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Home » Page 319

RHK Technology plays the ‘long game’ in SPM

Customer service, collaborative innovation, continuous improvement: these are the organizational reference points, writ large, for the scientists and engineers of RHK Technology, a Michigan-based technology company specializing in the design and manufacture of advanced scanning probe microscope (SPM) systems and associated instrumentation, controllers and accessories.

Founded in 1981 by Adam Kollin (who remains the company’s president today), RHK supports a growing – and increasingly global – customer base of university scientists and government laboratories. At the last count, RHK had shipped more than 300 SPM systems and over 1200 SPM controllers to a diverse community of end-users conducting fundamental and applied research in nanoscale surface science and technology.

The secret of RHK’s commercial success – and longevity – is the vendor’s granular understanding of its research customers’ evolving requirements. Think collaborative product development and innovation. “We’ve always maintained a symbiotic relationship with our customers,” explains Kollin. “In this way, we learn directly from end-users about the new SPM features and capabilities they need to advance their research. Ultimately, those insights make our products better and more useful to a wider range of scientific customers.”

Difficult, not impossible

Clearly, that emphasis on listening to (and responding to) the needs of research scientists goes hand-in-hand with organizational adaptability – and agility. In its formative years, RHK focused exclusively on the controllers for SPMs, serving customers who were building their own microscope platforms. Over time, however, the company moved up the value chain towards a more vertically integrated business model and now offers a broad portfolio of ambient, ultrahigh-vacuum (UHV) and cryogenic SPM systems.

Adam Kollin
Adam Kollin: “Happy and productive customers are the best source for future sales.” (Courtesy: RHK Technology)

“As part of our growth and development strategy,” notes Kollin, “we tried to focus on niche markets that were not well served and, as such, we became the ‘go-to’ company when a researcher wanted an SPM product with unique capabilities that were not available elsewhere.”

A case in point: RHK was the first company to develop a cryogen-free SPM – an innovation that opens up ultralow-temperature regimes to researchers whose budgets may already be stretched and so unable to meet the cost of a liquid-helium cryostat. “We were advised by numerous SPM users that the vibration of a closed-cycle cryogenic cooling system would always be too high,” says Kollin.

However, RHK’s product development team thought otherwise and invested the necessary time and resource to make the technology work. “There are now many groups using our cryogen-free SPMs,” adds Kollin. “These are scientists who previously, owing to the complexity and cost, would never have considered an ultralow-temperature option for their microscope.”

Improvement by design

Notwithstanding the relentless pursuit of SPM innovation, RHK has faced its fair share of operational challenges along the way – most recently, the supply-chain disruptions resulting from the COVID-19 pandemic. “When COVID hit, virtually all of our customers closed their doors at the same time,” notes Kollin. “Every order that was in purchasing ground to a halt – some were even cancelled because of extensive delays to users’ research projects.”

On the supply side, the delivery time for SPM components and subsystems – the building blocks of RHK’s SPM instrument portfolio – also increased dramatically. Advanced semiconductors that had previously been in stock, for example, were suddenly being quoted with a year lead-time (sometimes even longer). “We used this downtime to restructure,” says Kollin, “becoming more streamlined and efficient despite the challenging business environment. As a result, we were able to lower our SPM system prices, even as the component and raw material costs to build them increased.”

Having weathered the COVID storm, RHK has redoubled its efforts around continuous improvement of its existing product lines. With this in mind, Kollin still spends a significant chunk of his time meeting face-to-face with customers in their laboratories – a key conduit for RHK’s collective requirements-gathering and product development roadmap. “Often, customers don’t want to tell you anything negative,” he notes, “though I stress that they are doing us a disservice if they just tell us things they think we want to hear. It is important for me to hear first-hand what customers think our products don’t offer – where we fall short and where they think we should improve.”

