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Quantum weirdness, smart speakers, festive books: the December 2020 issue of Physics World is now out

Cover of Physics World December 2020 edition — Sounds good: the physics of smart speakers is the cover feature of the December 2020 edition of *Physics World*

“Alexa, play some Christmas music.”

“OK Google, turn on the fairy lights.”

“Hey Siri, how long do you need to cook a turkey?”

This festive season, we’ll undoubtedly be chatting to our smart speakers like they’re another member of the family, and every time, the disembodied response will be almost instantaneous.

It’s all thanks to some amazingly accurate voice-recognition technology based on ultrasensitive acoustic sensors and sophisticated machine-learning algorithms that can interpret our speech, as Pip Knight from the University of Cambridge, UK, explains in the cover feature of the December 2020 edition of Physics World magazine.

And good news for all print readers: as we promised in May, this will be the first issue of Physics World to be sent to readers in an environmentally friendly paper wrapper.

If you’re a member of the Institute of Physics, you can read the whole of Physics World magazine every month via our digital apps for iOS, Android and Web browsers. Let us know what you think about the issue on Twitter, Facebook or by e-mailing us at pwld@ioppublishing.org.

For the record, here’s a run-down of what else is in the issue.

• Heavy elements cause hefty debate – Were heavy elements produced by colliding neutron stars or supernovae? Keith Cooper tunes in to a new dispute

• ‘Delight’ as Biden elected US president – Joe Biden has already begun to initiate a science-driven agenda but faces challenges to unite a divided Congress, as Peter Gwynne reports

• Science must listen to opposing views –As the astronomy community celebrates this year’s Nobel Prize for Physics, Pruthvi Mehta says that the ongoing controversy over the Thirty Meter Telescope continues to stain the field

• Hot time for hard disks – James McKenzie looks at the power of incremental improvement andthe commercial success of magnetic‑recording technology

• Madness in the method – A new book suggests that traditional notions about “the scientific method” are flawed and misleading, as Robert P Crease discovers

• ‘Smart speaker, tell me about your acoustic sensor’ – Smart speakers that can register our everyday commands have become commonplace in homes around the world. While the acoustics sensors inside these devices are far flung from the first microphone, the technology is still evolving, as Pip Knight explains

• Thirty years of ‘against measurement’ Despite its many successes, physicists are still struggling to nail down a coherent interpretation of quantum mechanics, as it best represents “reality”. Jim Baggott explores the arguments first put forth by John Bell three decades ago, and looks at theoretical and experimental evidence accumulated since

Celebrating the Institute of Physics at 100: the November 2020 issue of Physics World is now out

• Following the first stars – Ian Randall reviews First Light: Switching on Stars at the Dawn of Time by Emma Chapman

• A universal theory of matter and mind – Tushna Commissariat reviews Synchronicity: the Epic Quest to Understand the Quantum Nature of Cause and Effect by Paul Halpern

• Ambassador for the Space Age – Andrew Glester reviews Not Necessarily Rocket Science: a Beginner’s Guide to Life in the Space Age by Kellie Gerardo

• Little book, big science – David Appell reviews The Little Book of Cosmology by Lyman Page 2020 Princeton University Press

• On the road less travelled – Postdoc Brooke Russell and graduate student Tamia Williams share their stories of being #BlackInPhysics, from the importance of finding your community and creating a good mentoring environment, to having the determination to succeed

• Ask me Anything – Careers advice from Carol Marsh, deputy head of electronics engineering at aerospace engineering company Leonardo who recently received an OBE for services to diversity and inclusion in electronics engineering.

• Resolving the squoon – Bradford physics teacher Nicholas Porter estimates the physical believability of Julia Donaldson’s planetary satellite in The Smeds and the Smoos

Quantum tunnelling video bags teen $250,000 scholarship, how to win a horse race

The Canadian teenager Maryam Tsegaye has bagged a total of $400,000 in prizes for making the above video about quantum tunnelling. Tsegaye, 17, is winner of the 2020 Breakthrough Junior Challenge, which was founded by the billionaires Yuri and Julia Milner. Tsegaye is a student at École McTavish Public High School in Fort MacMurray and her teacher Katherine Vladicka-Davies will get $50,000 of that prize money. The school will get $100,000 for a new science lab and the remaining $250,000 goes to Tsegaye as a college scholarship.

