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Category: quantum physics – Page 639

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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Einstein dubbed the idea of quantum entanglement as “spooky action at a distance.” Now for the first time ever, scientists have taken a picture of it.
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Today we understand quantum entanglement as when a pair of particles that cross paths and interact with each other can become connected and stay that way, even when the particles are spaced very far apart.

Once particles are intertwined in this way, changes to one particle can immediately shape the other particle, an odd scientific phenomenon that has been proven through experiments with atoms and molecules, and more recently through entangled objects of even larger scales.

Quantum entanglement is a key part of quantum mechanics, which forms the basis for fields such as quantum computing and cryptography, so there is considerable interest in advancing our understanding of it.

Continue reading “The World’s First Photo of Quantum Entanglement Could Disprove Einstein’s Theory” | >

According to MIT professor Seth Lloyd, the answer is yes. We could be living in the kind of digital world depicted in The Matrix, and not even know it.

A researcher in Mechanical Engineering at MIT, Lloyd is one of the leaders in the field of quantum information. He’s been with the field from its very conception to its sky-rocketing rise to popularity. Decades ago, the feasibility of developing quantum computing devices was challenged. Now, as quantum computation is producing actual technologies, we are only left to wonder—what kind of applications will it provide us with next?

But, first things first. In a round-table discussion with undergraduates, Lloyd speaks of his early days in the field with a touch of humor, irony, and most surprisingly—pride. When he just started to research quantum information in graduate school, most scientists told him to look into other areas. In fact, out of the postdoctoral programs he considered, not many were too invested in researching of information in quantum mechanics. Most universities and institutes were reluctant to take up quantum computing, but Murray Gell-Mann accepted Lloyd for a position at the California Institute of Technology. This is where many ideas behind quantum computation were born, and Lloyd is “excited by the popularity of the field today.”

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A ten-qubit system based on spins in impure diamond achieves coherence times of over a minute.

In the global race to build a quantum computer, it’s still unclear what material will make the best qubit. Companies have bet on a variety of architectures based on trapped ions, neutral atoms, superconducting circuits, and more. Now, Tim Taminiau of Delft University of Technology, Netherlands, and colleagues have demonstrated that they can manipulate magnetic spins inside diamond into the robust quantum states necessary for quantum computing. In their experiment, they entangle all possible pairs of a ten-qubit system and produce states in which seven different qubits are entangled simultaneously. They also show that individual qubits can retain quantum coherence for up to 75 s—a record for solid-state systems.

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