It helps, of course, that this continuous improvement mindset is hard-wired across the RHK workforce – from R&D and engineering functions to technical support and business development. Many RHK staff have also been with the company for 20 years or more, so the manufacturer’s specialist domain knowledge runs wide and deep. Another differentiator is the RHK ownership model, with the company under the management of the same family since its founding (while several SPM peers have been bought and sold multiple times over the past four decades).

Perseverance, it seems, brings its own rewards – and especially so when reinforcing RHK’s core value proposition for excellent customer service. “Customers trust us with their scarce research funds and we feel a strong obligation to provide them with the tools to be successful,” concludes Kollin. “It’s really just common sense: happy and productive customers are the best source for future sales.”

Collaboration, customization, innovation

The PanScan Freedom Lumin-SLT, RHK’s latest commercial SPM, is a case study in customer-driven product innovation. The customer in question – Luiz Zagonel, professor of applied physics at UNICAMP in São Paulo, Brazil – was seeking a multimodal SPM with market-leading light-collection efficiency to study the interplay between optical, electronic and morphological surface features in a range of advanced materials, including 2D nanostructures for flexible LEDs and halide perovskites for high-efficiency, long-lifetime photovoltaic cells.

“We envisaged a scientific-grade optical instrument that was not available commercially at the time,” explains Zagonel. The way forward, it turns out, was an R&D collaboration with RHK and co-development of its flagship PanScan system into a custom SPM platform with high-performance optical-collection capability (as much as 72% light capture from the sample surface).

The resulting RHK PanScan Freedom Lumin-SLT is nothing if not versatile. The instrument can collect light emitted by the sample upon excitation with the scanning tunnelling microscope (STM) tunnel current, a technique called STM-induced light emission. What’s more, when operating the STM in field-emission mode, higher-energy electrons hit the sample surface – an interaction that can trigger light emission from the deep-UV all the way down to near-IR via an effect called cathodoluminescence. The SPM can also be used to inject light into highly localized regions of a sample to enable photoluminescence and Raman spectroscopy studies.

“The PanScan Freedom Lumin-SLT is another example of a customer coming to us in need of a product that did not exist,” explains Adam Kollin, president of RHK. Customization and collaboration, however, laid the ground for the latest iteration on the PanScan theme. “To meet the exacting specifications of the UNICAMP team,” adds Kollin, “we lengthened the scan head to accommodate a parabolic mirror, while changes to the UHV chamber, inner and outer shields, and shutters were also required.”

Significantly, those modifications for UNICAMP are now part of the standard PanScan SPM design, such that any researcher can add the Lumin-SLT optical interface to their systems as their research priorities evolve. “The result of the UNICAMP-RHK collaboration,” Zagonel concludes, “is a widely applicable commercial instrument… a novel UHV SPM with atomic-scale resolution and up to 72% light capture.”

  • Click here for full technical data on the PanScan Freedom Lumin-SLT.

WiFi loophole allows drones to see through walls, power law defines football defending

Don’t panic, but researchers in Canada have created a drone-based system that can see through walls and locate electronic devices such as mobile phones and laptops. Dubbed Wi-Peep, the system uses the fact that a WiFi-enabled device will respond to a “ping” from another WiFi-enabled device – even if the devices are not on the same network. This shortcoming is called the “polite WiFi loophole” and it was discovered by the Canadian team in 2020.

The idea is that Wi-Peep flies around outside of a building while pinging a device of interest. It then uses the time taken for it to receive the responses to triangulate the position of the device. The system was created by Ali Abedi and colleagues at the University of Waterloo, who say that it was built using a hobbyist drone and about $20 worth of commercially available components.

“On a fundamental level, we need to fix the polite WiFi loophole so that our devices do not respond to strangers,” implores Abedi. “We hope our work will inform the design of next-generation protocols.”

Until WiFi protocols are changed, Abedi is asking WiFi manufacturers to introduce a random delay when a device responds to a ping. This would render Wi-Peep and similar systems ineffectual, he says.

Wi-Peep is described in a paper that was presented at MobiCom ’22, which was held in Sydney, Australia last month.