“Maryam’s video is a prime example of how to cleverly simplify a complex idea, and she provided a remarkable explanation of quantum tunnelling,” says Scott Kelly, a retired NASA astronaut who was a prize judge.

Tsegaye says the win is a “life-changing moment for me, and presents so many new opportunities that nothing will be the same from now on”.

Enough left in the tank

What is the ideal strategy to win a short-distance horse race – start off slow to conserve energy or go out hard and hope you have enough left in the tank for a final kick? Mathematicians Quentin Mercier and Amandine Aftalion at the School for Advanced Studies in the Social Sciences (EHESS) in Paris have now attempted to answer that question by analysing the mathematics behind thoroughbred horseracing.

They used a GPS tracking tool placed under the jockey’s saddles at the Chantilly racetracks north of Paris to create a model of winning strategies at three different lengths on a looped track: 1300 m, 1900 m and 2100 m. The model even considered the aerobic and anaerobic energy of the horses as well as the slope and bend of the track. Rather than holding the horses back for a strong finish, the researchers found that a strong start is a better strategy but keeping just in enough in reserve to provide a final kick to the finish line.

“Information on a horse speed, endurance or running economy coupled with simulations can help to predict how a horse profile is adapted to some distances to run,” the authors write, adding that “to maximize an individual horse’s potential for winning, it should be entered in races appropriate for its racing ability”.

Their paper in PLOS One is called “Optimal speed in Thoroughbred horse racing”.

Chemical precursors to life could form in dark interstellar clouds

Some key molecular building blocks of life could have been created far earlier on in the formation of the solar system than previously thought. Experiments and simulations done by Sergio Ioppolo at Queen Mary University of London and an international team have revealed how simple amino acids may have emerged via reactions on the surfaces of cold interstellar dust grains, long before the Sun first formed. The discovery could transform our understanding of how life-forming compounds first arrived on the primordial Earth.

Ice contained within comets is thought to be some of the oldest and most pristine material in the solar system. By determining its composition, scientists can glimpse conditions present when comets first formed, alongside the Sun and the planets.

In 2014, the ESA’s Rosetta probe arrived at the comet 67P/Churyumov-Gerasimenko and measured the chemical makeup of comet ice for the first time. Rosetta found evidence for the amino acid glycine and its precursor methylamine in 67P’s coma of sublimated ice. Both molecules are key building blocks of life on Earth.

Ancient molecules

Further investigation suggested that the molecules had become embedded in the pristine water ice coating the surfaces of dust particles ejected from 67P, and had never been substantially altered by heat or liquid water at any point in the comet’s history.

At the time, modelling suggested that glycine and methylamine could have been created in the ice by exposure to radiation including cosmic rays and ultraviolet photons. Now, however, Ioppolo’s team argue that this radiation would damage complex molecules after producing them.

In their study, the researchers looked at whether the molecules could have been made by “non-energetic” reactions that occurred within the dense, dark dust clouds that are characteristic of early star formation. Through lab-based experiments, they recreated these conditions using bare dust grains coated in a water-rich ice layer, which they released inside an ultra-high vacuum chamber.

Intermediate radicals

Even in such low-energy conditions, the chemistry observed by the team was surprisingly rich. Within the ice a wealth of non-energetic reactions involving atoms and free radicals was observed. This produced species including methane, ammonia, and carbon dioxide; as well as the intermediate radicals required to produce glycine and methylamine.

The team then investigated these processes further using astrochemical models. This involved using laboratory data as a basis to extrapolate the chemical reactions which would likely take place in the next million years. They calculated that glycine likely becomes abundant during the latter few 100,000s of years of evolution, as interstellar gas densities increase substantially.

Once formed, the glycine could then become a precursor to more complex amino acids, as functional groups are added to its backbone. Eventually, ice-coated dust grains would coalesce into planetesimals like comets – which can deliver complex biological molecules to newly forming planets.

