With Physics World’s first ever Quantum Week running on 14–18 June, staff at (or with links to) the Harwell Science and Innovation Campus in Oxfordshire, UK, have devised a fun quiz to see how much you really know about all things quantum. There are no prizes, and the answers are given below. No cheating! (And if you’d like to find out how Physics World online editor Hamish Johnston did on the quiz, take a listen to the 10 June episode of the Physics World Weekly podcast.)
1. What was the name of the scientist who proposed the principle behind the “dilution refrigerator” while working at the Atomic Research Energy Establishment on Harwell Campus in the early 1950s? A. André Heinz B. Heinz London C. Heinz Rome D. Fritz Mendelssohn
2. What was the name of the company, owned by de Beers, that launched the world’s first quantum-grade diamond? A. Blue Nile B. Rio Tinto C. Element Six D. Hatton Garden Jewellers
3. What does the acronym NISQC stand for? A. near-term intermediate-scale quantum computer B. nuclear isotopic spin quantum computer C. noisy intermediate-scale quantum computer D. nano-integrated superconducting quantum computer
4. The Science and Technology Facilities Council’s cryogenics team repurposed a cryocooler developed for the Planck space mission for the Quantum Imaging Hub in Glasgow. What temperature does the Planck cooler cool down to? A. 4 K B. 0.4 K C. 40 K D. 0.04 K
5. RAL Space’s quantum space laboratory exploits ultracold atoms cooled by lasers. What is the “effective temperature” of these atoms measured in? A. kelvin B. millikelvin C. microkelvin D. nanokelvin
6. What is the maximum number of qubits that a quantum computer has so far ever been built with? A. 1000 B. 65 C. 91 D. 750
7. Jonathan Jones and Michele Mosca built an early quantum computer at the University of Oxford in 1998. It was the first to have how many qubits? A. one B. two C. three D. four
8. The UK Quantum Computing and Simulation Hub, led by the University of Oxford, is developingquantum computers based on what technology? A. ion traps B. superconducting circuits C. colour centres in diamond D. all of the above
9. Tim Radford’s 2018 book The Consolations of Physics (Or, the Solace of Quantum) is about A. The physics of the James Bond movie Quantum of Solace. B. Quantum physics for people learning alone. C. How not to fail a quantum-physics exam. D. The Voyager space mission and beyond.
10. And finally, what was the name of Schrödinger’s cat? A. Tangle B. Kitty C. Quanto D. Albert
1. B 2. C 3. C 4. A 5. C [though they hope to achieve D in the near future] 6. B [at IBM] 7. B 8. D 9. D 10. There is no answer. Everybody gets a point!
The standard method of mixing biological and chemical compounds in test tubes has been shaken up in recent years by the emergence of microfluidics. This innovative field combines principles from micro-nanotechnology, biochemistry, engineering and physics, to manipulate the behaviour of fluids at the micron scale, performing traditionally laborious lab work on chips as small as postage stamps.
Microfluidics is providing a new avenue for real-time, high-throughput testing for point-of care diagnostics, helping to identify toxins or dangerous pathogens from tiny sample sizes. Outside the lab, microfluidics is behind a variety of technologies, from inkjet printer heads to pregnancy tests. While more streamlined than conventional methods, limitations remain that hamper the efficiency of microfluidic-based experiments.
For emulsion-based samples used in microfluidics, each individual droplet represents an experiment. Analysis can be conducted on every droplet, thus any spoiled droplets reflect a failed experiment. By minimizing droplet collision and breakup, the throughput and efficiency of the microfluidic system can be increased.
Traffic circle reduces congestion in microfluidic chip
Congestion and collisions tend to emerge when droplets are funnelled from a wide channel into a narrow one (a hopper chamber), causing the droplets to break. “It’s a traffic problem, like several lanes of cars trying to squeeze through a tollbooth,” says Sindy Tang, from Stanford School of Engineering.
To overcome this limitation, Tang and her team leveraged a known phenomenon from the behaviour of rigid particles, whereby an upstream obstacle, or “traffic circle”, suppresses particle clogging. This surprising observation can be seen in grain silos or people evacuating a room, but such behaviour had not been validated in soft particles.
Tang and her team, led by former Stanford Engineering graduate student Alison Bick, report on the transferability of this phenomena in Proceedings of the National Academy of Sciences. In their experiments, they perfused water-in-oil drops through a 2D hopper chamber of constrained geometry, with obstacles of varied size and location embedded on the chip.
