Cosmologists have long wondered whether dark energy and the accelerating expansion of the universe is an illusion. Now the evidence backing this idea is mounting.
One of the most common features found at large volcanoes are calderas, formed by the collapse of the land due to eruption. The scale of these features varies a lot depending on if you're on Earth or Mars.
From squirting cucumbers to cosmic stamps, physics has had its fair share of quirky stories this year. Here is our pick of the best 10, not in any particular order.
Escape from quantum physics
Staff at the clunkily titled Dresden-Würzburg Cluster of Excellence for Complexity and Topology in Quantum Matter (ct.qmat) had already created a mobile phone app “escape room” to teach children about quantum mechanics. But this year the app became reality at Dresden’s science museum. Billed as “Germany’s first quantum physics escape room”, the Kitty Q Escape Room has four separate rooms and 17 puzzles that offer visitors a multisensory experience that explores the quirky world of quantum mechanics. The goal for participants is to discover if Kitty Q – an imaginary being that embodies the spirit of Schrödinger’s cat – is dead or alive. Billed as being “perfect for family outings, children’s birthday parties and school field trips”, the escape room “embraces modern gamification techniques”, according to ct.qmat physicist Matthias Vojuta, “We ensure that learning happens in an engaging and subtle way,” he says. “The best part [is] you don’t need to be a maths or physics expert to enjoy the game.
Corking research
Coffee might be the drink of choice for physicists, but when it comes to studying the fascinating physics of liquids, champagne is hard to beat. That’s mostly because of the huge pressures inside the bottle and the explosion of bubbles that are released once the cork is removed. Experiments have already examined the expanding gas jet that propels the cork stopper out of a just-opened bottle caused by the radiation of shock waves up the neck. Now physicists in Austria have looked at the theory of how these supersonic waves move. The “Mach disc” that forms just outside the bottle opening is, they found, convex and travels away from the bottle opening before moving back towards it. A second Mach disc then forms when the first disc moves back although it’s not clear if this splits from the first or is a distinct disc. Measuring the distance of the Mach disc from the bottle also provides a way to determine the gas pressure or temperature in the champagne bottle.
Cosmic stamps
We love a good physics or astronomy stamp here at Physics World and this year’s offering from the US Postal Service didn’t disappoint. In January, they released two stamps to mark the success of NASA’s James Webb Space Telescope (JWST), which took off in 2021. The first features an image taken by the JWST’s Near-Infrared Camera of the “Cosmic Cliffs” in the Carina Nebula, located about 7600 light-years from Earth. The other stamp has an image of the iconic Pillars of Creation within the vast Eagle Nebula, which lies 6500 light-years away that was captured by the JWST’s Mid-Infrared Instrument. “With these stamps, people across the country can have their own snapshot of Webb’s captivating images at their fingertips,” noted NASA’s head of science, the British-born physicist Nicola Fox.
Record-breaking cicadas
This year marked the first time in more than 200 years that two broods belonging to two species of cicadas emerged at the same time. And the cacophony that the insects are famous for wasn’t the only aspect to watch out for. Researchers at Georgia Tech in the US examined another strange aspect of these creatures – how they wee. We know that most insects urinate via droplets as this is more energy efficient than emitting a stream of liquid. But cicadas are such voracious eaters of tree sap that individually flicking each drop away would be too taxing. To get around this problem, cicadas (just as we do) eject the pee via a jet, which the Georgia Tech scientists looked at for the first time. “Previously, it was understood that if a small animal wants to eject jets of water, then this [is] challenging, because the animal expends more energy to force the fluid’s exit at a higher speed,” says Elio Challita, who is based at Harvard University. “This is due to surface tension and viscous forces. But a larger animal can rely on gravity and inertial forces to pee.” According to the team, cicadas are the smallest animal to create such high-speed jets – a finding that could, say the researchers, lead to the design of better nozzles and robots.
