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Photonics startups rise to the healthcare challenge

Photonics West has always been an event that champions commercial breakthroughs as much as scientific progress. And nowhere were these two sides of the same coin more evident than at the Startup Challenge, where early-stage companies compete to win funding from some of the largest companies in the photonics industry. The event has been taking place all week, with companies entering the competition taking part in qualification rounds while also benefitting from expert advice and training on, among other things, how to hone their pitch. But the grand finale was on Wednesday afternoon, when six wannabee companies presented their ideas and business models to seasoned professionals from both established optics companies and technology investment firms.

The overall winner was Avenda Health, a Santa Monica firm that is helping patients suffering with prostate cancer by providing a personalized treatment plan that enables the tumour to be targeted more effectively – and therefore minimize common complications such as sexual and urinary dysfunction. Presenting the company’s business plan, co-founder and COO Brittany Berry-Pusey said the targeted approach mirrored the developments in breast cancer treatment, where full mastectomies have largely been replaced with less invasive surgeries.

The technique developed by Avenda combines focal laser ablation with real-time imaging and analysis to guide the procedure. This image guidance exploits a machine learning approach, with biopsy information from the patient compared with a large biopsy database that Avenda has assembled. One key advantage is that the procedure can be carried out under local anaesthetic by a urologist in a clinic, and in a single-site trial with 11 patients the procedure was found to be safe and effective – without any of the side effects that can accompany surgical techniques.

Healthcare solutions featured strongly in the other contenders too. In third place was opto biolabs, a German company that has developed an optical module to boost the throughput of optogenetic techniques – in which cells taken from the patient are genetically modified to respond to treatment by light. The problem is that each cell must be inspected under a fluorescence microscope before being transplanted back into the patient, at a typical rate of just 50 cells per minute. opto biolabs have solved this problem by building an optical module called the pxONE that can be bolted onto a commercial flow cytometer. This approach enables high-throughput analysis using machines that are widely available in bio-analysis labs.

Other companies aiming to improve cancer treatment were Leuko and dermadiagnostics. Leuko has developed a simple diagnostic system for monitoring white blood cells during chemotherapy, which has the potential to replace a test normally performed in the clinic. The non-invasive PointCheck device exploits a light-based system that links up to a mobile phone to record and share the data with the physician, which the company believes will help to prevent the danger of infection when white blood cells fall to dangerously low levels.

dermadiagnostics, meanwhile, has developed a non-invasive patch that exploits photonic detection of biomarkers to diagnose cervical cancer. Presenting the technology, Eydis Lima pointed out that conventional cervical smear tests only achieve an accuracy of 55.4%, and many women who are recalled for further tests choose not to go. In contrast, the patch offers an accuracy of 98% and delivers results within 35–40 minutes, much faster than the two to three weeks needed for current tests.

The two other finalists had their sights set on very different markets. Radiance 4D, the overall runner up of the competition, is pioneering the use of optical coherence tomography to print complete 3D objects in just nine minutes, unlike existing 3D printers that build up structures over a couple of hours. And Unistellar claims to be first company to offer a digital telescope that delivers powerful imaging capabilities in an easy-to-use device that costs just $2000. The aim, said Franck Marchis, is to democratize astronomy and to build a community of amateur astronomers who can share images and information.

Broken shoes and tyres could be history thanks to new materials that repair themselves

Scientists in the US have designed a new polymer that can “self-heal” fractures in just a few hours. Objects made from this material restore their shape and elastic strength after self-repairing critical damage, the researchers found. What’s more, they can quickly print structures made from the material in 3D, which could benefit businesses by speeding up manufacturing times and allowing products to last longer.

Polymers that can self-repair fractures and retain their original strengths have long been of interest to scientists, with existing self-healing materials being used in many areas such as flexible electronics and biomedical devices. However, these materials have been limited because it takes time to make them and there are no effective methods for building complex 3D structures, such as those found in nature, from these polymers.