The research is described in Nature Astronomy.

Dramatic footage emerges of Arecibo Observatory collapse

The Arecibo Observatory and the National Science Foundation (NSF) have released shocking footage of the moment earlier this week when the 900 tonne platform collapsed onto the 305 m-wide dish.

The video was captured by a drone that was filming as disaster struck. In a briefing along with the release of the footage, the NSF said it is now working to mitigate environmental issues and finding a way to support the scientific community.

“We recognise the significance of this loss to Puerto Rico and to so many that have called Arecibo their home whether for years or a week,” noted Ashley Zauderer, NSF programme director for Arecibo. “It inspired schoolchildren and visitors, and it inspired scientific discovery.”

‘Magnetic illusion’ can create magnetic fields at a distance

Physicists in the UK and Spain claim that they have found a way to generate and manipulate magnetic fields at a distance. This opens up the possibility of projecting magnetic fields into inaccessible spaces and enables the remote cancellation of magnetic sources, the researchers say. One application of this technique could be improving the control of magnetic microbots and nanoparticles within the human body, for medical applications such as drug delivery and magnetic hyperthermia therapies.

In recent years, metamaterials have enabled scientists to manipulate magnetic fields in unexpected ways, such as creating a magnetic cloak that can make an object magnetically undetectable and magnetic wormholes, which transport a magnetic field from one point in space to another.

In this latest work, published in Physical Review Letters, Rosa Mach-Batlle at the Universitat Autònoma de Barcelona and her colleagues wanted to see if they could generate a magnetic field that appears in free space, at a distance from its source.

Mach-Batlle tells Physics World that theory showed that to achieve this, they would need a magnetic material with negative permeability. Magnetic permeability is the ability of a material to acquire magnetization in magnetic fields. But there are no natural materials with negative permeability values.

Previously, the researchers had shown that a metamaterial with negative-permeability can be created by applying a precise arrangements of currents to the material. This time, their theory showed that a long cylindrical tube with a magnetic permeability of −1 would act as a lens for electromagnetic waves. If this cylinder was then placed around a magnetic source, the distribution of the magnetic field outside this shell would appear as if it had been created by another magnetic source – a kind of magnetic illusion – at a distance from the cylinder.

To create the metamaterial, the physicists used a 400 mm-long cylinder with a 40 mm radius. With an arrangement of 20 wires, they controlled the surface current densities on its internal and external surfaces. A wire running through the centre of the tube generated the magnetic field.

Calculated magnetic field distribution created by 20 current-carrying wires surrounding a centre wire (yellow dots) forming the replicator. The magnetic source created at a distance is seen in the shaded rectangle. (Courtesy: *Phys. Rev. Lett.* 10.1103/PhysRevLett.125.177204)

The researchers showed that with this set up they could create magnetic sources at a distance from the cylinder. They also demonstrated that the metamaterial can be used to remotely cancel another magnetic field, by setting up a wire with a current flowing through it at the point where they expected the projected magnetic field to appear. The magnetic fields generated by the wire and the metamaterial cancelled each other out. This technique could be used, the team say, to remotely cancel magnetic sources in inaccessible spaces, such as within a wall or inside a human body.

Mach-Batlle tells Physics World that it is worth noting that the magnetic field is not cancelled in all of the space. “There is a cylindrical region between our metamaterial and the source that we cancel,” she explains. “In this small region, the field is not cancelled, but in the rest of the space we would be cancelling the field of the source that we chose to cancel.”

The main practical application for this technique, Mach-Batlle believes, is not in cancelling magnetic sources, but in being able to create the illusion of a magnetic field at a distance inside inaccessible spaces. This could have important implications in medicine, as it could be possible to project a magnetic source inside the body.

If you create the illusion of a magnetic source inside the body, Mach-Batlle explains, you get a much stronger field compared with having the sources outside of the body. This could be useful for the control and manipulation of nanoparticles for drug delivery and nanorobots that could be used for various types of surgery.

