physicsworld--2020-06-23--Explorer versus salesman - Physics World

I need to start this review by saying that I loved the premise of this collection of essays by the physicist-turned-computer scientist Stephen Wolfram , who is chief executive of the Wolfram Group .
Promising “ surprising and engaging intellectual adventures ” , the cover blurb of Adventures of a Computational Explorer teases “ science consulting for a Hollywood movie , solving problems of AI ethics , hunting for the source of an unusual polyhedron , communicating with extraterrestrials ” and even “ finding the fundamental theory of physics and exploring the digits of pi ” .
What fun !
@ @ @ @ @ @ @ film Arrival by exploring how alien spacecraft might work , to considering how humanity might best leave behind a message for other civilizations ( one option being the Wolfram computational language , of course ) , the opening chapters are perfectly pitched for the general reader .
They ’ re all written in Wolfram ’ s compelling and , at its best , charmingly avuncular style .
Some later chapters also deliver well on the advertised concept – covering topics such as computationally analysing the Facebook data of consenting Wolfram customers , and @ @ @ @ @ @ @ be made by combining four current buzzwords ( to form “ Quantum Neural Blockchain AI ” ) .
Unfortunately , though , a key flaw of the book is that it lacks cohesion – perhaps as a result of being a compendium of seemingly loosely edited pre-existing essays .
Repetition abounds , and I have no idea who the target audience for Adventures of a Computational Explorer is , with the popular accessibility of the initial chapters giving way to those that presume existing knowledge of specialist acronyms such as QCD ( quantum @ @ @ @ @ @ @ protocol ) and TCP ( transmission control protocol ) .
A quick intro chapter to some of Wolfram ’ s key themes ( computational irreducibility , cellular automata and the main Wolfram Group products ) would also have provided a welcome explainer – especially given that , for Wolfram , the latter are the solution to almost all issues .
If you must write a book that serves as stealth advertising for your software suites , you might as well explain what they each do , clearly , and in the first instance @ @ @ @ @ @ @ with a stronger editorial hand – but one can imagine why this wasn ’ t delivered by the publisher , Wolfram Media .
A more involved editor might also have reined in Wolfram ’ s predilection not only for promoting his products but also himself .
This tendency is exhibited to such an extent that I eventually found it thoroughly off-putting .
One might forgive the odd indulgence , but not multiple chapters devoted to , for example , his particular approaches to work and preferred methods of file organization .
At one @ @ @ @ @ @ @ the lens of technology and artefacts from his considerable personal archive , beginning with a glowing elementary school report from 1967 – making for rather nauseating reading .
For the reader not put off by this particular display of self-indulgence , the following chapter – “ Things I learned in kindergarten ” – goes further , relating tales of a six-year-old Wolfram , presumably still in knee-high socks , outsmarting adults and already realizing “ obvious ” things that his peers were simply incapable of .
This sentiment of superlativeness is Adventures of @ @ @ @ @ @ @ leitmotif .
Wolfram “ independently came up with ” data hashing functions at the age of 13 ( p321 ) ; became a “ card-carrying physicist ” as a mere teenager ; and gathered “ what is probably one of the world ’ s largest collections of personal data ” ( p351 ) .
Wolfram also claims that when it comes to conceptualizing networks to represent physical space , many other physicists “ haven ’ t quite reached the level of abstractness that [ he is ] at ” ( p29 ) , @ @ @ @ @ @ @ how fundamental physics works just “ aren ’ t yet mainstream ” ( p24 ) .
The Wolfram language , meanwhile , is said to provide “ a compressed representation…of the core content of our civilization ” ( p58 ) , while mobile-phone-jingle-generating Wolfram Tones has “ surpassed our species in musical output ” ( p159 ) .
While one has no doubt that many , if not all , of these assertions are accurate – Wolfram is clearly extraordinarily talented and accomplished – they need not all be expressed .
In other @ @ @ @ @ @ @ takes on a more personal tone .
The sixth chapter , originally written in 2016 , pauses to take a seemingly random and unprofessional swipe at noted theoretical physicist Richard Feynman who , according to Wolfram , “ came to a bunch of the meetings I had to discuss the design of the SMP [ Symbolic Manipulation Program ] , offering various ideas – which I had to admit I considered hacky ” , he writes .
A later chapter reveals that Feynman was an examiner during Wolfram ’ s thesis defence in @ @ @ @ @ @ @ what Wolfram ( euphemistically ? )
calls a “ rather spirited discussion ” .
One can ’ t help but wonder if there isn ’ t a little grudge there .
The rest of that chapter , meanwhile , is devoted to the task of demonstrating that Wolfram ’ s record of being the youngest person to graduate from the California University of Technology had not been superseded by a close contender .
This , really , is the crux of the problem with Adventures of a Computational Explorer .
There was a @ @ @ @ @ @ @ , but the meat of it has been completely drowned by the sauce of Wolfram ’ s unbridled and embarrassing self-promotion .
Give this one a miss .

Physics World. Members of the Institute of Physics can enjoy the full issue Taken from the June 2020 issue of. Members of the Institute of Physics can enjoy the full issue via the Physics World app
Ian Randall reviews Adventures of a Computational Explorer by Stephen Wolfram
Sense and superiority Stephen Wolfram in July 2008. (Courtesy: Stephen Wolfram’s PR team/Stephen Faust)
I need to start this review by saying that I loved the premise of this collection of essays by the physicist-turned-computer scientist Stephen Wolfram, who is chief executive of the Wolfram Group. Promising “surprising and engaging intellectual adventures”, the cover blurb of Adventures of a Computational Explorer teases “science consulting for a Hollywood movie, solving problems of AI ethics, hunting for the source of an unusual polyhedron, communicating with extraterrestrials” and even “finding the fundamental theory of physics and exploring the digits of pi”. What fun!
From supporting the production of the 2016 film Arrival by exploring how alien spacecraft might work, to considering how humanity might best leave behind a message for other civilizations (one option being the Wolfram computational language, of course), the opening chapters are perfectly pitched for the general reader. They’re all written in Wolfram’s compelling and, at its best, charmingly avuncular style. Some later chapters also deliver well on the advertised concept – covering topics such as computationally analysing the Facebook data of consenting Wolfram customers, and playfully imagining what kind of tech might be made by combining four current buzzwords (to form “Quantum Neural Blockchain AI”) .
Unfortunately, though, a key flaw of the book is that it lacks cohesion – perhaps as a result of being a compendium of seemingly loosely edited pre-existing essays. Repetition abounds, and I have no idea who the target audience for Adventures of a Computational Explorer is, with the popular accessibility of the initial chapters giving way to those that presume existing knowledge of specialist acronyms such as QCD (quantum chromodynamics), UDP (user datagram protocol) and TCP (transmission control protocol). A quick intro chapter to some of Wolfram’s key themes (computational irreducibility, cellular automata and the main Wolfram Group products) would also have provided a welcome explainer – especially given that, for Wolfram, the latter are the solution to almost all issues. If you must write a book that serves as stealth advertising for your software suites, you might as well explain what they each do, clearly, and in the first instance.
These issues might have been avoided with a stronger editorial hand – but one can imagine why this wasn’t delivered by the publisher, Wolfram Media. A more involved editor might also have reined in Wolfram’s predilection not only for promoting his products but also himself. This tendency is exhibited to such an extent that I eventually found it thoroughly off-putting. One might forgive the odd indulgence, but not multiple chapters devoted to, for example, his particular approaches to work and preferred methods of file organization.
At one point, Wolfram recapitulates his life through the lens of technology and artefacts from his considerable personal archive, beginning with a glowing elementary school report from 1967 – making for rather nauseating reading. For the reader not put off by this particular display of self-indulgence, the following chapter – “Things I learned in kindergarten” – goes further, relating tales of a six-year-old Wolfram, presumably still in knee-high socks, outsmarting adults and already realizing “obvious” things that his peers were simply incapable of.
This sentiment of superlativeness is Adventures of a Computational Explorer’s most unappealing leitmotif. Wolfram “independently came up with” data hashing functions at the age of 13 (p321); became a “card-carrying physicist” as a mere teenager; and gathered “what is probably one of the world’s largest collections of personal data” (p351). Wolfram also claims that when it comes to conceptualizing networks to represent physical space, many other physicists “haven’t quite reached the level of abstractness that [he is] at” (p29), and adds that his idiomatic ideas on how fundamental physics works just “aren’t yet mainstream” (p24).
If you must write a book that serves as stealth advertising for your software, you might as well explain what they each do clearly
The Wolfram language, meanwhile, is said to provide “a compressed representation…of the core content of our civilization” (p58), while mobile-phone-jingle-generating Wolfram Tones has “surpassed our species in musical output” (p159). While one has no doubt that many, if not all, of these assertions are accurate – Wolfram is clearly extraordinarily talented and accomplished – they need not all be expressed.
In other sections, Wolfram’s unabashed braggadocio takes on a more personal tone. The sixth chapter, originally written in 2016, pauses to take a seemingly random and unprofessional swipe at noted theoretical physicist Richard Feynman who, according to Wolfram, “came to a bunch of the meetings I had to discuss the design of the SMP [Symbolic Manipulation Program], offering various ideas – which I had to admit I considered hacky”, he writes. A later chapter reveals that Feynman was an examiner during Wolfram’s thesis defence in 1979, and the pair apparently had what Wolfram (euphemistically?) calls a “rather spirited discussion”. One can’t help but wonder if there isn’t a little grudge there. The rest of that chapter, meanwhile, is devoted to the task of demonstrating that Wolfram’s record of being the youngest person to graduate from the California University of Technology had not been superseded by a close contender.
This, really, is the crux of the problem with Adventures of a Computational Explorer. There was a great book to be cooked up here, but the meat of it has been completely drowned by the sauce of Wolfram’s unbridled and embarrassing self-promotion. Give this one a miss.
2019 Wolfram Media, 430pp £16hb


physicsworld--2020-06-22--Thermodynamic study of D-Wave processor could lead to better quantum calculations - Physics World