Beautiful theories

With the World Cup in Qatar starting in just under two weeks, what better time than to look at the theory behind the “beautiful game”. In 2020, Andrés Chacoma of the Enrique Gaviola Institute of Physics, Argentina, and colleagues analysed teams on the attack and created a model to describe the dynamics of a football team passing the ball to each other, finding that most passages of play involve just two or three players.

Now they have turned their attention to the defending team and analysed tracking information taken during three professional football games. Using the data, they created a “bipartite” network, in which connections exist only between players on opposite teams. The researchers found that an attacking player was usually connected to two defending players, on average, with the size and duration of the “player clusters” obeying a power law. The research is described in Physical Review E.

 

Fusion-reactor instabilities can be optimized by adjusting plasma density and magnetic fields

A way of controlling the size of instabilities in the plasma of fusion reactors has been discovered by an international team of researchers. Large instabilities can damage a reactor, while small instabilities could prove useful for removing waste helium from the plasma. Therefore, the discovery could provide important guidance for the operation of large-scale fusion reactors.

The fusion of hydrogen nuclei in a magnetically confined plasma could deliver vast amounts of environmentally friendly energy. However, controlling the superhot plasma remains a significant challenge.

In the doughnut-shaped tokamak reactors most widely used in current fusion experiments, plasma is confined by strong magnetic fields. This generates steep pressure gradients between the edge of the plasma and the reactor walls. If the pressure gradient at the edge is too great, it can lead to instabilities called edge localized modes (ELMs). These emit bursts of particles and energy that can cause serious damage to the reactor walls.

This latest study was led by Georg Harrer at the Technical University of Vienna. To study the conditions that create ELMs, the team carried out experiments at the ASDEX Upgrade tokamak at the Max Planck Institute for Plasma Physics in Germany.

Boosting plasma density

They found that large ELMs can be avoided by increasing the plasma density, the result being smaller ELMs that occur more frequently. As well as causing less damage, small ELMs could help remove waste helium from the plasma.

The team also found that at high plasma densities, the emergence of ELMs can be controlled by adjusting the topology of the magnetic field lines confining the plasma. In a tokamak, these field lines wind helically around the plasma, meaning the forces they impart alternate in direction relative to the pressure gradients. In some regions of the plasma, the forces work against instability whereas in other regions the forces encourage instability. This trade-off can be characterized by an instability threshold, which defines the minimum pressure gradient needed to create ELMs.

Harrer and colleagues found that increasing the helical winding of the magnetic field boosted the instability threshold – and therefore reduced ELM production. Also, increasing the magnetic shear at the edge of the plasma led to a larger instability threshold. The magnetic shear is the angle between two crossing magnetic field lines.

Using a plasma with a large pressure gradient increases the fusion energy gain of a fusion reactor, with the trade-off being an increasing risk of ELM damage. However, small ELMs could prove useful for expelling waste helium. As a result, these phenomena must be finely balanced to optimize the operation of future fusion reactors. This latest research provides important insights into how that could be done.

The team reports its findings in Physical Review Letters.

Finding commercial success in the burgeoning quantum-technology sector

This episode of the Physics World Weekly podcast looks at the challenges and opportunities facing companies in the quantum-technology sector.

Our first guest is Rafal Janik, who is chief operating officer of Xanadu. He explains that the Canada-based company is developing both hardware and software for quantum computers. Janik also talks about the challenges of recruitment, the company’s residency programme for students and how Xanadu is working with Volkswagen to design better batteries.

Also featured in this week’s podcast are two UK-based chief executive officers – Carmen Palacios-Berraquero of Nu Quantum and Richard Murray of ORCA Computing. They are both co-founders of UKQuantum, a new organization that aims to be the voice of the UK’s quantum industry.

UKQuantum has just opened for membership and Palacios-Berraquero and Murray explain why the time is right for the UK’s burgeoning quantum industry to club together to face common challenges and find new opportunities. They also talk about what it takes to get a company off the ground as well as looking to the future of the UK’s quantum industry.