“Also, in neuroscience, we think that it can have implications for transcranial magnetic simulation,” Mach-Batlle says. This technique for generating electric current at a specific area of the brain is an evolving area of research that has shown diagnostic and therapeutic potential in a number of neurological diseases and mental health conditions.

Quantum advantage demonstrated using Gaussian boson sampling

A optical circuit has performed a quantum computation called “Gaussian boson sampling” (GBS) 100 trillion times faster than a supercomputer could, according to researchers in China. This feat was achieved by Jian-Wei Pan and Chao-Yang Lu at the University of Science and Technology of China in Hefei, and colleagues. Although GBS is devised to show that a quantum computation can be done much faster than the same calculation on a conventional computer – a capability called quantum advantage – it may also have specialized practical applications.

Boson sampling is a way of computing the output of a linear optical circuit that has multiple inputs and multiple outputs. Single photons enter the circuit in parallel and encounter optical components such as beam splitters. Due to their bosonic nature, if two photons arrive at a beam splitter at the same time, they will both follow the same path. This property makes it extremely difficult to use a conventional computer to calculate the output of the circuit even for modest numbers of input photons and output channels. While boson sampling is difficult to do and requires state-of-the art quantum optics, it should vastly outperform even the most powerful supercomputers

A Boson sampling circuit can be thought of as a matrix that makes a transformation of the input photons. Calculating the output involves working out the “permanent” of the matrix, which is related to the determinant of the matrix but is much more difficult to calculate. Boson sampling determines the permanent by sending groups of single photons into the optical circuit and measuring the output. The number of photons is less than the number of output modes of the circuit – so three photons could be sent into a six-mode circuit, for example.

Single mode squeezed states

In this latest research, the team used a related technique called Gaussian boson sampling (GBS), in which single mode squeezed states of light are used in place of single photons. Instead of determining the permanent of the circuit, Gaussian boson sampling gives a similar quantity that is also extremely difficult to compute using a conventional computer.

According to Pan, GBS offers two important advantages over the single-photon technique. First is that the photon generation rate is much higher for GBS than it is for single-photon boson sampling, and second there are “many proposals for practical applications based on [GBS]”.

The team’s optical circuit has 100 inputs and 100 outputs and comprises 300 beam splitters and 75 mirrors that are arranged in a random manner. The system is fully connected, so a photon at any input port can emerge from any of the output ports.

GBS took about 200 s to make the desired calculation, whereas the team estimate that China’s fastest supercomputer Sunway TaihuLight would take 2.5 billion years to do the calculation.

“Important milestone”

“This experiment is definitely an important milestone for quantum simulations based on linear optical systems,” says Christine Silberhorn at Paderborn University in Germany – who along with colleagues first proposed GBS in 2017. She points out that scaling-up the system to its 100×100 size would have been very challenging.

Ian Walmsley at Imperial College London agrees, adding that the team has made a “heroic effort” at “preparing quantum states that are entirely indistinguishable, and making sure the photons aren’t lost”. However, he points out that use of bulk optics rather than integrated optics could make it difficult to further scale-up the system.

Undaunted, Lu says that the team has made a “considerable improvement of the efficiency of the quantum light sources,” which he says should enable a 144×144 version of the experiment. Looking further ahead he says, “In 2021, we will make the GBS machine more tuneable, more compact and more stable, and look for practical applications”.

Molecular spectra

Although the current system has no practical application beyond demonstrating quantum advantage Pan says, “we are excited by the potential usefulness of boson sampling as the community has come up with many ideas”.

Walmsley adds, “There are some interesting simulation problems that might benefit from this new scale b boson sampler, including modelling of molecular spectra and vibrational dynamics. However, even those require the addition of a deterministic nonlinearity at the single-photon level in order to be able to handle real-world systems accurately.”

The research is described in Science.

A passion for nanotechnology in medicine: Black in Nanotech Week cofounder Olivia Geneus on inspiring new nanoscientists

The second week in December is Black in Nanotech Week and its co-founder Olivia Geneus is our guest in this episode of the Physics World Weekly podcast. Geneus talks to Margaret Harris about her interest in using nanotechnology to develop new ways of treating cancer, and about the need to highlight the accomplishments of Black scientists in the field of nanotechnology and inspire the next generation of nanoscientists.

