet of graphene is a decent electrical conductor, but when two graphene sheets are stacked into a moiré lattice, the bilayer morphs into a superconductor, a Mott insulator, or a magnet; depending on the twist angle. Analogously, when two light beams “patterned” by masks interact, the resulting moiré lattice can transform the signal beam into a diffuse smear or a single localized spot. Recently, a group of researchers led by Fangwei Ye at Shanghai Jiao Tong University, China discovered that optical moiré lattices can also produce solitons – self-trapped solitary waves – at extremely low power levels.
Solitons in the spotlight
Light tends to disperse as it propagates. For example, a ray of light from a torch gradually spreads out. Earlier this year, Ye’s team discovered a way to stop the spreading and localize a laser into a tight spot using moiré lattices. Now, the same group has taken their findings a step further by exciting the light in moiré lattices into self-sustaining pulses known as solitons. Solitons retain their shape as they propagate over long distances, so they are important in telecommunications as steadfast information carriers.
The enemy of light localization is diffraction. Ye’s optical solitons fend off diffraction by relying on the nonlinear effect, a self-reinforcing phenomenon whereby the medium through which light shines modifies the light’s behavior . Ye’s medium is a photorefractive strontium barium niobite crystal with nonlinear holographic properties. The researchers imprinted a moiré pattern onto the crystal by shining a light beam stenciled by two twisted lattice masks. Then, the researchers shone a second light beam and observed how the beam profile evolved while they changed the masks’ twist angle and the laser powers.
The researchers discovered that their moiré lattices can produce solitons above a certain laser power threshold, depending on the twist angles in the patterning masks. Nonlinearity is a weak phenomenon that usually only manifests at high laser powers. But Ye and his team found that their power threshold is whoppingly low: only nanowatts of power is required – a million times weaker than a laser pointer.
“First observation”
“Our work is the first observation of solitons in moiré lattices,” says Ye. “It turns out, it’s quite easy to create solitons this way.”
The key to the low power requirement is the flat energy band in the moiré lattice. The photons in optical moiré lattices are squeezed into a narrow range of energies at certain twist angles. This energy range only supports certain self-trapped modes of light. The light diffraction is inherently much weaker in such flat energy bands, so only a small nonlinear effect is necessary to generate solitons.
“Thanks to the almost flat bands in moiré lattices,” says Ye, “this experiment brings the power threshold down to an extremely low level, representing a big step in soliton research”.
Moiré surprises?
Optical moiré lattices present a rich playground to look for other elusive nonlinear phenomena, such as four-wave mixing and second harmonic generation. According to Ye, solitons may be just the beginning.


physicsworld--2020-09-29--Overlooked for the Nobel: the CERN physicists who discovered the Higgs boson - Physics World

The announcement of the 2013 Nobel Prize for Physics is memorable for the hour-long delay in announcing the winners – François Englert and Peter Higgs – and for the long citation .
The pair won “ for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles , and which recently was confirmed through the discovery of the predicted fundamental particle , by the ATLAS and CMS experiments at CERN ’ s Large Hadron Collider ” .
I can vividly remember the morning of 8 October 2013 while I sat at @ @ @ @ @ @ @ for the prize announcement .
The Higgs boson had been discovered at CERN in July 2012 , and it was pretty obvious that the 2013 prize would be related to the discovery .
The big question was would it go to the theorists who predicted the Higgs back in 1964 or to the experimentalists who discovered it – or both ?
Now when it comes to announcing the winners of each year ’ s Nobel prize , the Nobel Committee usually does so precisely at the scheduled time .
But as the minutes @ @ @ @ @ @ @ forthcoming , I started to wonder if 2013 was going to be the year when the committee finally dispensed with the rule that no more than three people can share the prize .
I imagined that , in an opulent , portrait-lined room at the Swedish Royal Academy of Sciences , a huge row had broken out about whether or not to give at least a portion of the award to the thousands of physicists working on ATLAS , CMS and the LHC .
After all , the Higgs was not found by @ @ @ @ @ @ @ a decades-long sustained and focussed effort to detect the particle .
Furthermore , modern science is highly collaborative , so recognizing the CERN physicists , I felt , would be the perfect way to update a prize that is more than a century old .
But alas , it wasn ’ t to be .
The hour-long delay in announcing the prize merely occurred because the committee could not contact Peter Higgs .
He was out-and-about in Edinburgh and in the end only heard about his win after lunch , several hours later @ @ @ @ @ @ @ street by a former neighbour .
What is more , I don ’ t think any scientific collaboration will be winning the Nobel Prize for Physics any time soon .
Last year I interviewed Lars Brink – a Swedish particle theorist who served on the Nobel Committee for Physics on eight separate occasions and who served as chair for the 2013 award .
Brink says that the Academy is hesitant to open the physics prize up to organizations or collaborations such as CERN .
“ We don ’ t want 5000 people calling @ @ @ @ @ @ @ me .
What the Nobel Committee did do , however , was to beef up that year ’ s citation .
By mentioning ATLAS , CMS and the LHC , the committee did go at least some way to recognise the legion of experimentalists who confirmed calculations done by Higgs and independently by Englert and Robert Brout – the latter having died in 2011 and who therefore also missed out on the prize .
But given that the Higgs prediction and subsequent discovery is a classic example of how theory and experiment work @ @ @ @ @ @ @ it is a shame that all those hard-working experimentalists were unable to share the prize .
My fantasy citation for the 2013 prize would therefore have been “ to François Englert , Peter Higgs and to all the physicists working on ATLAS , CMS and the LHC for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles and the experimental discovery of the predicted fundamental particle ” .
Still , who knows , perhaps the experimental discovery of the Higgs will be honoured @ @ @ @ @ @ @ years to come .

The 2020 Nobel Prize for Physics will be announced on Tuesday 6 October. In the run-up to the announcement, Physics World editors have picked some of the people who they think have been overlooked for a prize in the past
Nobel celebrations at CERN Should ATLAS, CMS and LHC physicists have shared the 2013 award? (Courtesy: CERN)
The announcement of the 2013 Nobel Prize for Physics is memorable for the hour-long delay in announcing the winners – François Englert and Peter Higgs – and for the long citation.
The pair won “for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN’s Large Hadron Collider”.
Theory, experiment or both?
I can vividly remember the morning of 8 October 2013 while I sat at my desk at Physics World headquarters waiting for the prize announcement. The Higgs boson had been discovered at CERN in July 2012, and it was pretty obvious that the 2013 prize would be related to the discovery. The big question was would it go to the theorists who predicted the Higgs back in 1964 or to the experimentalists who discovered it – or both?
Now when it comes to announcing the winners of each year’s Nobel prize, the Nobel Committee usually does so precisely at the scheduled time. But as the minutes ticked by, and no news was forthcoming, I started to wonder if 2013 was going to be the year when the committee finally dispensed with the rule that no more than three people can share the prize.
I imagined that, in an opulent, portrait-lined room at the Swedish Royal Academy of Sciences, a huge row had broken out about whether or not to give at least a portion of the award to the thousands of physicists working on ATLAS, CMS and the LHC. After all, the Higgs was not found by accident at CERN – there had been a decades-long sustained and focussed effort to detect the particle. Furthermore, modern science is highly collaborative, so recognizing the CERN physicists, I felt, would be the perfect way to update a prize that is more than a century old.
Out-and-about in Edinburgh
But alas, it wasn’t to be. The hour-long delay in announcing the prize merely occurred because the committee could not contact Peter Higgs. He was out-and-about in Edinburgh and in the end only heard about his win after lunch, several hours later, when he was congratulated in the street by a former neighbour.
What is more, I don’t think any scientific collaboration will be winning the Nobel Prize for Physics any time soon. Last year I interviewed Lars Brink – a Swedish particle theorist who served on the Nobel Committee for Physics on eight separate occasions and who served as chair for the 2013 award. Brink says that the Academy is hesitant to open the physics prize up to organizations or collaborations such as CERN. “We don’t want 5000 people calling themselves Nobel laureates,” he told me.
What the Nobel Committee did do, however, was to beef up that year’s citation. By mentioning ATLAS, CMS and the LHC, the committee did go at least some way to recognise the legion of experimentalists who confirmed calculations done by Higgs and independently by Englert and Robert Brout – the latter having died in 2011 and who therefore also missed out on the prize.
But given that the Higgs prediction and subsequent discovery is a classic example of how theory and experiment work hand in hand, I still think it is a shame that all those hard-working experimentalists were unable to share the prize. My fantasy citation for the 2013 prize would therefore have been “to François Englert, Peter Higgs and to all the physicists working on ATLAS, CMS and the LHC for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles and the experimental discovery of the predicted fundamental particle”.
Still, who knows, perhaps the experimental discovery of the Higgs will be honoured this year after all – or in years to come.


physicsworld--2020-10-02--D-Wave launches 5000 qubit system, solar-powered nanobeads could clean-up oil sands waste - Physics

D-Wave launches 5000 qubit system, solar-powered nanobeads could clean-up oil sands waste - Physics World

The Canadian quantum computer maker D-Wave Systems has unveiled its latest platform , which contains a whopping 5000 qubits .
Called Advantage , the system can be accessed via the company ’ s Leap 2 cloud service , which was launched earlier this year .
The system is designed for use by businesses and D-Wave already counts several companies as customers , including the carmaker Volkswagen .
Your can read more about D-Wave system in “ D-Wave ’ s 5,000-qubit quantum computing platform handles 1 million variables ” .
Staying in Canada , petroleum production from Alberta ’ s oil @ @ @ @ @ @ @ tailings ponds – which are notoriously toxic .
Now , researchers have used glass bubbles coated in titanium dioxide nanocrystals to deal with naphthenic acids , which are a particularly nasty group of chemicals found in the ponds The bubbles were developed at the University of Waterloo and their efficacy has been tested by a team led by Diane Orihel at Queens University in Kingston , Ontario .
The team found that as the bubbles float on a pond , these use energy form the Sun to create radicals that destroy naphthenic acids @ @ @ @ @ @ @ because they float , they can be gathered up and used again .
The research is described in the journal Facets and you can listen to Orihel explain the results to the CBC ’ s Bob McDonald on the science programme Quirks and Quarks .