‘Inherited nanobionics’ makes its debut

Bacteria that take up single-walled carbon nanotubes (SWCNTs) continue to divide as normal and even pass on the resulting extra capabilities to their descendants. This result, which was recently demonstrated by researchers at the EPFL in Switzerland, forms the basis of a new field they call “inherited nanobionics”. The researchers believe the modified bacteria could be used to make living photovoltaics – energy-producing devices that they say could provide “a real solution to our ongoing energy crisis and efforts against climate change”.

SWCNTs are rolled-up sheets of carbon just one atom thick, with a total diameter of about 1 nm. They boast excellent electrical, optical and mechanical properties that make them ideal for many applications in the field of nanobiotechnology. Researchers have, for example, placed these nanostructures in mammalian cells to monitor metabolism using near-infrared light emitted by the nanotubes. The light emitted can also be used to image biological tissue deep inside the body and help deliver therapeutic drugs into cells. In plant cells, SWCNTs have even been used to edit genomes.

SWCNT take-up is passive, length-dependent and selective

In the new work, researchers led by Ardemis Boghossian began by wrapping SWCNTs with a positively-charged protein coating. The nanostructures were then able to interact with the negatively charged outer membranes surrounding the bacterial cells they studied, which come from the genus Synechocystis and Nostos. The former is unicellular and spherical while the latter is multicellular and has a snake-like shape. Both are Gram-negative bacteria (so-called because they have a thin cell wall as well as an additional outer membrane, meaning that they do not retain the dye used in a common test known as a Gram stain), and they belong to the Cyanobacteria phylum. This group of bacteria obtain their energy though photosynthesis, like plants.

Boghossian and colleagues found that both Synechocystis and Nostos took up the SWCNTs through a passive, length-dependent and selective process that allows the nanoparticles to spontaneously enter the microorganisms’ cell walls. They also discovered that the nanotubes could be imaged very clearly in the infrared because they fluoresce in this region of the electromagnetic spectrum. Indeed, this light emission allowed the researchers to see that the SWCNTs were being passed on to the so-called daughter cells of the bacteria when they divide. The daughter cells thus inherit the exceptional properties of the nanotubes.

Like an artificial limb

“We call this ‘inherited nanobionics’,” explains Boghossian. “It’s like having an artificial limb that gives you capabilities beyond what you can achieve naturally. And now imagine that your children can inherit its properties from you when they are born. Not only did we impart the bacteria with this artificial behaviour, but this behaviour is also inherited by their descendants.”

And that was not all: the researchers also found that nanotube-containing bacteria produce a significantly greater amount of electricity when illuminated with light than do bacteria without nanotubes. “Such ‘living photovoltaics’ benefit from a carbon footprint that is negative – they actively take up, rather than release, carbon dioxide,” Boghossian tells Physics World. “This is in contrast to conventional photovoltaics, which while taking advantage of our most abundant energy source – the Sun – generate a lot of carbon dioxide during the manufacturing stage.” This is the “dirty secret” of photovoltaics, she says.

Living photovoltaics also have other important advantages: they have automated mechanisms for optimizing light absorption; can self-repair; and importantly, can reproduce, she adds. “You don’t have to worry about building a factory to manufacture each individual cell. These cells use the carbon dioxide they take up to automatically repair and make more of themselves. They rely on earth-abundant materials, and they are cheap. This is a materials science dream.”

Application areas

The work, which is detailed in Nature Nanotechnology, highlights applications that focus on light-harvesting as well as fluorescence imaging. “The imaging, for example, not only allows us to track the cells across generations, we are also able to use this technology to differentiate between living and non-living cells, and different cell types.” Boghossian says.

The researchers could even track the formation of different parts of the bacterial membranes after cell division thanks to the light emitted by the nanotubes and monitor physicochemical changes inside the cells. “What is special about this application is that the emitted light is distinct from the light that is naturally emitted by the cells, so we do not have to worry about interfering signals that have limited other such technologies,” Boghossian says.

