Skip to main content

Reset your password

Please enter the e-mail address you used to register to reset your password

Note: The verification e-mail to change your password should arrive immediately. However, in some cases it takes longer. Don't forget to check your spam folder.

If you haven't received the e-mail in 24 hours, please contact customerservices@ioppublishing.org

Registration complete

Thank you for registering with Physics World
If you'd like to change your details at any time, please visit My account

Close
Home » Page 41

Staying the course with lockdowns could end future pandemics in months

As a theoretical and mathematical physicist at Imperial College London, UK, Bhavin Khatri spent years using statistical physics to understand how organisms evolve. Then the COVID-19 pandemic struck, and like many other scientists, he began searching for ways to apply his skills to the crisis. This led him to realize that the equations he was using to study evolution could be repurposed to model the spread of the virus – and, crucially, to understand how it could be curtailed.

In a paper published in EPL, Khatri models the spread of a SARS-CoV-2-like virus using branching process theory, which he’d previously used to study how advantageous alleles (variations in a genetic sequence) become more prevalent in a population. He then uses this model to assess the duration that interventions such as lockdowns would need to be applied in order to completely eliminate infections, with the strength of the intervention measured in terms of the number of people each infected person goes on to infect (the virus’ effective reproduction number, R).

Tantalizingly, the paper concludes that applying such interventions worldwide in June 2020 could have eliminated the COVID virus by January 2021, several months before the widespread availability of vaccines reduced its impact on healthcare systems and led governments to lift restrictions on social contact. Physics World spoke to Khatri to learn more about his research and its implications for future pandemics.

What are the most important findings in your work?

One important finding is that we can accurately calculate the distribution of times required for a virus to become extinct by making a relatively simple approximation. This approximation amounts to assuming that people have relatively little population-level “herd” immunity to the virus – exactly the situation that many countries, including the UK, faced in March 2020.

Making this approximation meant I could reduce the three coupled differential equations of the well-known SIR model (which models pandemics via the interplay between Susceptible, Infected and Recovered individuals) to a single differential equation for the number of infected individuals in the population. This single equation turned out to be the same one that physics students learn when studying radioactive decay. I then used the discrete stochastic version of exponential decay and standard approaches in branching process theory to calculate the distribution of extinction times.

Simulation trajectories a) A plot of the decline in the number of infected individuals over time. b) Probability density of extinction times for the same parameters as in a), showing that the most likely extinction times are measured in months. (Courtesy: Bhavin S. Khatri 2025 EPL 152 11003 DOI 10.1209/0295-5075/ae0c31 CC-BY 4.0 https://creativecommons.org/licenses/by/4.0/)

Alongside the formal theory, I also used my experience in population genetic theory to develop an intuitive approach for calculating the mean of this extinction time distribution. In population genetics, when a mutation is sufficiently rare, changes in its number of copies in the population are dominated by randomness. This is true even if the mutation has a large selective advantage: it has to grow by chance to sufficient critical size – on the order of 1/(selection strength) – for selection to take hold.

The same logic works in reverse when applied to a declining number of infections. Initially, they will decline deterministically, but once they go below a threshold number of individuals, changes in infection numbers become random. Using the properties of such random walks, I calculated an expression for the threshold number and the mean duration of the stochastic phase. These agree well with the formal branching process calculation.

In practical terms, the main result of this theoretical work is to show that for sufficiently strong lockdowns (where, on average, only one of every two infected individuals goes on to infect another person, R=0.5), this distribution of extinction times was narrow enough to ensure that the COVID pandemic virus would have gone extinct in a matter of months, or at most a year.

How realistic is this counterfactual scenario of eliminating SARS-CoV-2 within a year?

Leaving politics and the likelihood of social acceptance aside for the moment, if a sufficiently strong lockdown could have been maintained for a period of roughly six months across the globe, then I am confident that the virus could have been reduced to very low levels, or even made extinct.

The question then is: is this a stable situation? From the perspective of a single nation, if the rest of the world still has infections, then that nation either needs to maintain its lockdown or be prepared to re-impose it if there are new imported cases. From a global perspective, a COVID-free world should be a stable state, unless an animal reservoir of infections causes re-infections in humans.

Photo of Bhavin Khatri. He has a salt-and-pepper beard and glasses, he's wearing a button-down shirt with fine red checks that's open at the collar, and he's sitting in front of a window in an office
Modelling the decline of a virus: Theoretical physicist and biologist Bhavin Khatri. (Courtesy: Bhavin Khatri)

As for the practical success of such a strategy, that depends on politics and the willingness of individuals to remain in lockdown. Clearly, this is not in the model. One thing I do discuss, though, is that this strategy becomes far more difficult once more infectious variants of SARS-CoV-2 evolve. However, the problem I was working on before this one (which I eventually published in PNAS) concerned the probability of evolutionary rescue or resistance, and that work suggests that evolution of new COVID variants reduces significantly when there are fewer infections. So an elimination strategy should also be more robust against the evolution of new variants.

