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Category: particle physics

Quantum computational advantage or supremacy is a long-anticipated milestone toward practical quantum computers. Recent work claimed to have reached this point, but subsequent work managed to speed up the classical simulation and pointed toward a sample size–dependent loophole. Quantum computational advantage, rather than being a one-shot experimental proof, will be the result of a long-term competition between quantum devices and classical simulation. Zhong et al. sent 50 indistinguishable single-mode squeezed states into a 100-mode ultralow-loss interferometer and sampled the output using 100 high-efficiency single-photon detectors. By obtaining up to 76-photon coincidence, yielding a state space dimension of about 1030, they measured a sampling rate that is about 1014-fold faster than using state-of-the-art classical simulation strategies and supercomputers.

Science, this issue p. 1460

Quantum computers promise to perform certain tasks that are believed to be intractable to classical computers. Boson sampling is such a task and is considered a strong candidate to demonstrate the quantum computational advantage. We performed Gaussian boson sampling by sending 50 indistinguishable single-mode squeezed states into a 100-mode ultralow-loss interferometer with full connectivity and random matrix—the whole optical setup is phase-locked—and sampling the output using 100 high-efficiency single-photon detectors. The obtained samples were validated against plausible hypotheses exploiting thermal states, distinguishable photons, and uniform distribution. The photonic quantum computer, Jiuzhang, generates up to 76 output photon clicks, which yields an output state-space dimension of 1030 and a sampling rate that is faster than using the state-of-the-art simulation strategy and supercomputers by a factor of ~1014.

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When it comes to magnetic tape storage capacity, smaller is larger. That is, as the magnetic particles that store data become smaller, more data can be stockpiled in the same amount of space.

Two leading tech giants put that simple principle to work and announced Wednesday that they have developed a magnetic tape cartridge boasting the most dense capacity of any media in the world. Fujifilm and IBM say research into a new material, strontium , led to the creation of a tape cartridge capable of storing 580 terabytes of data. That’s enough to store roughly 580 million books, according to an IBM blog post published Wednesday.

Considering there are about only 130 million books in existence today, that’ll leave plenty of room for extras.

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Jack Steinberger, who shared the 1988 Nobel Prize in Physics for expanding understanding of the ghostly neutrino, a staggeringly ubiquitous subatomic particle, died on Saturday at his home in Geneva. He was 99.

His wife, Cynthia Alff, confirmed the death.

The ancient Greeks proposed that there was one invisible, indivisible unit of matter: the atom. But modern physics has found more than 100 smaller entities lurking within atoms, and observations of their dizzying interactions compose the Standard Model of what is now taken to be the order of the universe.

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JILA physicists have boosted the signal power of their atomic “tweezer clock” and measured its performance in part for the first time, demonstrating high stability close to the best of the latest generation of atomic clocks.

The unusual clock, which uses to trap, control and isolate , offers unique possibilities for enhancing clock performance using the tricks of quantum physics as well as future applications in quantum information processing, , and measurement science.

Described in a Nature paper published online Dec. 16, the clock platform is a rectangular grid of about 150 strontium atoms confined individually by , which are created by a aimed through a microscope and deflected into 320 spots. This upgraded version of the clock has up to 30 times as many atoms as the preliminary design unveiled last year, due mainly to the use of several different lasers, including a green one for trapping the atoms and two red ones to make them “tick.”

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A new study illuminates surprising choreography among spinning atoms. In a paper appearing in the journal Nature, researchers from MIT and Harvard University reveal how magnetic forces at the quantum, atomic scale affect how atoms orient their spins.

In experiments with ultracold lithium , the researchers observed different ways in which the spins of the atoms evolve. Like tippy ballerinas pirouetting back to upright positions, the spinning atoms return to an equilibrium orientation in a way that depends on the between individual atoms. For example, the atoms can spin into equilibrium in an extremely fast, “ballistic” fashion or in a slower, more diffuse pattern.

The researchers found that these behaviors, which had not been observed until now, could be described mathematically by the Heisenberg model, a set of equations commonly used to predict magnetic behavior. Their results address the fundamental nature of magnetism, revealing a diversity of behavior in one of the simplest magnetic materials.

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“When we actually opened it, I was speechless,” JAXA scientist Hirotaka Sawada said, as quoted by The Guardian. “It was more than we expected and there was so much that I was truly impressed.”

The quality of the sample was outstanding.

“It wasn’t fine particles like powder, but there were plenty of samples that measured several millimeters across,” Sawada added, according to The Guardian.