Being able to introduce CNTs into bacteria in this way could also lead to new applications in therapeutics or DNA delivery that were previously hindered by the difficult-to-penetrate bacterial cell walls.

The EPFL team is now studying ways of re-programming their bacterial cells to produce electricity by modifying their DNA. “Light-harvesting organisms are naturally not very efficient at producing electricity,” explain Boghossian. “This is because they have been engineered by Nature for survival, not photovoltaics. With the recent expansion of synthetic biology, we’re now in a position to re-purpose these cells so that they are genetically inclined to produce electricity.”

OCV hysteresis and heat evolution – studying batteries with calorimetry

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Heat release during cycling of battery half-cells is investigated by a combination of electrochemical methods and isothermal micro-calorimetry with special emphasis on Li- and Mn-rich NCM cathode active material. Due to its pronounced hysteresis in the open-circuit voltage (OCV), the energy round-trip efficiency is significantly reduced in comparison to a regular NCA cathode. But how and when is this energy loss converted into waste heat?

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Franziska Friedrich

Franziska Friedrich completed her undergraduate studies at Ludwig-Maximilians University in Munich (LMU), where she received her bachelor’s degree in chemistry and biochemistry in 2016 and her master’s degree in 2018. The focus of her undergraduate studies at LMU were on electrochemistry, inorganic solid-state chemistry and material’s sciences. For her PhD, she joined the group of Prof. Hubert A Gasteiger for Technical Electrochemistry at Technical University of Munich (TUM) in 2018, where her research was centered on cathode active materials used for Lithium-Ion Batteries. Friedrich investigated aging phenomena of Ni-rich cathodes and published a JECS Editor’s Choice article in this research field. Furthermore, she studied hysteresis phenomena in Li-, and Mn-rich NCMs with potentiometric entropy measurements and isothermal micro-calorimetry to understand the effect of the hysteresis on the heat evolution of this type of cathode active material. In 2022, she received her PhD summa cum laude. Friedrich is currently working as a battery specialist for the BMW AG where her research interests mainly focus on all-solid-state batteries.

Why not sign up for our other Battery Series webinars? Look out for more to be added in coming months. Even if you’re not able to join the live event, registering now enables you to access the recording as soon as it’s available.

Flowing liquid ‘chains’ are best described by Niels Bohr, not Lord Rayleigh

If you pour water out of a bottle, the liquid stream will often adopt a chain-like structure. The physics behind this curious phenomenon has been hotly debated for more than a century, but now this mystery may have been solved by experiments done by Antoine Deblais, Daniel Bonn and Daniel Jordan at the University of Amsterdam and Neil Ribe at the University of Paris-Saclay.

When a jet of liquid drops from a non-circular nozzle it can form a wave of broad, flattened and evenly spaced sections of liquid that are alternately oriented at 90° to each other. These sections are separated by thinner links of liquid – making the structure resemble a chain (see figure).

At the heart of the effect is the non-cylindrical profile of the jet as it emerges. To minimize surface tension, the jet tries to become a cylinder, but this motion overshoots and results in an oscillation in the profile shape.

However, there is a long-standing disagreement between two theories that describe how these oscillations occur. One theory was put forward by Lord Rayleigh in 1879, and it was then modified by Niels Bohr in 1909. Rayleigh’s theory describes the oscillation as a linear effect, whereas Bohr’s theory introduces nonlinear effects that decrease the frequency of the oscillations as their amplitude increases.

Bohr wins out

Until now, no experiments have determined which of these theories offers a more accurate description. To resolve this issue, Deblais’ team designed a series of 12 elliptical nozzles with varying sizes and eccentricities. Then they measured both the frequencies and amplitudes of the chain structures which formed as they poured water through the nozzles at varying flow rates. While the patterns they observed disagreed slightly with Rayleigh’s predictions, they aligned more strongly with Bohr’s theory.