New Advantage: D-Wave’s latest quantum computer. (Courtesy: D-Wave Systems)
The Canadian quantum computer maker D-Wave Systems has unveiled its latest platform, which contains a whopping 5000 qubits. Called Advantage, the system can be accessed via the company’s Leap 2 cloud service, which was launched earlier this year. The system is designed for use by businesses and D-Wave already counts several companies as customers, including the carmaker Volkswagen.
Your can read more about D-Wave system in “D-Wave’s 5,000-qubit quantum computing platform handles 1 million variables”.
Staying in Canada, petroleum production from Alberta’s oil sands produces effluent that is stored in tailings ponds – which are notoriously toxic. Now, researchers have used glass bubbles coated in titanium dioxide nanocrystals to deal with naphthenic acids, which are a particularly nasty group of chemicals found in the ponds.
The bubbles were developed at the University of Waterloo and their efficacy has been tested by a team led by Diane Orihel at Queens University in Kingston, Ontario. The team found that as the bubbles float on a pond, these use energy form the Sun to create radicals that destroy naphthenic acids. The coated bubbles are nontoxic and because they float, they can be gathered up and used again.
The research is described in the journal Facets and you can listen to Orihel explain the results to the CBC’s Bob McDonald on the science programme Quirks and Quarks.


physicsworld--2020-10-02--Overlooked for the Nobel: Chien-Shiung Wu - Physics World

The 1957 Nobel Prize for Physics was shared by Chen Ning Yang and Tsung-Dao Lee “ for their penetrating investigation of the so-called parity laws which has led to important discoveries regarding the elementary particles ” .
However , some physicists argue that the Chinese-American physicist Chien-Shiung Wu should have shared the prize for providing the experimental evidence for Lee and Yang ’ s theoretical prediction of parity violation .
Furthermore , some believe that Wu was denied the prize because she was a woman .
Based at Columbia University in the late 1950s , Wu designed an experiment that @ @ @ @ @ @ @ at ultracold temperatures .
While Wu was an expert in measuring beta decay , she collaborated with scientists at the National Bureau of Standards ( NBS ) in Washington DC ( now NIST ) to meet the cryogenic requirements of what is now known as the “ Wu experiment ” .
In an 2012 article for Physics World ( “ Credit where credit ’ s due ?
” ) the Hungarian chemist and historian of science Magdolna Hargittai dug deep into the claims and counter claims of who , if anybody , should @ @ @ @ @ @ @ and Yang .
In a nutshell , it is complicated .
According to Hargittai ’ s article , Wu and colleagues saw the first hints of parity violation on 27 December 1956 .
Shortly after news of this preliminary result got out , an independent group working at the Columbia cyclotron did a quick measurement in early January and observed parity violation in muons – at about the same time as Wu and colleagues were making their definitive measurements .
What is more , a third group at the University of Chicago had @ @ @ @ @ @ @ summer of 1956 and had also found preliminary evidence by December .
The Wu–NBS and Columbia cyclotron teams published their results in the February 1957 issue of the Physical Review and the Chicago paper was published in the March issue of the same journal .
And therein lies a major barrier to Wu sharing the 1957 prize .
According to the Nobel rules , the 1957 prize can not be awarded for work published in 1957 .
Indeed , the Nobel Prize Nomination Archive shows that neither Wu , nor anyone else who @ @ @ @ @ @ @ had been nominated for the 1957 prize .
So what is Hargittai ’ s conclusion on whether Wu was overlooked for a Nobel ?
“ My view is that Wu made an outstanding contribution to bringing down the axiom of parity conservation in weak interactions , ” writes Hargittai .
“ But to say it was an injustice that she did not win a Nobel prize is an oversimplification of a complex story.
” It is worth pointing out that some of the most eminent physicists of the day did champion Wu ’ @ @ @ @ @ @ @ the Nobel laureates Willis Lamb , Polykarp Kusch and Emilio Segrè .
Starting in 1958 , she was nominated for the Nobel prize at least seven times until her death in 1997 ( only nominations made before 1966 are currently available online to the public , which means there could , in fact , have been more ) .
So regardless of whether it was the rules or sexism that denied Wu a Nobel prize , there is no doubt in my mind that she deserved one – if not in 1957 , @ @ @ @ @ @ @ in Physics World after Hargittai ’ s article was published , Chen-Ning Yang of China ’ s Tsinghua University said that Wu ’ s contribution went well beyond her considerable experimental prowess and included her deep perception of why parity must be tested .
In that same issue , Herwig Schopper , who was one of those to have nominated Wu for a Nobel prize , expressed the view that Wu and indeed others who made the experimental measurements were denied a prize because of the rule that only three winners can be @ @

The 2020 Nobel Prize for Physics will be announced on Tuesday 6 October. In the run-up to the announcement, Physics World editors have picked some of the people who they think have been overlooked for a prize in the past
Overlooked: Chien-Shiung Wu in 1963 at Columbia University. (Courtesy: Smithsonian Institution)
The 1957 Nobel Prize for Physics was shared by Chen Ning Yang and Tsung-Dao Lee “for their penetrating investigation of the so-called parity laws which has led to important discoveries regarding the elementary particles”. However, some physicists argue that the Chinese-American physicist Chien-Shiung Wu should have shared the prize for providing the experimental evidence for Lee and Yang’s theoretical prediction of parity violation. Furthermore, some believe that Wu was denied the prize because she was a woman.
Based at Columbia University in the late 1950s, Wu designed an experiment that tested parity laws by observing beta decay at ultracold temperatures. While Wu was an expert in measuring beta decay, she collaborated with scientists at the National Bureau of Standards (NBS) in Washington DC (now NIST) to meet the cryogenic requirements of what is now known as the “Wu experiment”.
In an 2012 article for Physics World (“Credit where credit’s due?”) the Hungarian chemist and historian of science Magdolna Hargittai dug deep into the claims and counter claims of who, if anybody, should have shared the 1957 prize with Lee and Yang.
Three competing groups
In a nutshell, it is complicated. According to Hargittai’s article, Wu and colleagues saw the first hints of parity violation on 27 December 1956. Shortly after news of this preliminary result got out, an independent group working at the Columbia cyclotron did a quick measurement in early January and observed parity violation in muons – at about the same time as Wu and colleagues were making their definitive measurements. What is more, a third group at the University of Chicago had been looking for parity violation since the summer of 1956 and had also found preliminary evidence by December.
The Wu–NBS and Columbia cyclotron teams published their results in the February 1957 issue of the Physical Review and the Chicago paper was published in the March issue of the same journal.
And therein lies a major barrier to Wu sharing the 1957 prize. According to the Nobel rules, the 1957 prize cannot be awarded for work published in 1957. Indeed, the Nobel Prize Nomination Archive shows that neither Wu, nor anyone else who had measured parity violation in 1956-57, had been nominated for the 1957 prize.
So what is Hargittai’s conclusion on whether Wu was overlooked for a Nobel?
“My view is that Wu made an outstanding contribution to bringing down the axiom of parity conservation in weak interactions,” writes Hargittai. “But to say it was an injustice that she did not win a Nobel prize is an oversimplification of a complex story.”
Eminent supporters
It is worth pointing out that some of the most eminent physicists of the day did champion Wu’s case for a prize – including the Nobel laureates Willis Lamb, Polykarp Kusch and Emilio Segrè. Starting in 1958, she was nominated for the Nobel prize at least seven times until her death in 1997 (only nominations made before 1966 are currently available online to the public, which means there could, in fact, have been more).
So regardless of whether it was the rules or sexism that denied Wu a Nobel prize, there is no doubt in my mind that she deserved one – if not in 1957, then certainly thereafter. Indeed, writing in Physics World after Hargittai’s article was published, Yang said that Wu’s contribution went well beyond her considerable experimental prowess and included her deep perception of why parity must be tested. In that same issue, Herwig Schopper, who was one of those to have nominated Wu for a Nobel prize, expressed the view that Wu and indeed others who made the experimental measurements were denied a prize because of the rule that only three winners can be named.


physicsworld--2020-10-05--Climate change threatens future astronomical observations - Physics World

