Aurelia Butler

Systems in which mechanical motion is controlled at the level of individual quanta are emerging as a promising quantum-​technology platform. New experimental work now establishes how quantum properties of such systems can be measured without destroying the quantum state — a key ingredient for tapping the full potential of mechanical quantum systems.
When thinking about quantum mechanical systems, single photons and well-​isolated ions and atoms may spring to mind, or electrons spreading through a crystal. More exotic in the context of quantum mechanics are genuinely mechanical quantum systems; that is, massive objects in which mechanical motion such as vibration is quantized. In a series of seminal experiments, quintessential quantum-​mechanical features have been observed in mechanical systems, including energy quantization and entanglement. However, with a view to putting such systems to use in fundamental studies and technological applications, observing quantum properties is but a first step. The next one is to master the handling of mechanical quantum objects, so that their quantum states can be controlled, measured, and eventually exploited in device-​like structures. The group of Yiwen Chu in the Laboratory of Solid State Physics at ETH Zurich has now made major progress in that direction. Writing in Nature Physics, they report the extraction of information from a mechanical quantum system without destroying the precious quantum state. This advance paves the path to applications such as quantum error correction, and beyond.
Massive quantum mechanics
The ETH physicists employ as their mechanical system a slab of high-​quality sapphire, a little under half a millimetre thick. On its top sits a thin piezoelectrical transducer that can excite acoustic waves, which are reflected at the bottom and thus extend across a well-​defined volume inside the slab. These excitations are the collective motion of a large number of atoms, yet they are quantized (in energy units known as phonons) and can be subjected, in principle at least, to quantum operations in very much the same ways as the quantum states of atoms, photons and electrons can be. Intriguingly, it is possible to interface the mechanical resonator with other quantum systems, and with superconducting qubits in particular. The latter are tiny electronic circuits in which electromagnetic energy states are quantized, and they are currently one of the leading platforms for building scalable quantum computers. The electromagnetic fields associated with the superconducting circuit enable the coupling of the qubit to the piezoelectrical transducer of the acoustic resonator, and thereby to its mechanical quantum states.
In such hybrid qubit-resonator devices, the best of two worlds can be combined. Specifically, the highly developed computational capabilities of superconducting qubits can be used in synchrony with the robustness and long lifetime of acoustical modes, which can serve as quantum memories or transducers. For such applications, however, merely coupling qubit and resonator states will be not enough. For example, a straightforward measurement of the quantum state in the resonator destroys it, making repeated measurements impossible. What is needed instead is the capability to extract information about the mechanical quantum state in a more gentle, well-​controlled manner.
The non-​destructive path
Demonstrating a protocol for such so-​called quantum non-​demolition measurements is what Chu’s doctoral students Uwe von Lüpke, Yu Yang and Marius Bild, working with Branco Weiss fellow Matteo Fadel and with support from semester project student Laurent Michaud, now achieved. In their experiments there is no direct energy exchange between the superconducting qubit and the acoustic resonator during the measurement. Instead, the properties of the qubit are made to depend on the number of phonons in the acoustic resonator, with no need to directly ‘touch’ the mechanical quantum state — think about a theremin, the musical instrument in which the pitch depends on the position of the musician’s hand without making physical contact with the instrument.
Creating a hybrid system in which the state of the resonator is reflected in the spectrum of the qubit is highly challenging. There are stringent demands on how long the quantum states can be sustained both in the qubit and in the resonator, before they fade away due to imperfections and perturbations from the outside. So the task for the team was to push the lifetimes of both the qubit and the resonator quantum states. And they succeeded, by making a series of improvements, including a careful choice of the type of superconducting qubit used and encapsulating the hybrid device in a superconducting aluminium cavity to ensure tight electromagnetic shielding.
