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Category: quantum physics – Page 660

Chinese quantum computer completes 2.5-billion-year task in minutes

Circa 2020 o.o

Researchers in China claim to have achieved quantum supremacy, the point where a quantum computer completes a task that would be virtually impossible for a classical computer to perform. The device, named Jiuzhang, reportedly conducted a calculation in 200 seconds that would take a regular supercomputer a staggering 2.5 billion years to complete.

Traditional computers process data as binary bits – either a zero or a one. Quantum computers, on the other hand, have a distinct advantage in that their bits can also be both a one and a zero at the same time. That raises the potential processing power exponentially, as two quantum bits (qubits) can be in four possible states, three qubits can be in eight states, and so on.

That means quantum computers can explore many possibilities simultaneously, while a classical computer would have to run through each option one after the other. Progress so far has seen quantum computers perform calculations much faster than traditional ones, but their ultimate test would be when they can do things that classical computers simply can’t. And that milestone has been dubbed “quantum supremacy.”

New quantum particle may have been accidentally discovered

Basically speaking, metals conduct electricity and insulators don’t. On the molecular level, that comes down to how freely electrons can move through the materials – in metals, electrons are very mobile, while insulators obviously have high resistance that prevents them moving much.

As a side effect of this, metals can exhibit a phenomenon known as quantum oscillations. When exposed to a magnetic field at very low temperatures, electrons can shift into a quantum state that causes the material’s resistivity to oscillate. This doesn’t happen in insulators, however, since their electrons don’t move very well.

Deconstructing Schrödinger’s Cat – Solving the Paradox

The French theoretical physicist Franck Laloë presents a modification of Schrödinger’s famous equation that ensures that all measured states are unique, helping to solve the problem that is neatly encompassed in the Schördinger’s cat paradox.

The paradox of Schrödinger’s cat – the feline that is, famously, both alive and dead until its box is opened – is the most widely known example of a recurrent problem in quantum mechanics: its dynamics seems to predict that macroscopic objects (like cats) can, sometimes, exist simultaneously in more than one completely distinct state. Many physicists have tried to solve this paradox over the years, but no approach has been universally accepted. Now, however, theoretical physicist Franck Laloë from Laboratoire Kastler Brossel (ENS-Université PSL) in Paris has proposed a new interpretation that could explain many features of the paradox. He sets out a model of this possible theory in a new paper in EPJ D.

One approach to solving this problem involves adding a small, random extra term to the Schrödinger equation, which allows the quantum state vector to ‘collapse’, ensuring that – as is observed in the macroscopic universe – the outcome of each measurement is unique. Laloë’s theory combines this interpretation with another from de Broglie and Bohm and relates the origins of the quantum collapse to the universal gravitational field. This approach can be applied equally to all objects, quantum and macroscopic: that is, to cats as much as to atoms.

The realization of a single-quantum-dot heat valve

While many research teams worldwide are trying to develop highly performing quantum computers, some are working on tools to control the flow of heat inside of them. Just like conventional computers, in fact, quantum computers can heat up significantly as they are operating, which can ultimately damage both the devices and their surroundings.

A team of researchers at University Grenoble Alpes in France and Centre of Excellence—Quantum Technology in Finland has recently developed a single-quantum-dot heat valve, a that can help to control the flow of heat in single-quantum-dot junctions. This heat valve, presented in a paper published in Physical Review Letters, could help to prevent quantum computers from overheating.

“With the miniaturization of electronic components handling of excess heat at nanoscales has become an increasingly important issue to be addressed,” Nicola Lo Gullo, one of the researchers who carried out the study, told Phys.org. “This is especially true when one wants to preserve the quantum nature of a device; the increase in temperature does typically result in the degradation of the quantum properties. The recent realization of a photonic heat-valve by another research group ultimately inspired us to create a heat valve based on a solid-state quantum dot.”

Discovery of quantum behavior in insulators suggests possible new particle

In a surprising discovery, Princeton physicists have observed an unexpected quantum behavior in an insulator made from a material called tungsten ditelluride. This phenomenon, known as quantum oscillation, is typically observed in metals rather than insulators, and its discovery offers new insights into our understanding of the quantum world. The findings also hint at the existence of an entirely new type of quantum particle.

The discovery challenges a long-held distinction between metals and insulators, because in the established quantum theory of materials, insulators were not thought to be able to experience quantum oscillations.

“If our interpretations are correct, we are seeing a fundamentally new form of quantum matter,” said Sanfeng Wu, assistant professor of physics at Princeton University and the senior author of a recent paper in Nature detailing this new discovery. “We are now imagining a wholly new quantum world hidden in insulators. It’s possible that we simply missed identifying them over the last several decades.”

Reality Does Not Depend on the Measurer According to New Interpretation of Quantum Mechanics

For 100 years scientists have disagreed on how to interpret quantum mechanics. A recent study by Jussi Lindgren and Jukka Liukkonen supports an interpretation that is close to classical scientific principles.

Quantum mechanics arose in the 1920s – and since then scientists have disagreed on how best to interpret it. Many interpretations, including the Copenhagen interpretation presented by Niels Bohr and Werner Heisenberg and in particular von Neumann-Wigner interpretation, state that the consciousness of the person conducting the test affects its result. On the other hand, Karl Popper and Albert Einstein thought that an objective reality exists. Erwin Schrödinger put forward the famous thought experiment involving the fate of an unfortunate cat that aimed to describe the imperfections of quantum mechanics.

Entangled photons can see through translucent materials

Quantum twist on optical coherence tomography offers million-fold improvement in imaging.

Entangled pairs of photons have been used by physicists in Germany and Austria to image structures beneath the surfaces of materials that scatter light. The research was led by Aron Vanselow and Sven Ramelow at Humboldt University of Berlin and achieved high-resolution images of the samples using “ultra-broadband” photon pairs with very different wavelengths. One photon probed the sample, while the other read out image information. Their compact, low-cost and non-destructive system could be put to work inspecting advanced ceramics and mixing in fluids.

Optical coherence tomography (OCT) is a powerful tool for imaging structures beneath the surfaces of translucent materials and has a number of applications including the 3D scanning of biological tissues. The technique uses interferometry to reject the majority of light that has scattered many times in an object, focussing instead on the rare instances when light only scatters once from a feature of interest. This usually involves probing the material with visible or near-infrared light, which can be easily produced and detected. Yet in some materials such as ceramics, paints, and micro-porous samples, visible and near-infrared light is strongly scattered – which limits the use of OCT. Mid-infrared light, however, can penetrate deeper into these samples without scattering – but this light is far more difficult to produce and detect.

Vanselow, Ramelow and colleagues circumvented this problem by using pairs of quantum-mechanically entangled photons in which one photon is mid-infrared and the other is either visible or near-infrared. The entangled pairs are generated by firing a “pump” laser beam at a specialized nonlinear crystal developed by the team. This creates entangled pairs of photons – one mid-infrared “idler” photon and one visible/near-infrared “signal” photon.

Quantum Experiment Reveals Particles Can Form Collectives Out of Almost Nothing

How many particles do you need before individual atoms start behaving collectively? According to new research, the number is incredibly low. As few as six atoms will start transitioning into a macroscopic system, under the right conditions.

Using a specially designed ultra-cold laser trap, physicists observed the quantum precursor of the transition from a normal to a superfluid phase – offering a way to study the emergence of collective atomic behaviour and the limits of macroscopic systems.

Many-body physics is the field that seeks to describe and understand the collective behaviour of large numbers of particles: a bucket of water, for example, or a canister of gas. We can describe these substances in terms of their density, or their temperature – the way the substance is acting as a whole.