Rising global temperatures could worsen seasonal El Niño events and cause telescope images to lose their quality .
That is the finding of an interdisciplinary team of researchers in Germany , who predict that climate-change-induced alterations in temperature , wind speed , humidity and “ seeing ” – atmospheric turbulence that causes blurring in images – will reduce the clarity of observations at ground-based telescopes around the world .
The researchers , led by Faustine Cantalloube of the Max Planck Institute for Astronomy , argue that climate change therefore needs to be taken into account when building new observatories such @ @ @ @ @ @ @ ) , which is currently under construction at Cerro Armazones in Chile ’ s Atacama desert .
In their study , the researchers focused on the European Southern Observatory ’ s facility at Cerro Paranal , which is about 20 km from Cerro Armazones .
There are three critical parameters for operating astronomical instruments : integrated water vapour ( IWV ) , relative humidity and cloud coverage .
They found that high IWV levels at Paranal , which affect astronomical observations in the infrared , were associated with high central equatorial sea surface @ @ @ @ @ @ @ such events are a natural , periodic phenomenon , increases in atmospheric CO concentration could make them more vicious , thanks to the associated global rise in humidity .
A rise in humidity could also cause previously rare catastrophes such as the March 2015 flooding of the Atacama region to become more frequent .
The study also examined the direct effects of increasing temperatures on the four telescopes that make up Paranal ’ s Very Large Telescope ( VLT ) array .
The dome enclosures that house these telescopes are kept cool during @ @ @ @ @ @ @ opens at sunset , the telescopes are at a similar temperature to the outside air .
This cooling is necessary because any temperature difference between the inside of the dome , where the telescopes are found , and its environment can cause air turbulence .
The air turbulence distorts the starlight that reaches the telescopes , much like how stars appear to twinkle to the naked eye thanks to turbulence in the higher atmosphere .
The VLT ’ s current thermal active control system , however , can not exceed target temperatures of @ @ @ @ @ @ @ of atmospheric CO is already linked to an increase of 1.5 °C in average temperatures at Paranal to over the past 40 years – 0.5 °C more than the global average – additional local increases in surface temperature could further impair observations .
The researchers used worst-case climate change scenarios on models such as the Coupled Model Intercomparison Project Phase 6 ( CMIP6 ) multi-model ensemble to determine climate projections for the region .
The results suggest that by the end of the 21st century , Paranal could experience a further 4 °C @ @ @ @ @ @ @ cause a greater difference between the temperatures inside and outside of telescope domes , and generate more air turbulence .
Adaptive optics can help correct for atmospheric turbulence .
However , the time lag associated with these corrections creates an imaging artefact known as a wind-driven halo .
Such halos are caused by winds from the southern subtropical jet stream , they are visible in ~30-40 % of images , and they dramatically reduce the image ’ s contrast .
Many wind-driven halos occur during El Niño events , which are likely to @ @ @ @ @ @ @ intense as global temperatures rise .
Mitigating the impact of climate change on research On a global level , Cantalloube notes that increased humidity and worse seeing are far from the most pressing threats to astronomy .
“ Fires in the US and in Australia already destroyed or were about to destroy observatories , ” she explains .
“ This is the most imminent threat that is a consequence of climate change.
” Cantalloube adds that hurricanes in Hawaii , which have become stronger in recent years “ could also threaten the Hawaiian-based @ @ @ @ @ @ @ she says , “ the effects are there ” .
According to Cantalloube , interdisciplinary teams like hers will become more prevalent over time as scientists seek to understand the many ways that climate change could impact research capabilities .
She notes that her team ’ s paper , which appears in Nature Astronomy , is a preliminary study , focusing solely on the effects of climate change on observations conducted in Chile .
Since climate change will likely affect different regions of the globe in different ways , the team hopes to @ @ @ @ @ @ @ .
In the meantime , Cantalloube urges members of the astronomy community to “ investigate whether climate change and/or environmental signals are also detectable in the observations of other observatories/others fields of research ” and “ convince political leaders to act now against climate change ” .

Cloudy skies Auxiliary telescopes at the Paranal Observatory in Chile. (Courtesy: J C Muñoz-Mateos/ESO)
Rising global temperatures could worsen seasonal El Niño events and cause telescope images to lose their quality. That is the finding of an interdisciplinary team of researchers in Germany, who predict that climate-change-induced alterations in temperature, wind speed, humidity and “seeing” – atmospheric turbulence that causes blurring in images – will reduce the clarity of observations at ground-based telescopes around the world. The researchers, led by Faustine Cantalloube of the Max Planck Institute for Astronomy, argue that climate change therefore needs to be taken into account when building new observatories such as the Extremely Large Telescope (ELT), which is currently under construction at Cerro Armazones in Chile’s Atacama desert.
In their study, the researchers focused on the European Southern Observatory’s facility at Cerro Paranal, which is about 20 km from Cerro Armazones. There are three critical parameters for operating astronomical instruments: integrated water vapour (IWV), relative humidity and cloud coverage. They found that high IWV levels at Paranal, which affect astronomical observations in the infrared, were associated with high central equatorial sea surface temperatures during El Niño events. Although such events are a natural, periodic phenomenon, increases in atmospheric CO 2 concentration could make them more vicious, thanks to the associated global rise in humidity. A rise in humidity could also cause previously rare catastrophes such as the March 2015 flooding of the Atacama region to become more frequent.
Atmospheric turbulence affecting images
The study also examined the direct effects of increasing temperatures on the four telescopes that make up Paranal’s Very Large Telescope (VLT) array. The dome enclosures that house these telescopes are kept cool during the day so that when the dome opens at sunset, the telescopes are at a similar temperature to the outside air. This cooling is necessary because any temperature difference between the inside of the dome, where the telescopes are found, and its environment can cause air turbulence. The air turbulence distorts the starlight that reaches the telescopes, much like how stars appear to twinkle to the naked eye thanks to turbulence in the higher atmosphere.
The VLT’s current thermal active control system, however, cannot exceed target temperatures of over 16 °C. Since the build-up of atmospheric CO 2 is already linked to an increase of 1.5 °C in average temperatures at Paranal to over the past 40 years – 0.5 °C more than the global average – additional local increases in surface temperature could further impair observations.
The researchers used worst-case climate change scenarios on models such as the Coupled Model Intercomparison Project Phase 6 (CMIP6) multi-model ensemble to determine climate projections for the region. The results suggest that by the end of the 21st century, Paranal could experience a further 4 °C increase in average temperatures. This would cause a greater difference between the temperatures inside and outside of telescope domes, and generate more air turbulence.
Adaptive optics can help correct for atmospheric turbulence. However, the time lag associated with these corrections creates an imaging artefact known as a wind-driven halo. Such halos are caused by winds from the southern subtropical jet stream, they are visible in ~30-40% of images, and they dramatically reduce the image’s contrast. Many wind-driven halos occur during El Niño events, which are likely to become more frequent as well as more intense as global temperatures rise.
Mitigating the impact of climate change on research
On a global level, Cantalloube notes that increased humidity and worse seeing are far from the most pressing threats to astronomy. “Fires in the US and in Australia already destroyed or were about to destroy observatories,” she explains. “This is the most imminent threat that is a consequence of climate change.” Cantalloube adds that hurricanes in Hawaii, which have become stronger in recent years “could also threaten the Hawaiian-based observatories.” As for Chilean observatories, she says, “the effects are there”.
According to Cantalloube, interdisciplinary teams like hers will become more prevalent over time as scientists seek to understand the many ways that climate change could impact research capabilities. She notes that her team’s paper, which appears in Nature Astronomy, is a preliminary study, focusing solely on the effects of climate change on observations conducted in Chile. Since climate change will likely affect different regions of the globe in different ways, the team hopes to extend its analysis to cover additional sites. In the meantime, Cantalloube urges members of the astronomy community to “investigate whether climate change and/or environmental signals are also detectable in the observations of other observatories/others fields of research” and “convince political leaders to act now against climate change”.


physicsworld--2020-10-05--Nobel prize sizzle: building excitement in the run-up to the physics award  - Physics World

Tomorrow , the winner ( s ) of this year ’ s Nobel Prize for Physics will be announced .
This will the 14th Nobel prize that I have covered for Physics World , and I can honestly say that the excitement has never waned .
A big challenge for journalists on Physics World , however , is coming up with new ways of creating a bit of “ sizzle ” in the run-up to the announcement .
This is difficult because unlike some other prizes , there is no public shortlist for the Nobel prize to whet the appetite @ @ @ @ @ @ @ and the deliberations of the Nobel committee are kept secret for at least 50 years – so it is impossible to know who is in the running and very difficult to understand how decisions are currently being made by the committee .
However , I am not complaining about this information deficit .
I think it is one of the many things that keeps the Nobel prize fresh and exciting every year .
Last year I was very fortunate to gain some insights into the selection process when I interviewed the Swedish physicist @ @ @ @ @ @ @ Nobel Committee for Physics on eight separate occasions .
So if you are keen to learn about the finer points of how winners are selected , check out my article “ Inside the Nobels : Lars Brink reveals how the world ’ s top physics prize is awarded ” .
One way of generating a bit of excitement in the run-up to the Nobel is to predict who will bag the prize .
The problem with predictions is that mine are almost always wrong .
And after a few years , I also @ @ @ @ @ @ @ as winners .
To see how good our Physics World predictions have been , I looked back at a blog I wrote in late September 2009 ( “ Nobel predictions ” ) .
The predictions were made by Physics World editors and the Nobel laureate Albert Fert .
Here are the 13 predictions we made ( all men , I ’ m afraid ) and the years that some of them actually won a Nobel prize : Alain Aspect , David Wineland ( 2012 ) , Peter Zoller , Juan Ignacio Cirac , @ @ @ @ @ @ @ ) , Didier Queloz ( 2019 ) , Andre Geim ( 2010 ) , Konstantin Novoselov ( 2010 ) , Yakir Aharanov , Michael Berry , Saul Perlmutter ( 2011 ) and Brian Schmidt ( 2011 ) .
That is better than 50 % , so maybe I am underselling our ability to predict winners ( I say “ our ” , because I only got one right ) .
Not content to rely on intuition to pick winners , in 2014 I took a close look at whether there is a temporal @ @ @ @ @ @ @ I divided physics into seven disciplines and created an infographic that shows when prizes were awarded in those fields .
The figure “ Nobel Prize disciplines timeline ” is version of the infographic updated to 2019 and if you squint at it for long enough you may convince yourself that there is a pattern in the prizes .
For example , there has not been an award in the field of quantum physics for eight years – so , my only prediction for this year will be a prize to physicists working in @ @ @ @ @ @ @ reasonable bet is that at least one of the 2020 laureates will be an immigrant .
That prediction comes courtesy of our 2015 Nobel sizzle , when I created an infographic that reveals that more than 25 % of physics laureates can be classed as immigrants .
That was updated in 2019 and you can read more in “ More than one-quarter of physics Nobel laureates are immigrants , reveal updated infographics ” .
I think that our best bit of Nobel sizzle so far was last year ’ s series of pieces @ @ @ @ @ @ @ pick was the 1982 prize to Kenneth Wilson “ for his theory for critical phenomena in connection with phase transitions ” .
I have always been fascinated by phase transitions , but I have to admit that it was a bit daunting to try to describe Wilson ’ s work in a few hundred words : ( “ My favourite Nobel prize : a universal theory for phase transitions ” ) .
This year we are focussing on people who we think missed out on a Nobel .
You can find those pieces @ @ @ @ @ @ @ panel called “ Overlooked for the Nobel ” .
I have contributed two pieces to this series : one championing the physicists at CERN who discovered the Higgs boson , and the other asking why the Chinese-American physicist Chien-Shiung Wu did not win a Nobel for her pioneering measurement of parity violation .