Why is important to study the thermodynamics of D-Wave quantum processors ?
Michele Campisi : Quantum technology has just entered the “ noisy intermediate-scale quantum ” ( NISQ ) era .
This is characterized by the ability to fabricate hardware with hundreds or even thousands ( in the case of D-Wave ) of qubits , but also the inability to control the qubits with the degree of accuracy and fidelity that is necessary to accomplish fault-tolerant quantum computations .
One of the main obstacles on the path to fault-tolerant quantum computations is noise – for example , the thermal noise @ @ @ @ @ @ @ qubits with the substrate on which they are patterned .
Understanding and quantifying the thermal phenomena that accompany the operation of a NISQ device is therefore crucial in the present stage of their development .
Lorenzo Buffoni : In a generic annealing process , you slowly drive a quantum device so as to change in time the Hamiltonian that describes its dynamics .
In forward annealing you start from some Hamiltonian , call it H , and end-up at some other Hamiltonian , say H , that does not commute with H .
@ @ @ @ @ @ @ evolution results in purely quantum phenomena , such as quantum tunnelling .
In reverse annealing you start with H ; then turn on an external control field to introduce an H term in the Hamilitonian ( thus causing quantum dynamics ) ; and then you go back to H .
Such reverse annealing protocols have been recently added to the set of operations that can be run on D-Wave because they can be used to perform local searches in the neighbourhood of a solution encoded in an eigenstate of H .
We chose @ @ @ @ @ @ @ the only choice for which the D-Wave interface gives you full freedom to prepare any eigenstate of your initial Hamiltonian ( H , in our case ) and that was a crucial requirement for our experiments .
How did you perform your experiments using D-Wave ’ s Leap service ?
LB : With D-Wave ’ s Leap service , virtually everyone can access one of the quantum annealers that D-Wave hosts locally via a cloud service .
The devices can be programmed using D-Wave ’ s own APIs , which are easy to @ @ @ @ @ @ @ APIs are well documented , and D-Wave provides a variety of examples and demos to get started .
Once you have programmed your own experiment , the script running on your computer automatically connects to the selected D-Wave quantum annealer , runs your programs on it , and gives the program output back to your computer , all in a matter of seconds .
For those interested in the implementation details of our experiments and/or willing to try out this service , we have open-sourced our code .
You conclude that the D-Wave @ @ @ @ @ @ @ ” , what do you mean by this ?
LB : In order to characterize the device from a thermodynamic point of view we have prepared it in a hot ( high-temperature ) state .
Then we have studied how much energy it exchanges in the form of work — exchanged with the external control electrical fields– and in the form of heat , which is exchanged with the cold chip substrate .
Thermodynamics allows only four possible ways for this to occur : • The device gives away energy both to the @ @ @ @ @ @ @ source : that is what standard heat engines do • The device receives energy both from the work source and from the cold substrate : in that case it would function as a refrigerator • Both the device and the cold substrate gain energy from the work source , so the device operates as a “ heater ” • The hot device loses energy to the cold substrate , while the work source spends energy to accelerate that natural energy flow , hence the expression “ thermal accelerator ” MC : It is @ @ @ @ @ @ @ quantify the actual heat and work involved during the operation of the D-Wave processor is a challenging , yet unsolved , problem .
However , by using recent results in non-equilibrium thermodynamics , we were able to put quantitative bounds on the heat and work , and that was sufficient to tell us that thermal acceleration was occurring .
Due to its generality , our method can be used in the thermodynamic study of other quantum devices as well .
Does you research have any implications for how D-Wave systems are used to @ @ @ @ @ @ @ suggests that in the specific case of D-Wave , thermal noise might indeed be beneficial .
In quantum annealing you want the processor to follow a path towards a specific target state .
It is very much the same as having to walk from A to B while holding a pendulum and you want to reach B without setting the pendulum into oscillation .
The D-wave strategy is to achieve that by walking very slowly .
Imagine however that you are now walking through a very viscous fluid , you spend now more @ @ @ @ @ @ @ it is easier to prevent the pendulum from oscillating , because oscillations are quickly dumped .
That is indeed what we have observed in our experiments .
We have thus learned that in designing optimal annealing paths , it might be useful to go through the more “ viscous ” regions , you pay an energetic cost to traverse them , but you might be able to do that faster , and more reliably .
Hopefully , our work will trigger further investigation in this new direction .
Buffoni and Campisi describe their @ @ @ @ @ @ @

Lorenzo Buffoni and Michele Campisi of Italy’s University of Florence have studied the thermodynamics of the D-Wave 2000Q quantum processor – which comprises 2000 interconnected superconducting circuits that each serve as a quantum bit (qubit). Here they tell Physics World what motivated them to study “reverse annealing” on the processor and how their results could lead to an improvement of how calculations are done on the D-Wave processor.
Thermal accelerator: a D-Wave quantum processor (Courtesy: D-Wave)
Why is important to study the thermodynamics of D-Wave quantum processors?
Michele Campisi: Quantum technology has just entered the “noisy intermediate-scale quantum” (NISQ) era. This is characterized by the ability to fabricate hardware with hundreds or even thousands (in the case of D-Wave) of qubits, but also the inability to control the qubits with the degree of accuracy and fidelity that is necessary to accomplish fault-tolerant quantum computations.
One of the main obstacles on the path to fault-tolerant quantum computations is noise – for example, the thermal noise that results from the interaction of the qubits with the substrate on which they are patterned. Understanding and quantifying the thermal phenomena that accompany the operation of a NISQ device is therefore crucial in the present stage of their development.
What is reverse annealing?
Lorenzo Buffoni: In a generic annealing process, you slowly drive a quantum device so as to change in time the Hamiltonian that describes its dynamics. In forward annealing you start from some Hamiltonian, call it H x , and end-up at some other Hamiltonian, say H z , that does not commute with H x . The presence of non-commuting terms during the evolution results in purely quantum phenomena, such as quantum tunnelling.
In reverse annealing you start with H z ; then turn on an external control field to introduce an H x term in the Hamilitonian (thus causing quantum dynamics); and then you go back to H z . Such reverse annealing protocols have been recently added to the set of operations that can be run on D-Wave because they can be used to perform local searches in the neighbourhood of a solution encoded in an eigenstate of H z . We chose to do reverse annealing because it is the only choice for which the D-Wave interface gives you full freedom to prepare any eigenstate of your initial Hamiltonian (H z , in our case) and that was a crucial requirement for our experiments.
How did you perform your experiments using D-Wave’s Leap service?
LB: With D-Wave’s Leap service, virtually everyone can access one of the quantum annealers that D-Wave hosts locally via a cloud service. The devices can be programmed using D-Wave’s own APIs, which are easy to embed in a Python script. The APIs are well documented, and D-Wave provides a variety of examples and demos to get started.
Once you have programmed your own experiment, the script running on your computer automatically connects to the selected D-Wave quantum annealer, runs your programs on it, and gives the program output back to your computer, all in a matter of seconds. For those interested in the implementation details of our experiments and/or willing to try out this service, we have open-sourced our code.
You conclude that the D-Wave system acts as a “thermal accelerator”, what do you mean by this?
LB: In order to characterize the device from a thermodynamic point of view we have prepared it in a hot (high-temperature) state. Then we have studied how much energy it exchanges in the form of work — exchanged with the external control electrical fields– and in the form of heat, which is exchanged with the cold chip substrate.
Thermodynamics allows only four possible ways for this to occur:
The device gives away energy both to the work source and to the cold thermal source: that is what standard heat engines do
The device receives energy both from the work source and from the cold substrate: in that case it would function as a refrigerator
Both the device and the cold substrate gain energy from the work source, so the device operates as a “heater”
The hot device loses energy to the cold substrate, while the work source spends energy to accelerate that natural energy flow, hence the expression “thermal accelerator”
MC: It is important to stress that how to precisely quantify the actual heat and work involved during the operation of the D-Wave processor is a challenging, yet unsolved, problem. However, by using recent results in non-equilibrium thermodynamics, we were able to put quantitative bounds on the heat and work, and that was sufficient to tell us that thermal acceleration was occurring. Due to its generality, our method can be used in the thermodynamic study of other quantum devices as well.
Does you research have any implications for how D-Wave systems are used to solve problems?
MC: Our work suggests that in the specific case of D-Wave, thermal noise might indeed be beneficial. In quantum annealing you want the processor to follow a path towards a specific target state. It is very much the same as having to walk from A to B while holding a pendulum and you want to reach B without setting the pendulum into oscillation. The D-wave strategy is to achieve that by walking very slowly.
Imagine however that you are now walking through a very viscous fluid, you spend now more energy to walk through it, but it is easier to prevent the pendulum from oscillating, because oscillations are quickly dumped. That is indeed what we have observed in our experiments. We have thus learned that in designing optimal annealing paths, it might be useful to go through the more “viscous” regions, you pay an energetic cost to traverse them, but you might be able to do that faster, and more reliably. Hopefully, our work will trigger further investigation in this new direction.
Buffoni and Campisi describe their research in Quantum Science and Technology.