Alison Bick and co-authors Jian Wei Khor (left) and Ya Gai (right) at the APS 2019 conference. (Courtesy: Alison Bick)
When an obstacle is optimally placed, droplets are first deformed between the obstacle and side wall, and then relax before constriction through the narrow chamber. “There’s a sweet spot in the placement of the obstacles that minimizes the reduction in breakups and collisions in the droplet flow,” Tang explains. An optimally located traffic circle reduced droplet breakup frequency by one thousand times, compared with a chip without the obstacle (see video above).
This dramatic improvement in experimental efficiency, throughput and robustness could reduce the time required to perform droplet-based microfluidic assays, including digital PCR tests and antibiotic screening. The researchers’ findings may also have implications further afield, for example, enabling faster flow rates while maintaining exit droplet size and uniformity in 3D printing of emulsions or foam-based materials.
The team concludes that by placing obstacles in a “sweet spot”, orderly droplet flow can be achieved. The elegance of this solution lies in its simplicity, making it convenient to implement in other microfluidic platforms.
Quantum error correction – a crucial ingredient in bringing quantum computers into the mainstream – relies on sharing entanglement between many particles at once. Thanks to researchers in the UK, Spain and Germany, measuring those entangled states just got a lot easier. The new measurement procedure, which the researchers term “conditional witnessing”, is more robust to noise than previous techniques and minimizes the number of measurements required, making it a valuable method for testing imperfect real-life quantum systems.
Quantum computers run their algorithms on quantum bits, or qubits. These physical two-level quantum systems play an analogous role to classical bits, except that instead of being restricted to just “0” or “1” states, a single qubit can be in any combination of the two. This extra information capacity, combined with the ability to manipulate quantum entanglement between qubits (thus allowing multiple calculations to be performed simultaneously), is a key advantage of quantum computers.
The problem with qubits
However, qubits are fragile. Virtually any interaction with their environment can cause them to collapse like a house of cards and lose their quantum correlations – a process called decoherence. If this happens before an algorithm finishes running, the result is a mess, not an answer. (You would not get much work done on a laptop that had to restart every second.) In general, the more qubits a quantum computer has, the harder they are to keep quantum; even today’s most advanced quantum processors still have fewer than 100 physical qubits.
The solution to imperfect physical qubits is quantum error correction (QEC). By entangling many qubits together in a so-called “genuine multipartite entangled” (GME) state, where every qubit is entangled with every other qubit in that bunch, it is possible to create a composite “logical” qubit. This logical qubit acts as an ideal qubit: the redundancy of the shared information means if one of the physical qubits decoheres, the information can be recovered from the rest of the logical qubit.
Gotta have a little bit of (quantum) orange juice
Developing quantum error-correcting systems requires verifying that the GME states used in logical qubits are present and working as intended, ideally as quickly and efficiently as possible. This new technique does just that.
The efficiency of the conditional witnessing technique relies on two processes. The first is termed localization, and in a recent press release, Farid Shahandeh, a researcher at Swansea University, UK and lead scientist on the study, compares it to making fruit juice. Just as a juicer extracts the essence of the fruit by squeezing it into a small space, he explains, “in many cases quantum correlations in large systems can also be localized in smaller parts of the system”. Without such localization, the task of certifying entanglement across all parts of a system requires checking every possible two-way splitting (“bipartition”) of the system, and the number of bipartitions scales exponentially with n, the number of parts. By exploiting localizable entanglement, however, Shahandeh and colleagues reduced the number of bipartitions that need checking to just n-1.
The second part of conditional witnessing is the witnessing itself, which functions as a sort of litmus test for entanglement. “Suppose the juicer directly converts the fruit into juice boxes without labels,” says Shahandeh, continuing the analogy. “We don’t know what is inside – it could be apple juice, orange juice or water. One way to tell would be to taste it. Witnessing is the quantum comparison of this, measuring a quantity that tells us whether quantum correlations exist or not.”
The team’s research shows that conditional witnessing works well in principle. If implemented experimentally, it could become a vital tool in the quantum computing research toolbox, says Andrea Rodríguez Blanco, the paper’s first author and a PhD student at the Complutense University of Madrid, Spain. Harnessing GME to find efficient implementations of QEC is a buzzing area of research, and Rodríguez Blanco notes that the uses of conditional witnessing extend beyond quantum computing. “Our method is also valid for a broad variety of protocols including quantum communications and quantum metrology,” she tells Physics World. “The nicest part of the work for me is to develop theoretical concepts that help experimentalists improve the quantum hardware.”
You were runner-up for the Nanotechnology Young Researcher Award, which recognizes early career brilliance. What was the research that led to this award?
I performed this work as part of my PhD at Eindhoven University of Technology. In the field of semiconductor physics, efficient light emission from silicon has been the “Holy Grail” for the past five decades. But despite remarkable efforts in the field, this has not yet been achieved due to silicon’s indirect band gap. Germanium-rich silicon-germanium alloys with a hexagonal crystal structure have been predicted to exhibit a direct band gap and efficient light emission. But the bottleneck here is that silicon and germanium naturally crystallize in a cubic structure and it is challenging to change this into a hexagonal structure.