Nobel Prize disciplines timeline (click to enlarge): The thickness of the coloured line denotes how many laureates shared the prize in that year. In years when the prize was split between two disciplines, two lines are used, with each denoting the number of laureates in that discipline. (This timeline was originally published in 2014 and was updated in 2019. © IOP Publishing)
Tomorrow, the winner(s) of this year’s Nobel Prize for Physics will be announced. This will the 14th Nobel prize that I have covered for Physics World, and I can honestly say that the excitement has never waned.
A big challenge for journalists on Physics World, however, is coming up with new ways of creating a bit of “sizzle” in the run-up to the announcement. This is difficult because unlike some other prizes, there is no public shortlist for the Nobel prize to whet the appetite. Indeed, who has been nominated and the deliberations of the Nobel committee are kept secret for at least 50 years – so it is impossible to know who is in the running and very difficult to understand how decisions are currently being made by the committee.
However, I am not complaining about this information deficit. I think it is one of the many things that keeps the Nobel prize fresh and exciting every year.
Last year I was very fortunate to gain some insights into the selection process when I interviewed the Swedish physicist Lars Brink, who served on the Nobel Committee for Physics on eight separate occasions. So if you are keen to learn about the finer points of how winners are selected, check out my article “Inside the Nobels: Lars Brink reveals how the world’s top physics prize is awarded”.
Predicting winners
One way of generating a bit of excitement in the run-up to the Nobel is to predict who will bag the prize. The problem with predictions is that mine are almost always wrong. And after a few years, I also run out of new people to predict as winners.
To see how good our Physics World predictions have been, I looked back at a blog I wrote in late September 2009 (“Nobel predictions”). The predictions were made by Physics World editors and the Nobel laureate Albert Fert. Here are the 13 predictions we made (all men, I’m afraid) and the years that some of them actually won a Nobel prize: Alain Aspect, David Wineland (2012), Peter Zoller, Juan Ignacio Cirac, Anton Zeilinger, Michel Mayor (2019), Didier Queloz (2019), Andre Geim (2010), Konstantin Novoselov (2010), Yakir Aharanov, Michael Berry, Saul Perlmutter (2011) and Brian Schmidt (2011). That is better than 50%, so maybe I am underselling our ability to predict winners (I say “our”, because I only got one right).
Not content to rely on intuition to pick winners, in 2014 I took a close look at whether there is a temporal pattern in how prizes are awarded. I divided physics into seven disciplines and created an infographic that shows when prizes were awarded in those fields.
Quantum information this year?
The figure “Nobel Prize disciplines timeline” is version of the infographic updated to 2019 and if you squint at it for long enough you may convince yourself that there is a pattern in the prizes. For example, there has not been an award in the field of quantum physics for eight years – so, my only prediction for this year will be a prize to physicists working in the field of quantum information.
Migration routes: the US is the champion when it comes to attracting Nobel laureates. (Courtesy: Paul Matson)
Another reasonable bet is that at least one of the 2020 laureates will be an immigrant. That prediction comes courtesy of our 2015 Nobel sizzle, when I created an infographic that reveals that more than 25% of physics laureates can be classed as immigrants. That was updated in 2019 and you can read more in “More than one-quarter of physics Nobel laureates are immigrants, reveal updated infographics”.
I think that our best bit of Nobel sizzle so far was last year’s series of pieces about our favourite Nobel prizes. My pick was the 1982 prize to Kenneth Wilson “for his theory for critical phenomena in connection with phase transitions”. I have always been fascinated by phase transitions, but I have to admit that it was a bit daunting to try to describe Wilson’s work in a few hundred words: (“My favourite Nobel prize: a universal theory for phase transitions”).
This year we are focussing on people who we think missed out on a Nobel. You can find those pieces on the Physics World website in a panel called “Overlooked for the Nobel”. I have contributed two pieces to this series: one championing the physicists at CERN who discovered the Higgs boson, and the other asking why the Chinese-American physicist Chien-Shiung Wu did not win a Nobel for her pioneering measurement of parity violation.


physicsworld--2020-10-05--Compton imaging opens up new avenues for diagnostic imaging - Physics World

Compton imaging , originally developed by astronomers for detecting gamma ray sources , is now also under investigation for clinical imaging .
In particular , a high-performance Compton camera could prove invaluable for applications within nuclear medicine and molecular imaging .
Unlike the established medical imaging technique of PET , which can only visualize positron emitters , Compton imaging has the potential to visualize a variety of gamma ray sources .
To date , however , Compton image quality has not matched up to that of typical PET scans .
To investigate its potential further , researchers at the National @ @ @ @ @ @ @ in Japan have created a combined whole gamma imaging ( WGI ) platform to directly compare the two modalities .
“ Compton imaging has potential to provide better images than conventional SPECT and PET , in particular for radionuclides emitting high-energy gamma rays , ” explains first author Hideaki Tashima .
“ We expect to explore new radionuclides that have never been used for nuclear medicine.
” A Compton camera incorporates two detectors that work in synchrony .
For an individual gamma emission , Compton scattering occurs in the first detector ( the @ @ @ @ @ @ @ second ( the absorber ) .
Both detectors record the interaction positions and corresponding deposited energies , enabling reconstruction of a Compton cone that indicates the emission point .
To create a WGI system that can perform both PET and Compton imaging , the researchers inserted a scatterer ring inside a whole-body depth-of-interaction PET scanner ( the absorber ring ) .
To enable small-animal imaging experiments , they remodelled a previous WGI prototype by halving the diameter of the scatterer ring .
As the spatial resolution of Compton imaging reduces in proportion to @ @ @ @ @ @ @ also improve the resulting images .
Tashima and colleagues tested the WGI platform using 89Zr as the imaging source , as it decays via emission of a positron and a 909 keV gamma ray , enabling direct comparison of PET and Compton imaging .
Alongside , they developed a 3D image reconstruction method incorporating detector response function ( DRF ) modelling , random correction and normalization .
They report their findings in Physics in Medicine & Biology .
The researchers first evaluated the uniformity of the WGI prototype , by imaging a cylindrical @ @ @ @ @ @ @ reconstructed without normalization , PET images exhibited ring artefacts and stripe patterns , while Compton images had higher coefficients of variation ( COV ) in the central region .
The normalized PET and Compton images were of comparable quality , showing uniform radioactivity intensity throughout the phantom , and with COVs of 3.7 % and 4.8 % for PET and Compton images , respectively .
To assess the spatial resolution of the modalities , the researchers imaged a small rod phantom with clusters of cylindrical holes filled with 89Zr solution .
The PET @ @ @ @ @ @ @ .
The Compton image resolved the 3.0-mm holes in the peripheral region , with lower spatial resolution in the central region .
Finally , the team injected a mouse with 9.8 MBq 89Zr-oxalate and , one day later , used the WGI prototype to image the animal for 1 hr .
The absorber ring ( containing the PET detectors ) had an axial length of 214 mm – enough to cover the whole animal .
The PET image thus showed the entire mouse , revealing that 89Zr localized in its bones .
The @ @ @ @ @ @ @ , so the researchers positioned the animal ’ s torso inside the ring and its head and tail outside .
Nevertheless , in Compton imaging mode , the WGI system could reconstruct the distribution outside the ring and create an image of almost the entire body .
The Compton images agreed well with the PET images , clearly showing 89Zr in the mouse bones , although the image quality was better for regions inside the scatterer ring than those outside .
The researchers conclude that the WGI prototype could achieve Compton imaging with @ @ @ @ @ @ @ They attribute this success to four key factors : the high energy of the gamma ray emitted from 89Zr , which improves the spatial resolution of Compton imaging ; the DRF model used for image reconstruction , which further improved spatial resolution ; the normalization step , essential for image uniformity ; and the full-ring geometry of the WGI system .
Future work will focus on improving Compton imaging such that it outperforms PET .
But the team ’ s ultimate goal is to unite the two techniques and implement a combined image @ @ @ @ @ @ @ different tracers with PET and Compton imaging can improve the efficiency of diagnosis , ” explains Tashima .
“ In addition , reconstruction of a single tracer image by combining two types of signals can improve image quality through high sensitivity.
” “ We are now exploring detector technologies for better energy resolution , ” adds project leader Taiga Yamaya .
“ We are looking ahead to the realization of a clinical WGI system .
”