No shrinking

A team of researchers from the University of Southern California and the University of Connecticut, US, have now addressed these limitations by designing a new elastic material that can be rapidly 3D printed in any structure with swift self-healing properties. After testing objects they produced from this elastomer, the scientists uncovered two surprising advantages of the material.

First, it does not appear to shrink in volume even after repeated breaking and healing. This sets it apart from most self-healing hydrogels, popular in medical applications. Second, its mechanical properties do not change even after being soaked in water, which makes it better than moisture-sensitive elastomers with hydrogen bonds.

The new elastomer starts off as a fluid containing lots of thiol groups (R-S-H) that form a long-chain polymer when exposed to light. This photopolymerization reaction allows elaborate, solid structures to be 3D printed simply by separating a model of the desired object into a sequence of images and projecting these onto a bath containing the liquid “ink”. The team used to the method to print structures with a resolution up to 13.5 µm at a rate of 13.5 cubic millimetres per minute.

The healing property of the printed objects comes from the disulphide groups (R-S-S-R’) in the elastomer ink. When the material is broken, the disulphide bonds – with the help of diffusion – reform across the interface of the material fracture and restore its original form.

Staying flexible

The researchers tested the elastic strength of their materials by using the technique to make identical dog-bone-shaped samples, which they then cut in half. After putting the pieces back in contact and leaving them for as little as an hour at 60 °C, the researchers found that the material had regained 100% of its original’s strength – confirming that the object had entirely repaired itself.

What’s more, after 10 repeated break-heal cycles the material’s strength did not fall below 90% of its original value. And as the self-healing is governed by diffusion, it speeds up with temperature, although the material can heal effectively even at ambient conditions.

By mixing carbon grease with the elastomer ink, the scientists also managed to make a conducting printed pad. The resulting self-healing force sensor can restore both its mechanical and conductive properties even after being broken. Qiming Wang from the University of Southern California shares the team’s surprise that the resistance of the printed pad changed by only 9% after healing a fracture. Wang believes the new material could not only be used for making novel self-healing shoes and vehicle tyres, but also in 3D printed flexible electronics.

Full results are published in NPG Asia Materials.

Big questions in astronomy and debating the value of an LHC successor

In this episode of Physics World Weekly, James Dacey is in conversation with cosmologist Jo Dunkley about her new book, Our Universe: an Astronomer’s Guide. Written for a general audience, the book takes readers on a voyage through some of the biggest questions in modern cosmology. Along the way we encounter the fabric of space–time, physics beyond the Standard Model of particle physics, and the search for life beyond our Earth. Jo also speaks about her own research, testing astronomical models with data from the Atacama Cosmology Telescope in Chile.

Later in the podcast, a selection of Physics World journalists discuss some of the week’s most interesting developments. Hamish Johnston and Michael Banks discuss the ongoing debate among the physics community over the plans to build a next generation particle accelerator. The debate has flared up recently with theoretical physicist Sabine Hossenfelder’s opinion piece in the New York Times, which questioned CERN’s plans to build a more powerful – and significantly more expensive – successor to the Large Hadron Collider (LHC).

Matin Durrani and Sarah Tesh also join the podcast to talk about the February 2019 issue of Physics World. They also speak about the impressive winning designs for the festive jumper competition that we launched just before Christmas.

If you enjoy what you hear, you can subscribe to Physics World Weekly via the Apple podcast app or your chosen podcast host.

Imaging detects signs of consciousness after brain damage

Brain signal patterns — In consciousness, brain regions communicate with a rich temperament, showing both positive and negative connections (coherence) that facilitate efficient exchange of information. When unconscious, brain regions do not connect with each another (coherence around zero). (Courtesy: E Tagliazucchi and A Demertzi)

Unconsciousness is characterized by an inability to report subjective experience. For patients under anaesthesia, or in a more enduring state of unconsciousness caused by brain injury, reliable markers that indicate the presence or absence of consciousness remain elusive. Now, an international team of scientists has reported functional MRI (fMRI)-based evidence of distinct patterns of brain activity that could differentiate consciousness from unconsciousness (Sci. Adv. 10.1126/sciadv.aat7603).

