Category Archives: Uncategorized

What is physics? Challenges and opportunities when working at the interface with other disciplines.

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Post by Stefanie Reichert, Nature Physics

This year’s Berlin Science Week kicked off with a diverse programme. Among many events, visitors could discuss the connection between art and astronomy or learn how new technologies can be inspired by nature, or participate in a panel discussion at the Springer Nature office. The panellists set out to find an answer on how we define physics today, and to map out the boundaries with other related areas such as chemistry or biology.

Meet the panellists in our interviews from the run-up to the event: Abigail Klopper, Alba Diz-Muñoz, Cosima Schuster, Magdalena Skipper Beatriz Roldán Cuenya.

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Heuristics for better figures

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Post by Jesse L. Silverberg

Here’s the tldr: (1) Images = Information, (2) Colour communicates meaning, (3) Understand the limits of visual communication, (4) Move through colour space deliberately to reduce complexity, (5) Combine #3 and #4 to pick your colours wisely.

Long before I thought about studying physics, I saw myself on the path to becoming a graphic designer.  I enrolled in a graphic design program at a nearby college, had a well-stocked supply of brushes, pencils, and Bristol board, and even generated a portfolio of nearly 100 compositions before taking my first course.  I ultimately left design school when I recognized the differences between “art for the sake of art” vs “art for the sake of selling a product,” but that’s a story for another day.  In my year studying graphic design, I practiced and learned a set of skills that became extremely useful during my PhD.  What I eventually came to discover was that when I was designing scientific figures, I felt confident that I was making rational design choices, such as visually distinct colours to represent categorical variables and thought-out colour gradients to represent continuous quantities.  This blog post is about those design skills and is intended for my fellow researchers who never had the opportunity to learn the language of design.  My hope is that I can serve as a useful translator to convey some of the practical ideas that designers routinely employ with respect to visual communication, and explain how they can be used in service of articulating a clearer scientific message. Continue reading →

How advances in active noise cancellation unlocked a new form of waves

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Post by Romain Fleury, commissioned by David Abergel.

The original paper in Nature Physics can be read here.

{credit}Credit: Jamani Caillet, EPFL{/credit}

Imagine you are playing the popular Nintendo game Mario Kart, and as you try to win the race one of the other players suddenly drives into the worst possible item box you can imagine: it covers the road in front of you with a very, very large number of banana peels, making it extremely unlikely for you to avoid these obstacles. If waves could have feelings, this is probably what they would think when a scientist tries to transmit them through a strongly localized disordered medium.

Yet, imagine now that you have the possibility to install some sort of magic boosters, or conveyor belts, that auto-pilot your kart seamlessly through these obstacles, while maintaining your precious velocity. This is certainly not possible in the game, but for our team of physicists and engineers, it made perfect sense to try this for waves in disordered media.

In our recent Nature Physics article, we have used acoustic boosters, or relays, to guide sound through a very nasty series of obstacles, and turned an Anderson-localized opaque medium into a perfectly transparent one by doping it with gain and loss. Interestingly, these acoustic boosters were made possible by recent advances in active noise control devices, similar to the ones you may use in your noise cancellation headphones during your next flight. Here is the story of how this idea came to life. Continue reading →

Frequency scanning optoelectronic oscillator

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Post by Ming Li, commissioned by Heather Partner

The original paper in Nature Communications can be read here.

Radar and microwave communication systems have been invented many decades ago, but are still a growing area of research. For example, it is important for modern communication systems to be able to create microwave signals with fast-varying frequencies, called chirps. Optoelectronic oscillators are one way to produce ultra-low-noise microwave signals, but using them to produce a fast-varying signal with high quality is difficult, because a cavity-like component is used to reduce noise within these oscillators, and when the frequency is changed it takes time for a new low-noise frequency signal to build up in the cavity. In work published last month, we showed it is possible to have many frequencies oscillating in the system at once, so that the frequency can be changed rapidly without waiting for this build-up time. These simultaneous oscillations, all with locked phases, are made possible in a scheme known as Fourier-domain mode locking, which was previously applied to optical signals in lasers, but in this work is applied to microwaves using an optoelectronic oscillator .