In our research, we have achieved this by copying the hexagonal crystal structure from a hexagonal template of gallium-arsenide nanowires, which have nearly matching structural properties to our silicon-germanium material. The nanowires act as a unique platform for realizing these new crystal structures, without the material reversing back to its natural cubic structure. And we have created hexagonal silicon-germanium material in large volumes using these gallium-arsenide nanowire templates.
Now that light emission has been achieved, what could be the main applications for this material?
The biggest application, which we are all waiting for, is a silicon-based laser for on-chip and chip-to-chip communications. We have demonstrated efficient band-gap emission from this material; and we have shown the tunability of this emission in the wavelength window 1.8–3.5 μm, close to the optical communications window. These results reveal the strong potential of hexagonal silicon germanium for silicon-based light-emitting devices, hopefully paving the way to uniting electronic and optoelectronic functionalities on a single chip.
We could also use this in lidar systems used, for example, in autonomous driving, biological sensors and solar cells. It is a very promising material that emits and detects in a technologically interesting wavelength range.
While studying this material, you found a new type of crystal defect, what was this?
The hexagonal crystal structure has been synthesized in silicon germanium in the past few years, but only in small volumes. When we fabricated this material with high quality and in very large volumes, we started to see a new type of crystal defect. And when we ran a thorough structural characterization, we identified this as an I3 basal stacking fault.
An I3 basal stacking fault appears like a partial defect – if you look at the crystal under a microscope, you see partial lines running through the material. It is actually a triangular defect, terminated by two partial dislocations. And between those two partial dislocations, separated by 60 ˚, there is a stacking fault where the atoms order in a different manner from the hexagonal ordering.
If you think about it, this hexagonal structure is not the stable, natural form of silicon germanium, so the material tries to minimize its energy by creating these defects. But we have created a deep understanding of the defects, such that we can try to avoid them in the future and fabricate high-quality material by tuning the growth dynamics.
Would such defects cause a problem if they ended up in a device?
We performed optical characterization and saw that the defects do not really deteriorate the optical properties of our material. This is because – as we saw when we theoretically calculated the band structure of these materials – the defect states are created outside the material’s band gap. But of course, if the material is heavily defected by this I3 defect, it may change into the wrong structure. So ultimately, we have to have a very low defect level so that it does not affect the optical properties.
What are you working on now?
The rest of my team is working hard to show lasing from the silicon-germanium material. If we show lasing, this would be another breakthrough. I have just finished my PhD and am embarking upon the next step in my career. I am moving to work as a laser engineer research scientist at Apple in Silicon Valley in California. But hopefully I will stay in the field of optoelectronics and materials; this is really my passion.
Your degree was in electronic engineering – what prompted your move into physics?
As a bachelor student at the American University in Cairo, I was really fond of circuits and electronics. So in the third year of my degree, I travelled to the US as a part of an exchange programme. There I was introduced to the physics of semiconductors and semiconductor devices.
As an engineer, when you’re working with electronic devices, you are almost working with a black box, tuning the input and output and so on. But with physics, you’re really diving deep into the underlying concepts. I felt like I was exploring the hidden world behind electronic devices. And this was a fascinating world for me.
With physics, you’re really diving deep into the underlying concepts. I felt like I was exploring the hidden world behind electronic devices
After coming back to Egypt, I decided to focus more on the physics of semiconductors. And then I started a Master’s degree in nanoscience and nanotechnology. It was still nanoelectronics, but I focused a lot more on physics and nanomaterials courses. My thesis project was on nanomaterials.
You have also been involved with a UN climate change programme. What did that entail?
Since I was young, I have been passionate about community development and engagement activities. When I was still an undergraduate, I was interested in environmental issues and advocating for action on climate change, so I participated in a conference in Indonesia in 2011 as part of the United Nations Environment Programme (UNEP). There, I was nominated and elected as an African youth adviser as part of the UNEP-TUNZA Youth Advisory Council for 2012 and 2013.
I was representing African youth in ministerial meetings, international conferences and international forums concerned with environmental programmes and climate-change issues. It was really a great experience; I learned a lot. I think community development is very complimentary to science, everything goes hand-in-hand.
In November 2020 the Institute of Physics (IOP) launched a new podcast, Looking Glass, to coincide with its 100th anniversary. Series 1: Society has six episodes, in which host Angela Saini talks to expert guests about the contributions and responsibilities of physics, and physicists, in society as a whole, particularly in relation to the challenges of today’s world.
