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Macroscopic Quantum Self-trapping
In quantum mechanics, macroscopic quantum self-trapping is when two Bose-Einstein condensates weakly linked by an energy barrier which particles can tunnel through, nevertheless end up with a higher average number of bosons on one side of the junction than the other. The junction of two Bose–Einstein condensates is mostly analogous to a Josephson junction, which is made of two superconductors linked by a non-conducting barrier. However, superconducting Josephson junctions do not display macroscopic quantum self-trapping, and thus macroscopic quantum self-tunneling is a distinguishing feature of Bose-Einstein condensate junctions. Self-trapping occurs when the self-interaction energy \Lambda between the Bosons is larger than a critical value called \Lambda^\text_c. \Lambda^\text_c = \frac It was first described in 1997. It has been observed in Bose-Einsten condensates of exciton-polaritons, and predicted for a condensate of magnons. While the tunneling of a particle through cl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Introduction To Quantum Mechanics
Quantum mechanics is the study of matter and its interactions with energy on the scale of atomic and subatomic particles. By contrast, classical physics explains matter and energy only on a scale familiar to human experience, including the behavior of astronomical bodies such as the moon. Classical physics is still used in much of modern science and technology. However, towards the end of the 19th century, scientists discovered phenomena in both the large (macro) and the small ( micro) worlds that classical physics could not explain. The desire to resolve inconsistencies between observed phenomena and classical theory led to two major revolutions in physics that created a shift in the original scientific paradigm: the ''theory of relativity'' and the development of ''quantum mechanics''. This article describes how physicists discovered the limitations of classical physics and developed the main concepts of the quantum theory that replaced it in the early decades of the 20th ce ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wave Function
A wave function in quantum physics is a mathematical description of the quantum state of an isolated quantum system. The wave function is a complex-valued probability amplitude, and the probabilities for the possible results of measurements made on the system can be derived from it. The most common symbols for a wave function are the Greek letters and (lower-case and capital psi, respectively). The wave function is a function of the degrees of freedom corresponding to some maximal set of commuting observables. Once such a representation is chosen, the wave function can be derived from the quantum state. For a given system, the choice of which commuting degrees of freedom to use is not unique, and correspondingly the domain of the wave function is also not unique. For instance, it may be taken to be a function of all the position coordinates of the particles over position space, or the momenta of all the particles over momentum space; the two are related by a Fourier ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gross–Pitaevskii Equation
The Gross–Pitaevskii equation (GPE, named after Eugene P. Gross and Lev Petrovich Pitaevskii) describes the ground state of a quantum system of identical bosons using the Hartree–Fock approximation and the pseudopotential interaction model. A Bose–Einstein condensate (BEC) is a gas of bosons that are in the same quantum state, and thus can be described by the same wavefunction. A free quantum particle is described by a single-particle Schrödinger equation. Interaction between particles in a real gas is taken into account by a pertinent many-body Schrödinger equation. In the Hartree–Fock approximation, the total wave-function \Psi of the system of N bosons is taken as a product of single-particle functions \psi: \Psi(\mathbf_1, \mathbf_2, \dots, \mathbf_N) = \psi(\mathbf_1) \psi(\mathbf_2) \dots \psi(\mathbf_N), where \mathbf_i is the coordinate of the i-th boson. If the average spacing between the particles in a gas is greater than the scattering length (that is, in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Double-well Potential
The so-called double-well potential is one of a number of quartic potentials of considerable interest in quantum mechanics, in quantum field theory and elsewhere for the exploration of various physical phenomena or mathematical properties since it permits in many cases explicit calculation without over-simplification. Thus the "symmetric double-well potential" served for many years as a model to illustrate the concept of instantons as a pseudo-classical configuration in a Euclideanised field theory. In the simpler quantum mechanical context this potential served as a model for the evaluation of Feynman path integrals. or the solution of the Schrödinger equation by various methods for the purpose of obtaining explicitly the energy eigenvalues. The "inverted symmetric double-well potential", on the other hand, served as a nontrivial potential in the Schrödinger equation for the calculation of decay rates and the exploration of the large order behavior of asymptotic expansions. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rest (physics)
Inertia is the idea that an object will continue its current motion until some force causes its speed or direction to change. The term is properly understood as shorthand for "the principle of inertia" as described by Newton in his first law of motion. After some other definitions, Newton states in his first law of motion: The word "perseveres" is a direct translation from Newton's Latin. Other, less forceful terms such as "to continue" or "to remain" are commonly found in modern textbooks. The modern use follows from some changes in Newton's original mechanics (as stated in the ''Principia'') made by Euler, d'Alembert, and other Cartesians. The term inertia comes from the Latin word ''iners'', meaning idle, sluggish. The term inertia may also refer to the resistance of any physical object to a change in its velocity. This includes changes to the object's speed or direction of motion. An aspect of this property is the tendency of objects to keep moving in a straight line ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quantum Tunneling