What lessons would you like experts (and the public) to take from this work when considering future pandemic scenarios?

I’d like them to conclude that pandemics with similar properties are, in principle, controllable to small levels of infection – or complete extinction – on timescales of months, not years, and that controlling them minimizes the chance of new variants evolving. So, although the question of the political and social will to enact such an elimination strategy is not in the scope of the paper, I think if epidemiologists, policy experts, politicians and the public understood that lockdowns have a finite time horizon, then it is more likely that this strategy could be adopted in the future.

I should also say that my work makes no comment on the social harms of lockdowns, which shouldn’t be minimized and would need to be weighed against the potential benefits.

What do you plan to do next?

I think the most interesting next avenue will be to develop theory that lets us better understand the stability of the extinct state at the national and global level, under various assumptions about declining infections in other countries that adopted different strategies and the role of an animal reservoir.

It would also be interesting to explore the role of “superspreaders”, or infected individuals who infect many other people. There’s evidence that many infections spread primarily through relatively few superspreaders, and heuristic arguments suggest that taking this into account would decrease the time to extinction compared to the estimates in this paper.

I’ve also had a long-term interest in understanding the evolution of viruses from the lens of what are known as genotype phenotype maps, where we consider the non-trivial and often redundant mapping from genetic sequences to function, where the role of stochasticity in evolution can be described by statistical physics analogies. For the evolution of the antibodies that help us avoid virus antigens, this would be a driven system, and theories of non-equilibrium statistical physics could play a role in answering questions about the evolution of new variants.

When is good enough ‘good enough’?

Whether you’re running a business project, carrying out scientific research, or doing a spot of DIY around the house, knowing when something is “good enough” can be a tough question to answer. To me, “good enough” means something that is fit for purpose. It’s about striking a balance between the effort required to achieve perfection and the cost of not moving forward. It’s an essential mindset when perfection is either not needed or – as is often the case – not attainable.

When striving for good enough, the important thing to focus on is that your outcome should meet expectations, but not massively exceed them. Sounds simple, but how often have we heard people say things like they’re “polishing coal”, striving for “gold plated” or “trying to make a silk purse out of a sow’s ear”. It basically means they haven’t understood, defined or even accepted the requirements of the end goal.

Trouble is, as we go through school, college and university, we’re brought up to believe that we should strive for the best in whatever we study. Those with the highest grades, we’re told, will probably get the best opportunities and career openings. Unfortunately, this approach means we think we need to aim for perfection in everything in life, which is not always a good thing.

How to be good enough

So why is aiming for “good enough” a good thing to do? First, there’s the notion of “diminishing returns”. It takes a disproportionate amount of effort to achieve the final, small improvements that most people won’t even notice. Put simply, time can be wasted on unnecessary refinements, as embodied by the 80/20 rule (see box).

The 80/20 rule: the guiding principle of “good enough”

Also known as the Pareto principle – in honour of the Italian economist Vilfredo Pareto who first came up with the idea – the 80/20 rule states that for many outcomes, 80% of consequences or results come from 20% of the causes or effort. The principle helps to identify where to prioritize activities to boost productivity and get better results. It is a guideline, and the ratios can vary, but it can be applied to many things in both our professional and personal lives.

Examples from the world of business include the following:

Business sales: 80% of a company’s revenue might come from 20% of its customers.

Company productivity: 80% of your results may come from 20% of your daily tasks.

Software development: 80% of bugs could be caused by 20% of the code.

Quality control: 20% of defects may cause 80% of customer complaints.

Good enough also helps us to focus efforts. When a consumer or customer doesn’t know exactly what they want, or a product development route is uncertain, it can be better to deliver things in small chunks. Providing something basic but usable can be used to solicit feedback to help clarify requirements or make improvements or additions that can be incorporated into the next chunk. This is broadly along the lines of a “minimum viable product”.

Not seeking perfection reminds us too that solutions to problems are often uncertain. If it’s not clear how, or even if, something might work, a proof of concept (PoC) can instead be a good way to try something out. Progress can be made by solving a specific technical challenge, whether via a basic experiment, demonstration or short piece of research. A PoC should help avoid committing significant time and resource to something that will never work.

Aiming for “good enough” naturally leads us to the notion of “continuous improvement”. It’s a personal favourite of mine because it allows for things to be improved incrementally as we learn or get feedback, rather than producing something in one go and then forgetting about it. It helps keep things current and relevant and encourages a culture of constantly looking for a better way to do things.

Finally, when searching for good enough, don’t forget the idea of ballpark estimates. Making approximations sounds too simple to be effective, but sometimes a rough estimate is really all you need. If an approximate guess can inform and guide your next steps or determine whether further action will be necessary then go for it. 