To search for these indicators, Athena Demertzi and colleagues recorded fMRI data from 159 subjects scanned at four independent research sites. Participants included healthy individuals, as well as patients diagnosed with unresponsive wakefulness syndrome (UWS), in which they can open their eyes but do not display voluntary movements, and patients in a minimally conscious state (MCS), in which they show additional behaviours potentially indicative of awareness.

The researchers analysed how fluctuations in the fMRI blood oxygenation level-dependent (BOLD) signal — a proxy for neuronal activity — were coordinated across 42 brain regions representing six brain networks that play an important role in cognition. They uncovered four distinguishable patterns, including a pattern of high complexity with long-distance brain-wide coordination between regions (pattern 1) and a pattern showing low inter-areal coordination (pattern 4).

Pattern 1 was most prevalent in healthy conscious participants, followed by patients in MCS, and least likely to be seen in patients with UWS. In contrast, pattern 4 was more likely to be found in unresponsive patients than patients in MCS, and least likely to occur in healthy controls. Patterns 2 and 3 were equally probable across all groups, and may represent transitional states.

To further characterize coordination dynamics, the researchers computed the probabilities of transitioning between the different brain patterns. They found that individuals with higher levels of consciousness – who are more likely to reside in pattern 1 – were also more likely to depart to and from this pattern toward patterns 2 and 3. The brains of patients in UWS were more likely to stay in pattern 4 and avoid exploration of other brain configurations.

The researchers also scanned some of the participants under anaesthesia. They found that in all anaesthetized patients, pattern 1 became less prevalent while pattern 4 became the most prevalent, irrespective of clinical diagnosis — supporting the specificity of the low-coordination pattern to unconsciousness. Anaesthetized patients also displayed a lower probability of transitioning between different brain states over time.

Detecting these brain patterns in real time could allow for externally induced manipulations to non-invasively restore consciousness. The researchers note that this detection process also has the potential to greatly facilitate medical decision-making for patients in whom consciousness is impaired.

“We conclude that these patterns of transient brain signal coordination are characteristic of conscious and unconscious brain states, warranting future research concerning their relationship to ongoing conscious content, and the possibility of modifying their prevalence by external perturbations, both in healthy and pathological individuals, as well as across species,” the authors write.

Physicists await Japanese government decision on the International Linear Collider

Particle physicists in Japan are facing a nervous wait as their government decides whether to host the International Linear Collider (ILC). Following years of delays, the government is expected to reach a conclusion next month. But the signs are not good: a report released in late December, which examined the case for an ILC in Japan, has raised several issues about the proposal and did not support its construction.

The ILC is a particle collider that would smash together electrons with positrons to study the Higgs boson, which was discovered in 2012 at CERN’s Large Hadron Collider, in unprecedented detail. First mooted over a decade ago, the ILC’s five-volume technical design report was published in June 2013 and called for a 30 km-long linear collider that would smash electrons with positrons at around 500 GeV (see timeline below). The Japanese physics community quickly got behind the project, expressing its desire to host the machine, with a site in the Tōhoku region, about 400 km north of Tokyo, chosen as a potential location.

However, the government has dragged its feet over whether to support the project, and last year – to make the ILC more palatable – physicists came up with a revised plan. This involved reducing the ILC’s energy to 250 GeV and shortening the length of the tunnel to around 20 km, with the option of upgrading the collider later on. The ILC is estimated to cost around ¥800bn ($7.5bn) over a 10-year period, with Japan expected to provide half the cash.

In July 2018 Japan’s Ministry of Education, Culture, Sports, Science and Technology (MEXT) asked the Science Council of Japan (SCJ) to form an independent committee to review the revised plan for the ILC including its technical feasibility and how it would be funded. Released on 19 December, the report includes some positive statements about the science the ILC would undertake. It says, for example, that the precise measurement of the Higgs coupling is “extremely important” and that the project is a substantial way to develop a hub of top researchers in the country.

