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Category: quantum physics – Page 561

A Jiggling Ultracold Atomic Gas Simulates Spin Dynamics

Researchers produce analogues of hard-to-study quantum phenomena in a gas of strontium atoms near absolute zero.

Recently, researchers have begun using ultracold atomic gases to simulate phenomena that are difficult to study in their natural environments. Using electromagnetic fields, for example, they can orchestrate interatomic interactions that are analogous to interactions in condensed-matter systems, which they can then study with greater experimental control than the real examples allow. Now David Wilkowski of Nanyang Technological University in Singapore and colleagues use an ultracold atomic gas to simulate a condensed-matter system’s spin dynamics [1].

Wilkowski’s team cools a gas of strontium-87 atoms to 30 nK. Then, using three convergent laser beams, they drive the gas through various transitions until the atoms populate two so-called dark states, in which quantum mechanics forbids the atoms from undergoing spontaneous emission.

A Solid Observation of Strong Kerr Nonlinearity

Researchers have demonstrated that a solid can exhibit an enhanced nonlinear optical phenomenon usually seen only in cold atomic gases.

Among the benefits brought about by the invention of the laser in the 1960s is the ability to generate light at an intensity great enough to produce nonlinear optical effects. Such nonlinear effects have entered daily use in applications that include infrared-to-visible-light wavelength conversion (in a green laser pointer, for example) and two-photon excitation (in fluorescence microscopes for observing biological living tissue). Now Corentin Morin of the École Normale Supérieure in Paris and colleagues address a third-order nonlinear process called the Kerr effect, which manifests as a change in a material’s refractive index when it is illuminated with light of different intensities [1]. The researchers demonstrate a giant Kerr nonlinearity in a solid, a state of matter that has, until now, exhibited only a weak Kerr effect. The result implies the possibility of scalable nonlinear quantum optics without the need of cold atoms in high vacuum.

The key to the discovery by Morin and colleagues is a quasiparticle called a Rydberg exciton, the understanding of which rests on two concepts. The first concept is the Rydberg series, which is the discrete energy-level structure available to an atom’s outermost electron, and which is indexed by the principal quantum number n. A high-lying Rydberg state has a large n and exhibits properties such as a large electron orbital radius, a long lifetime, and a large dipole moment, all of which are missing in the ground state. The second concept is a hydrogen-atom-like quasiparticle called an exciton—a negatively charged electron, photoexcited across a semiconductor’s band gap, Coulomb-bound to a positively charged hole left in the valence band.

Designing new quantum materials on the computer

How do you find novel materials with very specific properties—for example, special electronic properties which are needed for quantum computers? This is usually a very complicated task: various compounds are created, in which potentially promising atoms are arranged in certain crystal structures, and then the material is examined, for example in the low-temperature laboratory of TU Wien.

Now, a cooperation between Rice University (Texas), TU Wien and other international research institutions has succeeded in tracking down suitable materials on the computer. New theoretical methods are used to identify particularly promising candidates from the vast number of possible materials. Measurements at TU Wien have shown the materials do indeed have the required properties and the method works. This is an important step forward for research on quantum materials. The results have now been published in the journal Nature Physics.

The Schwinger Effect: Scientists Finally Created Matter From Nothing Just by Using Electromagnetic Fields [Research Study]

Wait, what? really?

For the first time, scientists were able to create particles without precursor particles or colliding two quanta together. Using the Schwinger effect, they could create matter with the aid of electromagnetic fields.

What Is a Schwinger Effect?

According to Wikipedia, a powerful electric field is thought to form matter due to the Schwinger effect. It is a quantum electrodynamics (QED) prediction that, in the presence of an electric field, electron-positron pairs spontaneously form, leading to the decay of the electric field.

This Environmentally Friendly Quantum Sensor Runs On Sunlight

Quantum tech is going green.

A new take on highly sensitive magnetic field sensors ditches the power-hungry lasers that previous devices have relied on to make their measurements and replaces them with sunlight. Lasers can gobble 100 watts or so of power — like keeping a bright lightbulb burning. The innovation potentially untethers quantum sensors from that energy need. The result is an environmentally friendly prototype on the forefront of technology, researchers report in an upcoming issue of Physical Review X Energy.

The big twist is in how the device uses sunlight. It doesn’t use solar cells to convert light into electricity. Instead, the sunlight does the job of the laser’s light, says Jiangfeng Du, a physicist at the University of Science and Technology of China in Hefei.

Superposition in Quantum Computers — Computerphile

Parting the veil of mystery on quantum superposition using waves. Professor Phil Moriarty takes us through it.

Phil’s blogpost on the subject: https://muircheartblog.wpcomstaging.com/2021/10/26/superposi…erstition/

This video was formerly called What is Quantum Superposition?

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This video was filmed and edited by Sean Riley.

Computer Science at the University of Nottingham: https://bit.ly/nottscomputer.

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Double-transmon coupler will realize faster, more accurate superconducting quantum computers

Researchers at Toshiba Corporation have achieved a breakthrough in quantum computer architecture: the basic design for a double-transmon coupler that will improve the speed and accuracy of quantum computation in tunable couplers. The coupler is a key device in determining the performance of superconducting quantum computers.

Tunable couplers in a superconducting quantum computer link two qubits and perform quantum computations by turning on and off the coupling between them. Current technology can turn off the coupling of transmon qubits with close frequencies, but this is prone to crosstalk errors that occur on one of the qubits when the other qubit is irradiated with for control. In addition, current technology cannot completely turn off coupling for qubits with significantly different frequencies, resulting in errors due to residual coupling.

Toshiba has recently devised a double-transmon coupler that can completely turn on and off the coupling between qubits with significantly different frequencies. Completely turning on enables high-speed quantum computations with strong coupling, while completely turning off eliminates residual coupling, which improves quantum computation speeds and accuracy. Simulations with the new technology have shown it realizes two-qubit gates, basic operations in quantum computation, with an accuracy of 99.99% and a processing time of only 24 ns.

Our Universe Resides In the Center of a Black Hole, New Theory reveals

What’s our position in the universe? Some astronomers believe that the relative emptiness in our location in space may be why we haven’t found other intelligent life yet. It may even go beyond that. One theory states that our universe is actually trapped inside a giant black hole, which itself is part of a much larger cosmos.

It all centers on a very different theory of what exactly a black hole is. The usual general understanding is nothing can escape a black hole’s intense gravity, not even light. Called the black hole information paradox, it’s thought that even the information about an object that gets sucked in vanishes into oblivion. But therein lies a problem.

This understanding violates a certain rule in quantum mechanics known as “unitarity,” which states that information can never be completely lost. Some trace of it will always remain. So how can scientists get over the hump?

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