physicsworld--2020-06-22--‘Magic-angle’ graphene doubles up - Physics World

Two years ago a team of researchers at the Massachusetts Institute of Technology ( MIT ) in the US kicked off the field of “ twistronics ” by discovering that two layers of graphene offset by a small angle could support an array of insulating and superconducting electron states .
This novel electronic platform , dubbed “ magic-angle ” graphene , heralded the beginning of a fundamentally new approach to device engineering .
Now the researchers , again led by Pablo Jarillo-Herrero , have extended the “ magic ” twist to another graphene system : twisted bilayer-bilayer graphene , made @ @ @ @ @ @ @ atom-thick carbon instead of monolayer ones .
The system , which can be tuned by applying an electric field , could be used to investigate the strong electron-electron interactions that lead to phenomena such as high-temperature superconductivity and correlated quantum phases .
Jarillo-Herrero and colleagues made the first magic-angle graphene by stacking two sheets of 2D carbon on top of each other to form a moiré lattice .
When they twisted these sheets so that the misalignment angle between them was 1.1° , they observed two unexpected effects .
The first was that @ @ @ @ @ @ @ electrically tune the system so that it became a correlated ( “ Mott ” ) insulator .
This transition to a Mott insulator occurs when electrons become localized in the moiré lattice – meaning that a material that would usually conduct electricity can no longer do so because of the strong repulsion between electrons .
The second effect they discovered was that , by further applying a small electric field ( and thus adding a few extra charge carriers ) to this insulator , they could tune the graphene superlattice so that it @ @ @ @ @ @ @ the insulating and the superconducting effects disappeared at slightly larger or smaller angle twists .
These results kick-started the field of twistronics , in which the weak coupling between different layers of 2D materials is used to manipulate their electronic properties simply by varying the angle between the layers .
Following this discovery , researchers have also reported on superconductivity and Mott insulation in other similar systems , including moiré superlattices of three graphene layers on 2D boron nitride and twisted four layers of graphene .
The twisted bilayer-bilayer graphene ( TBBG ) @ @ @ @ @ @ @ similar to twisted bilayer graphene , Jarillo-Herrero explains , except that it involves four layers of graphene instead of two .
In this system , the top and bottom layers remain aligned with respect to each other , and only the interface between the two middle layers is twisted .
At twist angles of around 1 to 1.5° , TBBG possesses “ flat ” electronic bands in its energy spectrum where the kinetic energy of electrons is strongly suppressed .
In a simple non-interacting description , this means that an electron is “ @ @ @ @ @ @ @ matter how much energy is pumped into it , it will not budge .
“ Correlated electron behaviour appears when we add interactions , however , and we indeed found correlated insulator states near these angles in our experiments , ” study lead author Yuan Cao says .
These states are highly sensitive to both the twist angle and the application of an electric field , he adds .
Flat bands also occur in twisted bilayer graphene and are thought to be involved in producing superconductivity in these systems , too .
The @ @ @ @ @ @ @ is that in TBBG , “ we can switch the correlated insulator states on and off by simply applying an electric field .
What is more , these correlated states appear to have a distinct spin-polarized ground state compared to twisted bilayer graphene – as we found in their peculiar response to magnetic fields.
” These findings , which are detailed in Nature , make TBBG a new and handy platform for studying strongly correlated physics in external electromagnetic fields , he says .
Once understood , this physics could be exploited to @ @ @ @ @ @ @ and correlated quantum materials .
“ Our work on TBBG demonstrates yet again how rich the behaviour of a seemingly simple superlattice made only of carbon can be , ” Jarillo-Herrero adds .
“ Extending the electrical field tunability to other configurations of twisted graphene systems and indeed other twisted material platforms will possibly allow us to uncover further exotic quantum phases of matter in the future .
”

Twisting again: magic-angle bilayer graphene. Courtesy: Pablo Jarillo-Herrero
Two years ago a team of researchers at the Massachusetts Institute of Technology (MIT) in the US kicked off the field of “twistronics” by discovering that two layers of graphene offset by a small angle could support an array of insulating and superconducting electron states. This novel electronic platform, dubbed “magic-angle” graphene, heralded the beginning of a fundamentally new approach to device engineering. Now the researchers, again led by Pablo Jarillo-Herrero, have extended the “magic” twist to another graphene system: twisted bilayer-bilayer graphene, made from misaligned stacks of bilayer sheets of atom-thick carbon instead of monolayer ones. The system, which can be tuned by applying an electric field, could be used to investigate the strong electron-electron interactions that lead to phenomena such as high-temperature superconductivity and correlated quantum phases.
Jarillo-Herrero and colleagues made the first magic-angle graphene by stacking two sheets of 2D carbon on top of each other to form a moiré lattice. When they twisted these sheets so that the misalignment angle between them was 1.1°, they observed two unexpected effects. The first was that by applying a voltage, they could electrically tune the system so that it became a correlated (“Mott”) insulator. This transition to a Mott insulator occurs when electrons become localized in the moiré lattice – meaning that a material that would usually conduct electricity can no longer do so because of the strong repulsion between electrons.
The second effect they discovered was that, by further applying a small electric field (and thus adding a few extra charge carriers) to this insulator, they could tune the graphene superlattice so that it became a superconductor at 1.7 K. Both the insulating and the superconducting effects disappeared at slightly larger or smaller angle twists.
The start of twistronics
These results kick-started the field of twistronics, in which the weak coupling between different layers of 2D materials is used to manipulate their electronic properties simply by varying the angle between the layers. Following this discovery, researchers have also reported on superconductivity and Mott insulation in other similar systems, including moiré superlattices of three graphene layers on 2D boron nitride and twisted four layers of graphene.
The twisted bilayer-bilayer graphene (TBBG) studied in the latest work is conceptually similar to twisted bilayer graphene, Jarillo-Herrero explains, except that it involves four layers of graphene instead of two. In this system, the top and bottom layers remain aligned with respect to each other, and only the interface between the two middle layers is twisted.
Flat electronic bands
At twist angles of around 1 to 1.5°, TBBG possesses “flat” electronic bands in its energy spectrum where the kinetic energy of electrons is strongly suppressed. In a simple non-interacting description, this means that an electron is “dispersionless” – that is, no matter how much energy is pumped into it, it will not budge. “Correlated electron behaviour appears when we add interactions, however, and we indeed found correlated insulator states near these angles in our experiments,” study lead author Yuan Cao says. These states are highly sensitive to both the twist angle and the application of an electric field, he adds.
Flat bands also occur in twisted bilayer graphene and are thought to be involved in producing superconductivity in these systems, too. The difference, Jarillo-Herrero tells Physics World, is that in TBBG, “we can switch the correlated insulator states on and off by simply applying an electric field. What is more, these correlated states appear to have a distinct spin-polarized ground state compared to twisted bilayer graphene – as we found in their peculiar response to magnetic fields.”
These findings, which are detailed in Nature, make TBBG a new and handy platform for studying strongly correlated physics in external electromagnetic fields, he says. Once understood, this physics could be exploited to engineer the next generation of high-temperature superconductor and correlated quantum materials.
“Our work on TBBG demonstrates yet again how rich the behaviour of a seemingly simple superlattice made only of carbon can be,” Jarillo-Herrero adds. “Extending the electrical field tunability to other configurations of twisted graphene systems and indeed other twisted material platforms will possibly allow us to uncover further exotic quantum phases of matter in the future.”


physicsworld--2020-06-20--Solar geoengineering could cause unwanted changes in climate, new modelling suggests - Physics World