Timeline: twists and turns of a linear accelerator

2004 An international panel of experts decide that a future linear collider should be based on superconducting technology that has been developed at the DESY laboratory in Germany

2005 Barry Barish of the California Institute of Technology in the US is chosen to lead the effort to build the International Linear Collider (ILC). The ILC’s first tentative design is released calling for a 20 km-long machine that would operate at 500 GeV with a possible future upgrade to 1 TeV that would require extending the tunnel by an additional 18.6 km

2007 Updated “reference design” is released for the ILC calling for two 12 km-long arms to collide electrons with positrons. The estimated cost of the ILC is $6.7bn

2011 The Japanese particle-physics community announces it will bid to host the ILC with possible candidate sites in Kyushu and Iwate

2013 Lyn Evans, who masterminded the Large Hadron Collider’s construction, takes up the reins as linear-collider director, overlooking the design of the ILC. The “technical design report” for the ILC is released calling for a 31 km-long track of superconducting cavities that accelerate electrons to 500 GeV. The ILC community identifies a location in the Iwate prefecture north of Tokyo as a possible site for the ILC

2016 Japan’s High Energy Accelerator Research Organization (KEK) releases a 12-page plan showing that they have measures in place if the Japanese government decides to begin negotiations with other countries to start construction

2017 The International Committee for Future Accelerators, which oversees work on the ILC, endorses plans to reduce the scope of the collider. Estimated to cost $7.5bn, the ILC would be built in a 20 km-long tunnel and with an initial design energy to 250 GeV with the option of further energy upgrades

However, the report adds that the ILC’s importance beyond research is “unclear” and “considered to be limited”. It also warns that given the lack of accelerator expertise in Japan there are “large uncertainties” that the country would have the necessary expertise. Another criticism is that the ILC does not yet have enough international support.

Yet Hitoshi Murayama from the Kavli Institute for the Mathematics and Physics of the Universe in Tokyo, says that this view is unfair. “Unless the Japanese government starts negotiation with potential partners, we will not know how much international support there will be,” he says. “Within the particle-physics community, international support has been very strong and linear collider workshops always draw hundreds of physicists.”

The SCJ committee concludes, however, that given the current status of the project it “cannot reach a consensus to support hosting the 250 GeV [ILC]” in Japan. “The committee considers that the government should be cautious regarding a decision to announce its commitment to host the ILC,” the report states. A government decision on the ILC is expected by 7 March.

Analysis: a Japanese way of saying no?

While physicists await the Japanese government’s decision to go-ahead with the International Linear Collider (ILC), the recent report by the Science Council of Japan (SCJ) has dealt them a possible fatal blow. Released in December, the SCJ’s report is at best a lukewarm response to the ILC (see above). That was perhaps expected, given that the chair of the committee – Yasuhiro Iye, director of the Japan Society for the Promotion of Science – has previously voiced sceptical views about the project.

Japanese particle physicists will surely hope that the government will take other factors into account before deciding. In particular China is ramping up its plans for its own collider and last month Europe unveiled a blueprint for the Future Circular Collider, which has stirred debate within the physics community over whether it is worth spending billions on a new collider that may not find any physics beyond the Standard Model.

Yet even if the SCJ’s report does not signal the end of the road for the ILC, the government may simply delay a decision further. As one senior physicist told Physics World, “the consistent delay in deciding to host the ILC seems like a Japanese way of saying ‘no’ ”.

If that happens, then it is likely that linear-collider physicists will surely have to get behind another proposal – the Compact Linear Collider, or CLIC – that can operate at higher collision energies than the ILC. The ball is now firmly in the Japanese government’s court.

Trees dying younger in Canada too

Trees in today’s boreal forests are living fast and dying young. Over the last 60 years the life expectancy for trees has decreased significantly, a new study reveals. The fastest-growing trees have shown the greatest decline in longevity.

Rising levels of carbon dioxide and reduced water availability appear to be a major driver of the trend. There is concern that forests may see large-scale die-off, with potentially serious implications for their ability to mop up carbon and slow climate change.