In physics, a quantum (plural quanta) is the minimum amount of any physical entity (physical property) involved in an interaction. The fundamental notion that a physical property can be "quantized" is referred to as "the hypothesis of quantization". This means that the magnitude of the physical property can take on only discrete values consisting of integer multiples of one quantum. For example, a photon is a single quantum of light (or of any other form of electromagnetic radiation). Similarly, the energy of an electron bound within an atom is quantized and can exist only in certain discrete values. (Atoms and matter in general are stable because electrons can exist only at discrete energy levels within an atom.) Quantization is one of the foundations of the much broader physics of quantum mechanics. Quantization of energy and its influence on how energy and matter interact ( quantum electrodynamics) is part of the fundamental framework for understanding and describing nature. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mechanical Equilibrium
In classical mechanics, a particle is in mechanical equilibrium if the net force on that particle is zero. By extension, a physical system made up of many parts is in mechanical equilibrium if the net force on each of its individual parts is zero. In addition to defining mechanical equilibrium in terms of force, there are many alternative definitions for mechanical equilibrium which are all mathematically equivalent. In terms of momentum, a system is in equilibrium if the momentum of its parts is all constant. In terms of velocity, the system is in equilibrium if velocity is constant. In a rotational mechanical equilibrium the angular momentum of the object is conserved and the net torque is zero. More generally in conservative systems, equilibrium is established at a point in configuration space where the gradient of the potential energy with respect to the generalized coordinates is zero. If a particle in equilibrium has zero velocity, that particle is in static equilibriu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Potential Well
A potential well is the region surrounding a local minimum of potential energy. Energy captured in a potential well is unable to convert to another type of energy (kinetic energy in the case of a gravitational potential well) because it is captured in the local minimum of a potential well. Therefore, a body may not proceed to the global minimum of potential energy, as it would naturally tend to do due to entropy. Overview Energy may be released from a potential well if sufficient energy is added to the system such that the local maximum is surmounted. In quantum physics, potential energy may escape a potential well without added energy due to the probabilistic characteristics of quantum particles; in these cases a particle may be imagined to tunnel ''through'' the walls of a potential well. The graph of a 2D potential energy function is a potential energy surface that can be imagined as the Earth's surface in a landscape of hills and valleys. Then a potential well would be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnon
A magnon is a quasiparticle, a collective excitation of the electrons' spin structure in a crystal lattice. In the equivalent wave picture of quantum mechanics, a magnon can be viewed as a quantized spin wave. Magnons carry a fixed amount of energy and lattice momentum, and are spin-1, indicating they obey boson behavior. Brief history The concept of a magnon was introduced in 1930 by Felix Bloch in order to explain the reduction of the spontaneous magnetization in a ferromagnet. At absolute zero temperature (0 K), a Heisenberg ferromagnet reaches the state of lowest energy (so-called ground state), in which all of the atomic spins (and hence magnetic moments) point in the same direction. As the temperature increases, more and more spins deviate randomly from the alignment, increasing the internal energy and reducing the net magnetization. If one views the perfectly magnetized state at zero temperature as the vacuum state of the ferromagnet, the low-temperature state with ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Exciton-polariton
In physics the Exciton–polariton is a type of polariton; a hybrid light and matter quasiparticle arising from the strong coupling of the electromagnetic dipolar oscillations of excitons (either in bulk or quantum wells) and photons. Because light excitations are observed classically as photons, which are massless particles, they do not therefore have mass, like a physical particle. This property makes them a quasiparticle. Theory The coupling of the two oscillators, photons modes in the semiconductor optical microcavity and excitons of the quantum wells, results in the energy anticrossing of the bare oscillators, giving rise to the two new normal modes for the system, known as the upper and lower polariton resonances (or branches). The energy shift is proportional to the coupling strength (dependent, e.g., on the field and polarization overlaps). The higher energy or upper mode (UPB, upper polariton branch) is characterized by the photonic and exciton fields oscillating ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Josephson Effect
In physics, the Josephson effect is a phenomenon that occurs when two superconductors are placed in proximity, with some barrier or restriction between them. It is an example of a macroscopic quantum phenomenon, where the effects of quantum mechanics are observable at ordinary, rather than atomic, scale. The Josephson effect has many practical applications because it exhibits a precise relationship between different physics quantities, such as voltage and frequency, facilitating highly accurate measurements. The Josephson effect produces a current, known as a supercurrent, that flows continuously without any voltage applied, across a device known as a Josephson junction (JJ). These consist of two or more superconductors coupled by a weak link. The weak link can be a thin insulating barrier (known as a superconductor–insulator–superconductor junction, or S-I-S), a short section of non-superconducting metal (S-N-S), or a physical constriction that weakens the superconductivi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