Using aerosols to reflect sunlight and cool the planet will weaken storm tracks in the temperate latitudes in both hemispheres , an international team of scientists warn .
Their modelling suggests that while such solar geoengineering schemes could reduce the severity of winter storms , they would also stagnate weather systems in the summer .
This could lead to more intense heat waves , increases in air pollution , and changes in ocean circulation .
Solar geoengineering involves cooling the Earth by reflecting incoming sunlight and is seen by some scientists as a way of mitigating the effects of global @ @ @ @ @ @ @ reflective aerosols in the stratosphere – using aircraft , balloons or blimps – to block sunlight .
But the effects of solar geoengineering are unknown .
It would not work as simply as cooling the planet and therefore returning Earth ’ s climate to pre-industrial levels .
Climate under solar geoengineering would be different , as there would still be marked increases in atmospheric carbon dioxide levels .
Charles Gertler , a graduate student in the Department of Earth , Atmospheric and Planetary Sciences at the Massachusetts Institute of Technology , in the @ @ @ @ @ @ @ how injecting aerosols into the atmosphere would impact the pole‐to‐equator temperature gradient in both hemispheres , and the effect that could have on extratropical storm tracks .
These are regions in the mid and high latitudes with heightened incidences of storms known as extratropical cyclones , which play a significant role in determining the day-to-day weather conditions in many parts of the world .
“ About half the world ’ s population lives in the extratropical regions where storm tracks dominate weather , ” Gertler explains .
He adds , “ Storm tracks @ @ @ @ @ @ @ and storm tracks are interesting because they help us to understand weather extremes.
” The team used various climate models to explore the effects of solar geoengineering on storm tracks .
First , they analysed simulations from experiment G1 of the Geoengineering Model Intercomparison Project which provides solar radiation management schemes for researchers to use with climate models .
In the G1 scenario solar radiation is reduced to balance warming caused by a quadrupling of carbon dioxide concentrations , relative to pre-industrial levels .
This was run for 50 years and compared with @ @ @ @ @ @ @ pre-industrial level and one that simulated a quadrupling of carbon dioxide concentrations , to provide a baseline and a global warming scenario , respectively .
The team ran two other climate simulations .
The first , known as ‘ half G1 ’ , aims to model a scenario half-way between the G1 geoengineering simulation and a future where carbon dioxide concentrations quadruple .
In the other model aerosols are injected into the stratosphere at four different latitudes controlled by a feedback algorithm .
Their results , described in Geophysical Research Letters , show @ @ @ @ @ @ @ warming would weaken storm tracks in both the northern and southern hemispheres .
These effects are driven by changes in mean temperature and humidity at different latitudes that reduce the pole‐to‐equator temperature gradient in both hemispheres .
Essentially , reducing incoming solar radiation cools the equator while the poles continue to warm .
“ Our results show that solar geoengineering will not simply reverse climate change , ” Gertler explains .
“ Instead , it has the potential itself to induce novel changes in climate.
” In the Northern hemisphere storm tracks are @ @ @ @ @ @ @ .
The latest work suggests that this would occur at a similar magnitude as with solar geoengineering .
In the southern hemisphere , however , global warming is expected to increase the intensity of the storm tracks and shift them south .
With solar geoengineering these storm track would weaken , with some of the models indicating that there may also be a poleward shift in these systems .
“ A weakened storm track , in both hemispheres , would mean weaker winter storms but also lead to more stagnant weather , which @ @ @ @ @ @ @ says .
“ Across all seasons , this could affect ventilation of air pollution .
It also may contribute to a weakening of the hydrological cycle , with regional reductions in rainfall .
These are not good changes , compared to a baseline climate that we are used to.
” In the southern hemisphere changes in storm track intensity could impact wind‐driven ocean circulations and affect the stability of Antarctic ice sheets , the researchers warn .
“ This work highlights that solar geoengineering is not reversing climate change , but is substituting @ @ @ @ @ @ @ ” Gertler says .

Unwanted change: solar geoengineering could affect the nature of heat waves in some locations. (Courtesy: Shutterstock/kwest)
Using aerosols to reflect sunlight and cool the planet will weaken storm tracks in the temperate latitudes in both hemispheres, an international team of scientists warn. Their modelling suggests that while such solar geoengineering schemes could reduce the severity of winter storms, they would also stagnate weather systems in the summer. This could lead to more intense heat waves, increases in air pollution, and changes in ocean circulation.
Solar geoengineering involves cooling the Earth by reflecting incoming sunlight and is seen by some scientists as a way of mitigating the effects of global warming. One popular strategy involves placing reflective aerosols in the stratosphere – using aircraft, balloons or blimps – to block sunlight.
But the effects of solar geoengineering are unknown. It would not work as simply as cooling the planet and therefore returning Earth’s climate to pre-industrial levels. Climate under solar geoengineering would be different, as there would still be marked increases in atmospheric carbon dioxide levels.
Extratropical storm tracks
Charles Gertler, a graduate student in the Department of Earth, Atmospheric and Planetary Sciences at the Massachusetts Institute of Technology, in the US, and colleagues were interested in how injecting aerosols into the atmosphere would impact the pole‐to‐equator temperature gradient in both hemispheres, and the effect that could have on extratropical storm tracks. These are regions in the mid and high latitudes with heightened incidences of storms known as extratropical cyclones, which play a significant role in determining the day-to-day weather conditions in many parts of the world.
“About half the world’s population lives in the extratropical regions where storm tracks dominate weather,” Gertler explains. He adds, “Storm tracks feed off of meridional temperature gradients, and storm tracks are interesting because they help us to understand weather extremes.”
The team used various climate models to explore the effects of solar geoengineering on storm tracks. First, they analysed simulations from experiment G1 of the Geoengineering Model Intercomparison Project which provides solar radiation management schemes for researchers to use with climate models.
Balancing warming
In the G1 scenario solar radiation is reduced to balance warming caused by a quadrupling of carbon dioxide concentrations, relative to pre-industrial levels. This was run for 50 years and compared with a model that kept carbon dioxide at pre-industrial level and one that simulated a quadrupling of carbon dioxide concentrations, to provide a baseline and a global warming scenario, respectively.
The team ran two other climate simulations. The first, known as ‘half G1’, aims to model a scenario half-way between the G1 geoengineering simulation and a future where carbon dioxide concentrations quadruple. In the other model aerosols are injected into the stratosphere at four different latitudes controlled by a feedback algorithm.
Their results, described in Geophysical Research Letters, show that reflecting solar radiation to counteract global warming would weaken storm tracks in both the northern and southern hemispheres. These effects are driven by changes in mean temperature and humidity at different latitudes that reduce the pole‐to‐equator temperature gradient in both hemispheres. Essentially, reducing incoming solar radiation cools the equator while the poles continue to warm.
“Novel changes in climate”
“Our results show that solar geoengineering will not simply reverse climate change,” Gertler explains. “Instead, it has the potential itself to induce novel changes in climate.”
In the Northern hemisphere storm tracks are also predicted to weaken with climate change. The latest work suggests that this would occur at a similar magnitude as with solar geoengineering. In the southern hemisphere, however, global warming is expected to increase the intensity of the storm tracks and shift them south. With solar geoengineering these storm track would weaken, with some of the models indicating that there may also be a poleward shift in these systems.
“A weakened storm track, in both hemispheres, would mean weaker winter storms but also lead to more stagnant weather, which could affect heat waves,” Gertler says. “Across all seasons, this could affect ventilation of air pollution. It also may contribute to a weakening of the hydrological cycle, with regional reductions in rainfall. These are not good changes, compared to a baseline climate that we are used to.” In the southern hemisphere changes in storm track intensity could impact wind‐driven ocean circulations and affect the stability of Antarctic ice sheets, the researchers warn.
“This work highlights that solar geoengineering is not reversing climate change, but is substituting one unprecedented climate state for another,” Gertler says.


physicsworld--2020-06-20--Scanning tunnelling microscopy images intramolecular details - Physics World

Scanning tunnelling microscopy ( STM ) is routinely employed to identify individual molecules , but it can not usually resolve their internal structure .
An interdisciplinary team of researchers at the universities of Warwick and Cardiff in the UK has now shown that a variation of high-resolution STM can in fact deliver information about the positions of atoms and bonds within molecules .
The technique , which can also determine the types of intermolecular bonds present , could be used in a wide range of fields , including materials science , biochemistry , and pharmaceuticals development and testing .
Invented @ @ @ @ @ @ @ way of visualizing the nano-world all the way down to its elementary constituents – that is , individual molecules and atoms , explains team leader Giovanni Costantini of Warwick .
It works by exploiting the tiny current which , thanks to quantum tunnelling , flows between a very sharp metallic tip and the surface of a sample less than 1 nm away .
The intensity of this tunnelling is typically fairly uniform across the molecules in the sample , however , which means that STM can not usually resolve the internal structure of @ @ @ @ @ @ @ limitation for researchers trying to determine the precise chemical structure of an unknown molecule or ascertain the way molecules interact with one another .
The STM tip in Costantini and colleagues ’ new work is equipped with a single carbon monoxide molecule at its end .
This molecule is held at liquid helium temperatures of about 1 K , which makes the tip even sharper than usual and chemically much better defined .
“ We are able to bring the tip extremely close to the molecule being analysed , at a distance where @ @ @ @ @ @ @ repulsion ) between the electrons in the molecule and in the last atom of the tip becomes significant , ” explains Costantini .
“ Under these conditions , the current measured in STM depends on the exact location of the tip within the molecule .
The resulting images can thus show up intramolecular details , such as the position of the constituent atoms and the bonds between them.
” The Br and O atoms in 3,9-Br PXX can be held together either by hydrogen or halogen bonds when arranged into supramolecular arrays on @ @ @ @ @ @ @ from weak C-H-O interactions , while the halogen bonds come from so-called “ sigma-holes ” on the Br atoms .
Costantini and colleagues say their technique allows them to establish that halogen bonding is in fact the intermolecular interaction holding the 3,9-Br PXX molecules together .
Such a result would not be possible using standard STM since the lower resolution images it produces do not distinguish between these two types of bonds .
The researchers also determined that the samples analysed contained impurities .
These come from the chemical synthesis process and are @ @ @ @ @ @ @ they can not be detected using classical spectroscopic analytical techniques .
The HR-STM technique might thus also be used to identify contamination in pharmaceutical compounds with the aim of making them purer in the future , they say .
Once they established the position of the atoms and the type of intermolecular bonds between the 3,9-Br PXX molecules , Costantini and colleagues could then identify which functional groups of one molecule were interacting with those of another molecule .
They could also see how far apart the molecules were and how the supramolecular @ @ @ @ @ @ @ other .
The main findings , explains Costantini , are that the positive sigma-holes of the Br atoms of one molecule face straight onto the negative O atoms of an adjacent molecule , and that these two non-covalently bound atoms are separated by a distance smaller than the sum of each atom ’ s van der Waals radius ( which is a measure for the size of an atom that is not ionically or covalently bound ) .
“ These two observations perfectly match the definition of a halogen bond as given by @ @ @ @ @ @ @ Chemistry ( IUPAC ) , ” he tells Physics World .
“ The structural information we obtained from our high-resolution molecular imaging also allowed us to perform several ( density functional theory ) calculations ( in collaboration with Gabriele Sosso ’ s group at Warwick ) that revealed a number of electronic features recognized by IUPAC as further identifying traits of halogen bonding.
” While a very fundamental study , the researchers hope it will be valuable for future work on understanding ( bio ) molecular recognition and designing novel materials by exploiting @ @ @ @ @ @ @ bonding has recently been found to play an important role in the structure of biological macromolecules and in the folding of protein-ligand and DNA structures , says Costantini .
The team , who report their work in Nature Communications , now plan to extend their HR-STM technique to study other types of intermolecular interactions , such as pnictogen and chalcogen bonding , and to untangle the interplay between halogen and hydrogen bonding when assembling small molecules for biochemical and materials applications .
“ The long-term goal is to take what , at present @ @ @ @ @ @ @ , developed and used in the rather limited research areas of surface- and nano-science , and to transform it into a new and potentially paradigm-shifting analytical tool for the much wider fields of synthetic and biological chemistry , materials science and pharmaceuticals development , ” they say .
As an aside , Costantini adds that the three corresponding authors on the study – himself , Sosso , and Davide Bonifazi ( formerly at Cardiff , now at the University of Vienna in Austria ) – are all originally from Italy .
“ This @ @ @ @ @ @ @ brain-drain that Italy has experienced in the last 10-20 years and which , unfortunately , today is stronger than ever , ” he says .
James Lawrence , the paper ’ s first author and a former PhD student in his group , is now a post-doc at the Donostia International Physics Center in San Sebastián , Spain .