I listened to this first series over the course of a week at the start of 2021. The UK had just entered the third national lockdown, the weather was grim and to be honest the future didn’t look so bright either. Did I want to hear about future challenges, when the current one seemed challenging enough? Not really. But listening to each episode got me thinking about the world wider than my own. The rich conversations between guests showcased a diversity of thought, from experts in multiple fields, from diverse backgrounds and ethnicities.
Some themes are expected, for example the huge challenge of the climate crisis, or exploring the ethics of new technologies in medicine, robotics and artificial intelligence (AI). Other episodes are surprising, such as the discussions around who has a platform (along with what happens when it is taken away) and the value of non-western knowledge systems. The discussions connected the dots around how physics intersects with these seemingly unrelated aspects of society.
Responsibility of physicists for their discoveries
Questions of the responsibility of physicists to society are of course not new. When discoveries and technologies can have an impact as large as an atomic bomb, then questions of accountability are not far behind. In episode 6 “A Blueprint for the Future” former IOP president Dame Frances Saunders sums up the quest for discovery for discovery’s sake alone: “Sometimes you (physicists) do just need to push a frontier, open the door to see what is behind it… I think the importance is how rapidly you respond to what you find on the other side of the door.” So, is responsibility just a matter of foresight and contingency planning? With good planning, is any research justified?
There is of course the impact of new technologies on the wider world to consider, and the intent behind the research. Along with exciting benefits, such as machine learning to detect cancer or solar-based technologies for water treatment, there are often unintended consequences of a new discovery. Questions of who gets access to new technologies are highlighted in episode 3 “Healthcare and Inequality”, and whether this propagates societal injustices. Or that even with good intentions our unconscious biases are literally coded into new technologies as discussed in episode 5 “The Ethics of Big Data and AI”.
So how do we ensure that the benefits of any new technology are equitable? The first thing to stress is that equity is not the same as equality; it is based on the needs of the recipients rather than everyone receiving an equal share. This is at the heart of many social justice issues. Angela Saini puts it nicely: “Here we have an unequal society; how do we even it up without some people feeling aggrieved about it?” One option explored in episode 3 is to create solutions specifically for those that are often overlooked. Of course, those solutions need to solve problems that actually exist and be accessible to those that would benefit from them.
Ivan Beckley, the founder of Suvera health, advocates for this approach with the principles behind his start-up, centred around the “accessibility, affordability and effectiveness (of care)” for the end user. Perhaps these principles are a good starting point for technologies developed in the wider physics community as well. If they were embedded into the research, development and delivery processes, might they help bring the needs of the recipients into the foreground? This is especially important for Sophie Martin from the Blackett Lab Family, who concludes in episode 6 that the physics community must put the impact on society at the heart of the push for knowledge and communicate that impact clearly.
How should we communicate what we discover?
The way that scientists communicate is a key theme through the series. Within the first minutes of episode 1 “The Climate Crisis”, the topic of communicating data and climate change scepticism is raised. How can climate researchers communicate convincingly that there is a problem, and ensure that they are listened to? Angela Saini empathizes with the frustration of those scientists who have been talking about the issue for decades. One way forward might be for scientists to collaborate with activists and campaigners when there is an intersection with their work.
Looking Glass credits Greta Thunberg and the climate strikers in raising awareness and, as a campaigner herself, Fatima-Zahra Ibrahim from the Green New Deal UK comments “There is all this great (scientific) work happening, but that great work doesn’t go anywhere unless it lives in our homes, unless we can understand and communicate it ourselves.” Dr Emily Shuckburgh, director of Cambridge Zero thinks that we can go even further; if we really want to build trust with the public, we must build open and transparent processes, and communicate those as well.
The different skillsets involved in making a discovery and talking about it effectively are highlighted again in episode 3. When Professor Kevin McGuigan from the Royal College of Surgeons in Dublin, is asked about how he promotes the benefits of clean water technologies to those that might use them, his answer is wry. “The science is the easy part! …[the problem is] trying to help communities realise that there is a problem, and the technology can help address that problem.” He goes on to say that both technology and communication must be culturally relevant, sensitive and non-patronising to the people who will be using it to have the greatest possible benefit.
Science is moving increasingly into the public eye; even the government is “following the science” with an almost religious fervour. If honest, open and effective communication with the public doesn’t become embedded within the scientific community do we risk being “othered” – put on a pedestal or used as a scapegoat for the consequences of policy decisions? To avoid this, physicists need to be able to communicate in the way society does.