Back in 2015, researchers were shocked to discover that although tree growth in the Amazon rainforest had increased over the last 30 years, trees were dying younger, resulting in less carbon dioxide sequestration in the region.

This led the team to speculate that faster growth due to climate change was leading to higher mortality rates. The big question was whether this was a localized phenomenon, or a global effect. To find out, Eric Searle and Han Chen, both at Lakehead University in Canada, carried out a similar study on high-latitude forests in Canada.

Since 1958 the forestry department in Alberta, Canada, has gathered a wealth of data on climate and tree health at 539 sample plots. Searle and Chen decided to focus on trees in their “twilight” years – over 100 years old. The species they studied included white spruce, black spruce, lodgepole pine, aspen, balsam fir, balsam poplar and paper birch.

Searle and Chen examined tree mortality year by year between 1960 and 2009. They observed an obvious and steady increase in mortality over time. Examining lifetime growth rates revealed that the fastest-growing trees experienced the greatest increase in mortality. But exactly why fast-growing trees are dying younger isn’t yet known.

“It could be that faster-growing trees attain larger sizes more quickly, leading them to be more vulnerable to size-related mortality – wind-throw, for example,” says Searle, who published the findings in Environmental Research Letters (ERL). “Or it might be linked to faster-growing trees allocating more resources to growth and less to defence, making them more susceptible to pests and infections.”

Searle and Chen saw a strong correlation between the mortality changes and the changes in carbon dioxide, temperature, and water availability in the region. Previous work has shown that larger trees tend to suffer more when water becomes scarce and the researchers think that declining water availability is likely to have been a key driver in the Alberta forests.

Given that carbon dioxide levels are expected to continue increasing, and water availability to continue decreasing, the future for boreal forests does not look promising.

“This could be quite serious,” says Searle. “It may reduce large trees in the forest and could lead to large scale die-offs at earlier ages. And, since larger trees typically continuously add more and more carbon as they age, losing faster-growing trees more frequently could mean significantly less carbon sequestration.”

Doppler effect lights up future of self-driving cars

This morning I got a glimpse of what the future might look like for cars that can drive themselves. Randy Reibel and Stephen Crouch from Blackmore, a US-based start-up that has developed a Doppler lidar system for guiding autonomous vehicles, picked me up in their specially kitted out BMW for a quick demo through the streets of San Francisco.

In the back seat, which was fitted with a screen that showed the readout from the laser-scanning system, I could clearly see the motion of cars, pedestrians and other moving objects – including, at one point, one of San Francisco’s famous trolley buses. Unlike conventional lidar systems – which measure distances using reflected pulses of laser light – Doppler-based systems are able to resolve the velocity of vehicles and pedestrians as well as their precise location.

On the screen, objects moving away from us were displayed in oranges and reds, with the hue depending on their speed, while people and vehicles coming towards us appeared in greens and blues. Buildings and other stationary objects were picked out in white, which makes the coloured moving objects really stand out from their background.

I was struck by the resolution that the system could achieve. Crouch pointed out that different parts of a moving pedestrian are displayed in different colours because their feet move faster than the rest of their body.

Blackmore’s system is one of only a few on the market to exploit frequency modulation to extract velocity information. It beams out light from an infrared laser operating at the telecoms wavelength of 1.55 microns, and then mixes the backscattered signal with a reference laser beam to determine the Doppler frequency shift. This allows the system to calculate the velocity with an accuracy of 0.1 m/s for objects moving at speeds of up to 150 m/s.

This frequency-modulated approach enables coherent detection of the reflected signal, which is crucial for future self-driving vehicles. “Imagine having fleets of autonomous vehicles fitted with lidar systems on the streets of a city like San Francisco,” said Crouch. “Coherent detection is the only way to disambiguate the signals.”

Reibel also pointed out that other chipset-driven industries – including mobile phones, automotive radars and GPS systems – have adopted frequency modulation to deliver interference-free data over long distances while using less power than those that rely on the intensity of the beam. “The reality is that physics ultimately wins,” he said. “More importantly, frequency-modulated Doppler lidar sensors are safer for self-driving applications.”