An optoelectronic oscillator is like a laser, except that it has an optoelectronic cavity rather than a pure optical cavity. Although frequency-tunable optoelectronic oscillators have been widely studied, it is still a challenge to achieve continuous frequency scanning. Following the demonstration of frequency scanning lasers based on the Fourier domain mode locking technique in recent years, we wondered if it would be appropriate to extend this mode-locking principle to an optoelectronic oscillator.

In order to apply this technique to an optoelectronic oscillator, we needed a filter that could scan the selected frequency very rapidly — faster than what is made possible by most electrical schemes — so we decided to employ a microwave photonics solution that could perform faster tuning than electrical solutions.

One of the research interests of our group is semiconductor lasers. It is known that the lasing frequency of certain kinds of semiconductor lasers can be tuned by changing the driving current in a fast way. Fortunately, the passband of a microwave photonics filter based on phase-modulation to intensity-modulation conversion is related to the lasing frequency of the signal laser. Thus we achieved a fast frequency scanning microwave photonics filter by sweeping the frequency of the signal laser. Continuous frequency scanning microwave waveforms with very large time-bandwidth product are generated based on a Fourier domain mode locked optoelectronic oscillator. We run simulations that show that a Fourier domain mode locked optoelectronic oscillator oscillates in the same way as a conventional single-mode optoelectronic oscillator that uses the same optical and electronic components, except that the energy is shared by the many oscillation modes.

The employment of a Fourier domain mode locking technique in an optoelectronic oscillator provides an effective solution to generate frequency scanning microwave signals with large time-bandwidth product, which can find applications in radar and communication systems.

Ming Li

Reference: Hao T. et al, Breaking the limitation of mode building time in an optoelectronic oscillator. Nat. Commun. 9, 1839 (2018)

Built on instability 

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Post by Daniel Rayneau-Kirkhope and Marcelo Azevedo Dias

Built-in motion

From hierarchical architectures to complex composites, nature’s inventive use of geometry yields remarkable functionality from some rather unremarkable construction materials. This same control of geometry alongside a mastery of mechanics is used to transform elastic ‘failure’ into a crucial ingredient in the inner working of plants and organisms. Nature employs elastic instability so that large-scale motions can be triggered by the smallest and most specific stimuli. The Venus flytrap is perhaps the best-known example of this design philosophy — swelling induces an elastic instability that allows its leaves to snap between two stable configurations [1]. Using this snap-through behaviour, the plant moves quickly to capture its prey, allowing for the slow process of digestion to begin. Bacteria exhibit another beautiful example of this design paradigm, whereby their flagella, which are used to create thrust, buckle into a secondary configuration allowing the bacteria to control direction [2].

It is only recently that designers have started to use loss of structural stability in a similar manner. From merely being a mode of failure, buckling has become an increasingly well-trodden route to introducing novel functionality in the design of man-made structures and materials on many different length scales. This transition in perspective has been encapsulated as a move from ‘buckliphobia’ to ‘buckliphilia’ [3].

A powerful example of this paradigm is the use of buckling to turn simple geometries into mechanical machines: work in Physical Review Letters recently demonstrated that the buckling-unbuckling transitions in a hollow spherical shell can be used to create thrust in spherical swimmers [5]. It is well known that a spherical shell will buckle into a new geometry when the internal and external pressures are sufficiently different; as this deformation is elastic, the structure can return to its initial configuration when the pressure differential is removed. It was found that the asymmetry of geometries in the process of buckling and unbuckling allows for a net thrust to be created by cycling through these geometries while the structure is immersed in liquid. Continue reading →

Plato, superheroes and a visit to the abattoir

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Post by Malte Gather, commissioned by Nina Meinzer

The original paper in Nature Communications can be read here.