First author Hideaki Tashima (left) and co-author Hidekatsu Wakizaka (right) image a mouse using a whole gamma imaging platform. (Courtesy: Taiga Yamaya, National Institute of Radiological Sciences)
Compton imaging, originally developed by astronomers for detecting gamma ray sources, is now also under investigation for clinical imaging. In particular, a high-performance Compton camera could prove invaluable for applications within nuclear medicine and molecular imaging.
Unlike the established medical imaging technique of PET, which can only visualize positron emitters, Compton imaging has the potential to visualize a variety of gamma ray sources. To date, however, Compton image quality has not matched up to that of typical PET scans. To investigate its potential further, researchers at the National Institute of Radiological Sciences (NIRS) in Japan have created a combined whole gamma imaging (WGI) platform to directly compare the two modalities.
“Compton imaging has potential to provide better images than conventional SPECT and PET, in particular for radionuclides emitting high-energy gamma rays,” explains first author Hideaki Tashima. “We expect to explore new radionuclides that have never been used for nuclear medicine.”
A Compton camera incorporates two detectors that work in synchrony. For an individual gamma emission, Compton scattering occurs in the first detector (the scatterer) and photoelectric absorption in the second (the absorber). Both detectors record the interaction positions and corresponding deposited energies, enabling reconstruction of a Compton cone that indicates the emission point.
To create a WGI system that can perform both PET and Compton imaging, the researchers inserted a scatterer ring inside a whole-body depth-of-interaction PET scanner (the absorber ring). To enable small-animal imaging experiments, they remodelled a previous WGI prototype by halving the diameter of the scatterer ring. As the spatial resolution of Compton imaging reduces in proportion to the source–detector distance, this modification should also improve the resulting images.
Design sketches of the modified WGI prototype (a, b); the scatterer detector and absorber detector (c); the developed prototype (d). (Courtesy: Phys. Med. Biol. 10.1088/1361-6560/abb92e)
System evaluation
Tashima and colleagues tested the WGI platform using 89Zr as the imaging source, as it decays via emission of a positron and a 909 keV gamma ray, enabling direct comparison of PET and Compton imaging. Alongside, they developed a 3D image reconstruction method incorporating detector response function (DRF) modelling, random correction and normalization. They report their findings in Physics in Medicine & Biology.
The researchers first evaluated the uniformity of the WGI prototype, by imaging a cylindrical phantom filled with 89Zr solution. When reconstructed without normalization, PET images exhibited ring artefacts and stripe patterns, while Compton images had higher coefficients of variation (COV) in the central region. The normalized PET and Compton images were of comparable quality, showing uniform radioactivity intensity throughout the phantom, and with COVs of 3.7% and 4.8% for PET and Compton images, respectively.
To assess the spatial resolution of the modalities, the researchers imaged a small rod phantom with clusters of cylindrical holes filled with 89Zr solution. The PET image clearly resolved the 2.2-mm diameter holes. The Compton image resolved the 3.0-mm holes in the peripheral region, with lower spatial resolution in the central region.
Finally, the team injected a mouse with 9.8 MBq 89Zr-oxalate and, one day later, used the WGI prototype to image the animal for 1 hr. The absorber ring (containing the PET detectors) had an axial length of 214 mm – enough to cover the whole animal. The PET image thus showed the entire mouse, revealing that 89Zr localized in its bones.
Reconstructed PET (left) and Compton (right) images of a mouse injected with 89Zr-oxalate. (Courtesy: Phys. Med. Biol. 10.1088/1361-6560/abb92e)
The scatterer ring was only 52 mm long, so the researchers positioned the animal’s torso inside the ring and its head and tail outside. Nevertheless, in Compton imaging mode, the WGI system could reconstruct the distribution outside the ring and create an image of almost the entire body. The Compton images agreed well with the PET images, clearly showing 89Zr in the mouse bones, although the image quality was better for regions inside the scatterer ring than those outside.
The researchers conclude that the WGI prototype could achieve Compton imaging with a quality approaching that of PET. They attribute this success to four key factors: the high energy of the gamma ray emitted from 89Zr, which improves the spatial resolution of Compton imaging; the DRF model used for image reconstruction, which further improved spatial resolution; the normalization step, essential for image uniformity; and the full-ring geometry of the WGI system.
Future work will focus on improving Compton imaging such that it outperforms PET. But the team’s ultimate goal is to unite the two techniques and implement a combined image reconstruction method. “Simultaneous measurement of different tracers with PET and Compton imaging can improve the efficiency of diagnosis,” explains Tashima. “In addition, reconstruction of a single tracer image by combining two types of signals can improve image quality through high sensitivity.”
“We are now exploring detector technologies for better energy resolution,” adds project leader Taiga Yamaya. “We are looking ahead to the realization of a clinical WGI system.”


physicsworld--2020-09-29--Nanoparticles warm up faster than they cool down - Physics World

On the nanoscale , objects warm up faster than they cool down .
That is the surprising conclusion of Alessio Lapolla and Aljaž Godec at the Max Planck Institute of Biophysical Chemistry in Germany , who have predicted this asymmetry using mathematical models of confined nanoparticles .
One basic assumption in thermodynamics is that an object that is either hotter or colder than its surrounding environment will cool down or heat up , respectively , at the same rate .
So , an object that is slightly warmer than room temperature will reach room temperature at the same time as @ @ @ @ @ @ @ room temperature .
Lapolla and Godec tested this principle in their study using a mathematical model of a tiny nanoparticle trapped inside a one-dimensional box .
As the particle undergoes Brownian motion , its position is mapped using a probability distribution – which peaks at the centre of the box , where the particle is most likely to be found .
Since Brownian motion increases with temperature , the duo predicted that heating should cause the probability distribution to spread out during heating , and become narrower during cooling .
However , this @ @ @ @ @ @ @ difference in how hot and cold particles reached equilibrium with their surroundings .
Contrary to expectations , however , Lapolla and Godec observed that warmer particles took longer to cool down than cooler objects did to warm up .
To explain this asymmetry , the duo suggests that the more dynamic motion of a warmer particle means that it bounces off the walls of the box more often .
As a result of this bouncing , the warm particle tends to drift towards the centre of the box more readily .
This counteracts @ @ @ @ @ @ @ – thereby narrowing the particle ’ s probability distributions to the centre of the box .
In contrast , this bouncing became less pronounced at cooler temperatures .
With less opposition to their Brownian motions , colder particles could relax to their equilibrium states more readily than their warmer counterparts .
Lapolla and Godec believe their results will improve our understanding of temperature changes in nanoscale systems .
It could also provide fresh insights into phenomena like the Mpemba effect – whereby water appears to freeze more quickly when its starting temperature is @ @ @ @ @ @ @ verify their results through practical experiments , which could be carried out relatively easily by confining particles within optical traps .
The insights gained through these studies could also help to improve efficiency in devices including micromotors and heat pumps .
The research is described in Physical Review Letters .

Hot and cold Bouncing off walls slows the cooling of hot nanoparticles. (Courtesy: iStock/Mervana)
On the nanoscale, objects warm up faster than they cool down. That is the surprising conclusion of Alessio Lapolla and Aljaž Godec at the Max Planck Institute of Biophysical Chemistry in Germany, who have predicted this asymmetry using mathematical models of confined nanoparticles.
One basic assumption in thermodynamics is that an object that is either hotter or colder than its surrounding environment will cool down or heat up, respectively, at the same rate. So, an object that is slightly warmer than room temperature will reach room temperature at the same time as an identical object that started slightly below room temperature.
Lapolla and Godec tested this principle in their study using a mathematical model of a tiny nanoparticle trapped inside a one-dimensional box. As the particle undergoes Brownian motion, its position is mapped using a probability distribution – which peaks at the centre of the box, where the particle is most likely to be found. Since Brownian motion increases with temperature, the duo predicted that heating should cause the probability distribution to spread out during heating, and become narrower during cooling. However, this was not expected to result in a difference in how hot and cold particles reached equilibrium with their surroundings.
Off the walls
Contrary to expectations, however, Lapolla and Godec observed that warmer particles took longer to cool down than cooler objects did to warm up. To explain this asymmetry, the duo suggests that the more dynamic motion of a warmer particle means that it bounces off the walls of the box more often. As a result of this bouncing, the warm particle tends to drift towards the centre of the box more readily. This counteracts the spreading out due to Brownian motion – thereby narrowing the particle’s probability distributions to the centre of the box. In contrast, this bouncing became less pronounced at cooler temperatures. With less opposition to their Brownian motions, colder particles could relax to their equilibrium states more readily than their warmer counterparts.
Lapolla and Godec believe their results will improve our understanding of temperature changes in nanoscale systems. It could also provide fresh insights into phenomena like the Mpemba effect – whereby water appears to freeze more quickly when its starting temperature is warmer. The duo now hope to verify their results through practical experiments, which could be carried out relatively easily by confining particles within optical traps. The insights gained through these studies could also help to improve efficiency in devices including micromotors and heat pumps.
The research is described in Physical Review Letters.


