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Category: quantum physics – Page 202

A new device consisting of a semiconductor ring produces pairs of entangled photons that could be used in a photonic quantum processor.

Quantum light sources produce entangled pairs of photons that can be used in quantum computing and cryptography. A new experiment has demonstrated a quantum light source made from the semiconductor gallium nitride. This material provides a versatile platform for device fabrication, having previously been used for on-chip lasers, detectors, and waveguides. Combined with these other optical components, the new quantum light source opens up the potential to construct a complex quantum circuit, such as a photonic quantum processor, on a single chip.

Quantum optics is a rapidly advancing field, with many experiments using photons to carry quantum information and perform quantum computations. However, for optical systems to compete with other quantum information technologies, quantum-optics devices will need to be shrunk from tabletop size to microchip size. An important step in this transformation is the development of quantum light generation on a semiconductor chip. Several research teams have managed this feat using materials such as gallium aluminum arsenide, indium phosphide, and silicon carbide. And yet a fully integrated photonic circuit will require a range of components in addition to quantum light sources.

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A nanoresonator trapped in ultrahigh vacuum features an exceptionally high quality factor, showing promise for applications in force sensors and macroscopic tests of quantum mechanics.

Nanomechanical oscillators could be used to build ultrasensitive sensors and to test macroscopic quantum phenomena. Key to these applications is a high quality factor (Q), a measure of how many oscillation cycles can be completed before the oscillator energy is dissipated. So far, clamped-membrane nanoresonators achieved a Q of about 1010, which was limited by interactions with the environment. Now a team led by Tracy Northup at the University of Innsbruck, Austria, reports a levitated oscillator—a floating particle oscillating in a trap—competitive with the best clamped ones [1]. The scheme offers potential for order-of-magnitude improvements, the researchers say.

Theorists have long predicted that levitated oscillators, by eliminating clamping-related losses, could reach a Q as large as 1012. Until now, however, the best levitated schemes, based on optically trapped nanoparticles, achieved a Q of only 108. To further boost Q, the Innsbruck researchers devised a scheme that mitigated two important dissipation mechanisms. First, they replaced the optical trap with a Paul trap, one that confines a charged particle using time-varying electric fields instead of lasers. This approach eliminates the dissipation associated with light scattering from the trapped particle. Second, they trapped the particle in ultrahigh vacuum, where the nanoparticle collides with only about one gas molecule in each oscillation cycle.

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Check out my course about quantum mechanics on Brilliant! First 30 days are free and 20% off the annual premium subscription when you use our link ➜ https://brilliant.org/sabine.

If you flip a light switch, the light will turn on. A cause and its effect. Simple enough… until quantum gravity come into play. Once you add quantum gravity, lights can turn on and make switches flip. And some physicists think that this could help build better computers. Why does quantum physics make causality so strange? And how can we use quantum gravity to build faster computers? Let’s have a look.

The paper on indefinite causal structures is here: https://arxiv.org/abs/quant-ph/0701019

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Programming the Universe: A Quantum Computer Scientist Takes on the Cosmos. Seth Lloyd. xii + 221 pp. Alfred A. Knopf, 2006. $25.95.

In the 1940s, computer pioneer Konrad Zuse began to speculate that the universe might be nothing but a giant computer continually executing formal rules to compute its own evolution. He published the first paper on this radical idea in 1967, and since then it has provoked an ever-increasing response from popular culture (the film The Matrix, for example, owes a great deal to Zuse’s theories) and hard science alike.

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Black holes are renowned and frightening phenomena—areas characterized by infinite gravitational force, rendering escape impossible. The process of forming a black hole is relatively uncomplicated: it involves compressing a sufficient amount of mass below a specific size threshold. Once this threshold is surpassed, gravity prevails over all other forces, resulting in the creation of a black hole.

The critical threshold varies depending on the quantity of mass being condensed. For an average human, this threshold is comparable to the size of an atomic nucleus. Conversely, for the Earth, compressing its entirety into the volume of a chickpea would generate a black hole of comparable size. Similarly, for a typical star with several times the mass of the Sun, the resulting black hole would span a few miles—a dimension akin to an average city.

Interestingly, amalgamating all the matter in the universe in an attempt to create the largest possible black hole would yield a black hole roughly the size of the universe itself.

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🔗 Top quark and top antiquark entanglement 🔗

The CMS experiment has just reported the observation and confirms the existence of #entanglement between the top #quark and its #Antiparticle beyond reasonable doubt.

The CMS experiment has just reported the observation of quantum entanglement between a top quark and a top antiquark, simultaneously produced at the LHC.

In quantum mechanics, a system is said to be entangled if its quantum state cannot be described as a simple superposition of the states of its constituents. If two particles are entangled, we cannot describe one of them independently of the other, even if the particles are separated by a very large distance. When we measure the quantum state of one of the two particles, we instantly know the state of the other. The information is not transmitted via any physical channel; it is encoded in the correlated two-particle system.

Quantum information is a field of physics that was born with the work of John Bell, a CERN physicist, in the mid 1960’s. Soon after, Aspect, Clouser, and other physicists did important pioneering experimental work to test “Bell’s theorem”, and in 2007 Zeilinger’s team convincingly demonstrated the existence of entanglement between two photons, too far away from each other for the information to travel between them at the speed of light. This breakthrough brought Aspect, Clauser, and Zeilinger the 2022 Nobel Prize in Physics, “for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science”. Quantum entanglement was mostly examined for states of photons and electrons until 2023, when ATLAS reported the observation of entanglement in the top quark-antiquark system.

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Quantum cognition is a new research program that uses mathematical principles from quantum theory as a framework to explain human cognition, including judgment and decision making, concepts, reasoning, memory, and perception. This research is not concerned with whether the brain is a quantum computer. Instead, it uses quantum theory as a fresh conceptual framework and a coherent set of formal tools for explaining puzzling empirical findings in psychology. In this introduction, we focus on two quantum principles as examples to show why quantum cognition is an appealing new theoretical direction for psychology: complementarity, which suggests that some psychological measures have to be made sequentially and that the context generated by the first measure can influence responses to the next one, producing measurement order effects, and superposition, which suggests that some psychological states cannot be defined with respect to definite values but, instead, that all possible values within the superposition have some potential for being expressed. We present evidence showing how these two principles work together to provide a coherent explanation for many divergent and puzzling phenomena in psychology. (PsycInfo Database Record © 2020 APA, all rights reserved)

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