2010, Boston. The 50th anniversary of the laser. A device that was originally famously proclaimed as “a solution in search of a problem” and that became the solution to so many crucial problems of modern society and science. What better way to pay tribute to the laser than to bring it quite literally to life? With this in mind, my former supervisor Andy Yun and I got to work on turning living cells into tiny lasers, using a green fluorescent protein produced by the cells themselves as optical gain medium. When our paper came out, it inspired many people in … well … unexpected ways: “Sharks with frickin’ lasers attached to their heads”, “bacterial infection that shoots lasers in your body”, “superheroes shooting laser beams from their eyes”. The first two seemed rather undesirable, let alone the red-tape involved in any study aimed at their realization. But superheroes with laser eyes? Back in ancient Greece, Plato even believed vision itself was mediated by “eye beams” that scan our environment. So could laser beams emitted from the eye have a more peaceful application than what is suggested in the comic books of modern times?

laser on a contact lens on a cows eye1

Fast forward to 2017, St Andrews, Scotland. Working with Professors Ifor Samuel and Graham Turnbull, our jointly supervised PhD student Markus Karl develops an ultra-thin organic semiconductor laser. He strips all non-essential components and ends up with a 200 nm-thick membrane that contains only gain medium and resonator; the pump is supplied externally by optical excitation. To fabricate these devices, Markus uses a carrier substrate and a sacrificial intermediate layer. In the final step of the fabrication, the membrane floats off the substrate and rises to the surface of a water bath. What now? Another solution in search of a problem?

We soon find that we can pick up the membranes with another substrate, or fish for them with a little net. Then we find that our membranes work like stickers, stickers that can turn any object into a laser. Ifor suggests to put them on banknotes as a new security feature. A membrane laser on every banknote in the United Kingdom would probably make our membrane lasers the world’s most numerous type of laser.

But what about Plato and the superheroes? Our lasers are not only among the world’s thinnest, they also have very low lasing thresholds. But how low? Say, compared to laser safety standards? It takes a bit of courage but eventually my student and I go to see the department laser safety officer to ask how their intensity – and more importantly the intensity of the optical pump – compare to permissible levels for intentional ocular exposure. In other words, could we use our membranes to shoot laser beams from one’s eyes without blinding ourselves? We check, twice, three times, four times, but the answers seems to be that it should be safe, with about a ten-fold margin before reaching maximum permissible exposure levels.

We refrained from testing our lasers on the human eye – at least for now. Instead, the last part of our study involved a trip to an abattoir near Edinburgh to buy some cow’s eyes. (Ophthalmology research often uses them as model for the human eye.) A few hours later a cow’s eyeball in a Petri dish shoots a green laser beam across our optics lab. In the future, we hope to use such lasers as an authentication and access control feature, complementing a biometric iris scan. For now, we are left with the slightly weird image of a zombie supercow shooting laser beams from its large blank eyes…

Malte Gather

Reference: Nature Commun. 9, 1525 (2018)  doi:10.1038/s41467-018-03874-w

X-rays : a tale of bones, molecules and mummies

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Post by Giulia Pacchioni

x-raysX-rays are the portion of the electromagnetic spectrum that falls between gamma rays and the ultraviolet (UV) — their wavelength is of the order 0.01−10 nanometres. What’s fascinating about them is their extremely wide range of applications, going from astronomy to art.

The history of X-rays goes back a long way: they were accidentally discovered by Wilhelm Röntgen in 1895. As it wasn’t clear what the nature of the new radiation was, Röntgen just labelled it ‘X’. The name was supposed to be temporary… but it stuck. As X-rays penetrate soft tissues but not bones, the potential for medical imaging was immediately clear, so much that X-rays were already in use during World War I. Röntgen received the Nobel Prize in Physics for this discovery − and not just a Nobel Prize, but the very first one − in 1901.