Currently, this seems to be through social media, with all the associated opportunity and risk. The echo chamber of a place like Twitter is discussed in episode 2 “Power, Privilege and Cancel Culture” where Brenda Trenowden, from PwC UK and global co-chair of the 30% Club, states that “debate can be shut down by the loudest voices”. Regardless of whether those voices are assenting or dissenting, both physicists and organizations like the IOP need to know how to respond appropriately and engage in true dialogue online.
The final piece of the puzzle is raised in episode 5, when the discussion turns to the balance, or imbalances, of power between organizations and individuals. Shiv Malik, former Guardian investigative journalist and head of growth at Streamr, believes that those with less power in a relationship become open to manipulation, especially by large tech companies like Twitter and Facebook. He says “There is a huge asymmetry of power, you have thousands of developers versus me as an individual… I am never going to win.” And this imbalance of power can lead to the spread of misinformation, pseudoscience and mistrust. The importance of trust is central to several episodes. How can we expect anyone to act against climate change if they don’t trust the information telling them it is real? How can we improve patient outcomes if medical technologies aren’t trusted?
What makes and should make a physicist “successful”?
In episode 6, Sophie Martin comments that the current measures within the academic community for what makes a physicist successful are very internal. They might include how many papers someone has published, how prominently they are listed as an author, and whether the research has followed scientific best practice. These methods of recognition and reward only preserve the status quo, rather than making systemic and sustainable change, but Looking Glass sheds some light on what a better definition of a successful physicist might be.
As well as enriching our physics community, including a diversity of thought, experience, and perspective brings tangible benefits too. Episode 4 “Who’s At The Table” addresses the benefits to our western scientific community that holistic knowledge and decision making could bring. Carolina Behe, the Indigenous knowledge/science adviser for the Inuit Circumpolar Council Alaska thinks that when the focus of scientific research involves eliminating variables, this surely must lead to siloed thinking as well. True diversity of thought comes not just from respecting the cultural knowledge of those who physicists work alongside, but also from accepting and not “translating” it into the western canon.
The second important point is that when invited into a community, these diverse voices are given equal weight at the table. In episode 2, Brenda Trenowden says that she would much rather talk about inclusion and diversity “I&D rather than D&I” because too many organizations recruit diverse teams and yet there’s no real change because those diverse teams aren’t truly included, and the dominant culture within an organization hasn’t been addressed. When asked how to ensure that diverse voices are heard rather than “tokenized” Frances Saunders says that she hates “the thought that I might be here because of my gender, rather than because I have something useful to say”.
Sophie Martin brings her own experiences as a member of the Blackett Lab family, stressing the importance of representation and connection between those in underrepresented communities. She also says that organizations looking to improve the representation of groups should recognise that there is a burden to existing as a minority in any community, an additional weight that their peers don’t carry whenever they put themselves forward. Carolina Behe adds to this in episode 4, when she discusses her experiences of being invited to negotiation meetings and ending up thinking “Was I too loud? They reacted to me so negatively… everybody else at the table is treating those negotiations differently than if we were all equitable.” If even experts invited to discussions are marginalized, there is definitely still work to be done.
The second series of Looking Glass is coming soon, presented by podcaster, author and journalist Gemma Milne. Find out more at iop.org/lookingglass
Maps of cerebral blood flow (CBF), arterial transit time (ATT) and BBB water exchange rate (kw) for three study participants. Increasing kw values are associated with increasing cerebrospinal fluid amyloid beta (CSF Aβ 42) concentration (from left to right). (Courtesy: Alzheimer’s Dement. 10.1002/alz.12357)
A novel non-invasive neuroimaging technique can detect early-stage dysfunction of the blood–brain barrier (BBB) associated with small vessel disease (SVD), according to new research published in Alzheimer’s & Dementia. Cerebral SVD is the most common cause of vascular cognitive impairment, with many cases leading to dementia.
The BBB is a semipermeable layer of cells that regulates the movement of ions and molecules between the blood and the central nervous system. It transports nutrients and protects the central nervous system from toxins, inflammation and pathogens. The BBB is also involved in clearing excessive amyloid-beta (Aβ) protein from the brain, accumulation of which is associated with the development of Alzheimer’s disease.
Researchers at the University of Kentucky and the University of Southern California used a novel MR imaging technique called diffusion-prepared arterial spin labelling (DP-ASL) to examine water exchange across the BBB and detect subtle BBB dysfunctions associated with altered water exchange rate. They hypothesized that decreased water exchange rate across the BBB may be associated with reduced Aβ clearance, and may represent a biomarker of the early stages of SVD.
The DP-ASL technique uses multiple diffusion weightings to differentiate magnetically tagged water signals from the capillary and brain tissue compartments based on a roughly 100-fold diffusion coefficient difference. The rate of water exchange between these compartments is then derived using a single-pass approximation model of the ASL signal.