Based on their results, Deblais and colleagues constructed numerical simulations of liquid chain oscillations – again, finding a strong agreement with Bohr’s predictions. Their results also help to explain why the surface of each jet became dimpled during their experiments – another interesting feature of everyday water jets. The team now hopes to extend the experiments and simulations to consider liquids other than water, as well as nozzles with more complex shapes.

Now that a basic theory has been established, future experiments could offer useful insights in a diverse range of applications where liquids are fired from elliptical nozzles, including ink-jet printing and metallurgy. Further research could also lead to new techniques for enhancing combustion efficiency, suppressing noise, or improving control over thrusters. Elsewhere, the findings could help researchers to better understand the emergence and possible treatment of certain medical issues, including urological diseases.

The research is described in Physical Review Fluids.

Advanced X-ray imaging reveals why golden medieval sculptures deteriorate

Using an advanced, non-invasive imaging technique, researchers in Switzerland and Germany have shed new light on a metal-leaf material that was widely used for gilding sculptures in medieval Europe. By processing a series of X-ray diffraction patterns, the team produced ultra-precise images of the material’s interior nanostructure. The analysis could help conservators of medieval art to better preserve sculptures against degradation.

The research was done by a team led by Qing Wu at the University of Applied Sciences and Arts of Western Switzerland and Benjamin Watts at the Paul Scherrer Institute. The study was done on the cSAXS beamline at the PSI’s Swiss Light Source.

In the late Middle Ages, many sculptures and religious artefacts were decorated with zwischgold, which is a highly sophisticated material comprising an ultrathin gold layer that is backed by a thicker layer of silver. This material is far stronger and less costly than pure gold leaf. However, unlike pure gold, zwischgold will corrode. When exposed to air, silver atoms in the backing layer will diffuse through the gold layer to react with sulphur and chlorine, causing the leaf to blacken over time.

Lost metallurgical techniques

While this process can be slowed by applying a varnish to the sculpture, this protective layer will degrade over centuries. As a result, many medieval sculptures require careful restoration. Conservation presents a further challenge because the advanced metallurgical techniques used to produce the nanostructured material have been lost to time.

In their study, Wu, Watts and colleagues learned more about the zwischgold’s unique nanostructure using ptychographic X-ray computed tomography (PXCT). This is a recently developed technique that produces full 3D images of samples using X-ray scattering. By processing diffraction patterns, PXCT can detect nanoscale variations in a sample’s interior refractive index, providing some of the highest resolutions of all X-ray imaging techniques.

The team used PXCT to analyse a small sample taken from a 15th century sculpture of Mary holding the baby Jesus, which is displayed at the Swiss National Museum in Zurich. Their analysis clearly showcased the skill of the medieval artisans who produced the material by beating the two delicate layers into each other to within nanoscale precision. The team also examined other examples of zwischgold, including a rare variant of the material that comprises multiple, extremely thin gold layers.

The study revealed that the gold layer in zwischgold is about 30 nm thick, compared to gold leaf, which is typically 140 nm. This illustrates the cost saving of using the gold and silver hybrid.

The researchers found that over the centuries, corrosion causes zwischgold leaf to become less dense and more porous. The team also observed the separation of the gold and silver layers as well as the separation of the zwischgold from the underlying sculpture.  This new understanding of how zwischgold degrades over time could help conservators to refine their techniques to restore medieval sculptures more effectively – preserving them for future generations to appreciate.

The research is described in Nanoscale.

How to explain quantum technology in just three minutes

Could you explain a complex concept from quantum physics in just three minutes – and hold the attention of your audience while you did it?

This was the premise of the inaugural “Quantum on the Clock” competition, which challenged A-level and equivalent students from across the UK and Ireland to create creative, clear, engaging and accurate short videos on any aspect of quantum science and technology. The winners of the competition received cash prizes donated by quantum companies and institutions, plus an expenses-paid trip to the Photon 2022 conference in Nottingham and – for the recipients of the “best individual” and “best team” video awards – a year’s subscription to Physics World magazine.