Ale in a day’s work Researchers conduct a beer-tasting session at the University of Leuven in Belgium. (Courtesy: Justin Jin)
Raising the bar
Machine learning was a big topic this year thanks to the 2024 Nobel prizes for both physics and chemistry. Not to be outdone, scientists from Belgium announced they had used machine-learning algorithms to predict the taste and quality of beer and what compounds brewers could use to improve the flavour of certain tipples. Kevin Verstrepen from KU Leuven and colleagues spent five years characterizing over 200 chemical properties from 250 Belgian commercial beers across 22 different styles, such as Blond and Tripel beers. They also gathered tasting notes from a panel of 15 people and from the RateBeer online beer review database. A machine-learning model that was trained on the data could predict the flavour and score of the beers using just the beverages’ chemical profile. By adding certain aromas predicted by the model, the team was even able to boost the quality – as determined by blind tasting – of existing commercial Belgian ale. The scientists hope the findings could be used to improve alcohol-free beer. Yet KU Leuven researcher Michiel Scheurs admits that they did celebrate the work “with the alcohol-containing variants”.
Beetling away
Whirligig beetles can reach speeds of up to 1m/s – or 100 body lengths per second – as they skirt across the water. Scientists thought the animals did this using their oar-like hind legs to generate “drag-based” thrust, a bit like how a rodent swims. To do so, however, the beetle would need to move its legs faster than its swimming speed, which in turn would require pushing against the water at unrealistic speeds. To solve this bugging problem, researchers at Cornell University used high-speed cameras to film the whirligigs as they swam. They found that the beetles instead use lift-based thrust, which has been documented in whales, dolphins and sea lions. The thrusting motion is perpendicular to the water surface and the researchers calculate that the forces generated by the beetle in this way can explain their speedy movements in the water. According to Cornell’s Yukun Sun, that makes whirligig beetles “by far the smallest organism to use lift-based thrust for swimming”.
Tough nut to crack: Pistachios come in different shapes and sizes with the shells being non-symmetric. (Courtesy: Shutterstock/everydayplus)
Pistachio packing problem
It sounds like a question you might get in an exam: if you have a full bowl of N pistachios, what size container do you need for the leftover 2N non-edible shells? Given that pistachios come in different shapes and sizes and the shells are non-symmetric, the problem’s a tougher nut to crack than you might think. Thankfully, the secret of pistachio-packing was revealed in a series of experiments by physicists Ruben Zakine and Michael Benzaquen from École Polytechnique in Palaiseau, France. After placing 613 pistachios in a two-litre cylinder, they found that the container holding the shells needs to be just over half the size of the original pistachio bowl for well-packed nuts and three-quarters for loosely packed pistachios. Zakine and Benzaquen say that numerical simulations could be carried out to compare with the experimental findings and that the work extends beyond just nuts. “Our analysis can be relevant in other situations, for instance to determine the optimal container needed [for] mussel or oyster shells after a Pantagruelian seafood diner,” they claim
The physics of paper cuts
If you’ve ever been on the receiving end of a paper cut, you’ll know how painful it can be. To find out why paper is able to slice through skin so well, Kaare Jensen – a physicist from the Technical University of Denmark – and colleagues carried out a series of experiments using paper with a range of thicknesses to make incisions into a piece of gelatine at various angles. When combined with modelling, they discovered that paper cuts are a competition between slicing and “buckling”. Thin paper with a thickness of about 30microns doesn’t cut skin so well because it buckles – a mechanical instability that happens when a slender object like paper is compressed. But thick paper (above about 200microns) is poor at making an incision because it distributes the load over a greater area, resulting in only small indentations. The team discovered, however, that there is a paper cut “sweet spot” at around 65microns, which just happens to be close to the paper thickness used in print magazines. The researchers have now put their findings to use, creating a 3D-printed scalpel that uses scrap paper for the cutting edge. Dubbed a “papermachete”, it can slice through apple, banana peel, cucumber and even chicken. “Studying the physics of paper cuts has revealed a surprising potential use for paper in the digital age: not as a means of information dissemination and storage, but rather as a tool of destruction,” the researchers write.