The study focused on levels of Aβ in the cerebrospinal fluid, which are abnormally low when this protein is not adequately cleared from the brain. “While Alzheimer’s disease has been linked with BBB dysfunction, few studies have examined the relationship between cerebrospinal fluid and Aβ concentration, and water exchange across the BBB using neuroimaging,” the researchers explain.
The researchers used DP-ASL MRI to scan 39 healthy adults, ranging in age from 67 to 86 years. Most participants also had a lumbar cerebrospinal fluid draw and underwent neuropsychological testing. They report that low water exchange rate across the BBB was associated with low cerebrospinal Aβ concentrations in multiple brain regions of relevance to Alzheimer’s disease (whole brain, frontal lobe, parietal lobe and precuneus, a region involved in complex functions including memory and perception). However, the water exchange rate was only moderately associated with neuropsychological performance.
“Our data indicate the important role of BBB water exchange in the clearance of amyloid-beta, and the potential for using DP-ASL to noninvasively assess BBB water exchange in clinical trials of small vessel disease,” comments senior author Danny Wang, of the USC Stevens Neuroimaging and Informatics Institute, in a press statement.
“The results suggest that DP-ASL may provide a non-invasive index of BBB clearance dysfunction prior to any detectable cognitive impairment,” adds lead author Brian Gold.
The findings also support growing evidence that BBB dysfunction may represent a link between SVD and clinical diagnosis of Alzheimer’s disease. Excess accumulation of Aβ is a hallmark feature of individuals diagnosed with Alzheimer’s disease, but is also seen in many cases of SVD.
The research team recommends that these measurements should be repeated in other cohorts, and in larger numbers of participants, to further evaluate the sensitivity and specificity of this potential marker of BBB-related clearance functions.
Innovation is crucial to a knowledge-based economy. Indeed, its importance has become starker than ever in the wake of the COVID-19 pandemic, which has underlined our reliance on science and technology. One simple way to boost innovation is to increase the diversity of the workforce – broadening the spectrum of experience and perspective. Yet physics has lagged woefully behind in this regard, meaning it is failing to realize its potential by enabling students from all backgrounds to study and succeed in the subject.
Despite so few students from under-represented minorities opting to study physics in secondary school, universities have tried hard to widen participation in physics. This work has been well researched and documented, but after four decades of concerted effort, barely 20% of students doing A-level physics are girls. Students from ethnic minorities and low socioeconomic backgrounds are shunning physics too.
To increase the number of students in physics from all walks of life, it is crucial therefore that we make the subject more accessible and the learning journey more inclusive. To get a better understanding of what it is like for those from a minority group to study physics, in 2019 the Physics Education Research Group at the University of Leeds gathered the learning experiences of 657 physics-qualified respondents aged 18 to 75. All had studied A-level physics and 96% had continued to graduate level in a technical subject. They were representative of the UK population and of the current ethnic spread among university physics students, although they included an almost equal gender balance with 52% of respondents being female.
Almost a quarter of respondents reported that their study had been impacted by belonging to a minority group – whether classified according to gender, ethnicity, social class, academic background or attainment. From this group, 28% said that their minority status had been an overall positive experience, with most of them (88%) having achieved top grades (A*, A, B). But for those who reported no impact of being from a minority group (32%), only 65% achieved those grades, while for respondents reporting a negative effect (40%), barely 58% achieved A*, A, B. Despite people in this negative impact group being so isolated and not feeling they belong in physics, they succeeded through huge personal effort.
Identity erosion
The largest single minority group in the study was made up of women. A negative effect was reported by 37% of female respondents, with their success often hindered by having few or even no fellow female students. In retrospect they saw the traditional negative stereotype directed at them through policies, as well as from teachers, school managers, male students and girls not doing physics. This led to isolation, unsupported learning and erosion of physics identity.
Despite those problems, some 22% of women still reported a long-term positive benefit of studying physics, which gave them a resilience and academic confidence that sustained them through further study and their career. And although the remaining 41% of women reported no effect from being a minority group in physics, many qualified their responses by describing themselves as different from other women, already resilient or high achievers.
Across all groups, women who responded to the survey said it was important to do well not just for their own personal success but for the wider good of physics. However, this pressure to counter stereotypes, develop resilience and do well academically adds a social load for girls that their male counterparts never need to deal with. It is a concern as surely these issues should be addressed in schools and not left for students at university to solve. Indeed, when the Institute of Physics ran its Gender Action pilot programme in schools, colleges and nurseries in London in 2019, there were very positive outcomes. This project involved training on unconscious bias, making careers advice more gender diverse and countering stereotypes in classroom discussions, so that girls in particular feel part of physics and more confident in their ability.