Quantum information on a need-​to-know basis
Having successfully pushed their system into the desired operational regime (known as the ‘strong dispersive regime’), the team were able to gently extract the phonon-​number distribution in their acoustic resonator after exciting it with different amplitudes. Moreover, they demonstrated a way to determine in one single measurement whether the number of phonons in the resonator is even or odd — a so-​called parity measurement — without learning anything else about the distribution of phonons. Obtaining such very specific information, but no other, is crucial in a number of quantum-​technological applications. For instance, a change in parity (a transition from an odd to an even number or vice versa) can signal that an error has affected the quantum state and that correcting is needed. Here it is essential, of course, that the to-​be-corrected state is not destroyed.
Before an implementation of such error-​correction schemes is possible, however, further refinement of the hybrid system is necessary, in particular to improve the fidelity of the operations. But quantum error correction is by far not the only use on the horizon. There is an abundance of exciting theoretical proposals in the scientific literature for quantum-​information protocols as well as for fundamental studies that benefit from the fact that the acoustic quantum states reside in massive objects. These provide, for example, unique opportunities for exploring the scope of quantum mechanics in the limit of large systems and for harnessing the mechanical quantum systems as a sensor. More

At first glance, a system consisting of 51 ions may appear easily manageable. But even if these charged atoms are only changed back and forth between two states, the result is more than two quadrillion (1015) different orderings which the system can take on.
The behavior of such a system is almost impossible to calculate with conventional computers, especially since an excitation introduced to the system can propagate erratically. The excitation follows a statistical pattern referred to as a Lévy Flight.
One characteristic of such movements is that, in addition to the smaller jumps which are to be expected, also significantly larger jumps take place. This phenomenon can also be observed in the flights of bees and in unusual fierce movements in the stock market.
Simulating quantum dynamics: Traditionally a difficult task
While simulating the dynamics of a complex quantum system is a very tall order for even traditional super computers, the task is child’s play for quantum simulators. But how can the results of a quantum simulator be verified without the ability to perform the same calculations it can?
Observation of quantum systems indicated that it might be possible to represent at least the long-term behavior of such systems with equations like the ones the Bernoulli brothers developed in the 18th century to describe the behavior of fluids. More

A recent study finds that realism is a key factor in determining whether viewers engage with virtual reality (VR) videos — and that engagement is itself a key factor in determining whether viewers are interested in watching VR videos in the future.
The researchers focused on VR videos that offer a 360-degree view of a given scene that viewers can navigate on conventional video screens; VR headsets were not required.
For the study, researchers surveyed 1,422 study participants located in the United States, all of whom had previous experience with virtual reality videos. Participants were asked a series of questions designed to explore both which factors drew them to VR videos and what elements of the videos increased viewer engagement.
“We found there were two aspects of virtual reality videos that were the most powerful predictors of whether viewers enjoyed VR videos and engaged with their content,” says Yang Cheng, first author of the study and an associate professor of communication at North Carolina State University. “Specifically, we found that realism and enjoyment were the key variables here. Another variable that contributed to user engagement was whether the VR videos were part of an interactive platform that allowed users to establish a sense of community.
“Our study is the first to identify that realism in these videos is a key variable in driving viewer engagement,” Cheng says. “And the more engaged viewers were, the more likely they were to want to view additional VR videos in the future.”
The researchers note that their findings can be used by video developers to improve user engagement and encourage continued use of immersive videos.
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Materials provided by North Carolina State University. Original written by Matt Shipman. Note: Content may be edited for style and length. More

Researchers at Karolinska Institutet in Sweden have studied how the screen habits of US children correlates with how their cognitive abilities develop over time. They found that the children who spent an above-average time playing video games increased their intelligence more than the average, while TV watching or social media had neither a positive nor a negative effect. The results are published in the journal Scientific Reports.
Children are spending more and more time in front of screens. How this affects their health and whether it has a positive or negative impact on their cognitive abilities are hotly debated. For this present study, researchers at Karolinska Institutet and Vrije Universiteit Amsterdam specifically studied the link between screen habits and intelligence over time.
Over 9,000 boys and girls in the USA participated in the study. At the age of nine or ten, the children performed a battery of psychological tests to gauge their general cognitive abilities (intelligence). The children and their parents were also asked about how much time the children spent watching TV and videos, playing video games and engaging with social media.