We love a quiz here at Physics World, so to celebrate this week’s Materials Research Society Virtual Meeting and Exhibit we have put together a quiz about songs and bands with materials in their titles or lyrics. In the podcast, quizmaster Matin Durrani tests the musical knowledge of Tom Miller, who runs several materials-related journals at IOP Publishing.

This week we learned that the Arecibo Observatory in Puerto Rico has been destroyed as its metal platform collapsed onto its reflecting dish. We chat about the sad demise of this iconic radio telescope and its effect on Puerto Rico and the astronomy community.

Astronomers reveal most detailed atlas of the Milky Way

The European Space Agency (ESA) has released the latest star map of the Milky Way taken by its €450m Gaia mission. Gaia’s third data set, released today, contains high-precision measurements of nearly 2 billion stars, allowing astronomers to trace the various populations of older and younger stars out towards the very edge of our galaxy – the so-called “galactic anticenter”. The new data will also let scientists study how the solar system formed as well as its acceleration compared to the universe.

Gaia was launched in December 2013 and started observations the following year from its position around 1.5 million kilometres from Earth in the opposite direction from the Sun. Gaia has two telescopes and the spacecraft rotates once every six hours so that they scan the sky, focusing light onto a huge CCD sensor with nearly a billion pixels – one of the largest ever flown in space. Gaia’s mission is to plot the precise positions, motions, temperatures, luminosities and compositions of over a billion stars across the Milky Way.

The first data release, based on just over one year of observations, was published in 2016 and contained the distances and motions of two million stars that was followed by a second release in 2018 that covered the period between July 2014 and May 2016. This included high-precision measurements of nearly 1.7 billion stars as well as measurements of asteroids within our solar system.

The third data set comes in two parts, with today’s announcement being an early release of the full set, which is planned for 2022. “The new Gaia data promise to be a treasure trove for astronomers,” says Jos de Bruijne, ESA’s Gaia deputy project scientist.

Durable perovskite solar cells

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Dr Anita Ho-Baillie will start the talk with an introduction of perovskite solar cells followed by an outline of the instability issues of perovskite solar cells. She will then move onto the strategies addressing these such as moisture instabilty. The why and how perovskite solar cells become unstable under thermal stress will be discussed followed by our strategies of overcoming this.

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Dr Anita Ho-Baillie research interest is to engineer materials and devices at nanoscale for integrating solar cells onto all kinds of surfaces generating clean energy. A Clarivate Highly Cited Researcher (2019), Dr Ho-Baillie is considered an international leader in advancing perovskite solar cells. Her achievements include setting solar-cell energy-efficiency world records in various categories.

Hot time for hard disks: why magnetic-recording technology is still going strong

When it comes to storing data, you might think that magnetic devices are rapidly becoming a thing of the past. Surely solid-state drives are the future? But when I visited Queen’s University Belfast earlier this year, I was surprised to see lots of exciting R&D going on in magnetic storage. My host was the physicist Robert Bowman, who works closely with Seagate Technology – one of the world’s largest manufacturers of magnetic storage devices and products.

Seagate is among the firms developing new approaches to magnetic storage to allow data to be stored more quickly and with higher density than ever before. Indeed, it sees no end in sight for the technology. The market-intelligence firm IDC, for example, expects the amount of data stored in such devices to rise from 33 zettabytes (33 × 10²¹ bytes) in 2018 to 175 zettabytes by 2025. If you stored that much information on Blu-ray discs, stacked together they would stretch 23 times the distance to the Moon.

Over 350 million hard disks are shipped every year and by 2029 the global market is expected to surpass $80bn globally

In terms of cost and speed of access, magnetic storage wins hands down. And even if solid-state storage were cheaper (which it isn’t and probably never will be), there just isn’t enough fabrication capacity to physically build the storage we are projected to need in time. Over 350 million hard disks are shipped every year and by 2029 the global market is expected to surpass $80bn globally. Seagate’s technology facility in Northern Ireland alone makes almost 30% of the global supply of read/write heads.