In the lab. Courtesy: University of Warwick
Scanning tunnelling microscopy (STM) is routinely employed to identify individual molecules, but it cannot usually resolve their internal structure. An interdisciplinary team of researchers at the universities of Warwick and Cardiff in the UK has now shown that a variation of high-resolution STM can in fact deliver information about the positions of atoms and bonds within molecules. The technique, which can also determine the types of intermolecular bonds present, could be used in a wide range of fields, including materials science, biochemistry, and pharmaceuticals development and testing.
Invented in 1981, STM is a powerful way of visualizing the nano-world all the way down to its elementary constituents – that is, individual molecules and atoms, explains team leader Giovanni Costantini of Warwick. It works by exploiting the tiny current which, thanks to quantum tunnelling, flows between a very sharp metallic tip and the surface of a sample less than 1 nm away. The intensity of this tunnelling is typically fairly uniform across the molecules in the sample, however, which means that STM cannot usually resolve the internal structure of individual molecules. This is a serious limitation for researchers trying to determine the precise chemical structure of an unknown molecule or ascertain the way molecules interact with one another.
Sharper and chemically more defined
The STM tip in Costantini and colleagues’ new work is equipped with a single carbon monoxide molecule at its end. This molecule is held at liquid helium temperatures of about 1 K, which makes the tip even sharper than usual and chemically much better defined. “We are able to bring the tip extremely close to the molecule being analysed, at a distance where a very strong repulsion (the Pauli repulsion) between the electrons in the molecule and in the last atom of the tip becomes significant,” explains Costantini. “Under these conditions, the current measured in STM depends on the exact location of the tip within the molecule. The resulting images can thus show up intramolecular details, such as the position of the constituent atoms and the bonds between them.”
The Br and O atoms in 3,9-Br 2 PXX can be held together either by hydrogen or halogen bonds when arranged into supramolecular arrays on a substrate. The H bonds come from weak C-H-O interactions, while the halogen bonds come from so-called “sigma-holes” on the Br atoms.
Halogen bonding is the intermolecular interaction
Costantini and colleagues say their technique allows them to establish that halogen bonding is in fact the intermolecular interaction holding the 3,9-Br 2 PXX molecules together. Such a result would not be possible using standard STM since the lower resolution images it produces do not distinguish between these two types of bonds.
The researchers also determined that the samples analysed contained impurities. These come from the chemical synthesis process and are often present in such small amounts that they cannot be detected using classical spectroscopic analytical techniques. The HR-STM technique might thus also be used to identify contamination in pharmaceutical compounds with the aim of making them purer in the future, they say.
Once they established the position of the atoms and the type of intermolecular bonds between the 3,9-Br 2 PXX molecules, Costantini and colleagues could then identify which functional groups of one molecule were interacting with those of another molecule. They could also see how far apart the molecules were and how the supramolecular assemblies were oriented with respect to each other. The main findings, explains Costantini, are that the positive sigma-holes of the Br atoms of one molecule face straight onto the negative O atoms of an adjacent molecule, and that these two non-covalently bound atoms are separated by a distance smaller than the sum of each atom’s van der Waals radius (which is a measure for the size of an atom that is not ionically or covalently bound).
“These two observations perfectly match the definition of a halogen bond as given by the International Union of Pure and Applied Chemistry (IUPAC),” he tells Physics World. “The structural information we obtained from our high-resolution molecular imaging also allowed us to perform several (density functional theory) calculations (in collaboration with Gabriele Sosso’s group at Warwick) that revealed a number of electronic features recognized by IUPAC as further identifying traits of halogen bonding.”
A very fundamental study
While a very fundamental study, the researchers hope it will be valuable for future work on understanding (bio)molecular recognition and designing novel materials by exploiting non-conventional intermolecular interactions. Indeed, halogen bonding has recently been found to play an important role in the structure of biological macromolecules and in the folding of protein-ligand and DNA structures, says Costantini.
The team, who report their work in Nature Communications, now plan to extend their HR-STM technique to study other types of intermolecular interactions, such as pnictogen and chalcogen bonding, and to untangle the interplay between halogen and hydrogen bonding when assembling small molecules for biochemical and materials applications.
“The long-term goal is to take what, at present, is still a niche experimental technique, developed and used in the rather limited research areas of surface- and nano-science, and to transform it into a new and potentially paradigm-shifting analytical tool for the much wider fields of synthetic and biological chemistry, materials science and pharmaceuticals development,” they say.
As an aside, Costantini adds that the three corresponding authors on the study – himself, Sosso, and Davide Bonifazi (formerly at Cardiff, now at the University of Vienna in Austria) – are all originally from Italy. “This is a direct testimony to the significant brain-drain that Italy has experienced in the last 10-20 years and which, unfortunately, today is stronger than ever,” he says. James Lawrence, the paper’s first author and a former PhD student in his group, is now a post-doc at the Donostia International Physics Center in San Sebastián, Spain.


physicsworld--2020-06-19--Toilets could be flush with coronavirus, masks struggle to contain repeated coughs - Physics World

Here is another very good reason to wash your hands after using the facilities – and you might also want to wear a mask .
Yun-Yun Li , Ji-Xiang Wang and Xi Chen of Southeast University in Nanjing , China have published a paper called “ Can a toilet promote virus transmission ?
From a fluid dynamics perspective ” .
The answer , at least according to their computer simulation , is an emphatic “ yes ” .
They found that as water pours into the toilet bowl it creates vortices that continue upward into the air carrying droplets to @ @ @ @ @ @ @ droplets are so small they float in the air for more than 1 min and could be inhaled or settle onto surfaces – say the researchers .
They point out that their discovery could be significant for controlling the spread of the SARS-CoV-2 , which is known to transmit via faecal matter .
One suggestion from the researchers is that public toilets could be designed so they will not flush unless the lid is closed .
In other virus news , Talib Dbouk and Dimitris Drikakis at the University of Nicosia in Cyprus @ @ @ @ @ @ @ happens when a mask wearer coughs repeatedly .
In “ On respiratory droplets and face masks ” they report that repeated coughs reduce a mask ’ s efficiency at preventing the spread of fluid – letting many more droplets through .