Quick fire round: just before launch the fruit of the squirting cucumber rotates from bring vertical to close to an angle of 45 degrees, improving the launch angle for the seeds (courtesy: Derek Moulton).
Squirting cucumbers
The plant kingdom is full of intriguing ways to distribute seeds such as the dandelion pappus effortlessly, drifting on air currents. Not to be outdone, the squirting cucumber (Ecballium elaterium), which is native to the Mediterranean and is often regarded as a weed, has its own unique way of ejecting seeds. When ripe, the ovoid-shaped fruits detach from the stem and as it does so explosively ejects seeds in a high-pressure jet of mucilage. The process, which lasts just 30 ms, launches the seeds at more than 20 m/s with some landing 10 m away. Researchers in the UK revealed the mechanism behind the squirt for the first time by using high-speed imaging and mathematical modelling. The researchers found that in the weeks leading up to the ejection, fluid builds up inside the fruits so they become pressurized. Then just before seed dispersal, some of this fluid moves from the fruit to the stem, making it longer and stiffer. This process crucially causes the fruit to rotate from being vertical to close to an angle of 45°, improving the launch angle for the seeds. During the first milliseconds of ejection, the tip of the stem holding the fruit then recoils away causing the pod to counter-rotate and detach. As it does so, the pressure inside the fruit causes the seeds to eject at high speed. By changing parameters in the model, such as the stiffness of the stem, reveals that the mechanism has been fine-tuned to ensure optimal seed dispersal.
Chimp Shakespeare
And finally, according to the infinite monkeys theorem, a monkey randomly pressing keys on a typewriter for an infinite amount of time would eventually type out the complete works of William Shakespeare purely by chance. Yet analysis by two mathematicians in Australia found that even a troop might not have time to do so within the supposed timeframe of the universe. The researchers came to their conclusion after creating a computational model that assumed a constant chimpanzee population of 200 000, each typing at one key per second until the end of the universe in about 10100 years. If that is true, there’d be only a 5% chance a single monkey would type “bananas” within its own lifetime of just over 30 years. But even all the chimps feverishly typing away couldn’t produce Shakespeare’s entire works (coming in at over 850 000 words) before the universe ends. “It is not plausible that, even with improved typing speeds or an increase in chimpanzee populations, monkey labour will ever be a viable tool for developing non-trivial written works,” the authors conclude, adding that while the infinite monkeys theorem is true, it is also “somewhat misleading”, or in reality it’s “not to be”.
You can be sure that next year will throw up its fair share of quirky stories from the world of physics. See you next year!
From childhood malaria vaccines to record-breaking solar panels to the discovery of a lost ancient city, this tumultuous year still had plenty of high points.
From vicious storms and relentless global heating, to volcanic eruptions and shimmering aurora, compelling images help tell the story of a drama-filled year.
The past few years have seen several missions to the Moon and that continued in 2024. Yet things didn’t get off to a perfect start. In 2023, the Japanese Space Agency, JAXA, launched its Smart Lander for Investigating Moon (SLIM) mission to the Moon. Yet when it landed in January, it did so upside down. Despite that slight mishap, Japan still became the fifth nation to successfully soft land a craft on the Moon, following the US, Soviet Union, China and India.
In February, meanwhile, US firm Intuitive Machines achieved a significant milestone when it became the first private mission to soft land on the Moon. Its Odysseus mission touched down on the Moon’s Malapert A region, a small crater about 300 km from the lunar south pole. In doing so it also became the first US mission to make a soft landing on the Moon since Apollo 17 in December 1972.
Astronomy is unique in having a significant amateur community and while radio astronomy emerged from amateur beginnings, it is now the focus of elite, international global consortia. In this fascinating feature, astrophysicist and amateur radio astronomer Emma Chapman from the University of Nottingham, UK, outlined how the subject developed and why it needs to strike a fine balance between its science and engineering roots. And also make sure not to miss Chapman discussing the history of radio astronomy on the Physics World Stories podcast.