An interesting fact is that in the early days there was no suspicion that the new radiation might be harmful, and, for a while, a proper X-rays mania arose, with products advertised as ‘X-rays headache tablets’ and ‘X-rays stove polish’ (and it’s still a mystery what X-rays actually had to do with them). Until the 1950s, X-rays machines could be found in shoe stores, with the purpose of ensuring a perfect fit.

As it soon became clear, X-rays have enormous potential beyond medical imaging as means to shed light on the structure of matter: for example, X-ray crystallography unlocked the structure of DNA in 1953, which led to a Nobel Prize in 1962 (yes, another one. 15 Nobel prizes were awarded for research related to X-rays over the years). The brightest X-rays are found in synchrotron facilities, and the fun fact here is that originally X-rays were an unwanted by-product of particle accelerators developed for high-energy physics (particles moving along a curved trajectory emit radiation, and when their speed is close to that of light this radiation comes in the form of X-rays). Starting from the 1980s synchrotrons entirely dedicated to X-rays came on-line, starting a very productive era of discoveries in materials science, chemistry, biology and drug discovery. Nowadays the first X-ray free electron lasers, which offer ultrafast and very bright X-rays, make it possible to film chemical reactions and determine the structure of single biomolecules.

But the range of X-ray applications does not end here. They are used to investigate the Universe, studying black holes and dark matter, to unveil underpaintings and changes in works of art, revealing what went through an artist’s mind while working on a masterpiece. X-rays allowed us to study Egyptian mummies without unwrapping or damaging them (examples here and here), to read ancient scrolls without unrolling them (here and here), to find out that a wooden statue contained an ancient Chinese mummy… and even to see inside the remains of dinosaurs. And not to mention applications in daily life, such as in airport security.

We went a long way from the very first X-ray image — the hand of Röntgen’s wife — and in directions he would never have imagined.

Interactions: Ron Milo and the BioNumbers database

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“BPAE cells” by Joseph Elsbernd is licensed under CC BY 2.0

What is the surface area of a mouse intestinal tract? What is the persistence length of DNA? What is the diameter of a typical human red blood cell?

These are the sorts of questions that arise when building physics models of biological systems, and finding answers can often involve extensive digging through the literature. One resource, that hopes to “facilitate quantitative analysis and reasoning” in biology, is the BioNumbers database, a website that catalogues numerical values of biological quantities.  The database can be browsed by category or searched by keyword, and provides a citation of the original source of every number. It’s been going since 2007 and now covers categories from algae to zinc.

(From BioNumbers: mouse intestinal tracts have a surface area of 1.41 m2; DNA has a persistence length of around 50 nm; human red blood cells have a diameter of 7.7 µm.)

We asked Ron Milo, a systems biologist and developer of BioNumbers, about the project.

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Courtesy Ron Milo

How did the idea for BioNumbers come about?

I was a fellow at Harvard medical school and was trying to do some back of the envelope calculation with my bay mates Mike Springer and Paul Jorgensen and we found none of the books and internet resources could give us what we needed so we decided to start a database ourselves.

How has the project grown and developed? Do you have any goals for the future?

It took shape rapidly in the first year and has been expanding ever since. The book that came out recently with Rob Phillips helps distill key insights from the available numbers and is available freely online. In the coming year I plan to revamp the interface to make it easier to use with mobile devices, make it more intuitive etc.

In your book Cell Biology by the Numbers you accompany tables of numbers with vignettes about the topics covered – do you have a favourite you’d like to share?

I love the one where we talk about how many H+ ions are in a cell – only about 100 in a bacterial cell! I also like the one about the turnover rate of different tissues in the body and how that was inferred with the help of signals from nuclear tests.

Do you have any advice for physicists who are interested in working on biology problems?