Followed up after two years
Just over 5,000 of the children were followed up after two years, at which point they were asked to repeat the psychological tests. This enabled the researchers to study how the children’s performance on the tests varied from the one testing session to the other, and to control for individual differences in the first test. They also controlled for genetic differences that could affect intelligence and differences that could be related to the parents’ educational background and income.
On average, the children spent 2.5 hours a day watching TV, half an hour on social media and 1 hour playing video games. The results showed that those who played more games than the average increased their intelligence between the two measurements by approximately 2.5 IQ points more than the average. No significant effect was observed, positive or negative, of TV-watching or social media.
“We didn’t examine the effects of screen behaviour on physical activity, sleep, wellbeing or school performance, so we can’t say anything about that,” says Torkel Klingberg, professor of cognitive neuroscience at the Department of Neuroscience, Karolinska Institutet. “But our results support the claim that screen time generally doesn’t impair children’s cognitive abilities, and that playing video games can actually help boost intelligence. This is consistent with several experimental studies of video-game playing.”
Intelligence is not constant
The results are also in line with recent research showing that intelligence is not a constant, but a quality that is influenced by environmental factors.
“We’ll now be studying the effects of other environmental factors and how the cognitive effects relate to childhood brain development,” says Torkel Klingberg.
One limitation of the study is that it only covered US children and did not differentiate between different types of video games, which makes the results difficult to transfer to children in other countries with other gaming habits. There was also a risk of reporting error since screen time and habits were self-rated.
The study was financed by the Swedish Research Council and the Strategic Research Area Neuroscience (StratNeuro) at Karolinska Institutet. The researchers report no conflicts of interest.
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Cells go through a life cycle that includes growing to the right size, being equipped to perform its functions, and finally dividing into two new cells. The cell cycle is critical because it ensures the perpetuation of the cell population and by extension of the greater structure they are a part of — for example a tissue in the body.
The cell cycle itself is tightly regulated by checkpoints, which prevent errors like mutations or DNA damage from being passed onto the next generation of cells. Each checkpoint acts as a kind of quality-control monitor (a biological “checklist”) that ensures the order, integrity, and fidelity of the cell cycle. But checkpoints themselves often fail or are overridden after a prolonged stop of the cell cycle. If this happens in the human body, the result could be unregulated cell growth and division, which is what happens in cancer.
“Checkpoints monitor cells or whole organisms and can stop either the cell cycle or the organism’s development when they detect problems,” says Sahand Jamal Rahi at EPFL’s School of Basic Sciences. “But if cells or organisms are stuck with an error for a very long time, in many cases, they just continue dividing or growing; they don’t stop forever. There is a real risk of dying if checkpoints do not stop at all, but also waiting forever is effectively equivalent to dying.”
The math of checkpoint override
The question is then, how does the cell balance risk and speed when dividing? Although critical, checkpoint override is not very well understood, neither theoretically nor experimentally. But in a new paper, Rahi and his colleagues put forward the first mathematical theory to describe the process of checkpoint override. “Many organisms have to predict what’s going to happen,” he says. “You have a problem and you have to assess how bad that problem could be because the consequences are not certain. You could survive this or you might not survive this. So, the cell makes a bet either way. And in this study, we analyze the odds of that bet.”
For a real-life model organism, the researchers looked at the budding yeast Saccharomyces cerevisiae, which has been used in winemaking, baking and brewing for centuries. “There are systems that monitor organisms, and among these systems, possibly the best studied is the DNA damage checkpoint in yeast,” says Rahi. “So, we thought, let’s look at that and see whether we can make sense of checkpoint overrides. We started with a mathematical analysis behind which was a very simple question: what if these organisms are balancing risk and speed because they have to predict the future?”
The risk-speed tradeoff More

An algorithm that can speed up by years the ability to identify from among thousands of possibilities, two or more drugs that work synergistically against a problem like cancer or a viral infection has been developed by bioinformatics experts.
