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Negative pressure governs not only the Universe or the quantum vacuum. This phenomenon, although of a different nature, appears also in liquid crystals confined in nanopores. At the Institute of Nuclear Physics of the Polish Academy of Sciences in Cracow, a method has been presented that for the first time makes it possible to estimate the amount of negative pressure in spatially limited liquid crystal systems.

At first glance, negative pressure appears to be an exotic phenomenon. In fact, it is common in nature, and what’s more, occurs on many scales. On the scale of the Universe, the cosmological constant is responsible for accelerating the expansion of spacetime. In the world of plants, attracting intermolecular forces (not: expanding thermal motions) guarantee the flow of water to the treetops of all trees taller than ten metres. On the quantum scale, the pressure of virtual particles of a false vacuum leads to the creation of an attractive force, appearing, for example, between two parallel metal plates (the famous Casimir effect).

“The fact that a negative pressure appears in liquid crystals confined in nanopores was already known. However, it was not known how to measure this pressure. Although we also cannot do this directly, we have proposed a method that allows this pressure to be reliably estimated,” says Dr. Tomasz Rozwadowski from the Institute of Nuclear Physics of the Polish Academy of Sciences (IFJ PAN) in Cracow, the first author of a publication in the Journal of Molecular Liquids.

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Researchers from the University of Maryland have for the first time measured an effect that was predicted more than 40 years ago, called the Casimir torque.

When placed together in a vacuum less than the diameter of a bacterium (one micron) apart, two pieces of metal attract each other. This is called the Casimir effect. The Casimir torque—a related phenomenon that is caused by the same quantum electromagnetic effects that attract the materials—pushes the materials into a spin. Because it is such a tiny effect, the Casimir torque has been difficult to study. The research team, which includes members from UMD’s departments of electrical and computer engineering and physics and Institute for Research in Electronics and Applied Physics, has built an apparatus to measure the decades-old prediction of this phenomenon and published their results in the December 20th issue of the journal Nature.

“This is an interesting situation where industry is using something because it works, but the mechanism is not well-understood,” said Jeremy Munday, the leader of the research. “For LCD displays, for example, we know how to create twisted liquid crystals, but we don’t really know why they twist. Our study proves that the Casimir torque is a crucial component of liquid crystal alignment. It is the first to quantify the contribution of the Casimir effect, but is not the first to prove that it contributes.”

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Researchers led by Francesca Ferlaino from the University of Innsbruck and the Austrian Academy of Sciences report in Physical Review X on the observation of supersolid behavior in dipolar quantum gases of erbium and dysprosium. In the dysprosium gas these properties are unprecedentedly long-lived. This sets the stage for future investigations into the nature of this exotic phase of matter.

Supersolidity is a paradoxical state where the matter is both crystallized and superfluid. Predicted 50 years ago, such a counter-intuitive phase, featuring rather antithetical properties, has been long sought in superfluid helium. However, after decades of theoretical and experimental efforts, an unambiguous proof of supersolidity in these systems is still missing. Two research teams led by Francesca Ferlaino, one at the Institute for Experimental Physics at the University of Innsbruck and one at the Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, now report on the observation of hallmarks of this exotic state in ultracold atomic gases.

While so far most work has focused on helium, researchers have recently turned to atomic gases—in particular, those with strong dipolar interactions. The team of Francesca Ferlaino has been investigating quantum gases made of atoms with a strong dipolar character for a long time. “Recent experiments have revealed that such gases exhibit fundamental similarities with superfluid helium,” says Lauriane Chomaz, referring to experimental achievements in Innsbruck and in Stuttgart over the last few years. “These features lay the groundwork for reaching a state where the several tens of thousands of particles of the gas spontaneously organize in a self-determined crystalline structure while sharing the same macroscopic wavefunction—hallmarks of supersolidity.”

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Quantum computers can’t selectively forget information. A new algorithm for multiplication shows a way around that problem.

To a non-physicist, an “atomic beam collimator” may sound like a phaser firing mystical particles. That might not be the worst metaphor to introduce a technology that researchers have now miniaturized, making it more likely to someday land in handheld devices.

Today, atomic beam collimators are mostly found in physics labs, where they shoot out atoms in a beam that produces exotic quantum phenomena and which has properties that may be useful in precision technologies. By shrinking collimators from the size of a small appliance to fit on a fingertip, researchers at the Georgia Institute of Technology want to make the technology available to engineers advancing devices like atomic clocks or accelerometers, a component found in smartphones.

“A typical device you might make out of this is a next-generation gyroscope for a precision navigation system that is independent of GPS and can be used when you’re out of satellite range in a remote region or traveling in space,” said Chandra Raman, an associate professor in Georgia Tech’s School of Physics and a co-principal investigator on the study.

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A team of researchers at NTT Corporation has developed a way to use light-based computer hardware that allows it to to compete with silicon. In their paper published in the journal Nature Photonics, the group describes their research, the devices they created and how well they worked.

Computer scientists have known for some time that the era of increasing computer speed by modifying silicon-based computer parts is coming to an end. To that end, many have turned to quantum computing as the way to speed up computers—but to date, such efforts have not led to useful machines and there is no guarantee they ever will. Because of that, others in the computer business are looking for other options, such as using light to move data around inside of computers instead of electrons. Currently, light is generally only used to carry data long distances. In this new effort, the researchers report that they have developed computing devices based partially on light that performed as well as electron-based hardware.

The idea of using only light as a data medium in computer hardware is still a long way off—instead, engineers are focusing on using light in areas where it seems feasible and electrons everywhere else. Because of that computer devices must be able to convert between the two mediums, a problem that until now has prevented such devices from being built. Prior efforts have required too much power to be feasible and the conversion process has been too slow. To get around both problems, the researchers developed a new kind of photonic crystal that was able to diffuse light in a way that allowed it to follow a designated path on demand and to also be absorbed when needed to be used for generating current. The crystal was also able to work in reverse.

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Simulations of stochastic processes play an important role in the quantitative sciences, enabling the characterisation of complex systems. Recent work has established a quantum advantage in stochastic simulation, leading to quantum devices that execute a simulation using less memory than possible by classical means. To realise this advantage it is essential that the memory register remains coherent, and coherently interacts with the processor, allowing the simulator to operate over many time steps. Here we report a multi-time-step experimental simulation of a stochastic process using less memory than the classical limit. A key feature of the photonic quantum information processor is that it creates a quantum superposition of all possible future trajectories that the system can evolve into. This superposition allows us to introduce, and demonstrate, the idea of comparing statistical futures of two classical processes via quantum interference. We demonstrate interference of two 16-dimensional quantum states, representing statistical futures of our process, with a visibility of 0.96 ± 0.02.

For the first time, Yale physicists have directly observed quantum behavior in the vibrations of a liquid body.

A great deal of ongoing research is currently devoted to discovering and exploiting quantum effects in the motion of macroscopic objects made of solids and gases. This new experiment opens a potentially rich area of further study into the way quantum principles work on liquid bodies.

The findings come from the Yale lab of physics and applied physics professor Jack Harris, along with colleagues at the Kastler Brossel Laboratory in France. A study about the research appears in the journal Physical Review Letters.

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Researchers have built a quantum computer prototype that can show 16 possible futures at the same time.