The benefits of good enough

Being good enough doesn’t just lead to practical outcomes, it can benefit our personal well-being too. Our time, after all, is a precious commodity and we can’t magically increase this resource. The pursuit of perfection can lead to stagnation, and ultimately burnout, whereas achieving good enough allows us to move on in a timely fashion.

A good-enough approach will even make you less stressed. By getting things done sooner and achieving more, you’ll feel freer and happier about your work even if it means accepting imperfection. Mistakes and errors are inevitable in life, so don’t be afraid to make them; use them as learning opportunities, rather than seeing them as something bad. Remember – the person who never made a mistake never got out of bed.

Recognizing that you’ve done the best you can for now is also crucial for starting new projects and making progress. By accepting good enough you can build momentum, get more things done, and consistently take actions toward achieving your goals.

Finally, good enough is also about shared ownership. By inviting someone else to look at what you’ve done, you can significantly speed up the process. In my own career I’ve often found myself agonising over some obscure detail or feeling something is missing, only to have my quandary solved almost instantly simply by getting someone else involved – making me wish I’d asked them sooner.

Caveats and conclusions

Good enough comes with some caveats. Regulatory or legislative requirements means there will always be projects that have to reach a minimum standard, which will be your top priority. The precise nature of good enough will also depend on whether you’re making stuff (be it cars or computers) or dealing with intangible commodities such as software or services.

So what’s the conclusion? Well, in the interests of my own time, I’ve decided to apply the 80/20 rule and leave it to you to draw your own conclusion. As far as I’m concerned, I think this article has been good enough, but I’m sure you’ll let me know if it hasn’t. Consider it as a minimally viable product that I can update in a future column.

Looking for inconsistencies in the fine structure constant

a crystal containing thorium atoms
The core element of the experiment: a crystal containing thorium atoms. (Courtesy: TU Wien)

New high-precision laser spectroscopy measurements on thorium-229 nuclei could shed more light on the fine structure constant, which determines the strength of the electromagnetic interaction, say physicists at TU Wien in Austria.

The electromagnetic interaction is one of the four known fundamental forces in nature, with the others being gravity and the strong and weak nuclear forces. Each of these fundamental forces has an interaction constant that describes its strength in comparison with the others. The fine structure constant, α, has a value of approximately 1/137. If it had any other value, charged particles would behave differently, chemical bonding would manifest in another way and light-matter interactions as we know them would not be the same.

“As the name ‘constant’ implies, we assume that these forces are universal and have the same values at all times and everywhere in the universe,” explains study leader Thorsten Schumm from the Institute of Atomic and Subatomic Physics at TU Wien. “However, many modern theories, especially those concerning the nature of dark matter, predict small and slow fluctuations in these constants. Demonstrating a non-constant fine-structure constant would shatter our current understanding of nature, but to do this, we need to be able to measure changes in this constant with extreme precision.”

With thorium spectroscopy, he says, we now have a very sensitive tool to search for such variations.

Nucleus becomes slightly more elliptic

The new work builds on a project that led, last year, to the worlds’s first nuclear clock, and is based on precisely determining how the thorium-229 (229Th) nucleus changes shape when one of its neutrons transitions from a ground state to a higher-energy state. “When excited, the 229Th nucleus becomes slightly more elliptic,” Schumm explains. “Although this shape change is small (at the 2% level), it dramatically shifts the contributions of the Coulomb interactions (the repulsion between protons in the nucleus) to the nuclear quantum states.”

The result is a change in the geometry of the 229Th nucleus’ electric field, to a degree that depends very sensitively on the value of the fine structure constant. By precisely observing this thorium transition, it is therefore possible to measure whether the fine-structure constant is actually a constant or whether it varies slightly.

After making crystals of 229Th doped in a CaF2 matrix at TU Wien, the researchers performed the next phase of the experiment in a JILA laboratory at the University of Colorado, Boulder, US, firing ultrashort laser pulses at the crystals. While they did not measure any changes in the fine structure constant, they did succeed in determining how such changes, if they exist, would translate into modifications to the energy of the first nuclear excited state of 229Th.

“It turns out that this change is huge, a factor 6000 larger than in any atomic or molecular system, thanks to the high energy governing the processes inside nuclei,” Schumm says. “This means that we are by a factor of 6000 more sensitive to fine structure variations than previous measurements.”

Increasing the spectroscopic accuracy of the 229Th transition

Researchers in the field have debated the likelihood of such an “enhancement factor” for decades, and theoretical predictions of its value have varied between zero and 10 000. “Having confirmed such a high enhancement factor will now allow us to trigger a ‘hunt’ for the observation of fine structure variations using our approach,” Schumm says.