Don’t be worried about all the jargon, it is a field where you can easily penetrate things by reading textbooks that are almost page-turners and consulting wikipedia when needed. There are low hanging fruits ready to be picked, but you have to be willing to solve the problems by making your own makeshift  biological model and not always turning things into the beloved Ising model.

Interactions: Conversation with Philip Ball

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Post by Gaia Donati

Philip Ball talks about his latest book “Beyond Weird” — an exploration of the meanings of quantum theory and a tale of a continued effort to make sense of it. Call it counter-intuitive, challenging or puzzling — just don’t call it weird.

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How did the idea for “Beyond Weird” take shape?

Over the past several years I found myself writing various articles about aspects of quantum mechanics, such as the classical–quantum transition and decoherence, uncertainty relations, quantum computing. It began to dawn on me that many of the standard “stories” we science writers — and often scientists themselves, especially when speaking to a general audience — fall back on to convey what happens in quantum physics are incomplete, misleading or plain wrong. Partly this is due to poor metaphors used to talk about what pioneers like Bohr and Einstein said; partly it’s because conceptual and technical advances have reshaped the narrative in the past few decades, for example by realising in the laboratory what were previously considered just thought experiments. So the book is an attempt to bring the presentation of quantum mechanics up to date, and to get away from the habit of referring to a ‘weird’ kind of behaviour bound up with ‘wave–particle duality’, ‘two paths at once’ and so on.

In the book it looks like you wish to deconstruct some statements and comments associated with the theory of quantum mechanics and its interpretation(s)— noting the limitations of these statements and the confusions stemming from these — in order to usher in a more positive message taking the form of a ‘quantum reconstruction’ — finding new axioms for quantum mechanics. Do you view your book as a manifesto?

If the book is a manifesto, then it’s for ceasing to use the shaky old clichés and find better language, better images. But what are these? I’m not sure we yet know, though I tentatively suggest a few. It is definitely not a manifesto for a particular interpretation of quantum mechanics, although I do think that the informational perspective has brought a fresh and fruitful view — literally so, given the technologies which it spawns. In this respect, I also wanted to point out that these ‘quantum technologies’ are not merely applications of quantum mechanics: they bind practical potential very closely to the fundamentals. Then even so, regarding quantum mechanics as ‘all about information’ is not without its problems either.

One big point I wanted to make is that we need to try harder to get away from ‘explaining’ quantum mechanics with classical stories. The idea that a particle ‘takes both paths at once’ through the double slit is a prime example: we think in terms of classical paths that happen to be weirdly simultaneous. I don’t think that helps. The same applies to ‘spooky action at a distance’: quantum nonlocality isn’t the technical term to that, it’s the alternative.

What do you hope the readers to take away from the book? What reactions do you expect?

I hope the readers will take away a fresh perspective on how to think about the counter-intuitive aspects of quantum mechanics, and feel dissatisfied with articles that merely say ‘quantum is weird’. I would be very happy if we could hear less about Schrödinger’s cat in the future too.

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Interactions: Juan Knaster

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Post by Giulia Pacchioni

Juan Knaster, project leader of IFMIF/EVEDA, answers our questions.
Knaster3What made you want to be a physicist?

Since childhood I have been obsessed with nature around me. Watching insect life, flowers, clouds moving, stars, moon, sunsets… Certainly Sagan’s television documentaries ‘Cosmos’ in the early 80s made a breakthrough in my spirit, but possibly the reading a few years later of the Spanish translation of Gamow’s Biography of Physics led me to be interested in nuclear fusion.

Gamow is the γ of the revolutionary αβγ-paper that unravelled nucleosynthesis in stars; possibly this led me unconsciously to my professional drive towards nuclear fusion from my teenage years, concurrently with the 80s Reagan–Gorbachov political move towards the research world’s adventure of ITER. I dreamt since I was a teenager to work for ITER. As soon as I finished my studies, I joined nuclear fusion research in CIEMAT in the last phases of design and start of construction of the TJ-II, the successful Spanish stellarator which remains in operation. After few years in CERN, where I matured professionally in the best possible environment I could have dreamt of, I re-joined the world’s fusion program through ITER.

