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Category: quantum physics

What is interaction, and when does it occur? Intuition suggests that the necessary condition for the interaction of independently created particles is their direct touch or contact through physical force carriers. In quantum mechanics, the result of the interaction is entanglement—the appearance of non-classical correlations in the system. It seems that quantum theory allows entanglement of independent particles without any contact. The fundamental identity of particles of the same kind is responsible for this phenomenon.

Quantum mechanics is currently the best and most accurate theory used by physicists to describe the world around us. Its characteristic feature, however, is the abstract mathematical language of , notoriously leading to serious interpretational problems. The view of reality proposed by this theory is still a subject of scientific dispute that, over time, is only becoming hotter and more interesting. New research motivation and intriguing questions are brought forth by a fresh perspective resulting from the standpoint of quantum information and the enormous progress of experimental techniques. These allow verification of the conclusions drawn from subtle thought experiments directly related to the problem of interpretation. Moreover, researchers are now making enormous progress in the field of quantum communication and quantum computer technology, which significantly draws on non-classical resources offered by quantum mechanics.

Pawel Blasiak from the Institute of Nuclear Physics of the Polish Academy of Sciences in Krakow and Marcin Markiewicz from the University of Gdansk focus on analyzing widely accepted paradigms and theoretical concepts regarding the basics and interpretation of quantum mechanics. The researchers are trying to determine to what extent the intuitions used to describe quantum mechanical processes are justified in a realistic view of the world. For this purpose, they try to clarify specific theoretical ideas, often functioning in the form of vague intuitions, using the language of mathematics. This approach often results in the appearance of inspiring paradoxes. Of course, the more basic the concept to which a given paradox relates, the better, because it opens up new doors to deeper understanding a given problem.

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A gravity laser :DDD.

We consider the possibility of creating a graviton laser. The lasing medium would be a system of contained, ultra cold neutrons. Ultra cold neutrons are a quantum mechanical system that interacts with gravitational fields and with the phonons of the container walls. It is possible to create a population inversion by pumping the system using the phonons. We compute the rate of spontaneous emission of gravitons and the rate of the subsequent stimulated emission of gravitons. The gain obtainable is directly proportional to the density of the lasing medium and the fraction of the population inversion. The applications of a graviton laser would be interesting.

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Higgs boson laser.

Electroweak processes in high-energy lepton collisions are considered in a situation where the incident center-of-mass energy lies below the reaction threshold, but is boosted to the required level by subsequent laser acceleration. Within the framework of laser-dressed quantum field theory, we study the laser-boosted process $\ell^+ \ell^- \to HZ^0$ in detail and specify the technical demands needed for its experimental realization. Further, we outline possible qualitative differences to field-free processes regarding the detection of the produced Higgs bosons.

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The amplitude mode is a ubiquitous collective excitation in condensed-matter systems with broken continuous symmetry. It is expected in antiferromagnets, short coherence length superconductors, charge density waves, and lattice Bose condensates. Its detection is a valuable test of the corresponding field theory, and its mass gap measures the proximity to a quantum critical point. However, since the amplitude mode can decay into low-energy Goldstone modes, its experimental visibility has been questioned. Here we show that the visibility depends on the symmetry of the measured susceptibility. The longitudinal susceptibility diverges at low frequency as Im χ σ σ ∼ ω − 1 (d = 2) or log (1 / | ω |) (d = 3), which can completely obscure the amplitude peak. In contrast, the scalar susceptibility is suppressed by four extra powers of frequency, exposing the amplitude peak throughout the ordered phase. We discuss experimental setups for measuring the scalar susceptibility. The conductivity of the O (2 ) theory (relativistic superfluid) is a scalar response and therefore exhibits suppressed absorption below the Higgs mass threshold, σ ∼ ω 2 d + 1. In layered, short coherence length superconductors, (relevant, e.g., to cuprates) this threshold is raised by the interlayer plasma frequency.

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Modern society relies on technologies with electronic integrated circuits (IC) at their heart, but these may prove to be less suitable in future applications such as quantum computing and environmental sensing. Photonic integrated circuits (PICs), the light-based equivalent of electronic ICs, are an emerging technology field that can offer lower energy consumption, faster operation, and enhanced performance. However, current PIC fabrication methods lead to large variability between fabricated devices, resulting in limited yield, long delays between the conceptual idea and the working device, and lack of configurability. Researchers at Eindhoven University of Technology have devised a new process for the fabrication of PICs that addresses these critical issues, by creating novel reconfigurable PICs in the same way that the emergence of programmable logic devices transformed IC production in the 1980s.

Photonic integrated circuits (PICs) – the light-based equivalent of electronic ICs—carry signals via visible and . Optical materials with adjustable refractive index are essential for reconfigurable PICs as they allow for more accurate manipulation of light passing through the materials, leading to better PIC performance.

Current programmable PIC concepts suffer from issues such as volatility and/or high optical signal losses—both of which negatively affect a material’s ability to keep its programmed state. Using hydrogenated (a-Si: H), a material used in thin-film silicon , and the associated Staebler-Wronski effect (SWE), which describes how the of a-Si: H can be changed via light exposure or heating, researchers at Eindhoven University of Technology have designed a new PIC fabrication process that addresses the shortfalls of current techniques and could lead to the emergence of universal programmable PICs.

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:oooooooo.

Recent findings of new Higgs modes in unconventional superconductors require a classification and characterization of the modes allowed by nontrivial gap symmetry. Here we develop a theory for a tailored nonequilibrium quantum quench to excite all possible oscillation symmetries of a superconducting condensate. We show that both a finite momentum transfer and quench symmetry allow for an identification of the resulting Higgs oscillations. These serve as a fingerprint for the ground state gap symmetry. We provide a classification scheme of these oscillations and the quench symmetry based on group theory for the underlying lattice point group. For characterization, analytic calculations as well as full scale numeric simulations of the transient optical response resulting from an excitation by a realistic laser pulse are performed. Our classification of Higgs oscillations allows us to distinguish between different symmetries of the superconducting condensate.

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A team led by Prof. Guo Guangcan from University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS) and collaborators first realized distribution of high-dimensional orbital angular momentum entanglement over a 1 km few-mode fiber. The result is published in Optica.

Increasing the channel capacity and tolerance to noise in is a strong practical motivation for encoding quantum information in multilevel systems, qudits as opposed to qubits. From a foundational perspective, entanglement in higher dimensions exhibits more complex structures and stronger non-classical correlations. High-dimensional entanglement has demonstrated its potential for increasing channel capacity and resistance to noise in processing. Despite these benefits, the distribution of high-dimensional entanglement is relatively new and remains challenging.

The orbital angular momentum of photon is a high dimensional system which has been paid much attention to in recent years. However, orbital angular momentum entanglement is susceptible to atmospheric turbulence or mode crosstalk and mode dispersion in optical fibers. It can only transmit a few meters, and is limited to two-dimensional entanglement distribution.

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In the heart of a galaxy cluster 200 million light-years away, astronomers have failed to detect hypothetical particles called axions.

This places new constraints on how we believe these particles work — but it also has pretty major implications for string theory, and the development of a Theory of Everything that describes how the physical Universe works.

“Until recently I had no idea just how much X-ray astronomers bring to the table when it comes to string theory, but we could play a major role,” said astrophysicist Christopher Reynolds of the University of Cambridge in the UK.

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