Andrea Caputo of CERN’s theoretical physics department, who was not involved in this work, calls the experimental result “truly remarkable”, as it probes nuclear structure with a precision that has never been achieved before. However, he adds that the theoretical framework is still lacking. “In a recent work published shortly before this work, my collaborators and I showed that the nuclear-clock enhancement factor K is still subject to substantial theoretical uncertainties,” Caputo says. “Much progress is therefore still required on the theory side to model the nuclear structure reliably.”

Schumm and colleagues are now working on increasing the spectroscopic accuracy of their 229Th transition measurement by another one to two orders of magnitude. “We will then start hunting for fluctuations in the transition energy,” he reveals, “tracing it over time and – through the Earth’s movement around the Sun – space.

The present work is detailed in Nature Communications.

Heat engine captures energy as Earth cools at night

A new heat engine driven by the temperature difference between Earth’s surface and outer space has been developed by Tristan Deppe and Jeremy Munday at the University of California Davis. In an outdoor trial, the duo showed how their engine could offer a reliable source of renewable energy at night.

While solar cells do a great job of converting the Sun’s energy into electricity, they have one major drawback, as Munday explains: “Lack of power generation at night means that we either need storage, which is expensive, or other forms of energy, which often come from fossil fuel sources.”

One solution is to exploit the fact that the Earth’s surface absorbs heat from the Sun during the day and then radiates some of that energy into space at night. While space has a temperature of around −270° C, the average temperature of Earth’s surface is a balmy 15° C. Together, these two heat reservoirs provide the essential ingredients of a heat engine, which is a device that extracts mechanical work as thermal energy flows from a heat source to a heat sink.

Coupling to space

“At first glance, these two entities appear too far apart to be connected through an engine. However, by radiatively coupling one side of the engine to space, we can achieve the needed temperature difference to drive the engine,” Munday explains.

For the concept to work, the engine must radiate the energy it extracts from the Earth within the atmospheric transparency window. This is a narrow band of infrared wavelengths that pass directly into outer space without being absorbed by the atmosphere.

To demonstrate this concept, Deppe and Munday created a Stirling engine, which operates through the cyclical expansion and contraction of an enclosed gas as it moves between hot and cold ends. In their setup, the ends were aligned vertically, with a pair of plates connecting each end to the corresponding heat reservoir.

For the hot end, an aluminium mount was pressed into soil, transferring the Earth’s ambient heat to the engine’s bottom plate. At the cold end, the researchers attached a black-coated plate that emitted an upward stream of infrared radiation within the transparency window.

Outdoor experiments

In a series of outdoor experiments performed throughout the year, this setup maintained a temperature difference greater than 10° C between the two plates during most months. This was enough to extract more than 400 mW per square metre of mechanical power throughout the night.

“We were able to generate enough power to run a mechanical fan, which could be used for air circulation in greenhouses or residential buildings,” Munday describes. “We also configured the device to produce both mechanical and electrical power simultaneously, which adds to the flexibility of its operation.”

With this promising early demonstration, the researchers now predict that future improvements could enable the system to extract as much as 6 W per square metre under the same conditions. If rolled out commercially, the heat engine could help reduce the reliance of solar power on night-time energy storage – potentially opening a new route to cutting carbon emissions.

The research has described in Science Advances.

Microscale ‘wave-on-a-chip’ device sheds light on nonlinear hydrodynamics

A new microscale version of the flumes that are commonly used to reproduce wave behaviour in the laboratory will make it far easier to study nonlinear hydrodynamics. The device consists of a layer of superfluid helium just a few atoms thick on a silicon chip, and its developers at the University of Queensland, Australia, say it could help us better understand phenomena ranging from oceans and hurricanes to weather and climate.

“The physics of nonlinear hydrodynamics is extremely hard to model because of instabilities that ultimately grow into turbulence,” explains study leader Warwick Bowen of Queensland’s Quantum Optics Laboratory. “It is also very hard to study in experiments since these often require hundreds-of-metre-long wave flumes.”

While such flumes are good for studying shallow-water dynamics like tsunamis and rogue waves, Bowen notes that they struggle to access many of the complex wave behaviours, such as turbulence, found in nature.

Amplifying the nonlinearities in complex behaviours

The team say that the geometrical structure of the new wave-on-a-chip device can be designed at will using lithographic techniques and built in a matter of days. Superfluid helium placed on its surface can then be controlled optomechanically. Thanks to these innovations, the researchers were able to experimentally measure nonlinear hydrodynamics millions of times faster than would be possible using traditional flumes. They could also “amplify” the nonlinearities of complex behaviours, making them orders of magnitude stronger than is possible in even the largest wave flumes.

“This promises to change the way we do nonlinear hydrodynamics, with the potential to discover new equations that better explain the complex physics behind it,” Bowen says. “Such a technique could be used widely to improve our ability to predict both natural and engineered hydrodynamic behaviours.”