Respondents to our survey were also asked to identify what they thought had helped them to learn physics and feel part of the subject. Around 60% referred to the learning gained through childhood pursuits (construction toys, puzzles, computer games and musical instruments, as well as creative play and outdoor exploration such as climbing trees or orienteering) that developed problem solving, logical thinking, perseverance and mental focus. Recognizing physics phenomena, developing investigation skills and establishing prior knowledge also helped – for example, playing various sports assisted with recognizing air resistance, trajectories, parabolic and linear motion, and the associated forces.
In other words, to help students from under-represented groups have a stronger “physics identity” we should recognize and value their “physics perspective” and place more value on non-traditional science capital in everyday skills of creating, inventing, repairing and tinkering. Following technical instructions and patterns in crafts, as in knitting or playing a musical instrument, can give people a deep appreciation for the logical order of the physical world.
We believe the time has come for a new narrative in physics to address the under-representation of women and other minorities. If students from lower socioeconomic and minority ethnic backgrounds are to see their place in the physics classroom, it is vital for us to value and recognize non-traditional sources of prior physics knowledge and competences. Then we can, at last, make physics welcoming for all.
A striking similarity between flows of liquids and a hot, dense state of matter called a quark–gluon plasma (QGP) has been revealed in calculations done by Kostya Trachenko at Queen Mary University of London, Vadim Brazhkin at the Institute for High Pressure Physics near Moscow and Matteo Baggioli at the Autonomous University of Madrid. The trio’s analysis could lead to a new understanding of the QGPs generated in particle accelerators, as well as providing new insights into the conditions that occurred the early universe.
Above a transition temperature of around 1.8 trillion K, quarks and gluons are no longer bound to each other within protons and neutrons and exist independently within a hot, dense substance called a QGP. Microseconds after the Big Bang, it is widely believed that all matter existed in this exotic state, until temperatures became cool enough for protons and neutrons to form. Today, tiny QGPs can be created in accelerators by smashing nuclei together. While experiments have given physicists fleeting glimpses of QGPs over the past two decades, many questions remain about their nature.
The properties of a QGP are governed by the strong nuclear force, so it came as a surprise when experimental evidence began to emerge that a QGP behaves like a fluid – which has properties governed by much weaker intermolecular forces.
Kinematic viscosity
Kinematic viscosity is the ratio of a fluid’s viscosity to its density and is key to understanding how freely a fluid like water will flow. Last year, Trachenko and Brazhkin showed that a minimum kinetic viscosity for liquids can be calculated from fundamental constants. While the kinematic viscosity can change as a function of temperature, it will never fall below this value – something that is borne out by measurements on real fluids such as water
Now, Trachenko, Brazhkin and Baggioli have turned their attention to calculating the minimum kinematic viscosity of the QGP. While the density and viscosity of a QGP are both about 16 orders of magnitude greater than water, the minimum value that the trio came up with is the same as the minimum value they had previously calculated for fluids like water. As a result, the team points out that if a QGP could somehow be poured out of a tap, it would flow much like water.
“It is conceivable that the current result can provide a better understanding of the QGP,” says Brazhkin. “The reason is that viscosity in liquids at their minimum corresponds to a very particular regime of liquid dynamics that we understood only recently. The similarity with the QGP suggests that particles in this exotic system move in the same way as in tap water.”
Supersolids – materials that exhibit both spatial ordering (seen in solids) and lossless flow (seen in superfluids such as helium-II) – are poorly understood at the finite temperatures that prevail in real-world experiments. Physicists at the Institute for Quantum Optics and Quantum Information (IQOQI) in Innsbruck, Austria have now furthered our understanding of this exotic quantum phase of matter by experimentally probing the finite-temperature behaviour of a supersolid over its full “life cycle”, observing its formation, dynamics, and subsequent destruction.
When supersolids were first proposed in the 1960s, they appeared to contradict the idea that superfluidity – a state in which a material has zero viscosity and thus flows without loss of energy – can only exist when the system is in a fluid-like state. In 2017, however, research groups at MIT and ETH Zürich observed some properties of supersolids for the first time in a Bose-Einstein condensate (BEC) – a dilute gas of ultracold atoms deep in the quantum regime.
More recently, the Innsbruck team (simultaneously with two research groups from Universität Stuttgart and CNR-INO, Pisa) observed supersolidity in a dipolar BEC – a special type of condensate where highly magnetic atoms exhibit dipolar interactions, leading to a favourable dispersion relation. This type of condensate offers an ideal playground to create and investigate supersolidity because in a dipolar BEC, the interactions themselves create the crystalline modulation. This contrasts with previous experiments in which the modulation was imposed via laser light.
