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Category: quantum physics

Physicists from Swansea University are part of an international research collaboration which has identified a new technique for testing the quality of quantum correlations.

Quantum computers run their algorithms on large quantum systems of many parts, called qubits, by creating quantum correlations across all of them. It is important to verify that the actual computation procedures lead to quantum correlations of desired quality.

However, carrying out these checks is resource-intensive as the number of tests required grows exponentially with the number of qubits involved.

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It may be possible in the future to use information technology where electron spin is used to store, process and transfer information in quantum computers. It has long been the goal of scientists to be able to use spin-based quantum information technology at room temperature. A team of researchers from Sweden, Finland and Japan have now constructed a semiconductor component in which information can be efficiently exchanged between electron spin and light at room temperature and above. The new method is described in an article published in Nature Photonics.

It is well known that electrons have a negative charge; they also have another property called spin. This may prove instrumental in the advance of . To put it simply, we can imagine the electron rotating around its own axis, similar to the way in which the Earth rotates around its own axis. Spintronics—a promising candidate for future information technology—uses this quantum property of electrons to store, process and transfer information. This brings important benefits, such as higher speed and lower energy consumption than traditional electronics.

Developments in spintronics in recent decades have been based on the use of metals, and these have been highly significant for the possibility of storing large amounts of data. There would, however, be several advantages in using spintronics based on semiconductors, in the same way that semiconductors form the backbone of today’s electronics and photonics.

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Classical hydrodynamics laws can be very useful for describing the behavior of systems composed of many particles (i.e., many-body systems) after they reach a local state of equilibrium. These laws are expressed by so-called hydrodynamical equations, a set of mathematical equations that describe the movement of water or other fluids.

Researchers at Oak Ridge National Laboratory and University of California, Berkeley (UC Berkeley) have recently carried out a study exploring the hydrodynamics of a quantum Heisenberg spin-1/2 chain. Their paper, published in Nature Physics, shows that the spin dynamics of a 1D Heisenberg antiferromagnet (i.e., KCuF3) could be effectively described by a dynamical exponent aligned with the so-called Kardar-Parisi-Zhang universality class.

“Joel Moore and I have known each other for many years and we both have an interest in quantum magnets as a place where we can explore and test new ideas in physics; my interests are experimental and Joel’s are theoretical,” Alan Tennant, one of the researchers who carried out the study, told Phys.org. “For a long time, we have both been interested in temperature in quantum systems, an area where a number of really new insights have come along recently, but we had not worked together on any projects.”

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Circa 2020

Lasing—the emission of a collimated light beam of light with a well-defined wavelength (color) and phase—results from a self-organization process, in which a collection of emission centers synchronizes itself to produce identical light particles (photons). A similar self-organized synchronization phenomenon can also lead to the generation of coherent vibrations—a phonon laser, where phonon denotes, in analogy to photons, the quantum particles of sound.

Photon lasing was first demonstrated approximately 60 years ago and, coincidentally, 60 years after its prediction by Albert Einstein. This stimulated emission of amplified found an unprecedented number of scientific and technological applications in multiple areas.

Although the concept of a “laser of sound” was predicted almost at the same time, only few implementations have so far been reported and none has attained technological maturity. Now, a collaboration between researchers from Instituto Balseiro and Centro Atómico in Bariloche (Argentina) and Paul-Drude-Institut in Berlin has introduced a novel approach for the efficient generation of coherent vibrations in the tens of GHz range using semiconductor structures. Interestingly, this approach to the generation of coherent phonons is based on another of Einstein’s predictions: that of the 5th state of matter, a Bose-Einstein condensate (BEC) of coupled light-matter particles (polaritons).

Continue reading “A phonon laser: Coherent vibrations from a self-breathing resonator” | >

Place one clock at the top of a mountain. Place another on the beach. Eventually, you’ll see that each clock tells a different time. Why?

In his book “The Order of Time,” Italian theoretical physicist Carlo Rovelli suggests that our perception of time — our sense that time is forever flowing forward — could be a highly subjective projection. After all, when you look at reality on the smallest scale (using equations of quantum gravity, at least), time vanishes.

“If I observe the microscopic state of things,” writes Rovelli, “then the difference between past and future vanishes … in the elementary grammar of things, there is no distinction between ‘cause’ and ‘effect.’”

So, why do we perceive time as flowing forward? Rovelli notes that, although time disappears on extremely small scales, we still obviously perceive events occur sequentially in reality. In other words, we observe entropy: Order changing into disorder; an egg cracking and getting scrambled.

Continue reading “Physics without time” | >

In high-end 21st century communications, information travels in the form of a stream of light pulses typically traveling through fiber optic cables. Each pulse can be as faint as a single photon, the smallest possible unit (quantum) of light. The speed at which such systems can operate depends critically on how fast and how accurately detectors on the receiving end can discriminate and process those photons.

Now scientists at the National institute of Standards and Technology (NIST) have devised a method that can detect individual photons at a rate 10 times faster than the best existing technology, with lower error rates, higher detection efficiency, and less noise.

“While classical communication and detection can operate at blazing speeds, , which need that ultimate sensitivity for those faintest of pulses, are limited to much lower speeds,” said group leader Alan Migdall. “Combining that ultimate sensitivity with the ability to achieve the counting of photons at has been a long-standing challenge. Here we are pushing both performance limits all in the same device.”

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Circa 2014 essentially this could make endless computer chips from light.

Princeton researchers have managed to cause light to behave like a crystal within a specialized computer chip, according to a recent paper. This is the first time anyone has accomplished this effect in a lab.

Here’s why it’s so hard: Atoms can easily form solids, liquids, and gasses, because when they come into contact they push and pull on each other. That push and pull forms the underlying structure of all matter. Light particles, or photons, do not typically interact with one another, according to Dr. Andrew Houck, a professor of electrical engineering at Princeton and an author on the study. The trick of this research was forcing them to do just that.

“We build essentially an artificial atom, using lots of atoms acting in concert,” Houck tells Popular Science, “What emerges is a quantum mechanical object that [at about half a millimeter] is visible on the classical scale.”

Continue reading “Light Forms Crystal-Like Structure On Computer Chip” | >

Superconductivity – the ability of a material to transmit an electric current without loss – is a quantum effect that, despite years of research, is still limited to very low temperatures. Now a team of scientists at the MPSD has succeeded in creating a metastable state with vanishing electrical resistance in a molecular solid by exposing it to finely tuned pulses of intense laser light. This effect had already been demonstrated in 2016 for only a very short time, but in a new study the authors of the paper have shown a far longer lifetime, nearly 10000 times longer than before. The long lifetimes for light-induced superconductivity hold promise for applications in integrated electronics. The research by Budden et al. has been published in Nature Physics.

Superconductivity is one of the most fascinating and mysterious phenomena of modern physics. It describes the sudden loss of electrical resistance in certain materials when they are cooled below a critical temperature. However, the need for such cooling still limits the technological usability of these materials.

In recent years, research by Andrea Cavalleri’s group at the MPSD has revealed that intense pulses of infrared light are a viable tool to induce superconducting properties in a variety of different materials at much higher temperatures than would be possible without photo-stimulation. However, these exotic states have so far persisted for only a few picoseconds (trillionths of a second), thus limiting the experimental methods for studying them to ultrafast optics.

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