There’s more work to do, however. Reibel and Crouch are well aware of the need to lower the cost and shrink the size of their system, but they seem confident that they are on track to deliver those crucial improvements – not least because their optics works at telecoms wavelengths and so they can take advantage of an established supply chain. They are also investigating other applications of the technology, such as for airborne vehicles and long-distance haulage, which could potentially be deployed more rapidly.

Open doors and minds

A degree in physics is a brilliant starting point for a diverse range of careers, be it in scientific research, industry, finance, education, IT and much more besides. But the broadness of the discipline means that picking the right path for you is not always straightforward. For the past three years, we have been curating a special, free-to-read annual Physics World Careers guide (2018, 2017), to help to focus your mind. The 2019 guide is packed with careers advice and analysis; insightful case studies showcasing career options; and a comprehensive employer directory, full of companies looking to hire physicists just like you.

Our case studies have been penned by real physics graduates, working in everything from materials science and astroparticle physics, to environmental studies and terahertz imaging. If you’re a physics student with an eye on a career in nuclear physics, then have a look at the Nuclear Technology Education Consortium (NTEC) and the University of Bristol’s South West Nuclear Hub. The 2019 guide also includes a bumper article on careers in medical physics. As well as giving you an overview of what’s on offer in the field, you’ll get to meet eight physicists working in nuclear medicine, radiotherapy, detector physics, computational simulations and more. The article reveals what the day-to-day life is really like for medical physicists in a diagnostic, clinical or industrial setting. And if you’re tempted by a future in medical physics, take a look at employers and institutions such as the Christie Medical Physics and Engineering centre; Elekta; and the Institute of Cancer Research and the Royal Marsden NHS Foundation Trust Joint Department of Physics, who are all looking to employ you.

Another new offering in the 2019 guide is the “Start-up stories” section, in which you can meet the bold researchers who’ve taken the plunge and set up their own businesses. Coming from research fields such as printable electronics and neutron science, these researchers share the lessons learned from their brave ventures – and if you feel inspired to take the leap yourself, be sure to take check out our career-development article about setting up a successful business.

But if you’re looking for a real change of scenery, then take a peek at our “Beyond physics” section, where we interview trained physicists who are now in very different careers, ranging from public health and science policy, to film making and photography.

From defence and security to laser technology and data science, the 2019 Physics World Careers guide is truly representative of the wide scope of stimulating and inspiring careers available to physicists all over the globe, and I hope that it helps you on your own special path. You can read Physics World Careers free online here or via the Physics World app, available for iOS and Android.

Mapping out the market for quantum technologies

Thierry Robin of French technology strategy company Tematys offered delegates a sneak preview of a report due out at the end of March on the market potential for quantum technologies. While some devices are ready for commercialization now – notably temporal quantum sensors for smaller and better atomic clocks, which are needed in applications such as network synchronization – Robin predicts that wider adoption of quantum technologies will really take off from about 2022. From an estimated market value of just under of €400m in 2020, Tematys’s analysis suggests that the quantum industry will be worth more than €1bn by 2028.

The market evaluation covers quantum sensing and quantum communications – but not quantum computing, which Robin believes will have a much longer trajectory. Driving the growth over the next decade will be quantum sensors for precision measurements of electric and magnetic fields, as well as pressure, temperature, and rotation and acceleration, along with secure data transmission using quantum key distribution (QKD).

In his talk Robin highlighted a number of different implementations of quantum sensors, including the use of atomic gases for sensitive magnetometers that don’t need cryogenic temperatures – such as those being developed by start-up companies Twinleaf and QuSpin – along with devices that use trapped ions, solid-state spins, and superconducting circuits. One example he singled out was recent experiments using nitrogen-vacancy centres in diamonds, which achieved a 100-fold increase in the spectral resolution of nuclear magnetic resonance (NMR) spectroscopy – enough to allow researchers for the first time to perform NMR chemical analysis at the scale of single biological cells.