As one of the competition’s 17 expert judges (a group that also included such luminaries as the “quantum ballerina” Merrit Moore, the science broadcaster Jim Al-Khalili, and the quantum YouTuber Mithuna Yoganathan), I got a sneak preview of the winning entries. Some of my favourites were Hannah Chapman’s rhyming animation on the Copenhagen and Everett interpretations of quantum mechanics (the “best individual video” winner) and May Cui and Margaret Liu’s clear, well-presented Q&A on blackbody radiation (“best team video”). I also had a soft spot for Olympia Andipa’s video about quantum tunnelling, which reinforced its message with a catchy chorus and picked up a “highly commended” award.

The competition was organized by the Institute of Physics’ QQQ group (Quantum Optics, Quantum Information and Quantum Control) as a means of getting more young people engaged in the growing field of quantum technology. With 124 entries to choose from, picking the winners was a challenge. Many students used graphics or animations in their videos, and several were slick enough to appear professionally produced – something that caught the attention of judge Andrew Hanson, the outreach manager at the UK’s National Physical Laboratory (NPL). “As a physicist film maker working in science communication, I was very impressed with the depth of understanding and clarity of explanation in many of the videos,” Hanson says. “The students’ enthusiasm and technical excellence made it a pleasure to watch every one of them.”

It wasn’t all about flashy tech, though. Sophia Gilbert and Karna Majdian received NPL’s “most creative” award for a news-report-spoofing video that relied on humour more than graphics to get its message across. Maisie Saunders and Lewis Payne won the IBM Quantum prize for “most engaging” video using nothing more than cartoons drawn on pieces of paper. And my hat is well and truly off to one of the runners-up, Diane de Nonneville, for choosing to make her video on pilot-wave theory. This is a topic that many professional physicists, never mind students, would be hard-pressed to explain, and I definitely learned something new from watching it.

The videos of all the winners, runners-up and highly commended entrants are now available on the Institute of Physics’ YouTube channel. Check them out for a glimpse into the future of quantum science – and science communication.

Bohr, Einstein and Bell: what the 2022 Nobel Prize for Physics tells us about quantum mechanics

Philosophers of science have been intrigued by this year’s Nobel Prize for Physics. That’s because Alain Aspect, John Clauser and Anton Zeilinger have been recognized for designing and performing a variety of ingenious experiments to demonstrate entangled particles. For philosophers, the work is fascinating because at its heart lies the challenge of understanding what quantum mechanics is all about.

This challenge has been around for as long the subject itself, with both Niels Bohr and Albert Einstein debating the implications of various thought experiments as far back as 1927. For Bohr, the experiments showed that the formalism of quantum mechanics, however strange, renders the world as it really is. For Einstein, they showed that quantum mechanics does not render the world as it really is – and therefore lacks any true meaning.

Einstein’s arguments culminated in the famous “EPR” paper that he wrote in 1935 with Boris Podolsky and Nathan Rosen, which supposedly proved that quantum mechanics could not represent reality (Physical Review 47 777). The EPR paper is unique among physics papers in that it begins by attempting to define reality. “A sufficient condition for the reality of a physical quantity,” the authors declared, “is the possibility of predicting it with certainty, without disturbing the system.”

If John Bell was disappointed by physicists who were apathetic about the meaning of quantum mechanics, he was even more irritated by physicists who were deferential to Niels Bohr

The paper is also significant in that “reality” was being approached for the first time in modern science as a testable hypothesis. Reality’s uncertainty sprang from what Erwin Schrödinger, in a post-EPR 1935 letter to Einstein, dubbed “entanglement” – or the condition that the quantum state of one particle in a system cannot be defined independently from all the others. Einstein and Schrödinger considered that a crime, and were shocked that their colleagues were not more shocked.