Shut the lid: viruses could be lurking in this spotless loo. (Courtesy: Evert Meijs/ CC BY-SA 3.0)
Here is another very good reason to wash your hands after using the facilities – and you might also want to wear a mask. Yun-Yun Li, Ji-Xiang Wang and Xi Chen of Southeast University in Nanjing, China have published a paper called “Can a toilet promote virus transmission? From a fluid dynamics perspective”. The answer, at least according to their computer simulation, is an emphatic “yes”.
They found that as water pours into the toilet bowl it creates vortices that continue upward into the air carrying droplets to a height of nearly 1 m. These droplets are so small they float in the air for more than 1 min and could be inhaled or settle onto surfaces – say the researchers.
They point out that their discovery could be significant for controlling the spread of the SARS-CoV-2, which is known to transmit via faecal matter. One suggestion from the researchers is that public toilets could be designed so they will not flush unless the lid is closed.
In other virus news, Talib Dbouk and Dimitris Drikakis at the University of Nicosia in Cyprus have created a computer model of what happens when a mask wearer coughs repeatedly. In “On respiratory droplets and face masks” they report that repeated coughs reduce a mask’s efficiency at preventing the spread of fluid – letting many more droplets through.


physicsworld--2020-06-19--XENON1T may have detected something very interesting, or maybe not - Physics World

Earlier this week we received a curious embargoed press release from the XENON collaboration about a preprint that they have since posted to the arXiv server .
The team has measured an excess of detection events in the XENON1T dark-matter detector , which ran for two years deep under a mountain at the Gran Sasso National Laboratory in Italy .
The team is very explicitly not claiming this to be the first-ever direct detection of dark matter , a mysterious substance that comprises most of mass in the universe .
Instead , they are suggesting that the excess could be @ @ @ @ @ @ @ hypothetical particles whose existence is not predicted by the Standard Model of particle physics .
Another suggestion made by the team is that the excess is caused by the unexpected detection of neutrinos .
This could mean that our current understanding of neutrinos is deficient – they could have larger magnetic moments than currently predicted by the Standard Model , for example – which would also be interesting .
A more mundane explanation is that the excess is related to the radioactive decay of an extremely tiny amount of tritium that managed to @ @ @ @ @ @ @ 2 ton of ultra-pure xenon .
But the physics is not why we thought the press release was curious .
One thing is that the preprint has not yet been peer-reviewed by external experts prior to publication – although I have no doubt that this will be done in due course and a paper will be published .
The second thing is that from a statistical point of view , the excess could very well be a fluctuation rather than a real thing .
Normally a statistical significance of 5σ or greater is @ @ @ @ @ @ @ physics , whereas values of 3.5σ or less are quoted for the axion , neutrino and tritium hypotheses .
As a result , we passed on rushing out a news story about this – so perhaps we missed the boat on all the excitement .
And who knows , maybe a successor to XENON1T will discover solar axions .

Inside the tank: the XENON1T detector being assembled
Earlier this week we received a curious embargoed press release from the XENON collaboration about a preprint that they have since posted to the arXiv server. The team has measured an excess of detection events in the XENON1T dark-matter detector, which ran for two years deep under a mountain at the Gran Sasso National Laboratory in Italy.
The team is very explicitly not claiming this to be the first-ever direct detection of dark matter, a mysterious substance that comprises most of mass in the universe. Instead, they are suggesting that the excess could be caused by axions from the Sun – hypothetical particles whose existence is not predicted by the Standard Model of particle physics.
Another suggestion made by the team is that the excess is caused by the unexpected detection of neutrinos. This could mean that our current understanding of neutrinos is deficient – they could have larger magnetic moments than currently predicted by the Standard Model, for example – which would also be interesting.
Tiny amount of tritium
A more mundane explanation is that the excess is related to the radioactive decay of an extremely tiny amount of tritium that managed to get into the detector, which comprises 2 ton of ultra-pure xenon.
But the physics is not why we thought the press release was curious. One thing is that the preprint has not yet been peer-reviewed by external experts prior to publication – although I have no doubt that this will be done in due course and a paper will be published. The second thing is that from a statistical point of view, the excess could very well be a fluctuation rather than a real thing. Normally a statistical significance of 5σ or greater is required to claim a discovery in particle physics, whereas values of 3.5σ or less are quoted for the axion, neutrino and tritium hypotheses.
As a result, we passed on rushing out a news story about this – so perhaps we missed the boat on all the excitement. And who knows, maybe a successor to XENON1T will discover solar axions.


physicsworld--2020-06-19--Artificial intelligence spots unusual feature at Earth’s core-mantle boundary - Physics World

An artificial intelligence algorithm originally developed for astrophysics has revealed a previously unknown feature on the core-mantle boundary deep inside the Earth .
The algorithm allowed researchers in the US to find patterns in seemingly unconnected seismic data from different sources and the team believes that the new technique could glean insights from other types of geophysical datasets in future .
The motion of tectonic plates continues to shape the surface of the Earth and this activity is monitored constantly by a worldwide network of seismometers .
Studying how seismic signals travel through the different layers of the Earth has @ @ @ @ @ @ @ structure of Earth ’ s interior .
In the early 20th century , for example , researchers inferred that the Earth has a liquid outer core because shear waves from an earthquake were not detected by seismometers on the opposite side of the globe – because a liquid can not shear .
As seismology has grown more sophisticated and more monitoring stations have been installed , researchers have discovered much more about Earth ’ s interior , such as physical stratification and plumes of rising hot material within the mantle and mysterious “ @ @ @ @ @ @ @ boundary , where waves travel much more slowly than expected .
“ They ’ re inferred from the data but we don ’ t really know what these things are , ” says seismologist Doyeon Kim of University of Maryland , College Park , who led the latest research .
Researchers normally make such deductions from patterns of seismological signals that clearly stand out to a human observer .
However , the ever-growing volume of seismic data from across the world may contain patterns that humans can not perceive .
Kim and colleagues @ @ @ @ @ @ @ University in nearby Baltimore to apply a computer algorithm called the Sequencer developed by astrophysicists .
Last year , the algorithm revealed a previously unknown relationship between the masses of supermassive black holes and the properties of their host galaxies .
In a paper published in Science , the team describes how the Sequencer systematically sifted through thousands of seismic signals of diffracted waves , measuring the value of a specific quantity called the Wasserstein metric .
Then it played a mathematical game of join the dots – finding the shortest path between @ @ @ @ @ @ @ was clearly one optimal path , this showed a trend in the data .
When the researchers focused on signals beneath the northern Pacific Ocean , two regions stood out as strong generators of diffracted , delayed waves called postcursors , which are produced when seismic waves interact with anomalous structures .
The first is beneath Hawaii .
This was known to host a seismic wave anomaly , but data from the Sequencer — as well as additional analysis — shored up the hypothesis that it may result from a mantle plume and @ @ @ @ @ @ @ The second notable anomaly is , they believe , a previously unknown “ mega ultralow-velocity zone ” beneath the remote Marquesas Islands in French Polynesia .
Scientists already know of some similar zones — beneath Iceland and Samoa , for example – that have been associated with areas of highly unusual geochemical compositions .
This has led to suggestions these features may harbour material predating the giant impact on Earth that is thought to have formed the Moon .
The new discovery beneath Marquesas , suggests Kim , could potentially test this hypothesis @ @ @ @ @ @ @ of a trend in many sciences towards the use of artificial intelligence to optimize search strategies and find patterns in data that elude humans .
“ Broadly speaking in seismology and geophysics in general , we use supervised machine learning to search for ‘ labelled ’ objects such as earthquake signals from seismic recordings , ” he explains , “ However , where it gets interesting is in unsupervised learning , where we don ’ t know what we ’ re looking for in our datasets .
That ’ s where this algorithm @ @ @ @ @ @ @ datasets as points in a high-dimensional space and looking for patterns and clusters.
” He says a forthcoming paper by the Johns Hopkins researchers describes how the Sequencer was used to sort samples of another type of earthquake wave called surface waves .
“ This is very innovative , and represents a direction we need to go in seismology , ” says earth scientist Edward Garnero of Arizona State University in the US .
“ Methods like this may help us to find things we may not even have been looking for – @ @ @ @ @ @ @ cautious , however , about the assumption that the delay in the postcursor signals came solely from the core-mantle boundary , wondering whether mantle heterogeneity elsewhere might have played a role .
Ultimately , he says : “ In seismic modelling , we are always up against the issue of knowing if our favoured solution model is [ both ] unique and the real earth .
”