In the realm of quantum communications, Robin believes that QKD will become a compelling technology for secure data transfer in the next five to ten years. At the moment, he says, QKD systems are limited by data rate and the distance over which information can be sent. What’s more, these quantum systems are too expensive when compared with conventional cryptographic techniques, both in terms of the initial capital outlay and ongoing operational costs.

The good news, says Robin, is that innovations in photonic chip integration should lead to significant price reductions and improved performance, while adding QKD to existing communications systems would reduce running costs. And he believes that some customers, including financial institutions, would pay a price premium of 25–50% for the enhanced security offered by QKD systems. That would need the unit price to be cut from about $50,000–$100,000 today to less than $10,000, and if that can be achieved he expects that sales could reach a few tens of thousands of units per year.

Talking to Robin after his presentation, it seems that the impetus for the market survey came from a pan-European research network on nanoscale quantum optics that was funded through the COST (European Cooperation on Science and Technology) programme. “We started the COST Action back in 2014, and it will be coming to end in April 2019,” Mario Agio of the University of Siegen, Germany, told me at the end of Robin’s talk. “We wanted to find out how research in nanoscale quantum optics might be used in commercial applications, so we reached out to Tematys for their help.”

‘Squeezed thermal states’ could make computers more energy-efficient

The energy cost of erasing a bit of data can be decreased exponentially by embedding the bit in a “squeezed thermal environment”. That is the conclusion of Jan Klaers at the University of Twente in the Netherlands, who has studied a simple model of a bit that comprises a particle trapped in a box.

He says that the process could be applied to real computers, which have oscillating temperature fluctuations that could lead to squeezed thermal environments. By timing computing operations to occur at certain times in the fluctuation cycle, the energy required to perform a computer operation could be reduced significantly.

Erasing a bit of information in a system near to thermal equilibrium takes a minimum amount of energy. This was postulated by Rolf Landauer in 1961, yet it was only confirmed experimentally in 2012. Today, electronic bits dissipate about a thousand times more heat than this Landauer limit. However, energy consumption per bit is falling and the Landauer limit could be reached in the next few decades.

Piston and partition

In his calculations, Klaers used a simple theoretical model of a bit that consists of a particle in a quadratic potential box separated in two halves by a partition. The left and right sides of the box correspond to the logic states 0 and 1 respectively. The erasure procedure begins with the particle confined to the right side of the box in logic state 1. The barrier is then dropped, and the particle is free to move throughout the box. Next, a piston pushes the particle to the left and the barrier comes up again, confining the particle to the left (0) side.

Klaers found a way of going beyond the Landauer limit by considering bit erasure for a particle in a squeezed thermal state. This is a state in which thermal fluctuations in the particle momentum are reduced, while fluctuations its position are increased. Squeezed thermal states are nonequilibrium by nature and have previously been considered as means to overcome other fundamental thermodynamic limits such as the Carnot engine efficiency.

The bit is put into a squeezed state by driving it with a regularly-oscillating external force that also has components of noise. According to Klaers, this is also experienced by real-life bits in computers. “A periodically driven system, like a CPU, very naturally creates squeezing in its thermal environment,” he explains.

Squeezing factor

Klaers has calculated that the heat dissipated from erasing a bit oscillates in time. The magnitude of the oscillation is an exponential function of the “squeezing factor” – a parameter that characterizes the nonequilibrium squeezed state. This suggests that if erasure is appropriately timed, it could be done using significantly less energy than if squeezing was not done.

Wiping data will cost you energy

Actually implementing this process in a computer is still some way ahead, Klaers says, and he now plans to work on models that could realistically describe heat flow in a CPU. Klaers hopes to find how large the squeezing effect is in a real CPU and how much the computation energy cost decreases. Another question he is looking forward to tackling is what order of precision is required in the bit erasure timing for a real computer.

This research offers an exciting future for energy-efficient computing. And while application is not yet within grasp, Klaers says the technology exists to reproduce his results experimentally in nanoparticle systems.

Full results are presented in Physical Review Letters.

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