So far, the team has measured several effects, including wave steepening, shock fronts and solitary wave fission thanks to the chip. While these nonlinear behaviours had been predicted in superfluids, they had never been directly observed there until now.

Waves can be generated in a very shallow depth

The Quantum Optics Laboratory researchers have been studying superfluid helium for over a decade. A key feature of this quantum liquid is that it flows without resistance, similar to the way electrons move without resistance in a superconductor. “We realized that this behaviour could be exploited in experimental studies of nonlinear hydrodynamics because it allows waves to be generated in a very shallow depth – even down to just a few atoms deep,” Bowen explains.

In conventional fluids, Bowen continues, resistance to motion becomes hugely important at small scales, and ultimately limits the nonlinear strengths accessible in traditional flume-based testing rigs. “Moving from the tens-of-centimetre depths of these flumes to tens-of-nanometres, we realized that superfluid helium could allow us to achieve many orders of magnitude stronger nonlinearities – comparable to the largest flows in the ocean – while also greatly increasing measurement speeds. It was this potential that attracted us to the project.”

The experiments were far from simple, however. To do them, the researchers needed to cryogenically cool the system to near absolute zero temperatures. They also needed to fabricate exceptionally thin superfluid helium films that interact very weakly with light, as well as optical devices with structures smaller than a micron. Combining all these components required what Bowen describes as “something of a hero experiment”, with important contributions coming from the team’s co-leader, Christopher Baker, and Walter Wasserman, who was then a PhD student in the group. The wave dynamics themselves, Bowen adds, were “exceptionally complex” and were analysed by Matthew Reeves, the first author of a Science paper describing the device.

As well as the applications areas mentioned earlier, the team say the new work, which is supported by the US Defense Advanced Research Project Agency’s APAQuS Program, could also advance our understanding of strongly-interacting quantum structures that are difficult to model theoretically. “Superfluid helium is a classic example of such a system,” explains Bowen, “and our measurements represent the most precise measurements of wave physics in these. Other applications may be found in quantum technologies, where the flow of superfluid helium could – somewhat speculatively – replace superconducting electron flow in future quantum computing architectures.”

The researchers now plan to use the device and machine learning techniques to search for new hydrodynamics equations.

Electrical charge on objects in optical tweezers can be controlled precisely

An effect first observed decades ago by Nobel laureate Arthur Ashkin has been used to fine tune the electrical charge on objects held in optical tweezers. Developed by an international team led by Scott Waitukaitis of the Institute of Science and Technology Austria, the new technique could improve our understanding of aerosols and clouds.

Optical tweezers use focused laser beams to trap and manipulate small objects about 100 nm to 1 micron in size. Their precision and versatility have made them a staple across fields from quantum optics to biochemistry.

Ashkin shared the 2018 Nobel prize for inventing optical tweezers and in the 1970s he noticed that trapped objects can be electrically charged by the laser light. “However, his paper didn’t get much attention, and the observation has essentially gone ignored,” explains Waitukaitis.

Waitukaitis’ team rediscovered the effect while using optical tweezers to study how charges build up in the ice crystals accumulating inside clouds. In their experiment, micron-sized silica spheres stood in for the ice, but Ashkin’s charging effect got in their way.

Bummed out

“Our goal has always been to study charged particles in air in the context of atmospheric physics – in lightning initiation or aerosols, for example,” Waitukaitis recalls. “We never intended for the laser to charge the particle, and at first we were a bit bummed out that it did so.”

Their next thought was that they had discovered a new and potentially useful phenomenon. “Out of due diligence we of course did a deep dive into the literature to be sure that no one had seen it, and that’s when we found the old paper from Ashkin, “ says Waitukaitis.

In 1976, Ashkin described how optically trapped objects become charged through a nonlinear process whereby electrons absorb two photons simultaneously. These electrons can acquire enough energy to escape the object, leaving it with a positive charge.

Yet beyond this insight, Ashkin “wasn’t able to make much sense of the effect,” Waitukaitis explains. “I have the feeling he found it an interesting curiosity and then moved on.”

Shaking and scattering

To study the effect in more detail, the team modified their optical tweezers setup so its two copper lens holders doubled as electrodes, allowing them to apply an electric field along the axis of the confining, opposite-facing laser beams. If the silica sphere became charged, this field would cause it to shake, scattering a portion of the laser light back towards each lens.

The researchers picked off this portion of the scattered light using a beam splitter, then diverted it to a photodiode, allowing them to track the sphere’s position. Finally, they converted the measured amplitude of the shaking particle into a real-time charge measurement. This allowed them to track the relationship between the sphere’s charge and the laser’s tuneable intensity.