physicsworld--2020-10-05--Overlooked for the Nobel: Lise Meitner - Physics World

The discovery of nuclear fission in 1938 is among the most momentous events in 20th-century physics .
Within seven years , this experimental and theoretical breakthrough – made jointly by Otto Hahn and Fritz Strassmann , who obtained the data , and by Lise Meitner and Otto Frisch , who interpreted it – led to the first atomic weapons .
Less than a decade later , it led to the first nuclear power plants .
If ever there was a discovery that should have won its instigators a Nobel Prize in Physics , nuclear fission is surely it .
But @ @ @ @ @ @ @ Though the terms of Alfred Nobel ’ s bequest would have allowed three of Hahn , Frisch , Meitner and Strassmann to share a prize , only Hahn got the nod , becoming the sole recipient of the 1944 Nobel Prize in Chemistry “ for his discovery of the fission of heavy nuclei ” .
The contributions of Frisch , Meitner and Strassmann were relegated to a few lines in the official Nobel presentation speech , which took place in December 1945 .
That same speech , incidentally , claims that Hahn “ @ @ @ @ @ @ @ atomic energy ” – which is a bit rich , given that Hahn worked on the Nazi atomic weapons programme and was in fact still incarcerated by the British authorities at the time .
The 1944 Nobel Prize in Chemistry represents a strong challenge to anyone who claims that the Nobels are fair or reflective of how collaborative science works .
Strassmann , whom the presentation speech patronizingly called “ one of [ Hahn ’ s ] young colleagues ” , had in fact been his assistant for the best part of a @ @ @ @ @ @ @ , Strassmann worked for half wages or none ; his opposition to the Nazi regime meant that he was blacklisted from other jobs , leaving him dependent on Hahn and unable to develop a solo career .
Meitner fared slightly better in the speech , since it did at least acknowledge her as Hahn ’ s collaborator for more than 30 years .
Not mentioned , though , is the reason she was absent during the crucial 1938 experiments : Meitner , like her nephew Frisch , was an ethnic Jew , and @ @ @ @ @ @ @ did not protect her from Nazi predation .
In the summer of 1938 , both Meitner and Frisch were forced to flee Germany .
They made their seminal contributions to fission in exile , communicating with the Berlin-based Hahn and Strassmann by letter and telephone .
Of the three researchers left out of the 1944 Nobel Prize in Chemistry , the injustice done to Meitner is the most severe .
Unlike the other “ overlooked ” physicists in this series , the records of her Nobel nominations are now public .
They show @ @ @ @ @ @ @ the scientists in the Nobel nomination pools were all male then , notwithstanding the existence of contemporary female luminaries like Ida Noddack and Iréne Joliot-Curie ) nominated her for the physics Nobel 29 times , and for the chemistry Nobel 19 times .
Her earliest nomination came from the Norwegian chemist Heinrich Goldschmidt in 1924 .
Her last was in 1965 , three years before her death , when Max Born made her his fourth choice after Pyotr Kapitsa ( who went on to win in 1978 ) , Cornelis Gorter ( who @ @ @ @ @ @ @ ditto ) .
The records do not entirely explain why none of these nominations were successful .
However , they do suggest that Meitner has something other than gender in common with two other entries in this series .
The chemistry Nobel committee in 1944 was as divided about the relative importance of theory and experiment as the physics committee was in 1957 , when Chien-Shiung Wu was denied a share of the parity-violation prize that went to Chen Ning Yang and Tsung-Dao Lee .
The 1944 committee also failed to appreciate the @ @ @ @ @ @ @ Strassmann played in the fission collaboration , much as a later committee failed to understand that Jocelyn Bell Burnell was not merely Antony Hewish ’ s assistant in discovering pulsars .
On top of that , a whole suite of prejudices – racial , sexual , political and disciplinary – seems to have made it impossible for the parochial chemists of neutral Sweden to see the contributions of a refugee Jewish woman physicist in their proper light .
Early in her career , Meitner faced and overcame a considerable degree of personal prejudice @ @ @ @ @ @ @ Nobel laureate Emil Fischer refused to let her work in his lab because he thought women ’ s long hair was a fire hazard ( apparently Fischer ’ s massive beard was perfectly fine ) .
Meitner ’ s subsequent achievements – as well as nuclear fission , she also discovered the element protactinium – won her legions of admirers , 26 of whom went on to nominate her for a Nobel Prize at least once .
In the end , though , neither her efforts nor theirs were enough to counterbalance the @ @ @ @ @ @ @ and still do help ) to keep the Nobel prizes overwhelmingly white and male , 82 years after Lise Meitner ’ s earth-shattering discovery .

The 2020 Nobel Prize for Physics will be announced on Tuesday 6 October. In the run-up to the announcement, Physics World editors have picked some of the people who they think have been overlooked for a prize in the past
Collaborators: Otto Hahn and Lise Meitner in 1912, a few years into their 30-year working relationship.
The discovery of nuclear fission in 1938 is among the most momentous events in 20th-century physics. Within seven years, this experimental and theoretical breakthrough – made jointly by Otto Hahn and Fritz Strassmann, who obtained the data, and by Lise Meitner and Otto Frisch, who interpreted it – led to the first atomic weapons. Less than a decade later, it led to the first nuclear power plants. If ever there was a discovery that should have won its instigators a Nobel Prize in Physics, nuclear fission is surely it.
But that’s not what happened. Though the terms of Alfred Nobel’s bequest would have allowed three of Hahn, Frisch, Meitner and Strassmann to share a prize, only Hahn got the nod, becoming the sole recipient of the 1944 Nobel Prize in Chemistry “for his discovery of the fission of heavy nuclei”. The contributions of Frisch, Meitner and Strassmann were relegated to a few lines in the official Nobel presentation speech, which took place in December 1945. That same speech, incidentally, claims that Hahn “never dreamed of giving Man control over atomic energy” – which is a bit rich, given that Hahn worked on the Nazi atomic weapons programme and was in fact still incarcerated by the British authorities at the time.
The 1944 Nobel Prize in Chemistry represents a strong challenge to anyone who claims that the Nobels are fair or reflective of how collaborative science works. Strassmann, whom the presentation speech patronizingly called “one of [Hahn’s] young colleagues”, had in fact been his assistant for the best part of a decade. For much of that period, Strassmann worked for half wages or none; his opposition to the Nazi regime meant that he was blacklisted from other jobs, leaving him dependent on Hahn and unable to develop a solo career. Meitner fared slightly better in the speech, since it did at least acknowledge her as Hahn’s collaborator for more than 30 years. Not mentioned, though, is the reason she was absent during the crucial 1938 experiments: Meitner, like her nephew Frisch, was an ethnic Jew, and her conversion to Protestantism 30 years earlier did not protect her from Nazi predation. In the summer of 1938, both Meitner and Frisch were forced to flee Germany. They made their seminal contributions to fission in exile, communicating with the Berlin-based Hahn and Strassmann by letter and telephone.
Of the three researchers left out of the 1944 Nobel Prize in Chemistry, the injustice done to Meitner is the most severe. Unlike the other “overlooked” physicists in this series, the records of her Nobel nominations are now public. They show that Meitner’s male colleagues (the scientists in the Nobel nomination pools were all male then, notwithstanding the existence of contemporary female luminaries like Ida Noddack and Iréne Joliot-Curie) nominated her for the physics Nobel 29 times, and for the chemistry Nobel 19 times. Her earliest nomination came from the Norwegian chemist Heinrich Goldschmidt in 1924. Her last was in 1965, three years before her death, when Max Born made her his fourth choice after Pyotr Kapitsa (who went on to win in 1978), Cornelis Gorter (who never won) and Walter Heitler (ditto).
The records do not entirely explain why none of these nominations were successful. However, they do suggest that Meitner has something other than gender in common with two other entries in this series. The chemistry Nobel committee in 1944 was as divided about the relative importance of theory and experiment as the physics committee was in 1957, when Chien-Shiung Wu was denied a share of the parity-violation prize that went to Chen Ning Yang and Tsung-Dao Lee. The 1944 committee also failed to appreciate the major role that Meitner, Frisch and Strassmann played in the fission collaboration, much as a later committee failed to understand that Jocelyn Bell Burnell was not merely Antony Hewish’s assistant in discovering pulsars. On top of that, a whole suite of prejudices – racial, sexual, political and disciplinary – seems to have made it impossible for the parochial chemists of neutral Sweden to see the contributions of a refugee Jewish woman physicist in their proper light.
Early in her career, Meitner faced and overcame a considerable degree of personal prejudice. In one laughable example, the Nobel laureate Emil Fischer refused to let her work in his lab because he thought women’s long hair was a fire hazard (apparently Fischer’s massive beard was perfectly fine). Meitner’s subsequent achievements – as well as nuclear fission, she also discovered the element protactinium – won her legions of admirers, 26 of whom went on to nominate her for a Nobel Prize at least once. In the end, though, neither her efforts nor theirs were enough to counterbalance the subtle, structural forces that helped (and still do help) to keep the Nobel prizes overwhelmingly white and male, 82 years after Lise Meitner’s earth-shattering discovery.


physicsworld--2020-10-05--New microwave bolometers could boost quantum computers - Physics World

Two graphene-based bolometers that are sensitive to detect single microwave photons have been built by independent teams of physicists .
The devices could find a range of applications in quantum technologies , radio astronomy and even in the search for dark matter .
One bolometer was created in Finland by Mikko Möttönen and colleagues at Aalto University and VTT Technical Research Centre of Finland , while the other was created by an international team led by Kin Chung Fong at Raytheon BBN Technologies in the US .
A bolometer measures the energy of incoming radiation by determining how much the @ @ @ @ @ @ @ capable of detecting single microwave photons would be very useful in creating quantum computers and other technologies that use superconducting quantum bits ( qubits ) .
This is because superconducting qubits interact via microwaves and single photons provide a very efficient way of transferring quantum information between qubits .
So far , however , creating single-photon microwave detectors has been difficult because of the relatively low energies of microwave photons .
The Finnish team had addressed the low-energy problem by creating a bolometer that used a gold-palladium alloy to absorb photons .
While @ @ @ @ @ @ @ levels , it is not fast enough to be useful when it comes to measuring the state of a superconducting qubit .
Now , Möttönen and colleagues have replaced the gold-palladium absorber with one made from graphene , which has a very low heat capacity .
This makes graphene ideal for making a bolometer because heat capacity is a measure of the energy required to raise the temperature of a material by one degree .
“ Changing to graphene increased the detector speed by 100 times , while the noise level remained the @ @ @ @ @ @ @ Hakonen .
Indeed , the new device can make a measurement in less than microsecond , which is on par with technology that is currently used to measure the state of qubits .
Hakonen adds , “ After these initial results , there is still a lot of optimization we can do to make the device even better ” .
Meanwhile , Fong and colleagues created a bolometer in which graphene is integrated within a superconducting device called a Josephson junction .
When the graphene warms up by absorbing a microwave photon , @ @ @ @ @ @ @ the Josephson junction – thus creating the detection signal .
This device is a whopping 100,000 times faster than microwave bolometers based on other materials .
Team member Dmitri Efetov at ICFO in Barcelona comments “ such achievements were thought impossible with traditional materials , and graphene did the trick again .
This opens entirely new avenues for quantum sensors for quantum computation and quantum communication.
” Fong and colleagues and Hakonen and colleagues describe their bolometers in separate papers in Nature .

