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The Second Quantum Revolution: Unexplored Facts and Latest News
The Second Quantum Revolution refers to a contemporary wave of advancements and breakthroughs in the field of quantum physics that extends beyond the early developments of Quantum Mechanics that occurred in the 20th century. One crucial aspect of this revolution is the deeper exploration and practical application of quantum entanglement. Entanglement serves as a cornerstone in the ongoing revolution, contributing to quantum computing, communication, fundamental physics experiments, and advanced sensing technologies. Here, we present and discuss some of the recent applications of entanglement, exploring its philosophical implications and non-locality beyond Bell’s theorem, thereby critically examining the foundations of Quantum Mechanics. Additionally, we propose educational activities that introduce high school students to Quantum Mechanics by emphasizing entanglement as an essential concept to understand in order to become informed participants in the Second Quantum Revolution. Furthermore, we present the state-of-art developments of a largely unexplored and promising realization of real qubits, namely the molecular spin qubits. We review the available and suggested device architectures to host and use molecular spins. Moreover, we summarize the experimental findings on solid-state spin qubit devices based on magnetic molecules. Finally, we discuss how the Second Quantum Revolution might significantly transform law enforcement by offering specific examples and methodologies to address the evolving challenges in public safety and security.
  • 414
  • 02 Apr 2024
Topic Review Peer Reviewed
Integrated Fabry–Perot Cavities: A Quantum Leap in Technology
Integrated Fabry–Perot cavities (IFPCs), often referred to as nanobeams due to their form factor and size, have profoundly modified the landscape of integrated photonics as a new building block for classical and quantum engineering. In this entry, the main properties of IFPCs will be summarized from the classical and quantum point of view. The classical will provide some of the main results obtained in the last decade, whereas the quantum point of view will exp
  • 221
  • 29 Mar 2024
Topic Review
Solid-State Color Centers for Single-Photon Generation
Single-photon sources are important for integrated photonics and quantum technologies, and can be used in quantum key distribution, quantum computing, and sensing. Color centers in the solid state are a promising candidate for the development of the next generation of single-photon sources integrated in quantum photonics devices. They are point defects in a crystal lattice that absorb and emit light at given wavelengths and can emit single photons with high efficiency. 
  • 69
  • 20 Mar 2024
Topic Review
Preparation of Rare-Earth-Ion-Doped High-Purity Glasses
The main source of impurities in the doped selenide glasses are rare-earth metals and their precursors (halides, chalcogenides). The total optical losses in glasses caused by impurities brought with rare-earth metals at a doping level of 1000 wt ppm can reach 10–85 dB/m.
  • 141
  • 06 Dec 2023
Topic Review
Two-Dimensional Quantum Billiards
Two-dimensional quantum billiards are one of the most important paradigms for exploring the connection between quantum and classical worlds. Researchers are mainly focused on nonintegrable and irregular shapes to understand the quantum characteristics of chaotic billiards. The emergence of the scarred modes relevant to unstable periodic orbits (POs) is one intriguing finding in nonintegrable quantum billiards. On the other hand, stable POs are abundant in integrable billiards. The quantum wavefunctions associated with stable POs have been shown to play a key role in ballistic transport. 
  • 287
  • 19 Oct 2023
Topic Review
High-Precision Quantum Tests of the Weak Equivalence Principle
General relativity has been the best theory to describe gravity and space–time and has successfully explained many physical phenomena. At the same time, quantum mechanics provides the most accurate description of the microscopic world, and quantum science technology has evoked a wide range of developments today. Merging these two very successful theories to form a grand unified theory is one of the most elusive challenges in physics. All the candidate theories that wish to unify gravity and quantum mechanics predict the breaking of the weak equivalence principle, which lies at the heart of general relativity. It is therefore imperative to experimentally verify the equivalence principle in the presence of significant quantum effects of matter. Cold atoms provide well-defined properties and potentially nonlocal correlations as the test masses and will also improve the limits reached by classical tests with macroscopic bodies. The results of rigorous tests using cold atoms may tell us whether and how the equivalence principle can be reformulated into a quantum version. 
  • 193
  • 26 Sep 2023
Topic Review
Quantum Information Education
Quantum information is an emerging scientific and technological discipline attracting a growing number of professionals from various related fields. Although it can potentially serve as a valuable source of skilled labor, the Internet provides a way to disseminate information about education, opportunities, and collaboration.
  • 215
  • 12 May 2023
Topic Review Peer Reviewed
Wavefunction Collapse Broadens Molecular Spectrum
Spectral lines in the optical spectra of atoms, molecules, and other quantum systems are characterized by a range of frequencies ω or a range of wavelengths λ=2πc/ω, where c is the speed of light. Such a frequency or wavelength range is called the width of the spectral lines (linewidth). It is influenced by many specific factors. Thermal motion of the molecules results in broadening of the lines as a result of the Doppler effect (thermal broadening) and by their collisions (pressure broadening). The electric fields of neighboring molecules lead to Stark broadening. The linewidth to be considered here is the so-called parametric broadening (PB) of spectral lines in the optical spectrum. PB can be considered the fundamental type of broadening of the electronic vibrational–rotational (rovibronic) transitions in a molecule, which is the direct manifestation of the basic concept of the collapse of a wavefunction that is postulated by the Copenhagen interpretation of quantum mechanics. Thus, that concept appears to be not only valid but is also useful for predicting physically observable phenomena.
  • 742
  • 11 Apr 2023
Topic Review
Si-Compatible Nanostructured Photodetectors
Latest advances in the field of nanostructured photodetectors are considered, stating the types and materials, and highlighting the features of operation. Special attention is paid to the group-IV material photodetectors, including Ge, Si, Sn, and their solid solutions. Among the various designs, photodetectors with quantum wells, quantum dots, and quantum wires are highlighted. Such nanostructures have a number of unique properties, that made them striking to scientists’ attention and device applications. Nanostructures with quantum wells (QW) and quantum dots (QD) are very widely used to create photodetectors in the visible and infrared ranges. At the same time, for various applications, various semiconductor material systems are used that most fully satisfy the specific requirements for device structures: III–V (GaAs, AlGaAs, etc.), II–VI (CdHgTe), IV–IV (GeSi, GeSn, GeSiSn), and others.
  • 460
  • 01 Feb 2023
Topic Review
Bragg Grating External Cavity Semiconductor Lasers
External cavity semiconductor lasers (ECSLs) usually refer to the gain chip based on the introduction of external optical components (such as waveguides, gratings, prisms, etc.) to provide optical feedback. By designing the type, position and structure of external optical components, the optical properties of SLs (such as center wavelength, linewidth, tuning range, side-mode suppression ratio (SMSR), etc.) can be changed. Bragg grating external cavity semiconductor laser (BG-ECSL) is a device with a specific optical element (Bragg grating) in the external cavity. BG-ECSLs have excellent performances, such as narrow linewidth, tunability and high SMSR. They are widely used in WDM systems, coherent optical communication, gas detection, Lidar, atomic physics and other fields. 
  • 653
  • 09 Dec 2022
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