Their measurements confirmed Ashkin’s 1976 hypothesis that electrons on optically-trapped objects undergo two-photon absorption, allowing them to escape. Waitukaitis and colleagues improved on this model and showed how the charge on a trapped object can be controlled precisely by simply adjusting the laser’s intensity.

As for the team’s original research goal, the effect has actually been very useful for studying the behaviour of charged aerosols.

“We can get [an object] so charged that it shoots off little ‘microdischarges’ from its surface due to breakdown of the air around it, involving just a few or tens of electron charges at a time,” Waitukaitis says. “This is going to be really cool for studying electrostatic phenomena in the context of particles in the atmosphere.“

The study is described in Physical Review Letters.

Quantum gravity: we explore spin foams and other potential solutions to this enduring challenge

Earlier this autumn I had the pleasure of visiting the Perimeter Institute for Theoretical Physics in Waterloo Canada – where I interviewed four physicists about their research. This is the second of those conversations to appear on the podcast – and it is with Bianca Dittrich, whose research focuses on quantum gravity.

Albert Einstein’s general theory of relativity does a great job at explaining gravity but it is thought to be incomplete because it is incompatible with quantum mechanics. This is an important shortcoming because quantum mechanics is widely considered to be one of science’s most successful theories.

Developing a theory of quantum gravity is a crucial goal in physics, but it is proving to be extremely difficult. In this episode, Dittrich explains some of the challenges and talks about ways forward – including her current research on spin foams. We also chat about the intersection of quantum gravity and condensed matter physics; and the difficulties of testing theories against observational data.

IOP Publishing’s new Progress In Series: Research Highlights website offers quick, accessible summaries of top papers from leading journals like Reports on Progress in Physics and Progress in Energy. Whether you’re short on time or just want the essentials, these highlights help you expand your knowledge of leading topics.

Can fast qubits also be robust?

National center of competence in research spin
Qubit central: This work was carried out as part of the National Center of Competence in Research SPIN (NCCR SPIN), which is led by the University of Basel, Switzerland. NCCR SPIN focuses on creating scalable spin qubits in semiconductor nanostructures made of silicon and germanium, with the aim of developing small, fast qubits for a universal quantum computer. (Courtesy: A Efimov)

Qubits – the building blocks of quantum computers – are plagued with a seemingly unsurmountable dilemma. If they’re fast, they aren’t robust. And if they’re robust, they aren’t fast. Both qualities are important, because all potentially useful quantum algorithms rely on being able to perform many manipulations on a qubit before its state decays. But whereas faster qubits are typically realized by strongly coupling them to the external environment, enabling them to interact more strongly with the driving field, robust qubits with long coherence times are typically achieved by isolating them from their environment.

These seemingly contradictory requirements made simultaneously fast and robust qubits an unsolved challenge – until now. In an article published in Nature Communications, a team of physicists led by Dominik Zumbühl from the University of Basel, Switzerland show that it is, in fact, possible to increase both the coherence time and operational speed of a qubit, demonstrating a pathway out of this long-standing impasse.

The magic ingredient

The key ingredient driving this discovery is something called the direct Rashba spin-orbit interaction. The best-known example of spin-orbit interaction comes from atomic physics. Consider a hydrogen atom, in which a single electron revolves around a single proton in the nucleus. During this orbital motion, the electron interacts with the static electric field generated by the positively charged nucleus. The electron in turn experiences an effective magnetic field that couples to the electron’s intrinsic magnetic moment, or spin. This coupling of the electron’s orbital motion to its spin is called spin-orbit (SO) interaction.

Aided by collaborators at the University of Oxford, UK and TU Eindhoven in the Netherlands, Zumbühl and colleagues chose to replace this simple SO interaction with a far more complex landscape of electrostatic potential generated by a 10-nanometer-thick germanium wire coated with a thin silicon shell. By removing a single electron from this wire, they create states known as holes that can be used as qubits, with quantum information being encoded in the hole’s spin.

Importantly, the underlying crystal structure of the silicon-coated germanium wire constrains these holes to discrete energy levels called bands. “If you were to mathematically model a low-level hole residing in one of these bands using perturbation theory – a commonly applied method in which more remote bands are treated as corrections to the ground state – you would find a term that looks structurally similar to the spin–orbit interaction known from atomic physics,” explains Miguel Carballido, who conducted the work during his PhD at Basel, and is now a senior research associate at the University of New South Wales’ School of Electrical Engineering and Telecommunications in Sydney, Australia.

By encoding the quantum states in these energy levels, the spin-orbit interaction can be used to drive the hole-qubit between its two spin states. What makes this interaction special is that it can be tuned using an external electric field. Thus, by applying a stronger electric field, the interaction can be strengthened – resulting in faster qubit manipulation.