Hidden stories
Still on the podcast front, this Physics World Stories podcast from this year features a fascinating chat with astronaut Eileen Collins, who shared her extraordinary journey as the first woman to pilot and command a spacecraft. In the process, she broke several barriers in space exploration and inspired generations with her courage and commitment to discovery.
Star power: This spectacular image taken by Euclid shows Messier 78 – a nursery of star formation that is enveloped in a shroud of interstellar dust – that lies 1300 light-years away in the constellation of Orion
Euclid’s spectacular images
Astronomy and spectacular images go hand in hand and this year didn’t disappoint. While the James Webb Space Telescope continued to amaze, in May the European Space Agency released five spectacular images of the cosmos along with 10 scientific papers as part of Euclid’s early release observations. Euclid’s next data release will focus on its primary science objectives and is currently slated for March 2025, so keep an eye out for those next year.
What makes a physics story popular? The answer is partly hidden in the depths of Internet search algorithms, but it’s possible to discern a few trends in this list of the 10 most read stories published on the Physics World website in 2024. Well, one trend, at least: it seems that many of you really, really like stories about quantum physics. Happily, we’ll be publishing lots more of them in 2025, the International Year of Quantum Science and Technology. But in the meantime, here are 2024’s most popular stories – quantum and otherwise.
As main characters in quantum thought experiments go, Wigner’s friend isn’t nearly as well-known as Schrödinger’s cat. While the alive-or-dead feline was popularized in the mid-20th century by the science fiction and fantasy writer Ursula K LeGuin, Wigner and his best mate remain relatively obscure, and unlikely to appear in an image created with entangled light (more on this later). Still, there’s plenty to ponder in this lesser-known thought experiment, which provocatively suggests that in the quantum world, what’s true may depend, quite literally, on where you stand: with Wigner’s friend inside a lab performing the quantum experiment, or with Wigner outside it awaiting the results.
Popularity isn’t everything. This story focused on a paper about a high-temperature superconducting wire that appeared to have a current density 10 times higher than any previously reported. Unfortunately, the paper’s authors made an error when converting the magnetic units they used to calculate current density. This error – which the authors acknowledged, leading to the paper’s retraction – meant that the current density was too high by… well, by a factor of 10, actually.
Surprisingly, this wasn’t the most blatant factor-of-10 flop to enter the scientific literature this year. That dubious honour belongs to a team of environmental chemists who multiplied 60 kg x 7000 nanograms/kg to calculate the maximum daily dose of potentially harmful chemicals, and got an answer of…42 000 nanograms. Oops.
Remember the entangled-light Schrödinger’s cat image? Well, here it is again, this time in its original context. In an experiment that made it onto our list of the top 10 breakthroughs of 2024, researchers in France used quantum correlations to encode an image into light such that the image only becomes visible when particles of light (photons) are observed by a single-photon sensitive camera. Otherwise, the image is hidden from view. It’s a neat result, and we’re glad you agree it’s worth reading about.
At this time of year, some of us in the Northern Hemisphere feel like we’re inhabiting an icy exoplanet already, and some of you experiencing Southern Hemisphere heat waves probably wish you were. Sadly, none of us is ever going to live on (or even visit) the temperate exoplanet LHS 1140 b, which is located 49 light-years away from Earth and has a mass 5.6 times larger. Still, astronomers think this watery, icy world could be only the third planet (after Earth and Mars) in its star’s habitable zone known to have an atmosphere, and that was enough to pique readers’ interest.
Toroidal pulses Air cannons produce visible vortex rings by generating rotating air pressure differences, while electromagnetic cannons emit electromagnetic vortex pulses using coaxial horn antennas. (Courtesy: Ren Wang; Pan-Yi Bao; Zhi-Qiang Hu; Shuai Shi; Bing-Zhong Wang; Nikolay I Zheludev; Yijie Shen)
An electromagnetic vortex cannon might sound like an accessory from Star Trek. In fact, it’s a real object made from a device called a horn microwave antenna. It gets its name because it generates an electromagnetic field in free space that rotates around the propagation direction of the wave structure, similar to how an air cannon blows out smoke rings. According to its inventors, the electromagnetic vortex cannon could be used to develop communication, sensing, detection and metrology systems that overcome the limitations of existing wireless applications.