Inside out: illustration showing the locations of earthquakes (orange stars); seismometers (blue triangles); and hotspots (yellow triangles). (Courtesy: Doyeon Kim)
An artificial intelligence algorithm originally developed for astrophysics has revealed a previously unknown feature on the core-mantle boundary deep inside the Earth. The algorithm allowed researchers in the US to find patterns in seemingly unconnected seismic data from different sources and the team believes that the new technique could glean insights from other types of geophysical datasets in future.
The motion of tectonic plates continues to shape the surface of the Earth and this activity is monitored constantly by a worldwide network of seismometers. Studying how seismic signals travel through the different layers of the Earth has informed much of our knowledge of the structure of Earth’s interior. In the early 20th century, for example, researchers inferred that the Earth has a liquid outer core because shear waves from an earthquake were not detected by seismometers on the opposite side of the globe – because a liquid cannot shear.
As seismology has grown more sophisticated and more monitoring stations have been installed, researchers have discovered much more about Earth’s interior, such as physical stratification and plumes of rising hot material within the mantle and mysterious “ultra-low velocity zones” on the core-mantle boundary, where waves travel much more slowly than expected. “They’re inferred from the data but we don’t really know what these things are,” says seismologist Doyeon Kim of University of Maryland, College Park, who led the latest research.
Ever-growing volume of data
Researchers normally make such deductions from patterns of seismological signals that clearly stand out to a human observer. However, the ever-growing volume of seismic data from across the world may contain patterns that humans cannot perceive. Kim and colleagues therefore worked with astrophysicists at Johns Hopkins University in nearby Baltimore to apply a computer algorithm called the Sequencer developed by astrophysicists. Last year, the algorithm revealed a previously unknown relationship between the masses of supermassive black holes and the properties of their host galaxies.
In a paper published in Science, the team describes how the Sequencer systematically sifted through thousands of seismic signals of diffracted waves, measuring the value of a specific quantity called the Wasserstein metric. Then it played a mathematical game of join the dots – finding the shortest path between all the data points. When there was clearly one optimal path, this showed a trend in the data.
When the researchers focused on signals beneath the northern Pacific Ocean, two regions stood out as strong generators of diffracted, delayed waves called postcursors, which are produced when seismic waves interact with anomalous structures. The first is beneath Hawaii. This was known to host a seismic wave anomaly, but data from the Sequencer — as well as additional analysis — shored up the hypothesis that it may result from a mantle plume and helped to localize it more precisely.
“Mega ultralow-velocity zone”
The second notable anomaly is, they believe, a previously unknown “mega ultralow-velocity zone” beneath the remote Marquesas Islands in French Polynesia. Scientists already know of some similar zones — beneath Iceland and Samoa, for example – that have been associated with areas of highly unusual geochemical compositions. This has led to suggestions these features may harbour material predating the giant impact on Earth that is thought to have formed the Moon. The new discovery beneath Marquesas, suggests Kim, could potentially test this hypothesis.
Kim explains the work is part of a trend in many sciences towards the use of artificial intelligence to optimize search strategies and find patterns in data that elude humans. “Broadly speaking in seismology and geophysics in general, we use supervised machine learning to search for ‘labelled’ objects such as earthquake signals from seismic recordings,” he explains, “However, where it gets interesting is in unsupervised learning, where we don’t know what we’re looking for in our datasets. That’s where this algorithm fits – you’re looking at datasets as points in a high-dimensional space and looking for patterns and clusters.” He says a forthcoming paper by the Johns Hopkins researchers describes how the Sequencer was used to sort samples of another type of earthquake wave called surface waves.
“This is very innovative, and represents a direction we need to go in seismology,” says earth scientist Edward Garnero of Arizona State University in the US. “Methods like this may help us to find things we may not even have been looking for – and apparently they did.” He is cautious, however, about the assumption that the delay in the postcursor signals came solely from the core-mantle boundary, wondering whether mantle heterogeneity elsewhere might have played a role. Ultimately, he says: “In seismic modelling, we are always up against the issue of knowing if our favoured solution model is [both] unique and the real earth.”


physicsworld--2020-06-19--Physicists propose how to entangle macroscopic objects using pulses of light - Physics World

Physicists at Imperial College London , UK , and Stockholm University , Sweden , have proposed a new way of creating entanglement between mechanical motion and an optical field , and also between two mechanical oscillators , using short pulses of light .
Here research students Jack Clarke and Paulo Sahium along with group director Michael Vanner from the Quantum Measurement Lab at Imperial explain the work .
The research is reported in full in New Journal of Physics , published by IOP Publishing – which also publishes Physics World .
What was the motivation for the research ?
Quantum @ @ @ @ @ @ @ aspects of physics and allows objects to be more strongly correlated than is allowed classically .
Albert Einstein called this perplexing behaviour “ spooky action at a distance ” and many objections to this radical idea were raised in the early days of quantum mechanics .
Fast forward 80 years , and quantum entanglement is a now a well-established phenomenon and is routinely generated between objects such as photons , atoms and molecules .
Making an entangled state of something bigger allows us to test quantum physics on a macroscopic scale and paves @ @ @ @ @ @ @ new quantum technologies , such as sensing and quantum networking .
In this work , we propose a new technique to create such quantum states by using quantum optomechanics .
In our scheme , light bounces off two tiny mechanical oscillators causing them to move , creating an entangled state in their motion .
What did you do in the work ?
It is a very exciting time in quantum optomechanics at present , as early signatures of quantum motion of mechanical oscillators are now being observed .
In this work , we @ @ @ @ @ @ @ approach to create entanglement between mechanical motion and an optical field , and also between two mechanical oscillators , using short pulses of light .
With this work , we have laid the foundation for future experiments in this area by showing how to both generate and , importantly , verify the entanglement .
To make this a more useful study , we also dived into the details and computed the effects of optical loss and mechanical quantum decoherence on the quantum states .
We are very encouraged by these results , as @ @ @ @ @ @ @ able to operate with weak optomechanical coupling , and being resilient to optical loss and mechanical decoherence .
What was the most Our research is the first theoretical proposal for preparing and verifying mechanical and optomechanical entanglement in the emerging field of pulsed optomechanics .
This highlights a route to observe quantum entanglement in a regime where it hasn ’ t been seen before .
More specifically , there are two main regimes in quantum optomechanics .
One is the “ resolved-sideband regime ” , where light circulates inside an optical cavity for @ @ @ @ @ @ @ the mechanical period .
The other is the “ unresolved-sideband regime ” , which allows for rapid pulsed interactions over a timescale much shorter than the mechanical period .
Optomechanical entanglement has not yet been observed in this latter regime and our work makes key steps in this direction .
One of the most important results from our work is that in the pulsed regime creating such entanglement looks experimentally accessible , and is robust to effects that often hinder its observation .
Why is this research significant ?
Entanglement can be exploited @ @ @ @ @ @ @ quantum networks and quantum-enhanced force sensors .
Studying it also allows us to address very fundamental questions , such as “ what are the limits of quantum theory ?
” To these ends , a key current goal of research is to create and observe entanglement on larger and larger mass scales .
Quantum optomechanics has significant potential to contribute to both areas , which helps to make it such an exciting field .
This research project makes a significant step in these directions , as it opens a rich new avenue for @ @ @ @ @ @ @ regime .
What do you plan to do next ?
In our research group – the Quantum Measurement Lab – we pursue a combination of experimental and theoretical quantum science to advance our understanding of the foundations of physics and to leverage this understanding to develop new quantum technologies .
We will build on our research in three key ways .
First , our results have sparked new theoretical questions on optomechanical entanglement creation and its verification , which we have begun investigating .
Second , it ’ s a very exciting time @ @ @ @ @ @ @ new lab in London has completed a refurbishment phase and we are eager to build experiments in these directions once the current coronavirus pandemic is over .
Third , we hope our research in pulsed optomechanics inspires other experimental groups around the world and that we will engage with our global research community to initiate new collaborative projects .

In a flash: researchers have proposed how to entangle macroscopic objects using short pulses of light. (Courtesy: Jack Clarke, Quantum Measurement Lab, Imperial College London)
Physicists at Imperial College London, UK, and Stockholm University, Sweden, have proposed a new way of creating entanglement between mechanical motion and an optical field, and also between two mechanical oscillators, using short pulses of light. Here research students Jack Clarke and Paulo Sahium along with group director Michael Vanner from the Quantum Measurement Lab at Imperial explain the work.
The research is reported in full in New Journal of Physics, published by IOP Publishing – which also publishes Physics World.
What was the motivation for the research?
Quantum entanglement is one of the most intriguing aspects of physics and allows objects to be more strongly correlated than is allowed classically. Albert Einstein called this perplexing behaviour “spooky action at a distance” and many objections to this radical idea were raised in the early days of quantum mechanics. Fast forward 80 years, and quantum entanglement is a now a well-established phenomenon and is routinely generated between objects such as photons, atoms and molecules.
Making an entangled state of something bigger allows us to test quantum physics on a macroscopic scale and paves the way for the development of powerful new quantum technologies, such as sensing and quantum networking. In this work, we propose a new technique to create such quantum states by using quantum optomechanics. In our scheme, light bounces off two tiny mechanical oscillators causing them to move, creating an entangled state in their motion.
What did you do in the work?
It is a very exciting time in quantum optomechanics at present, as early signatures of quantum motion of mechanical oscillators are now being observed. In this work, we theoretically proposed and analysed a powerful new approach to create entanglement between mechanical motion and an optical field, and also between two mechanical oscillators, using short pulses of light.
With this work, we have laid the foundation for future experiments in this area by showing how to both generate and, importantly, verify the entanglement. To make this a more useful study, we also dived into the details and computed the effects of optical loss and mechanical quantum decoherence on the quantum states. We are very encouraged by these results, as our schemes offer many advantages including being able to operate with weak optomechanical coupling, and being resilient to optical loss and mechanical decoherence.
What was the most interesting or important finding?
Our research is the first theoretical proposal for preparing and verifying mechanical and optomechanical entanglement in the emerging field of pulsed optomechanics. This highlights a route to observe quantum entanglement in a regime where it hasn’t been seen before.
More specifically, there are two main regimes in quantum optomechanics. One is the “resolved-sideband regime”, where light circulates inside an optical cavity for a timescale that is long compared to the mechanical period. The other is the “unresolved-sideband regime”, which allows for rapid pulsed interactions over a timescale much shorter than the mechanical period. Optomechanical entanglement has not yet been observed in this latter regime and our work makes key steps in this direction. One of the most important results from our work is that in the pulsed regime creating such entanglement looks experimentally accessible, and is robust to effects that often hinder its observation.
Why is this research significant?
Entanglement can be exploited to develop new quantum technologies such as quantum networks and quantum-enhanced force sensors. Studying it also allows us to address very fundamental questions, such as “what are the limits of quantum theory?” To these ends, a key current goal of research is to create and observe entanglement on larger and larger mass scales. Quantum optomechanics has significant potential to contribute to both areas, which helps to make it such an exciting field. This research project makes a significant step in these directions, as it opens a rich new avenue for studies of optomechanical entanglement in the pulsed regime.
What do you plan to do next?
In our research group – the Quantum Measurement Lab – we pursue a combination of experimental and theoretical quantum science to advance our understanding of the foundations of physics and to leverage this understanding to develop new quantum technologies.
We will build on our research in three key ways. First, our results have sparked new theoretical questions on optomechanical entanglement creation and its verification, which we have begun investigating. Second, it’s a very exciting time for our group at present as our new lab in London has completed a refurbishment phase and we are eager to build experiments in these directions once the current coronavirus pandemic is over. Third, we hope our research in pulsed optomechanics inspires other experimental groups around the world and that we will engage with our global research community to initiate new collaborative projects.
The full results are reported in New Journal of Physics.


