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Category: quantum physics

(Phys.org)—Light behaves both as a particle and as a wave. Since the days of Einstein, scientists have been trying to directly observe both of these aspects of light at the same time. Now, scientists at EPFL have succeeded in capturing the first-ever snapshot of this dual behavior.

Quantum mechanics tells us that can behave simultaneously as a particle or a wave. However, there has never been an experiment able to capture both natures of light at the same time; the closest we have come is seeing either wave or particle, but always at different times. Taking a radically different experimental approach, EPFL scientists have now been able to take the first ever snapshot of light behaving both as a wave and as a particle. The breakthrough work is published in Nature Communications.

When UV light hits a metal surface, it causes an emission of . Albert Einstein explained this “photoelectric” effect by proposing that light – thought to only be a wave – is also a stream of particles. Even though a variety of experiments have successfully observed both the particle- and wave-like behaviors of light, they have never been able to observe both at the same time.

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A model based on Brownian motion describes the tsunami-like propagation of chaotic behavior in a system of quantum particles.

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In daily life, “chaos” describes anything messy. In physics, the term has a more specific meaning: It refers to systems that, while subject to deterministic laws, are totally unpredictable because of an exponential sensitivity to initial conditions—think of the butterfly flapping its wings and causing a distant tornado. But how does the chaos observed in the classical, macroscopic world emerge from the quantum-mechanical laws that govern the microscopic world? A recently proposed explanation invokes quantum “information scrambling” [1, 3], in which information gets rapidly dispersed into quantum correlations among the particles of a system. This scrambling is a memory-loss mechanism that can cause the unpredictability of chaos. Developing a theory that fully describes information scrambling remains, however, a daunting task.

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A team from Dartmouth College and MIT has designed and conducted the first lab test to successfully detect and characterize a class of complex, “non-Gaussian” noise processes that are routinely encountered in superconducting quantum computing systems.

The characterization of non-Gaussian noise in superconducting quantum bits is a critical step toward making these systems more precise.

The joint study, published in Nature Communications, could help accelerate the realization of systems. The experiment was based on earlier conducted at Dartmouth and published in Physical Review Letters in 2016.

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A team of researchers from the University of Glasgow and the University of Southampton has devised a novel way to test quantum mechanics in a non-inertial reference frame by using a rotating interferometer. In their paper published in the journal Physical Review Letters, the group describes studying the Hong-Ou-Mandel interference using fiber coils on a rotating disk, and what they found.

As physicists struggle with the problem of uniting and , they devise new ways to both. In this new effort, the researchers noted that the two theories are consistent under some conditions—such as when gravity is very weak, or when modest acceleration is involved. In their experiment, they chose to test the Hong-Ou-Mandel interference, in which entangled photons are sent on different paths along a circular track—one clockwise, the other counterclockwise. Theory suggests that when such entangled photons are reunited, they should bunch together and move toward one detector or the other. Conversely, non-entangled photons should travel toward either detector randomly.

In their experiment, the researchers set fiber cables on a rotating disk along with sensors for reading where the photons went after passing through the cables. They then sent a stream of entangled photons through the fiber cables (one clockwise, the other counterclockwise) and noted how they behaved as the disk was rotated—a means of applying a non-inertial reference frame. The researchers report that, as expected, the entangled photons did, indeed, bunch up and march off to a sensor together after being reunited with a beam splitter. More importantly, they noted that applying a non-inertial reference frame resulted in one of a pair of photons arriving a little later than the other, which in turn had an impact on the bunching signals the team recorded.

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The code used below is on GitHub.

In this project, we’ll be solving a problem familiar to any physics undergrad — using the Schrödinger equation to find the quantum ground state of a particle in a 1-dimensional box with a potential. However, we’re going to tackle this old standby with a new method: deep learning. Specifically, we’ll use the TensorFlow package to set up a neural network and then train it on random potential functions and their numerically calculated solutions.

Why reinvent the wheel (ground state)? Sure, it’s fun to see a new tool added to the physics problem-solving toolkit, and I needed the practice with TensorFlow. But there’s a far more compelling answer. We know basically everything there is to know about this topic already. The neural network, however, doesn’t know any physics. Crudely speaking, it just finds patterns. Suppose we examine the relative strength of connections between input neurons and output. The structure therein could give us some insight into how the universe “thinks” about this problem. Later, we can apply deep learning to a physics problem where the underlying theory is unknown. By looking at the innards of that neural network, we might learn something new about fundamental physical principles that would otherwise remain obscured from our view. Therein lies the true power of this approach: peering into the mind of the universe itself.

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Charge density fluctuations are observed in all families of high-critical temperature (Tc) superconducting cuprates. Although constantly found in the underdoped region of the phase diagram at relatively low temperatures, physicists are unclear how the substrates influence unusual properties of these systems. In a new study now published on Science, R. Arpaia and co-workers in the departments of microtechnology and nanoscience, the European Synchrotron, and quantum device physics in Italy, Sweden and France used resonant X-ray scattering to carefully determine the charge density modulations in Yttrium Barium Copper Oxide (YBa2Cu3O7– ẟ) and Neodymium Barium Copper Oxide (Nd1+x Ba2–x Cu3O7–ẟ) for several doping levels. The research team isolated short-range dynamic charge density fluctuations (CDFs) in addition to the previously known quasi-critical charge density waves (CDW). The results persisted well above the pseudo-gap temperature T*, which they characterized by a few milli-electron volts (meV) to spread across a large area of the phase diagram.

Cuprate high temperature superconductors (HTS) are different from the Landau Fermi liquid paradigm due to quasi-two dimensionality (2-D) of their layered structure and large electron-electron repulsion. During optimal doping and the pseudo gap state (states at which less than optimal current carrier concentrations result in anomalous electronic properties), short to medium-range charge density wave order can emerge to weakly compete with superconductivity. Physicists first developed theoretical proposals of CDW and low energy charge fluctuations after first discovering HTS. Subsequently, they developed experimental evidence in selective materials and in all cuprate families. Researchers had observed long-range tridimensional CDW (3D CDW) order inside the superconductivity dome within high magnetic fields that weaken superconductivity or in epitaxially grown (deposition of a crystalline layer on a crystalline substrate) samples.

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