Returning to the quantum theme, the fifth-most-read story of 2024 concerned an experiment that demonstrated a new violation of the Leggett-Garg inequality (LGI). While the better-known Bell’s inequality describes how the behaviour of one object relates to that of another object with which it is entangled, the conceptually similar LGI describes how the state of a single object varies at different points in time. If either inequality is violated, the world is quantum. Previous experiments had already observed LGI violations in several quantum systems, but this one showed, for the first time, that neutrons in a beam must be in a coherent superposition of states – a fundamental property of quantum mechanics.
True impact: a new study finds that “foundational” ideas in science are often not properly cited, which can skew rankings. (Courtesy: iStock/ilbusca)
When a scientific paper introduces a concept that goes on to become common knowledge, you might expect later researchers to cite the living daylights out of it – and you would be wrong. According to the study described in this article, the ideas in many such papers become so well known that the opposite happens: no-one bothers to cite them anymore.
This means that purely citation-based metrics of research “impact” tend to underestimate the importance of seminal works such as Alan Guth’s 1981 paper that introduced the theory of cosmic inflation. So if your amazing paper isn’t getting the citation love it deserves, take heart: maybe it’s too foundational for its own good.
Physicists have been trying to produce a theory that incorporates both gravity and quantum mechanics for almost a century now. One of the sticking points is that we don’t really know what a quantum theory of gravity might look like. Presumably, it would have to combine the world of gravity (where space and time warp in the presence of massive objects) with the world of quantum mechanics (which assumes that space and time are fixed) – but how?
For the University College London theorist Jonathan Oppenheim, this is the wrong question. As this article explains, Oppenheim has developed a new theoretical framework that aims to unify quantum mechanics and classical gravity – but, crucially, without the need to define a theory of quantum gravity first.
Can a quantum system remain maximally entangled in a noisy environment? According to Julio I de Vicente from the Universidad Carlos III de Madrid, Spain, the answer is “no”. While the question and its answer might seem rather esoteric, this article explains that the implications extend beyond theoretical physics, with so-called “maximally entangled mixed states” having the potential to revolutionize our approach to other problems in quantum mechanics.
The science fiction writer Arthur C Clarke famously said that “Any sufficiently advanced technology is indistinguishable from magic.” Sadly for Clarke fans, the magic in this article doesn’t involve physicists chanting incantations or waving wands over their experiments. Instead, it refers to quantum states that are especially hard to simulate on classical machines. These so-called “magic” states are a resource for quantum computers, and the amount of them available is a measure of a system’s quantum computational power. Indeed, certain error-correcting codes can improve the quality of magic states in a system, which makes a pleasing connection between this, the most-read article of 2024 on the Physics World website, and our pick for 2024’s “Breakthrough of the year.” See you in 2025!
This year marked the 70th anniversary of the European Council for Nuclear Research, which is known universally as CERN. To celebrate, we have published a bumper crop of articles on particle and nuclear physics in 2024. Many focus on people and my favourite articles have definitely skewed in that direction. So let’s start with the remarkable life of accelerator pioneer Bruno Touschek.
Man of many talents Bruno Touschek pictured in 1955. (Courtesy: CC-BY-3.0: https://cds.cern.ch/record/135949)
Born in Vienna in 1921 to a Jewish mother, Bruno Touschek’s life changed when Nazi Germany annexed Austria in 1938. After suffering antisemitism in his hometown and then in Rome, he inexplicably turned down an offer to study in the UK and settled in Germany. There he worked on a “death ray” for the military but was eventually imprisoned by the German secret police. He was then left for dead during a forced march to a concentration camp in 1945. When the war ended a few weeks later, Touschek’s expertise came to the attention of the British, who occupied north-western Germany. He went on to become a leading accelerator physicist and you can read much more about the extraordinary life of Touschek in this article by the physicist and biographer Giulia Pancheri.