I studied physics wishing to work for this beautiful dream of human kind, as old as humanity, of harnessing the fire of stars, and we are now very close! ITER will make a breakthrough in human history, since we will harness fire for the 2nd time in our history on Earth: this time the real one. Coming back to the question, before I keep on digressing… Fusion energy development led me to become a physicist.

Which historical figure would you most like to have dinner with — and why?

That’s a tricky question. I don’t think there is only one historical figure I wish to have dinner with.

I am fascinated with Neoplatonism, which was the philosophical consolidation of Gnosticism, which we could understand as the esoteric branch of a new religion, Christianity, that they attempted to eradicate following Council of Nicaea in 325 a.d. The line of thought of ‘oneness’ in the Universe, with humans  being not only observers, but very special actors in this united perception, pervades all cultures in all times, like flowers blooming in a field. Among these flowers, if I had to choose historical figures to have dinner with, possibly I would select Plotinus or Iambliqus as prominent figures of Neoplatonism, or moving east possibly the zen Chinese patriarch Huineng from the 7th century, whom I adore for his deeply Neoplatonic views; or the 11th century Persian Sufist Suhrawardi; or Pico della Mirandola, one of the fathers of the Rennaissance; or Boehme in 18th century; or Hegel in the 19th century; or Husserl or Jung in the 20th century.

Eating is one of my private pleasures, so possibly ascetic individuals like most of those previously mentioned would not be good company for a dinner; then, if I had to choose someone to really have a good time with, possibly I would choose Jung, with whom I know I would get along very well because of so many common interests in life. I am certainly persuaded that we would enjoy more than one dinner together, addressing topics of common interests combining my physics background with his studies on Hermetism, accompanied with a nice glass of red wine. He was interested in modern physics, and he collaborated with Pauli; some of the dreams he analyses in his Psychology and Alchemy are Pauli’s.

What are you working on, and what do you hope will be the impact of your research?

I am leading a European-Japanese research project, IFMIF/EVEDA, that aims to overcome the pending technological challenges to construct a fusion-relevant neutron source. The project is framed by the Broader Approach Agreement between Europe and Japan in the field of Fusion energy research. IFMIF, the International Fusion Materials Irradiation Facility, is a project whose concept was proposed in the mid-70s, but it demands a high-current linear accelerator, a liquid metal facility and an irradiation facility with unprecedented performances, that frankly were rather science fiction during its first serious attempt with FMIT, the Fusion Materials Irradiation Test facility, in the mid-80s in the US.

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Interactions: Conversation with Ben Still

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Post by Iulia Georgescu.

Ben Still talks about his new book Particle physics brick by brick, an accessible and extremely enjoyable introduction to particle physics all LEGO fans will love – and who is not a LEGO fan?

Still

You have been involved with various outreach activities, how did you get the idea for this book?

The idea has been with me since 2009 when I first started participating in outreach as a newly appointed postdoc. I took it to the outreach team at Queen Mary, University of London and we fleshed out the ideas into workshops. These workshops and materials covered only a small portion of particles and used similar blocks to represent quarks in one instance and nucleons in another. They were fantastically popular.  Since then, I have had in the back of my mind an attempt to use a LEGO analogy to encapsulate as much of particle physics as possible. The result is Particle physics brick by brick.

Are you a LEGO fan? Which is your favourite set?

I am a huge fan, I got hooked as a kid.  I am an avid collector of the Architecture series, but I have to say that my favourite kit is the Saturn V rocket released recently in the Creator series.

Is LEGO a good tool to teach science in general? What is the best physics/science LEGO?

