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Quantum Mechanics Quantum mechanics (QM; also known as quantum physics or quantum theory), including quantum field theory, is a fundamental theory in physics which describes nature at the smallest scales of energy levels of atoms and subatomic particles.[2] Classical physics Classical physics (the physics existing before quantum mechanics) is a set of fundamental theories which describes nature at ordinary (macroscopic) scale [...More...] 


Wave Propagation Wave Wave propagation is any of the ways in which waves travel. With respect to the direction of the oscillation relative to the propagation direction, we can distinguish between longitudinal wave and transverse waves. For electromagnetic waves, propagation may occur in a vacuum as well as in a material medium. Other wave types cannot propagate through a vacuum and need a transmission medium to exist[citation needed].Contents1 Reflection of plane Waves in a halfspace1.1 SV wave propagation 1.2 P wave propagation2 Wave Wave velocity 3 See also 4 References 5 External linksReflection of plane Waves in a halfspace[edit] The propagation and reflection of plane waves, i.e. Pressure waves (Pwave) or Shear waves (SH or SVwaves), in a homogeneous halfspace have been of significant interest in the classical seismology [...More...] 


Spontaneous Parametric Downconversion Spontaneous parametric downconversion Spontaneous parametric downconversion (also known as SPDC, or parametric scattering) is an important process in quantum optics, used especially as a source of entangled photon pairs, and of single photons.Contents1 Basic process 2 Example 3 History 4 Applications 5 Alternatives 6 See also 7 ReferencesBasic process[edit]An SPDC scheme with the Type I outputPlay mediaThe video of an experiment showing vacuum fluctuations (in the red ring) amplified by SPDC (corresponding to the image above)A nonlinear crystal is used to split photon beams into pairs of photons that, in accordance with the law of conservation of energy and law of conservation of momentum, have combined energies and momenta equal to the energy and momentum of the original photon and crystal lattice, are phasematched in the frequency domain, and have correlated polarizations. The state of the crystal is unchanged by the process [...More...] 


Symmetry Breaking This article needs attention from an expert in Physics. Please add a reason or a talk parameter to this template to explain the issue with the article. WikiProject Physics may be able to help recruit an expert. (May 2014)A ball is initially located at the top of the central hill (C). This position is an unstable equilibrium: a very small perturbation will cause it to fall to one of the two stable wells left (L) or (R). Even if the hill is symmetric and there is no reason for the ball to fall on either side, the observed final state is not symmetric.In physics, symmetry breaking is a phenomenon in which (infinitesimally) small fluctuations acting on a system crossing a critical point decide the system's fate, by determining which branch of a bifurcation is taken. To an outside observer unaware of the fluctuations (or "noise"), the choice will appear arbitrary [...More...] 


QCD Vacuum Th Quantum Chromodynamic Vacuum or QCD vacuum is the vacuum state of quantum chromodynamics (QCD). It is an example of a nonperturbative vacuum state[further explanation needed], characterized by nonvanishing condensates such as the gluon condensate and the quark condensate in the complete theory which includes quarks. The presence of these condensates characterizes the confined phase of quark matter.Unsolved problem in physics: QCD in the nonperturbative regime: confinement. The equations of QCD remain unsolved at energy scales relevant for describing atomic nuclei [...More...] 


QED Vacuum The Quantum Electrodynamic Vacuum or QED vacuum QED vacuum is the fieldtheoretic vacuum of quantum electrodynamics [...More...] 


Operator (physics) In physics, an operator is a function over a space[clarification needed] of physical states to another space of physical states. The simplest example of the utility of operators is the study of symmetry (which makes the concept of a group useful in this context). Because of this, they are a very useful tool in classical mechanics [...More...] 


Photon Entanglement Photon Photon entanglement is a supplement to the article BohrEinstein debates and is designed to help clarify the discussion of the EinsteinPodolskyRosen argument in quantum theory which takes place in the previous article.Contents1 Entanglement 2 Applications 3 See also 4 References 5 External linksEntanglement[edit] A quantum system is described, at every instant, by a vector state which, according to the theory, represents the maximum amount of information that it is possible to have. To simplify discussion, taking the example of the state of polarization of a photon and associate with it the vector state 45 ⟩ displaystyle left45rightrangle The knowledge of the vector state, in fact, provides us exclusively with information on the possible results of measurements which we decide to carry out on the system [...More...] 