Today, the best atomic clocks would only be off by about 10 ms after running for the current age of the universe. But, could these timekeepers soon be upstaged by clocks that use a nuclear, rather than an atomic transition? Such nuclear clocks could rival their atomic cousins when it comes to precision and accuracy. They also promise to be fully solid-state, which means that they could be used in a wide range of commercial applications. This year saw physicists make new measurements and develop new technologies that could soon make nuclear clocks a reality. Click on the headline above to discover how physicists in the US have fabricated all of the components needed to create a nuclear clock made from thorium-229. Also, earlier this year physicists in Germany and Austria showed that they can put nuclei of the isotope into a low-lying metastable state that could be used in a nuclear clock. You can find out more here: “Excitation of thorium-229 brings a working nuclear clock closer”.
Expert panel Tulika Bose, Philip Burrows and Tara Shears were speaking on a Physics World Live panel discussion about the future of particle physics held on 26 September 2024. (Courtesy: Tulika Bose; Philip Burrows; McCoy Wynne)
In 2024 we launched our Physics World Live series of panel discussions. In September, we explored the future of particle physics with Tara Shears of the UK’s University of Liverpool, Phil Burrows at the University of Oxford in the UK and Tulika Bose at the University of Wisconsin–Madison in the US. Moderated by Physics World’s Michael Banks, the discussion focussed on next-generation particle colliders and how they could unravel the mysteries of the Higgs boson and probe beyond the Standard Model of particle physics. You can watch a video of the event by clicking on the above headline (free registration) or read an article based on the discussion here: “How a next-generation particle collider could unravel the mysteries of the Higgs boson”.
Neutrinos do not fit in nicely with the Standard Model of particle physics because of their non-zero masses. As a result some physicists believe that they offer a unique opportunity to do experiments that could reveal new physics. In a wide-ranging interview, the particle physicist Juan Pedro Ochoa-Ricoux explains why he has devoted much of his career to the study of these elusive subatomic particles. He also looks forward to two big future experiments – JUNO and DUNE – which could change our understanding of the universe.
Çiğdem İşsever “My main focus is to shed light, experimentally, on the so-called Higgs mechanism.” (Credit: DESY Courtesy of Cigdem Issever)
“Children decide quite early in their life, as early as primary school, if science is for them or not,” explains Çiğdem İşsever – who is leads the particle physics group at DESY in Hamburg, and the experimental high-energy physics group at the Humboldt University of Berlin. İşsever has joined forces with physicists Steven Worm and Becky Parker to create ATLAScraft, which creates a virtual version of CERN’s ATLAS detector in the hugely popular computer game Minecraft. In this profile, the science writer Rob Lea talks to İşsever about her passion for outreach and how she dispels gender stereotypes in science by talking to school children as young as five about her career in physics. İşsever also looks forward to the future of particle physics and what could eventually replace the Large Hadron collider as the world’s premier particle-physics experiment.
This year marked the 70th anniversary of the world’s most famous physics laboratory, so the last two items in my list celebrate that iconic facility nestled between the Alps and the Jura mountains. Formed in the aftermath of the Second World War, which devastated much of Europe, CERN came into being on 29 September 1954. That year also saw the start of construction of the Geneva-based lab’s proton synchrotron, which fired-up in 1959 with an energy of 24 GeV, becoming the world’s highest-energy particle accelerator. The original CERN had 12 member states and that has since doubled to 24, with an additional 10 associate members. The lab has been associated with a number of Nobel laureates and is a shining example of how science can bring nations together after a the trauma of war. Read more about the anniversary here.