Exploring temperature effects
While the behaviour of supersolids at zero temperature is well-described theoretically, good models of finite-temperature supersolids with realistic particle numbers remain elusive due to the added complexity of thermal effects. In the current work, which is published in Physical Review Letters, the Innsbruck team bypassed this challenge and used their experiment to investigate the role temperature plays in the formation, dynamics, and subsequent death of supersolids.
“Back in 2019, we observed that an ultracold gas of dipolar particles can spontaneously break two symmetries: the one that leads to superfluidity (known as gauge invariance), and the one that defines solidity by creating periodic density waves (known as translational symmetry),” explains group leader Francesca Ferlaino. “While the first broken symmetry is well studied since similar physics occurs in other Bose-Einstein condensates, the second broken symmetry is rather unique in quantum gases.” The central focus of the Innsbruck work was to answer the question, how do these symmetries break? In other words, does the solidity arise first or the superfluidity, or both simultaneously?
The dipolar system was prepared in an elongated cigar shaped trap at a relatively high temperature. It was then cooled until the quantum effects necessary for supersolidity became dominant. Via high-resolution imaging of the system, the team directly witnessed the density peaks – a signature of solidity – that form in the condensate. To measure the system’s superfluid nature, the atoms were released, and images taken after a short expansion. This allowed the researchers to extract the relative phase across the condensate – a key ingredient for establishing superfluidity.
“Our most striking result is the observation which shows that when cooled down, the system first breaks translational symmetry entering a ‘crystal’-type state,” says Ferlaino. “Then, when further proceeding in the cooling trajectory, the system builds a macroscopic coherence to create superfluid properties hence becoming a supersolid state.”
Expanding the dimensionality
These experiments have not only achieved a deeper understanding of supersolids but paved the way for better theoretical interpretation. Matthew Norcia, a postdoc at IQOQI and a co-author of the paper, says that the next step will be to extend their studies beyond one-dimensional supersolids. “This is an exciting development because going to two-dimensional supersolids should enable us to study phenomena such as vorticity, which is expected to have quite different properties compared to unmodulated states, such as regular superfluids,” he says.
My career is somewhat unusual in that it really is a combination of several jobs, each requiring a different skill set. First and foremost, I am an academic physicist and with my university job I have the usual teaching, research and admin responsibilities. I have always enjoyed teaching and have lectured to undergraduates at the University of Surrey every year since 1992. While teaching university students, who are young adults, does not require the same skills as, say, teaching primary school children, there are many attributes that all teachers must have: to be engaging; to empathize with the students and see the subject matter from their point of view; and to try and enthuse and inspire.
I spend roughly half of my time outside of academia, working in broadcasting (both TV and radio), communicating science more widely to the public and of course writing. This requires a very different mindset. On my BBC radio programme The Life Scientific I use interviewing skills to try to get the best out of my guests. Delivering a piece to camera for a documentary, meanwhile, requires a different state of mind, body language and style from standing in front of a live audience.
Then there are the skills that I have learned over two decades of writing popular-science books. Finding the words to describe difficult concepts in an engaging way is a challenge I relish. Recently, I wrote my first novel, which meant learning a whole new set of skills. The creativity and imagination needed to write fiction is a world apart from non-fiction.
Eclipsing all the above is the skill I would retain if I had to choose just one: the aptitude and competence I hope I have developed over the years to do research in theoretical physics. This means not only understanding the subject matter, but also using all the attributes needed to do my research: manipulating algebraic equations on paper; writing and debugging computer code; asking the right questions; checking hypotheses; supervising students; writing papers and grant applications; and so on. These are what have most shaped me over my career.
What do you like best and least about your job?
What excites me most is still my research and uncovering the secrets of physical reality buried within dense mathematics. My specialism is quantum mechanics, which I find endlessly rewarding, fascinating and frustrating, all in equal measure.
What do I like least? Well, I suspect it will come as no surprise to most academics that I would say sitting in long, boring meetings in which nothing gets decided or done… and of course marking exam scripts.
What excites me most is uncovering the secrets of physical reality buried within dense mathematics
What do you know today, that you wish you knew when you were starting out in your career?
That I should follow my instincts more when it comes to choosing what research problems to tackle. I have discovered later in my career that there are some wonderfully exciting areas of research (for me anyway), like quantum thermodynamics and far-from-equilibrium statistical mechanics, that I wish I had explored in more depth years ago.
Likewise, I wouldn’t have shied away from tackling issues in the philosophy of science, particularly regarding the interpretations of quantum mechanics. I treated it as a secret hobby because I didn’t think colleagues would regard it as a respectable area of research. Today, I feel differently. But I think that is quite normal for scientists as they enter their dotage – we have less to lose if we are controversial.