Quantum Foam Quantum foam (also referred to as spacetime foam) is a concept in quantum mechanics devised by John Wheeler in 1955.[1]Contents1 Background 2 Experimental results2.1 Constraints and limits2.1.1 Random diffusion model 2.1.2 Holographic model3 Relation to other theories 4 See also 5 Notes 6 ReferencesBackground[edit] With an incomplete theory of quantum gravity, it is impossible to be certain what spacetime would look like at small scales. However, there is no reason that spacetime needs to be fundamentally smooth [...More...] 


Quantum Teleportation Quantum teleportation Quantum teleportation is a process by which quantum information (e.g. the exact state of an atom or photon) can be transmitted (exactly, in principle) from one location to another, with the help of classical communication and previously shared quantum entanglement between the sending and receiving location. Because it depends on classical communication, which can proceed no faster than the speed of light, it cannot be used for fasterthanlight transport or communication of classical bits. While it has proven possible to teleport one or more qubits of information between two (entangled) atoms,[1][2][3] this has not yet been achieved between molecules or anything larger. Although the name is inspired by the teleportation commonly used in fiction, quantum teleportation is limited to the transfer of information rather than matter itself [...More...] 


Vacuum State In quantum field theory, the quantum vacuum state (also called the quantum vacuum or vacuum state) is the quantum state with the lowest possible energy. Generally, it contains no physical particles. Zeropoint field is sometimes used as a synonym for the vacuum state of an individual quantized field. According to presentday understanding of what is called the vacuum state or the quantum vacuum, it is "by no means a simple empty space".[1][2] According to quantum mechanics, the vacuum state is not truly empty but instead contains fleeting electromagnetic waves and particles that pop into and out of existence.[3][4][5] The QED vacuum QED vacuum of quantum electrodynamics (or QED) was the first vacuum of quantum field theory to be developed [...More...] 


Quantum Fluctuation In quantum physics, a quantum fluctuation (or vacuum state fluctuation or vacuum fluctuation) is the temporary change in the amount of energy in a point in space,[1] as explained in Werner Heisenberg's uncertainty principle. This allows the creation of particleantiparticle pairs of virtual particles. The effects of these particles are measurable, for example, in the effective charge of the electron, different from its "naked" charge. Quantum fluctuations may have been very important in the origin of the structure of the universe: according to the model of expansive inflation the ones that existed when inflation began were amplified and formed the seed of all current observed structure [...More...] 


Quantum Noise In physics, quantum noise refers to the uncertainty of a physical quantity that is due to its quantum origin. In certain situations, quantum noise appears as shot noise; for example, most optical communications use amplitude modulation, and thus, the quantum noise appears as shot noise only. For the case of uncertainty in the electric field in some lasers, the quantum noise is not just shot noise; uncertainties of both amplitude and phase contribute to the quantum noise. This issue becomes important in the case of noise of a quantum amplifier, which preserves the phase [...More...] 


Spontaneous Symmetry Breaking Spontaneous symmetry breaking Spontaneous symmetry breaking is a spontaneous process of symmetry breaking, by which a physical system in a symmetric state ends up in an asymmetric state.[1][2][3] In particular, it can describe systems where the equations of motion or the Lagrangian obey symmetries, but the lowestenergy vacuum solutions do not exhibit that same symmetry. When the system goes to one of those vacuum solutions, the symmetry is broken for perturbations around that vacuum even though the entire Lagrangian retains that [...More...] 


Quantum Annealing Quantum annealing Quantum annealing (QA) is a metaheuristic for finding the global minimum of a given objective function over a given set of candidate solutions (candidate states), by a process using quantum fluctuations. Quantum annealing Quantum annealing is used mainly for problems where the search space is discrete (combinatorial optimization problems) with many local minima; such as finding the ground state of a spin glass.[1] It was formulated in its present form by T. Kadowaki and H. Nishimori (ja) in " Quantum annealing Quantum annealing in the transverse Ising model"[2] though a proposal in a different form had been made by A. B. Finilla, M. A. Gomez, C. Sebenik and J. D [...More...] 


Quantum Levitation In quantum field theory, the Casimir effect Casimir effect and the Casimir–Polder force are physical forces arising from a quantized field [...More...] 