physicsworld--2020-08-12--Agilent vacuum technology: trusted answers - Physics World

Bartly Carlson is a full-time trainer and applications engineer at Agilent Technologies .
In this video , Carlson introduces Agilent @ @ @ @ @ to dry vacuum technology – describing the advantages for customers in academia and industry .
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Explore the ways in which today’s world relies on AI, and ponder how this technology might shape the world of tomorrow


physicsworld--2020-08-12--Putting new physics on the syllabus - Physics World

On 4 July 2012 the CERN particle-physics lab near Geneva announced the discovery of the Higgs boson .
“ I think we have it…but we are only at the beginning , ” noted Rolf-Dieter Heuer , the then director-general of CERN , in front of a packed auditorium .
When I heard those words , I felt a sense of awe and even got a lump in my throat as I watched Peter Higgs wipe away a tear as his theoretical construct from 50 years ago became reality .
Then my smile slowly faded and I realized that my Thursday @ @ @ @ @ @ @ of questions about the new discovery .
As a geophysicist , my particle physics is entirely self-taught , so I knew that I had a challenge ahead of me .
I spent the rest of that July evening researching and preparing my explanations to the expected questions .
The next day I answered the students with confidence .
I used analogies that were accessible and not too simplistic .
I was careful not to obscure the fact that there are still many unknowns yet to discover and my students were genuinely engaged .
@ @ @ @ @ @ @ our exam ?
” they asked me .
I reassured them that it would not be this year , but next year ’ s students would probably need to know about it .
However , I was wrong .
Almost eight years later and I ’ m still wrong .
Each year , my students ask me why the Higgs boson is missing from the syllabus and when will it be added .
Today , the three major exam boards in the UK – AQA , Edexcel and OCR – are still yet @ @ @ @ @ @ @ A-level physics curriculum .
Particle physics in education appears to be stuck , which is frustrating because some of the most important recent work in physics has been in this field .
Unfortunately , very little of it is making its way into A-level education .
I have worked for a small exam board and gained some insight into the process of writing a new syllabus .
This board provided qualifications to a handful of colleges around the UK and I consulted on a rewrite for the curriculum and managed to insist that @ @ @ @ @ @ @ at least acknowledged .
I also amended the definition of the neutrino to include the fact that it had mass – a feat that was acknowledged by the 2015 Nobel Prize for Physics .
These were small victories , but ones that could not grow beyond the reach of that small sphere of influence .
While I have no experience of larger exam boards or the processes of scrutiny and consultation that go on behind closed doors , I find myself questioning the efficacy of those panels .
When reading a typical syllabus @ @ @ @ @ @ @ few pages tend to include a “ why choose us ?
” section .
It states that the exam board has conducted extensive work with a range of educational providers and employers to ensure that the content is inspiring and up-to-date , but I have never seen any mention of the involvement of professional physicists , researchers or industry professionals .
They don ’ t appear to consult with anyone who has been actively working to expand knowledge and understanding in our field .
Science communicator Henry Reich , who created the minutephysics @ @ @ @ @ @ @ challenging science , penned an open letter in 2012 to the then US president Barack Obama highlighting this very issue .
As Reich pointed out , the omission of discoveries after the mid-1800s means that US high-school physics completely overlooks much of the science that contributed to many of the technologies that the US should be proud of .
We ’ re not quite in such a situation in the UK , but it is becoming increasingly so .
Students in the UK are now finding that the Nobel Prize for Physics is @ @ @ @ @ @ @ everyday lives , when in fact , with the acceleration of technology , the opposite should be true .
Whose responsibility is it then to make sure that key discoveries are integrated into our education system ?
I would argue that in an ideal world , the onus should be on the exam boards to reach out .
But failing this , the responsibility falls to physicists to lobby exam boards to help them understand that the gap is widening between what we now know and what we are teaching our young people @ @ @ @ @ @ @ years old when the Higgs boson was discovered .
When they come across it during a reading assignment , it is often a new concept to them .
But because it is not on the exam they are not motivated to study it in any depth .
Year on year , I notice that the number of students asking about the Higgs boson is decreasing so much that now , most new students haven ’ t heard of it .
That class from 2012 who asked me all those questions about the Higgs @ @ @ @ @ @ @ 25 .
The news may well have inspired them to pursue a career in physics – they could even be working at CERN .
But the classes I taught in subsequent years have been increasingly isolated from new discoveries from particle physics and beyond .
My current students find it harder to see modern physics as the exciting and fast-moving topic that it is .
Surely that must change .

Physics World. Members of the Institute of Physics can enjoy the full issue Taken from the August 2020 issue of. Members of the Institute of Physics can enjoy the full issue via the Physics World app
Niki Bell calls on physicists to insist that exam boards integrate modern discoveries into the education system
Overcome Part of the story of the discovery of the Higgs boson was Peter Higgs’ emotional reaction to the news. (Courtesy: CERN)
On 4 July 2012 the CERN particle-physics lab near Geneva announced the discovery of the Higgs boson. “I think we have it…but we are only at the beginning,” noted Rolf-Dieter Heuer, the then director-general of CERN, in front of a packed auditorium. When I heard those words, I felt a sense of awe and even got a lump in my throat as I watched Peter Higgs wipe away a tear as his theoretical construct from 50 years ago became reality. Then my smile slowly faded and I realized that my Thursday morning A-level physics students would be full of questions about the new discovery. As a geophysicist, my particle physics is entirely self-taught, so I knew that I had a challenge ahead of me. I spent the rest of that July evening researching and preparing my explanations to the expected questions.
The next day I answered the students with confidence. I used analogies that were accessible and not too simplistic. I was careful not to obscure the fact that there are still many unknowns yet to discover and my students were genuinely engaged. “Will the Higgs boson be on our exam?” they asked me. I reassured them that it would not be this year, but next year’s students would probably need to know about it. However, I was wrong.
Almost eight years later and I’m still wrong. Each year, my students ask me why the Higgs boson is missing from the syllabus and when will it be added. Today, the three major exam boards in the UK – AQA, Edexcel and OCR – are still yet to include the Higgs boson in their A-level physics curriculum. Particle physics in education appears to be stuck, which is frustrating because some of the most important recent work in physics has been in this field. Unfortunately, very little of it is making its way into A-level education.
Stuck in a rut
I have worked for a small exam board and gained some insight into the process of writing a new syllabus. This board provided qualifications to a handful of colleges around the UK and I consulted on a rewrite for the curriculum and managed to insist that the existence of the Higgs boson was at least acknowledged. I also amended the definition of the neutrino to include the fact that it had mass – a feat that was acknowledged by the 2015 Nobel Prize for Physics. These were small victories, but ones that could not grow beyond the reach of that small sphere of influence.
While I have no experience of larger exam boards or the processes of scrutiny and consultation that go on behind closed doors, I find myself questioning the efficacy of those panels. When reading a typical syllabus for an exam board, the first few pages tend to include a “why choose us?” section. It states that the exam board has conducted extensive work with a range of educational providers and employers to ensure that the content is inspiring and up-to-date, but I have never seen any mention of the involvement of professional physicists, researchers or industry professionals. They don’t appear to consult with anyone who has been actively working to expand knowledge and understanding in our field.
Science communicator Henry Reich, who created the minutephysics YouTube channel that is dedicated to communicating challenging science, penned an open letter in 2012 to the then US president Barack Obama highlighting this very issue. As Reich pointed out, the omission of discoveries after the mid-1800s means that US high-school physics completely overlooks much of the science that contributed to many of the technologies that the US should be proud of. We’re not quite in such a situation in the UK, but it is becoming increasingly so. Students in the UK are now finding that the Nobel Prize for Physics is seemingly less and less relevant to their everyday lives, when in fact, with the acceleration of technology, the opposite should be true.
Whose responsibility is it then to make sure that key discoveries are integrated into our education system? I would argue that in an ideal world, the onus should be on the exam boards to reach out. But failing this, the responsibility falls to physicists to lobby exam boards to help them understand that the gap is widening between what we now know and what we are teaching our young people.
My current students were only eight years old when the Higgs boson was discovered. When they come across it during a reading assignment, it is often a new concept to them. But because it is not on the exam they are not motivated to study it in any depth. Year on year, I notice that the number of students asking about the Higgs boson is decreasing so much that now, most new students haven’t heard of it.
That class from 2012 who asked me all those questions about the Higgs boson are now aged between 24 and 25. The news may well have inspired them to pursue a career in physics – they could even be working at CERN. But the classes I taught in subsequent years have been increasingly isolated from new discoveries from particle physics and beyond. My current students find it harder to see modern physics as the exciting and fast-moving topic that it is. Surely that must change.