Sometimes you need a hook to get those otherwise disengaged in science to get involved and LEGO certainly helps bring in a broad audience. It made sense to me to use LEGO after many utterances of fundamental particles being the building blocks of nature. I think that the best use of LEGO in any sense, whether for teaching or for leisure, is creativity. I tried to stress in the book that with just the rules I cover you can be creative and build particles and chemical elements which don’t appear in the book. I think that LEGO is a great way of linking science with creativity and showing that science is about exploration.

Technic and Mindstorm are fantastic for the advanced technical creative, but I still love good old fashioned bricks.

In the book you explain particle physics in a very accessible way, but you do not shy away from abstract concepts that might intimidate the layperson. Who is this book for?

The book was officially aimed at ‘science interested adults’, but I think that teens from 14 years with an interest in science will find the book equally exciting. I did not want to shy away from the more abstract concepts because they are important, particle physics is abstract compared with our day-to-day lives. The book is structured, however, in a way that I hope eases the reader into the abstraction. I think the earlier chapters involving the history of the universe can be used with younger readers when hands-on with the LEGO as the workshops have shown in the past.

lego

What do you think are the biggest challenges in explaining particle physics to the general public? How to avoid the pitfalls of hype or misleading analogies?

Our everyday lives are deterministic, we know if we strike a football in a certain way it will follow a path which we can calculate. Particle physics lives in the quantum world where probability, not determinism, rules. In this world all sorts of weird wonderful and mind-bending things can happen because so much is possible if not probable. It is this separation from our daily experiences that makes particle physics a tough subject to get across sometimes. It would be much easier if we were living in the quantum world too because the goings on of particle physics would be day-to-day.

In the book I openly talk of the limitations of analogies and throughout admit to the shortcomings of the LEGO analogy I use. In a very real sense our scientific understanding is nothing but an analogy of the underlying fundamental laws of nature. New science is found at the edge of our knowledge and so understanding the limitations of any scientific analogy is the way that science progresses.

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Adventures in New York and beyond: lab visits at the Advanced Science Research Center and Princeton

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Post by Giulia Pacchioni

You might think that tweeting is a waste of time, but on my recent trip to New York it got me an unexpected and very much appreciated invitation to visit the Advanced Science Research Center (ASRC) at the Graduate Center of the City University of New York (CUNY), after I announced that I would visit a few institutions in the area to introduce the soon-to-launch journal Nature Reviews Physics to its future readers (and maybe authors). As I learned during my visit (and as you probably already know) CUNY is the largest urban university system in the US. ASRC is an initiative launched in 2008 with the aim of — according to their website — fulfil “its multi-billion-dollar commitment to becoming a national leader in visionary scientific research of vital, real-world consequence”. The centre, which runs 24/7, combines a wide range of state-of-the-art facilities with 5 research initiatives in specific areas (nanoscience, photonics, structural biology, neuroscience and environmental sciences) and is hosted in a glass building with breath-taking views of New York (if I worked there I would spend most of my time in one of the corner tables with full-length windows on both sides!) As they told me, the spaces are designed so that there is plenty of opportunity to interact in shared areas to foster cross-pollination between researchers working in different areas. I was intrigued to hear that brief presentations are regularly given so that everybody knows what is going on in fields they might not be very familiar with (see our recent post on how a biologist sees physics!)

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Some pics of the facilities and the giant TEM in CUNY ASRC

The facilities, which occupy an impressive amount of space, are open to universities in the New York area, start-up companies and industrial manufacturers and include, along with a range of fabrication techniques, imaging systems and characterization techniques such as NMR and mass spectroscopy. Having worked with a (much smaller) TEM during my master thesis, I was particularly impressed by the 120 kev TEM, shown in the picture above. The floor that will become the home of the initiative in photonics, led by Andrea Alù (my host), is still mostly empty — I’m looking forward to visiting again and seeing all the equipment in place!

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Safety in the lab is important!

I have to thank very much Andrea who invited me and organized a last minute talk to let me present the new journal, and Jacob Trevino who walked me around. It was great fun to meet the people working there — thanks Twitter!