The new algorithm enables investigators to use large existing databases with information about how one cancer drug changed the gene expression of a particular breast cancer cell line, and how well it killed the cell, then mathematically combine those results with the impact of another drug to see if they could work better together, says Dr. Richard McIndoe, director of the Center for Biotechnology and Genomic Medicine at the Medical College of Georgia.
While the algorithm does not immediately make available the kind of information that would set a clinical trial in motion, it does speed up the path to the trials, he says.
“The idea is we ultimately want to find these synergistic drug combinations that will hopefully help patients with cancer,” McIndoe says. “For researchers it becomes a particularly faster way to find those synergistic combinations, without having to screen one drug at a time, which is really not feasible.”
Drug combination therapies can improve drug efficiency, reduce drug dosage (and related toxicity) and overcome drug resistance in cancer treatments,” the investigators write in the journal PLOS ONE, and is becoming an important tool in cancer treatment.
“It’s not uncommon for the cancer to become resistant to chemotherapy drugs so one of the ways that clinicians try to get around that is using combinations, two chemotherapy drugs together,” McIndoe says. “The likelihood that you will develop resistance to both of them simultaneously is lower than if you had just one.”
But given the number of drugs and drug combinations available, there are not efficient, effective ways to identify the best combinations, the investigators say. More

Researchers have used a widespread species of blue-green algae to power a microprocessor continuously for a year — and counting — using nothing but ambient light and water. Their system has potential as a reliable and renewable way to power small devices.
The system, comparable in size to an AA battery, contains a type of non-toxic algae called Synechocystis that naturally harvests energy from the sun through photosynthesis. The tiny electrical current this generates then interacts with an aluminium electrode and is used to power a microprocessor.
The system is made of common, inexpensive and largely recyclable materials. This means it could easily be replicated hundreds of thousands of times to power large numbers of small devices as part of the Internet of Things. The researchers say it is likely to be most useful in off-grid situations or remote locations, where small amounts of power can be very beneficial.
“The growing Internet of Things needs an increasing amount of power, and we think this will have to come from systems that can generate energy, rather than simply store it like batteries,” said Professor Christopher Howe in the University of Cambridge’s Department of Biochemistry, joint senior author of the paper.
He added: “Our photosynthetic device doesn’t run down the way a battery does because it’s continually using light as the energy source.”
In the experiment, the device was used to power an Arm Cortex M0+, which is a microprocessor used widely in Internet of Things devices. It operated in a domestic environment and semi-outdoor conditions under natural light and associated temperature fluctuations, and after six months of continuous power production the results were submitted for publication.
The study is published today in the journal Energy & Environmental Science.
“We were impressed by how consistently the system worked over a long period of time — we thought it might stop after a few weeks but it just kept going,” said Dr Paolo Bombelli in the University of Cambridge’s Department of Biochemistry, first author of the paper.
The algae does not need feeding, because it creates its own food as it photosynthesises. And despite the fact that photosynthesis requires light, the device can even continue producing power during periods of darkness. The researchers think this is because the algae processes some of its food when there’s no light, and this continues to generate an electrical current.
The Internet of Things is a vast and growing network of electronic devices — each using only a small amount of power — that collect and share real-time data via the internet. Using low-cost computer chips and wireless networks, many billions of devices are part of this network — from smartwatches to temperature sensors in power stations. This figure is expected to grow to one trillion devices by 2035, requiring a vast number of portable energy sources.
The researchers say that powering trillions of Internet of Things devices using lithium-ion batteries would be impractical: it would need three times more lithium than is produced across the world annually. And traditional photovoltaic devices are made using hazardous materials that have adverse environmental effects.
The work was a collaboration between the University of Cambridge and Arm, a company leading the design of microprocessors. Arm Research developed the ultra-efficient Arm Cortex M0+ testchip, built the board, and set up the data-collection cloud interface presented in the experiments.
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Materials provided by University of Cambridge. The original text of this story is licensed under a Creative Commons License. Note: Content may be edited for style and length. More