Getting real

One physicist who did care about the crime was John Stewart Bell. Born in 1928 after Bohr and Einstein had already begun their debates, he had no doubt that quantum mechanics was fine for all practical purposes. However, Bell felt that both the EPR paper and Bohr’s muddled reply skirted the fundamental issue, which had nothing to do either with the technical efficiency of quantum physics or with its accuracy as a theory.

If Bell was disappointed by physicists who were apathetic about the meaning of quantum mechanics, he was even more irritated by physicists who were deferential to Bohr. Many assumed he had successfully countered Einstein’s objections and had laid the fundamental issues to rest – somehow – in the “Copenhagen interpretation”. Conceptually vague, that interpretation involves something wave-like (either mathematical or real) collapsing in some unknown way into something particle-like.

In 1960, at a conference at CERN, Bell unexpectedly found himself sharing an elevator with Bohr, and tried to muster the courage to tell the 75-year-old grand old man of physics how flawed and irresponsible his interpretation of quantum mechanics was. Sadly, Bell lost his nerve. In fact, he wondered how many of his colleagues had been doing the same.

Then, in 1964 Bell devised a creative thought experiment that, if carried out for real, would show whether entanglement is caused by local “hidden variables” – properties that exist before taking a measurement. Initially, Bell thought Einstein was right, that hidden variables would be the answer to problems with quantum mechanics, and that he could show Bohr was wrong. But Bell increasingly saw that he couldn’t.

If Einstein had turned reality into a testable hypothesis, Bell also did something novel, which was to show that Einstein’s assumption of pre-existing variables could also be tested (Physics 1 195). For philosophers, Bell’s paper is fascinating in that it scrutinized the soundness of what Einstein had taken for granted; it asked what the microscopic world is really like and inquired into the consequences of that picture. What Einstein had taken for granted conceptually – the existence of definite properties of particles prior to measurement – could now be evaluated.

What’s more, the paper showed that Bohr had not made clear why the existence of entanglement must exclude these pre-existing properties. In other words, Bell’s paper gave experimentalists a target that neither Einstein nor Bohr had considered. That work started in 1972 when Clauser did a “Bell test” with the late Stuart Freedman that offered the first hard evidence against local hidden variables. Aspect continued that work later.

As for Zeilinger, he had (unlike Bell) long embraced the quantum-mechanical description developed by Bohr. In 1989, the year before Bell died, he and his team demonstrated three-particle entanglement, removing the need for Bell’s inequality with a single measurement. Since then, Zeilinger has closed more and more potential loopholes to local hidden variable theories by designing more and more elaborate entanglement experiments.

The critical point

Bell’s philosophical sensitivity and physical subtlety has earned him a quasi-mythical status among reflective physicists and thoughtful philosophers of science. His re-engagement with the enigma of entanglement was sparked by philosophical concerns left unanswered by physicists who fought over the EPR paper. Bell could frame his qualms about the meaning of quantum mechanics in a way that appealed to physicists, highlighting conceptual differences via quirky and playful thought experiments.

But why weren’t scientifically sensitive philosophers first on the crime scene? Why hadn’t they recognized the challenge of EPR and pounced? One part of the answer, no doubt, involves their lack of technical training. Another is the restrictions of academic disciplinary life. Still, Bell’s rich philosophical conceptualization and ingenious metaphysical imagination should be more of an ingredient not only in mainstream theoretical physics, but in philosophy as well.

The physicist David Mermin once recalled a meeting in 1989 when Bell literally shouted at a fellow physicist, seeking to rally his colleagues to not let their imaginations atrophy in the shadow of conventional wisdom. This year’s Nobel prize highlights the audacity and openness of physicists who challenged the conceptual frame presumed by their equations and showed that philosophical questions about physics, at least, can often be made physically testable and rigorous.

Robert P Crease (click link below for full bio) is chair of the Department of Philosophy, Stony Brook University, US, and Gino Elia is a doctoral candidate in philosophy at Stony Brook University

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