Nordic device: Artistic image of the Aalto University graphene bolometer controlled by electric field. (Courtesy: Heikka Valja)
Two graphene-based bolometers that are sensitive to detect single microwave photons have been built by independent teams of physicists. The devices could find a range of applications in quantum technologies, radio astronomy and even in the search for dark matter.
One bolometer was created in Finland by Mikko Möttönen and colleagues at Aalto University and VTT Technical Research Centre of Finland, while the other was created by an international team led by Kin Chung Fong at Raytheon BBN Technologies in the US.
A bolometer measures the energy of incoming radiation by determining how much the radiation heats up a material. Bolometers capable of detecting single microwave photons would be very useful in creating quantum computers and other technologies that use superconducting quantum bits (qubits). This is because superconducting qubits interact via microwaves and single photons provide a very efficient way of transferring quantum information between qubits.
Too slow
So far, however, creating single-photon microwave detectors has been difficult because of the relatively low energies of microwave photons. The Finnish team had addressed the low-energy problem by creating a bolometer that used a gold-palladium alloy to absorb photons. While this device operates at very low noise levels, it is not fast enough to be useful when it comes to measuring the state of a superconducting qubit.
Now, Möttönen and colleagues have replaced the gold-palladium absorber with one made from graphene, which has a very low heat capacity. This makes graphene ideal for making a bolometer because heat capacity is a measure of the energy required to raise the temperature of a material by one degree.
“Changing to graphene increased the detector speed by 100 times, while the noise level remained the same,” explains team member Pertti Hakonen. Indeed, the new device can make a measurement in less than microsecond, which is on par with technology that is currently used to measure the state of qubits. Hakonen adds, “After these initial results, there is still a lot of optimization we can do to make the device even better”.
Josephson junction
Meanwhile, Fong and colleagues created a bolometer in which graphene is integrated within a superconducting device called a Josephson junction. When the graphene warms up by absorbing a microwave photon, it affects the electrical current flowing through the Josephson junction – thus creating the detection signal. This device is a whopping 100,000 times faster than microwave bolometers based on other materials.
Team member Dmitri Efetov at ICFO in Barcelona comments “such achievements were thought impossible with traditional materials, and graphene did the trick again. This opens entirely new avenues for quantum sensors for quantum computation and quantum communication.”
Fong and colleagues and Hakonen and colleagues describe their bolometers in separate papers in Nature.


physicsworld--2020-10-01--Online conferences, auxetic materials and a new kind of rocket engine: the October 2020 issue of Phy

Online conferences, auxetic materials and a new kind of rocket engine: the October 2020 issue of Physics World is now out - Physics World

When it comes to scientific conferences , we ’ ve all been affected by the restrictions from the COVID-19 pandemic .
But even when the pandemic is over , as it surely will be one day , I don ’ t think we ’ ll ever entirely go back to massive scientific conferences as we knew them .
Sending thousands of people halfway round the world at great expense to mix in stuffy rooms increasingly seems a thing of the past , not least on the grounds of cost and pollution .
What ’ s more , we can do @ @ @ @ @ @ @ it ’ ll take time to figure out what works best , but there are some intriguing developments already under way .
In the new issue of Physics World , for example , you can read about a recent online conference in attophysics that deliberately set out to create scientific “ battles ” .
More importantly , online conferences can make physics meetings more accessible and open .
If you ’ re a member of the Institute of Physics , you can read the whole of Physics World magazine every month via our @ @ @ @ @ @ @ Web browsers .
Let us know what you think about the issue on Twitter , Facebook or by e-mailing us at pwld @ ioppublishing.org .
For the record , here ’ s a rundown of what else is in the issue .
• US election focuses on science – from dealing with the COVID-19 pandemic to stimulating industries of the future , science policy will play a larger role than usual in next month ’ s US election , as Peter Gwynne reports • Redefining the scientific conference – Eleanor S Armstrong , @ @ @ @ @ @ @ argue that the COVID-19 pandemic offers an opportunity to start making scientific meetings more inclusive • Courting controversy online – Carla Figueira de Morisson Faria and Andrew Brown say that academic debate can still be fostered in an online-only world • Monumental mistake – Robert P Crease laments the disappearance of a landmark in US science history : the cooling tower at the Brookhaven National Laboratory • Green strings attached – solving many of today ’ s environmental problems will require advanced technological solutions , says James McKenzie • Eliminating the boundary between @ @ @ @ @ @ @ vital to make access to space more affordable , but conventional rocket engines have their limits .
Oliver Nailard describes how UK firm Reaction Engines hopes to revolutionize space access with a new class of propulsion system , the Synergetic Air Breathing Rocket Engine ( SABRE ) • Stretching the limits – most materials get thinner when stretched , but “ auxetics ” do the opposite and get thicker .
Helen Gleeson describes her group ’ s discovery of a material that is auxetic at the molecular level , which could be used @ @ @ @ @ @ @ glass • Optical microscopy – how small can it go ?
For centuries diffraction limited the resolution of optical microscopy .
The past 50 years have , however , seen one limitation after another buckle under the ingenuity of a host of wide-ranging techniques , from lenses to tips , chips and doughnuts .
Anna Demming reports • Age of cosmic explosion – Tushna Commissariat reviews Look Up : Our Story with the Stars by Sarah Cruddas • Intrepid interstellar adventurers – Ian Randall reviews Spacefarers : How Humans Will Settle the Moon @ @ @ @ @ @ @ Wan • Path of least resistance – graduate student Rosemary Teague and undergraduate Amber Yallop share their non-traditional degree pathways , some difficult choices they made along the way , and what a future in physics looks like for them now • Is anybody there ?
– Chris Holt on the physics of ghosts

The new issue of your favourite magazine examines the benefits of virtual meetings
Revolutionary rocket? The October 2020 issue of Physics World also looks at a new kind of engine.
When it comes to scientific conferences, we’ve all been affected by the restrictions from the COVID-19 pandemic. But even when the pandemic is over, as it surely will be one day, I don’t think we’ll ever entirely go back to massive scientific conferences as we knew them.
Sending thousands of people halfway round the world at great expense to mix in stuffy rooms increasingly seems a thing of the past, not least on the grounds of cost and pollution. What’s more, we can do so much more online.
Sure, it’ll take time to figure out what works best, but there are some intriguing developments already under way. In the new issue of Physics World, for example, you can read about a recent online conference in attophysics that deliberately set out to create scientific “battles”. More importantly, online conferences can make physics meetings more accessible and open.
If you’re a member of the Institute of Physics, you can read the whole of Physics World magazine every month via our digital apps for iOS, Android and Web browsers. Let us know what you think about the issue on Twitter, Facebook or by e-mailing us at pwld@ioppublishing.org.
For the record, here’s a rundown of what else is in the issue.
• US election focuses on science – from dealing with the COVID-19 pandemic to stimulating industries of the future, science policy will play a larger role than usual in next month’s US election, as Peter Gwynne reports
• Redefining the scientific conference – Eleanor S Armstrong, Divya M Persaud and Christopher A-L Jackson argue that the COVID-19 pandemic offers an opportunity to start making scientific meetings more inclusive
• Courting controversy online – Carla Figueira de Morisson Faria and Andrew Brown say that academic debate can still be fostered in an online-only world
• Monumental mistake – Robert P Crease laments the disappearance of a landmark in US science history: the cooling tower at the Brookhaven National Laboratory
• Green strings attached – solving many of today’s environmental problems will require advanced technological solutions, says James McKenzie
• Eliminating the boundary between sky and space – reusable vehicles are vital to make access to space more affordable, but conventional rocket engines have their limits. Oliver Nailard describes how UK firm Reaction Engines hopes to revolutionize space access with a new class of propulsion system, the Synergetic Air Breathing Rocket Engine (SABRE)
• Stretching the limits – most materials get thinner when stretched, but “auxetics” do the opposite and get thicker. Helen Gleeson describes her group’s discovery of a material that is auxetic at the molecular level, which could be used in everything from body armour to laminated glass
• Optical microscopy – how small can it go? For centuries diffraction limited the resolution of optical microscopy. The past 50 years have, however, seen one limitation after another buckle under the ingenuity of a host of wide-ranging techniques, from lenses to tips, chips and doughnuts. Anna Demming reports
• Age of cosmic explosion – Tushna Commissariat reviews Look Up: Our Story with the Stars by Sarah Cruddas
• Intrepid interstellar adventurers – Ian Randall reviews Spacefarers: How Humans Will Settle the Moon, Mars, and Beyond by Christopher Wan
• Path of least resistance – graduate student Rosemary Teague and undergraduate Amber Yallop share their non-traditional degree pathways, some difficult choices they made along the way, and what a future in physics looks like for them now
• Is anybody there? – Chris Holt on the physics of ghosts


physicsworld--2020-10-06--Quantum treatment sheds fresh light on triboelectricity - Physics World