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Me with Jacob Trevino (left) and Andrea Alù (right)

My next stop was Princeton University — thanks to Ali Yazdani for the invitation! There I had a lot of interesting conversations, gave another talk (this time accompanied by pizza, thanks to the wonderful organization by Jennifer Bornkamp) and had two super interesting lab visits. They assigned me an office for the day, and it turned out that it used to be the office of Val Logsdon Fitch, who won the 1980 Nobel Prize for the discovery of CP violation. So, off to a good start!

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Will I get great ideas from sitting in an office that belonged to a Nobel laureate? In case, the corridors in the physic department in Princeton offer ideal spaces for discussing them.

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Behind the paper: Quantum simulators at their best

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Post by Guido Pagano, commissioned by Giulia Pacchioni. The paper in Nature is here: https://rdcu.be/CHsG.
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A universal quantum computer promises to tackle a wide range of problems such as materials design and molecular modelling, with the ultimate goal of addressing general classes of hard problems. A quantum simulator is a restricted type of quantum computer that uses qubits to study a specific many-body system. One of the main challenges in the development of such devices is scalability, namely the ability to increase the number of qubits while exerting individual control on each of them. In this work we performed the largest spin model quantum simulation to date, using 53 qubits.

Our trapped-ion quantum simulator consists of individual ytterbium ions—charged atoms trapped in place by gold-coated electrodes—which are used to study quantum magnetism in out-of-equilibrium systems. In particular, we studied a dynamical phase transition that occurs after a sudden change of the system parameters, a.k.a. a quantum quench. The system is described by the following Hamiltonian:

hamil

where σxi  is the Pauli matrix acting on the ith spin along the x direction, Jij the Ising coupling between spins i and j, and Bz the transverse magnetic field. The spin–spin interaction is long range and falls off approximately as a power law Jij~J0/|i–j|α . We studied the response of the system as a function of the ratio of the two competing energy scales in the Hamiltonian, namely J0 and B. The experiment we had in mind was very simple: prepare the spins along the x-axis, quench the Hamiltonian and then measure the magnetization of the spins along the x-basis over long times. The question we wanted to answer was: is there a dynamical phase transition, namely a non-analytic change in the properties of the system, as we vary the ratio B/ J0?

Ideally, to answer this question and observe a non-analytic response of the system, we should have taken the thermodynamic limit both numerically and experimentally. Numerically this is possible for those few cases where the system can be solved analytically, but experimentally it was definitely out of question to put an infinite number of ions in the trap!

We decided more modestly to perform finite-size scaling, namely to measure how the properties of the system changed as the number of particles increased and try to observe non-analytic behaviors smoothed in a crossover by finite-size effects.

Therefore, we tried to perform the experiment looking at the long-time average magnetization of the systems, but our system sizes were not large enough to see any significant signature of the phase transition. At some point, we had the idea to look for the second-order correlations at long times and there we found something very interesting in the data: at what we thought to be the critical point, we observed a dip in the correlations! We checked in the numerics and had the confirmation that the dip—which is a signature of a dynamical phase transition—was physical. We numerically checked that the correlation dip went to zero in the thermodynamic limit of a toy model with all-to-all interaction (α=0 , which is analytically solvable), and it did. We had finally the first evidence of the phase transition! Since the finite scaling of this signal was not really satisfactory for systems with up to 16 ions, we tried to increase the signal-to-noise ratio as much as possible by going to larger and larger system sizes, and eventually we managed to take data with 53 ions.

This experiment offered a very concrete perspective on doing experiments with a very large number of qubits, putting us on the cusp of exploring physics that is unreachable by even with the fastest modern supercomputers.

Guido Pagano

Reference: Zhang J. et al. Observation of a many-body dynamical phase transition with a 53-qubit quantum simulator. Nature,  551, 601–604 (2017).