Comms boss James Gillies in 2013. (Courtesy: CERN/Claudia Marcelloni)
When former physicist James Gillies sat down for dinner in 2009 with actors Tom Hanks and Ayelet Zurer, joined by legendary director Ron Howard, he could scarcely believe the turn of events. Gillies was the head of communications at CERN, and the Hollywood trio were in town for the launch of Angels & Demons. The blockbuster film is partly set at CERN with antimatter central to its plot, and is based on the Dan Brown novel. In this Physics World Stories podcast, Gillies looks back on those heady days. Gillies has also written a feature article for us about his Hollywood experience: “Angels & Demons, Tom Hanks and Peter Higgs: how CERN sold its story to the world”.
The reference frames from which observers view quantum events can themselves have multiple possible locations at once—an insight with potentially major ramifications.
With so much fascinating research going on in quantum science and technology, it’s hard to pick just a handful of highlights. Fun, but hard. Research on entanglement-based imaging and quantum error correction both appear in Physics World’slist of 2024’s top 10 breakthroughs, but beyond that, here are a few other achievements worth remembering as we head into 2025 – the International Year of Quantum Science and Technology.
Quantum sensing
In July, physicists at Germany’s Forschungszentrum Jülich and Korea’s IBS Center for Quantum Nanoscience (QNS) reported that they had fabricated a quantum sensor that can detect the electric and magnetic fields of individual atoms. The sensor consists of a molecule containing an unpaired electron (a molecular spin) that the physicists attached to the tip of a scanning-tunnelling microscope. They then used it to measure the magnetic and electric dipole fields emanating from a single iron atom and a silver dimer on a gold substrate.
Not to be outdone, an international team led by researchers at the University of Melbourne, Australia, announced in August that they had created a quantum sensor that detects magnetic fields in any direction. The new omnidirectional sensor is based on a recently-discovered carbon-based defect in a two-dimensional material, hexagonal boron nitride (hBN). This same material also contains a boron vacancy defect that enables the sensor to detect temperature changes, too.
Quantum communications
One of the challenges with transmitting quantum information is that pretty much any medium you send it through – including high-spec fibre optic cables and even the Earth’s atmosphere – is at least somewhat good at absorbing photons and preventing them from reaching their intended destination.
Networking: Liang Jiang reviews the proposed quantum network using vacuum beam guides, which would have ranges of thousands of kilometers and capacities of 10 trillion qubits per second. (Courtesy: UChicago Pritzker School of Molecular Engineering/John Zich)
In July, a team at the University of Chicago, the California Institute of Technology and Stanford University proposed a novel solution. A continent-scale network of vacuum-sealed tubes, they suggested, could transmit quantum information at rates as high as 1013 qubits per second. This would exceed currently-available quantum channels based on satellites or optical fibres by at least four orders of magnitude. Whether anyone will actually build such a network is, of course, yet to be determined – but you have to admire the ambition behind it.
Quantum fundamentals
Speaking of ambition, this year saw a remarkable flurry of ideas for using quantum devices and quantum principles to study gravity. One innovative proposal involves looking for the gravitational equivalent of the photoelectric effect in a system of resonant bars that have been cooled and tuned to vibrate when they absorb a graviton from an incoming gravitational wave. The idea is that absorbing a graviton would change the quantum state of the column, and this change of state would, in principle, be detectable.
Detecting gravity: Researchers have proposed an experiment that could detect the elusive graviton – a quantum of gravity – using quantum sensing. (Courtesy: Pikovski research group)
Another quantum gravity proposal takes its inspiration from an even older experiment: the Cavendish torsion balance. The quantum version of this 18th-century classic would involve studying the correlations between two torsion pendula placed close together as they rotate back and forth like massive harmonic oscillators. If correlations appear that can’t be accounted for within a classical theory of gravity, this could imply that gravity is not, in fact, classical.
Perhaps the most exciting development in this space, though, is a new experimental technique for measuring the pull of gravity on a micron-scale particle. Objects of this size are just above the limit where quantum effects start to become apparent, and the Leiden and Southampton University researchers who performed the experiment have ideas for how to push their system further towards this exciting regime. Definitely one to keep an eye on.
The best of the rest
It wouldn’t be quantum if it wasn’t at least little bit weird, so here’s a few head-scratchers for you to puzzle over.
Connexion