Comparison of graphs of qubit speed and qubit coherence times, showing showing qubit speed plateauing (top panel) and qubit coherence times peaking (bottom) at an applied electric field around 1330 mV
Uncompromising performance: Results showing qubit speed plateauing (top panel) and qubit coherence times peaking (bottom) at an applied electric field around 1330 mV, showing that qubit speed and coherence times can be simultaneously optimized. (CC BY ND 4.0 MJ Carballido et al. “Compromise-free scaling of qubit speed and coherence” 2025 Nat. Commun. 16 7616)

Reaching a plateau

This ability to make a qubit faster by tuning an external parameter isn’t new. The difference is that whereas in other approaches, a stronger interaction also means higher sensitivity to fluctuations in the driving field, the Basel researchers found a way around this problem. As they increase the electric field, the spin-orbit interaction increases up to a certain point. Beyond this point, any further increase in the electric field will cause the hole to remain stuck within a low energy band. This restricts the hole’s ability to interact with other bands to change its spin, causing the SO interaction strength to drop.

By tuning the electric field to this peak, they can therefore operate in a “plateau” region where the SO interaction is the strongest, but the sensitivity to noise is the lowest. This leads to high coherence times (see figure), meaning that the qubit remains in the desired quantum state for longer. By reaching this plateau, where the qubit is both fast and robust, the researchers demonstrate the ability to operate their device in the “compromise-free” regime.

So, is quantum computing now a solved problem? The researchers’ answer is “not yet”, as there are still many challenges to overcome. “A lot of the heavy lifting is being done by the quasi 1D system provided by the nanowire,” remarks Carballido, “but this also limits scalability.” He also notes that the success of the experiment depends on being able to fabricate each qubit device very precisely, and doing this reproducibly remains a challenge.

Did cannibal stars and boson stars populate the early universe?

In the early universe, moments after the Big Bang and cosmic inflation, clusters of exotic, massive particles could have collapsed to form bizarre objects called cannibal stars and boson stars. In turn, these could have then collapsed to form primordial black holes – all before the first elements were able to form.

This curious chain of events is predicted by a new model proposed by a trio of scientists at SISSA, the International School for Advanced Studies in Trieste, Italy.

Their proposal involves a hypothetical moment in the early universe called the early matter-dominated (EMD) epoch. This would have lasted only a few seconds after the Big Bang, but could have been dominated by exotic particles, such as the massive, supersymmetric particles predicted by string theory.

“There are no observations that hint at the existence of an EMD epoch – yet!” says SISSA’s Pranjal Ralegankar. “But many cosmologists are hoping that an EMD phase occurred because it is quite natural in many models.”

Some models of the early universe predict the formation of primordial black holes from quantum fluctuations in the inflationary field. Now, Ralegankar and his colleagues, Daniele Perri and Takeshi Kobayashi propose a new and more natural pathway for forming primordial holes via an EMD epoch.

They postulate that in the first second of existence when the universe was small and incredibly hot, exotic massive particles emerged and clustered in dense haloes. The SISSA physicists propose that the haloes then collapsed into hypothetical objects called cannibal stars and boson stars.

Cannibal stars are powered by particles annihilating each other, which would have allowed the objects to resist further gravitational collapse for a few seconds. However, they would not have produced light like normal stars.

“The particles in a cannibal star can only talk to each other, which is why they are forced to annihilate each other to counter the immense pressure from gravity,” Ralegankar tells Physics World. “They are immensely hot, simply because the particles that we consider are so massive. The temperature of our cannibal stars can range from a few GeV to on the order of 1010 GeV. For comparison, the Sun is on the order of keV.”

Boson stars, meanwhile, would be made from pure a Bose–Einstein condensate, which is a state of matter whereby the individual particles quantum mechanically act as one.

Both the cannibal stars and boson stars would exist within larger haloes that would quickly collapse to form primordial black holes with masses about the same as asteroids (about 1014–1019 kg). All of this could have taken place just 10 s after the Big Bang.

Dark matter possibility

Ralegankar, Perri and Kobayashi point out that the total mass of primordial black holes that their model produces matches the amount of dark matter in the universe.

“Current observations rule out black holes to be dark matter, except in the asteroid-mass range,” says Ralegankar. “We showed that our models can produce black holes in that mass range.”

Richard Massey, who is a dark-matter researcher at Durham University in the UK, agrees that microlensing observations by projects such as the Optical Gravitational Lensing Experiment (OGLE) have ruled out a population of black holes with planetary masses, but not asteroid masses. However, Massey is doubtful that these black holes could make up dark matter.

“It would be pretty contrived for them to make up a large fraction of what we call dark matter,” he says. “It’s possible that dark matter could be these primordial black holes, but they’d need to have been created with the same mass no matter where they were and whatever environment they were in, and that mass would have to be tuned to evade current experimental evidence.”

In the coming years, upgrades to OGLE and the launch of NASA’s Roman Space Telescope should finally provide sensitivity to microlensing events produced by objects in the asteroid mass range, allowing researchers to settle the matter.