Spinning a yarn

It’s incredible how far we’ve come in magnetic storage since 1888 when the US engineer Oberlin Smith first proposed storing audio in tiny metallic particles on a thread of cotton or silk. Practical difficulties stopped Smith’s ideas in their tracks, but in 1928 the German-Austrian engineer Fritz Pfleumer developed the first magnetic tape recorder – an analogue device for storing sound. Magnetic tape was first used for data storage in 1951 when the UNIVAC I computer was developed.

These days digital “linear-tape” cart-ridges are the cheapest form of storage, costing well below $0.01 per gigabyte. They have an immense storage capacity, with the latest cartridges being able to cram 30 TB (30 × 10¹² bytes) of data – a figure that’s expected to grow to 40 TB by the end of the decade. It’s a $5.8bn market that will rise to $6.5bn by 2026 according to market intelligence company PMR, partly driven by the need for offline back-ups and copies for disaster recovery and to counter the growing “ransomware” threat.

Linear thinking

The trouble with tapes is that they’re linear strips, which means it takes time to go from one part to another. That’s one reason why we have hard disks, which allow data to be accessed more quickly by jumping from one circular ring, or track, to another. The first commercial computer to use a moving-head disk drive was IBM’s RAMAC 305, produced in 1956. Containing 50 disks, each 24 inches in diameter, it offered 5 MB of storage, which was huge back then. These days a hard disk has up to 20 TB of capacity, costs less than $0.02 per gigabyte and fits in the palm of your hand.

Hard disks are marvels of physics and technological innovation. Tiny read/write heads fly above their mirror-like surface (itself a complex multi-layer ferromagnetic coating) with a clearance of as little as 3 nm. Operating in a humidity-controlled air- or helium-filled cavity, the height is controlled by an air bearing etched onto the head’s disk-facing surface and attached to a photo-etched precision-machined slider (itself controlled by an ultra-precise stepper motor).

Each hard-disk track – of which there are about a million per inch – contains bits of information recorded into tiny areas just 42 nm wide (roughly six to eight magnetic grains) and 10 nm long (barely two to three grains). The disks rotate at speeds of up to 15,000 revs per minute (as fast as the engine on a Formula 1 car) while the read/write heads themselves are fabricated on 200 mm wafers using state-of-the-art photolithography and micro- and nano-fabrication processes.

A hard disk’s unique mix of semiconductor technologies, precision machining and ultra-precise stepper motors is a staggeringly impressive piece of engineering

Modern heads are based on tunnelling magnetoresistance (a quantum effect linked to the 2007 Nobel Prize for Physics), but more advanced designs are being explored to increase the density further still. Each hard disk also has multiple heads and multiple double-sided disks (depending on the storage required), plus lots of precision-control electronics. What a pity that most hard disks are encased in dull-looking metal boxes that live in thousands of dull‑looking “cloud” data centres around the world.

For me, a hard disk’s unique mix of semiconductor technologies, precision machining and ultra-precise stepper motors is a staggeringly impressive piece of engineering. If modern hard disks didn’t exist and you asked a team of engineers to design one from scratch – with a sub-$50 price tag – they’d think you were crazy and give you a thousand reasons why it couldn’t be done, not at any price. Yet thanks to half a century of hard work and the power of incremental technological development, such devices do clearly exist.

A date with density

And as Bowman explained, thanks to “heat-assisted magnetic recording” (HAMR), Seagate has been able to increase the storage density of its hard disks to more than 2 TB per square inch, with the bits written via a laser and plasmonic near-field transducer integrated into the read/write head. The firm will soon ship its first HAMR-based drives and Seagate is targeting 50 TB drives by 2026. So next time you check social media, browse the Web or look at a photo stored in the cloud, remember your data are on a hard disk on low-power standby, at a data centre somewhere in the world, waiting for your command.

The humble hard disk is one of the least humble things imaginable.

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Quantum weirdness, smart speakers, festive books: the December 2020 issue of Physics World is now out

Celebrating the Institute of Physics at 100: the November 2020 issue of Physics World is now out