Shuffling around on a carpet to give someone an electric shock might seem like the oldest trick in the book , yet scientists know surprisingly little about why it happens .
“ I believed – like I think most physicists – that these phenomena were understood by the experts , ” says Robert Alicki , a mathematical and theoretical physicist at the University of Gdansk , Poland .
“ But it was not the case .
It was still an open question.
” Thanks to Alicki and his colleague Alejandro Jenkins of the Universidad de Costa Rica , the mystery @ @ @ @ @ @ @ by rubbing ” effect is known ) may be clearing up .
According to Alicki and Jenkins , a major barrier to understanding triboelectricity is that physicists tend to view the phenomenon in terms of electrostatic potentials , even though “ from a potential effect , you are never going to sustain a current that is going around a circuit , ” Jenkins says .
“ It ’ s like the problem of perpetual motion.
” Alicki and Jenkins formulated their alternative description by incorporating the concept of pumping into a new , @ @ @ @ @ @ @ processes .
“ Pumping can replenish a potential , but it is not describable by a potential , ” Jenkins explains .
“ It can do something that no potential can do , and that is to drive something around on a closed path.
” Using this pumping-based model , the pair successfully reproduced several experimentally observed characteristics of triboelectricity , such as its dependence on material surface and geometry and the speed of rubbing .
In particular , the model accurately predicts that the most electrically negative and electrically positive materials will @ @ @ @ @ @ @ – something that models based on electric potentials models can not explain .
The new model also predicts a maximum tribovoltage in terms of the sliding velocity of the two surfaces , which Alicki and Jenkins say could be tested using an experimental set-up with sufficient control over a constant sliding velocity .
While Alicki has been working on quantum thermodynamics for decades , Jenkins is a more recent recruit , having started out in high-energy theory .
As their paths converged – Jenkins has just begun a fellowship at Gdansk ’ s @ @ @ @ @ @ @ ICTQT ) – they discovered that they shared an interest in systems found in motors and engines that operate away from equilibrium , where energy is irreversibly converted from one form to another .
While such systems are the bread and butter of engineers , and Alicki and collaborators started working on them as far back as the late 1970s , Jenkins says that on the whole , they have attracted less attention from theorists than systems at equilibrium , fluctuating around equilibrium or relaxing to equilibrium .
At first , this common @ @ @ @ @ @ @ Jenkins to formulate a mathematical description of “ superradiance ” , or the enhanced effects of radiation associated with rotating objects .
Such effects were first described in 1971 by Yakov Zel ’ dovich , whose suggestion that superradiance ought to apply to a spinning gravitational mass led to follow-up work by Jacob Bekenstein and Stephen Hawking on the thermodynamics of black holes .
By describing rotating systems in terms of quantum fields , and treating the moving object as a heat bath , Alicki and Jenkins showed how work could be extracted @ @ @ @ @ @ @ laser ’ s operation .
But while their laser analogy offered a new perspective on such systems , the underlying process , while exotic , was already pretty well-understood .
It was only later that they realized that their formulation of a quantum field and two heat baths could lead to something “ qualitatively new ” : a description for the motion that drives an active current of fermionic electrons from one material to another in the humble triboelectric effect .
The pair built up their model by defining Hamiltonians with creation and @ @ @ @ @ @ @ surface of the moving material ( where the population inversion takes place ) and within the interior of the two rubbed materials ( which act as the heat baths ) .
They then defined the pumping of the system in terms of the rate of change of the populations of these electron states .
Although the Pauli exclusion principle forbids fermions such as electrons to exhibit superradiance , Alicki and Jenkins were able to show that with the bulk bodies of the two surfaces acting as two heat baths , a motion-induced population @ @ @ @ @ @ @ sustain a macroscopic current .
While magnetic and triboelectric effects have been known to scientists since antiquity – in the 6th century BCE , the pre-Socratic philosopher Thales of Miletus referred to them as “ evidence of a kind of soul ” – Jenkins notes that “ the interesting point is neither can be described classically ” .
The need for quantum mechanics to explain the behaviour of permanent magnets was established by Niels Bohr and Hendrika Johanna van Leeuwen over 100 years ago , and Jenkins says that his and Alicki ’ @ @ @ @ @ @ @ is true of triboelectricity .
Although pumping and work cycles exist in classical thermodynamics , the pair insist that only a quantum treatment can make sense of electrons ’ fermionic behaviour as they move between surfaces in the triboelectric effect .
In effect , Alicki says , “ Quantum mechanics is the soul of inanimate objects.
” Alicki and Jenkins are now considering ways to further investigate dry friction to explore how it relates to the triboelectric effect .
They are also interested in understanding details of energy transduction in active devices such @ @ @ @ @ @ @ generators , as well as active processes in various applications from astrophysics and cosmology , to fundamental physics .
Full details of the work are reported in Physical Review Letters

Ancient observations, modern explanation Robert Alicki (left) and Alejandro Jenkins (right). Alicki holds a bust of Thales, the pre-Socratic philosopher who described magnetic and “amber” effects as evidence of a material’s soul. (Credit: Maria Alicki)
Shuffling around on a carpet to give someone an electric shock might seem like the oldest trick in the book, yet scientists know surprisingly little about why it happens. “I believed – like I think most physicists – that these phenomena were understood by the experts,” says Robert Alicki, a mathematical and theoretical physicist at the University of Gdansk, Poland. “But it was not the case. It was still an open question.”
Thanks to Alicki and his colleague Alejandro Jenkins of the Universidad de Costa Rica, the mystery surrounding triboelectricity (as the “charging by rubbing” effect is known) may be clearing up. According to Alicki and Jenkins, a major barrier to understanding triboelectricity is that physicists tend to view the phenomenon in terms of electrostatic potentials, even though “from a potential effect, you are never going to sustain a current that is going around a circuit,” Jenkins says. “It’s like the problem of perpetual motion.”
Alicki and Jenkins formulated their alternative description by incorporating the concept of pumping into a new, quantum model of a system undergoing triboelectric processes. “Pumping can replenish a potential, but it is not describable by a potential,” Jenkins explains. “It can do something that no potential can do, and that is to drive something around on a closed path.”
Using this pumping-based model, the pair successfully reproduced several experimentally observed characteristics of triboelectricity, such as its dependence on material surface and geometry and the speed of rubbing. In particular, the model accurately predicts that the most electrically negative and electrically positive materials will have symmetrical maximum charge densities when rubbed – something that models based on electric potentials models cannot explain. The new model also predicts a maximum tribovoltage in terms of the sliding velocity of the two surfaces, which Alicki and Jenkins say could be tested using an experimental set-up with sufficient control over a constant sliding velocity.
From lasing bosons to fermions
While Alicki has been working on quantum thermodynamics for decades, Jenkins is a more recent recruit, having started out in high-energy theory. As their paths converged – Jenkins has just begun a fellowship at Gdansk’s Institute for Theory of Quantum Technologies (ICTQT) – they discovered that they shared an interest in systems found in motors and engines that operate away from equilibrium, where energy is irreversibly converted from one form to another. While such systems are the bread and butter of engineers, and Alicki and collaborators started working on them as far back as the late 1970s, Jenkins says that on the whole, they have attracted less attention from theorists than systems at equilibrium, fluctuating around equilibrium or relaxing to equilibrium.
At first, this common interest in out-of-equilibrium systems led Alicki and Jenkins to formulate a mathematical description of “superradiance”, or the enhanced effects of radiation associated with rotating objects. Such effects were first described in 1971 by Yakov Zel’dovich, whose suggestion that superradiance ought to apply to a spinning gravitational mass led to follow-up work by Jacob Bekenstein and Stephen Hawking on the thermodynamics of black holes.
By describing rotating systems in terms of quantum fields, and treating the moving object as a heat bath, Alicki and Jenkins showed how work could be extracted via stimulated emission, similar to a laser’s operation. But while their laser analogy offered a new perspective on such systems, the underlying process, while exotic, was already pretty well-understood. It was only later that they realized that their formulation of a quantum field and two heat baths could lead to something “qualitatively new”: a description for the motion that drives an active current of fermionic electrons from one material to another in the humble triboelectric effect.
“The soul of inanimate objects”
The pair built up their model by defining Hamiltonians with creation and annihilation operators for electron states on the surface of the moving material (where the population inversion takes place) and within the interior of the two rubbed materials (which act as the heat baths). They then defined the pumping of the system in terms of the rate of change of the populations of these electron states. Although the Pauli exclusion principle forbids fermions such as electrons to exhibit superradiance, Alicki and Jenkins were able to show that with the bulk bodies of the two surfaces acting as two heat baths, a motion-induced population inversion of fermions could nevertheless result and sustain a macroscopic current.
While magnetic and triboelectric effects have been known to scientists since antiquity – in the 6th century BCE, the pre-Socratic philosopher Thales of Miletus referred to them as “evidence of a kind of soul” – Jenkins notes that “the interesting point is neither can be described classically”. The need for quantum mechanics to explain the behaviour of permanent magnets was established by Niels Bohr and Hendrika Johanna van Leeuwen over 100 years ago, and Jenkins says that his and Alicki’s latest work shows that the same is true of triboelectricity. Although pumping and work cycles exist in classical thermodynamics, the pair insist that only a quantum treatment can make sense of electrons’ fermionic behaviour as they move between surfaces in the triboelectric effect. In effect, Alicki says, “Quantum mechanics is the soul of inanimate objects.”
Alicki and Jenkins are now considering ways to further investigate dry friction to explore how it relates to the triboelectric effect. They are also interested in understanding details of energy transduction in active devices such as batteries, solar cells and thermoelectric generators, as well as active processes in various applications from astrophysics and cosmology, to fundamental physics.
Full details of the work are reported in Physical Review Letters