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In a new study an international research team led by the University of Vienna has shown that structures built around a single layer of graphene allow for strong optical nonlinearities that can convert light. The team achieved this by using nanometer-sized gold ribbons to squeeze light, in the form of plasmons, into atomically-thin graphene. The results, which are published in Nature Nanotechnology are promising for a new family of ultra-small tunable nonlinear devices.

In the last years, a concerted effort has been made to develop plasmonic devices to manipulate and transmit through nanometer-sized devices. At the same time, it has been shown that nonlinear interactions can be greatly enhanced by using plasmons, which can arise when light interacts with electrons in a material. In a plasmon, light is bound to electrons on the surface of a conducting material, allowing plasmons to be much smaller than the light that originally created them. This can lead to extremely strong nonlinear interactions. However, plasmons are typically created on the surface of metals, which causes them to decay very quickly, limiting both the propagation length and nonlinear interactions. In this new work, the researchers show that the long lifetime of plasmons in and the strong nonlinearity of this material can overcome these challenges.

In their experiment, the research team led by Philip Walther at the University of Vienna (Austria), in collaboration with researchers from the Barcelona Institute of Photonic Sciences (Spain), the University of Southern Denmark, the University of Montpellier, and the Massachusetts Institute of Technology (USA) used stacks of two-dimensional materials, called heterostructures, to build up a nonlinear plasmonic device. They took a single atomic layer of graphene and deposited an array of metallic nanoribbons onto it. The metal ribbons magnified the incoming light in the graphene layer, converting it into graphene plasmons. These plasmons were then trapped under the gold nanoribbons, and produced light of different colors through a process known as harmonic generation. The scientists studied the generated light, and showed that, the nonlinear interaction between the graphene plasmons was crucial to describe the harmonic generation.

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Since the very beginning of quantum physics, a hundred years ago, it has been known that all particles in the universe fall into two categories: fermions and bosons. For instance, the protons found in atomic nuclei are fermions, while bosons include photons — which are particles of light — as well as the BroutEnglert-Higgs boson, for which Francois Englert, a professor at ULB, was awarded a Nobel Prize in Physics in 2013.

Bosons — especially photons — have a natural tendency to clump together. One of the most remarkable experiments that demonstrated photons’ tendency to coalesce was conducted in 1987, when three physicists identified an effect that was since named after them: the Hong-Ou-Mandel effect. If two photons are sent simultaneously, each towards a different side of a beam splitter — a sort of semitransparent mirror — one could expect that each photon will be either reflected or transmitted.

Logically, photons should sometimes be detected on opposite sides of this mirror, which would happen if both are reflected or if both are transmitted. However, the experiment has shown that this never actually happens: the two photons always end up on the same side of the mirror, as though they ‘preferred’ sticking together! In an article published recently in US journal Proceedings of the National Academy of Sciences, Nicolas Cerf — a professor at the Centre for Quantum Information and Communication (École polytechnique de Bruxelles) — and his former PhD student Michael Jabbour — now a postdoctoral researcher at the University of Cambridge — describe how they identified another way in which photons manifest their tendency to stay together. Instead of a semi-transparent mirror, the researchers used an optical amplifier, called an active component because it produces new photons.

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New technique could be useful for quantum information processing.

A new technique to cool reactive molecules to temperatures low enough to achieve quantum degeneracy – something not generally possible before – has been created by researchers in the US. In this temperature regime, the dominance of quantum effects over thermal fluctuations should allow researchers to study new quantum properties of molecules. As a first example, the researchers demonstrated how a slight change in applied electric field can alter the reaction rate between molecules by three orders of magnitude. The researchers hope their platform will enable further exploration of molecular quantum degeneracy, with potential applications ranging from quantum many body physics to quantum information processing.

When atoms are cooled close to absolute zero, the blur created by thermal effects that govern their behaviour in the classical world around us is removed, making their quantum nature clear. This has led to some fascinating discoveries. In ultracold quantum bosonic or fermion-pair quantum gases, for example, all the atoms in a trap can simultaneously occupy the quantum ground state, resulting in a wavefunction that is macroscopic.

Cooling and trapping molecules is much trickier because they are inherently more complex than atoms. Whereas atoms can only contain quanta of energy in electronic excitations, the chemical bonds in molecules can stretch, rotate and bend – and cooling molecules involves removing energy from all of these degrees of freedom. Moreover, the complexity of molecules increases the complexity of their collisions. Although elastic collisions are necessary to knock the fastest-moving molecules out of a trap and cool it, inelastic collisions dissipate heat in the trap.

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