It is also possible that cannibal and boson stars exist today, produced by collapsing haloes of dark matter. But unlike those proposed for the early universe, modern cannibal and boson stars would be stable and long-lasting.

“Much work has already been done for boson stars from dark matter, and we are simply suggesting that future studies should also think about the possibility of cannibal stars from dark matter,” explains Ralegankar. “Gravitational lensing would be one way to search for them, and depending on models, maybe also gamma rays from dark-matter annihilation.”

The research is described in Physical Review D.

Academic assassinations are a threat to global science

The deliberate targeting of scientists in recent years has become one of the most disturbing, and overlooked, developments in modern conflict. In particular, Iranian physicists and engineers have been singled out for almost two decades, with sometimes fatal consequences. In 2007 Ardeshir Hosseinpour, a nuclear physicist at Shiraz University, died in mysterious circumstances that were widely attributed to poisoning or radioactive exposure.

Over the following years, at least five more Iranian researchers have been killed. They include particle physicist Masoud Ali-Mohammadi, who was Iran’s representative at the Synchrotron-light for Experimental Science and Applications in the Middle East project. Known as SESAME, it is the only scientific project in the Middle East where Iran and Israel collaborate.

Others to have died include nuclear engineer Majid Shahriari, another Iranian representative at SESAME, and nuclear physicist Mohsen Fakhrizadeh, who were both killed by bombing or gunfire in Tehran. These attacks were never formally acknowledged, nor were they condemned by international scientific institutions. The message, however, was implicit: scientists in politically sensitive fields could be treated as strategic targets, even far from battlefields.

What began as covert killings of individual researchers has now escalated, dangerously, into open military strikes on academic communities. Israeli airstrikes on residential areas in Tehran and Isfahan during the 12-day conflict between the two countries in June led to at least 14 Iranian scientists and engineers and members of their family being killed. The scientists worked in areas such as materials science, aerospace engineering and laser physics. I believe this shift, from covert assassinations to mass casualties, crossed a line. It treats scientists as enemy combatants simply because of their expertise.

The assassinations of scientists are not just isolated tragedies; they are a direct assault on the global commons of knowledge, corroding both international law and international science. Unless the world responds, I believe the precedent being set will endanger scientists everywhere and undermine the principle that knowledge belongs to humanity, not the battlefield.

Drawing a red line

International humanitarian law is clear: civilians, including academics, must be protected. Targeting scientists based solely on their professional expertise undermines the Geneva Convention and erodes the civilian–military distinction at the heart of international law.

Iran, whatever its politics, remains a member of the Nuclear Non-Proliferation Treaty and the International Atomic Energy Agency. Its scientists are entitled under international law to conduct peaceful research in medicine, energy and industry. Their work is no more inherently criminal than research that other countries carry out in artificial intelligence (AI), quantum technology or genetics.

If we normalize the preemptive assassination of scientists, what stops global rivals from targeting, say, AI researchers in Silicon Valley, quantum physicists in Beijing or geneticists in Berlin? Once knowledge itself becomes a liability, no researcher is safe. Equally troubling is the silence of the international scientific community with organizations such as the UN, UNESCO and the European Research Council as well as leading national academies having not condemned these killings, past or present.

Silence is not neutral. It legitimizes the treatment of scientists as military assets. It discourages international collaboration in sensitive but essential research and it creates fear among younger researchers, who may abandon high-impact fields to avoid risk. Science is built on openness and exchange, and when researchers are murdered for their expertise, the very idea of science as a shared human enterprise is undermined.

The assassinations are not solely Iran’s loss. The scientists killed were part of a global community; collaborators and colleagues in the pursuit of knowledge. Their deaths should alarm every nation and every institution that depends on research to confront global challenges, from climate change to pandemics.

I believe that international scientific organizations should act. At a minimum, they should publicly condemn the assassination of scientists and their families; support independent investigations under international law; as well as advocate for explicit protections for scientists and academic facilities in conflict zones.

Importantly, voices within Israel’s own scientific community can play a critical role too. Israeli academics, deeply committed to collaboration and academic freedom, understand the costs of blurring the boundary between science and war. Solidarity cannot be selective.

Recent events are a test case for the future of global science. If the international community tolerates the targeting of scientists, it sets a dangerous precedent that others will follow. What appears today as a regional assault on scientists from the Global South could tomorrow endanger researchers in China, Europe, Russia or the US.

Science without borders can only exist if scientists are recognized and protected as civilians without borders. That principle is now under direct threat and the world must draw a red line – killing scientists for their expertise is unacceptable. To ignore these attacks is to invite a future in which knowledge itself becomes a weapon, and the people who create it expendable. That is a world no-one should accept.

Copyright © 2026 by IOP Publishing Ltd and individual contributors