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In physics, dephasing is a mechanism that recovers classical behaviour from a quantum system. It refers to the ways in which coherence caused by perturbation decays over time, and the system returns to the state before perturbation. It is an important effect in molecular and atomic spectroscopy, and in the condensed matter physics of mesoscopic devices.
Cavity loses coherence due to dephasing.
The reason can be understood by describing the conduction in metals as a classical phenomenon with quantum effects all embedded into an effective mass that can be computed quantum mechanically, as also happens to resistance that can be seen as a scattering effect of conduction electrons. When the temperature is lowered and the dimensions of the device are meaningfully reduced, this classical behaviour should disappear and the laws of quantum mechanics should govern the behavior of conducting electrons seen as waves that move ballistically inside the conductor without any kind of dissipation. Most of the time this is what one observes. But it appeared as a surprise[to whom?] to uncover that the so-called dephasing time, that is the time it takes for the conducting electrons to lose their quantum behavior, becomes finite rather than infinite when the temperature approaches zero in mesoscopic devices violating the expectations of the theory of Boris Altshuler, Arkady Aronov and David E. Khmelnitskii.[1] This kind of saturation of the dephasing time at low temperatures is an open problem even as several proposals have been put forward.
The coherence of a sample is explained by the off-diagonal elements of a density matrix. An external electric or magnetic field can create coherences between two quantum states in a sample if the frequency corresponds to the energy gap between the two states. The coherence terms decay with the dephasing time or spin–spin relaxation, T2.
After coherence is created in a sample by light, the sample emits a polarization wave, the frequency of which is equal to and the phase of which is inverted from the incident light. In addition, the sample is excited by the incident light and a population of molecules in the excited state is generated. The light passing through the sample is absorbed because of these two processes, and it is expressed by an absorption spectrum. The coherence decays with the time constant, T2, and the intensity of the polarization wave is reduced. The population of the excited state also decays with the time constant of the longitudinal relaxation, T1. The time constant T2 is usually much smaller than T1, and the bandwidth of the absorption spectrum is related to these time constants by the Fourier transform, so the time constant T2 is a main contributor to the bandwidth. The time constant T2 has been measured with ultrafast time-resolved spectroscopy directly, such as in photon echo experiments.
What is the dephasing rate of a particle that has an energy E if it is subject to a fluctuating environment that has a temperature T? In particular what is the dephasing rate close to equilibrium (E~T), and what happens in the zero temperature limit? This question has fascinated the mesoscopic community during the last two decades (see references below).
^Altshuler, B L; Aronov, A G; Khmelnitsky, D E (1982-12-30). "Effects of electron-electron collisions with small energy transfers on quantum localisation". Journal of Physics C: Solid State Physics. 15 (36): 7367–7386. Bibcode:1982JPhC...15.7367A. doi:10.1088/0022-3719/15/36/018. ISSN 0022-3719.
Otheredit
Imry, Y. (1997). Introduction to Mesoscopic Physics. Oxford University Press. (And references therein.)
Aleiner, I. L.; Altshuler, B. L.; Gershenson, M. E. (1999). "Comment on "Quantum Decoherence in Disordered Mesoscopic Systems"". Physical Review Letters. 82 (15): 3190. arXiv:cond-mat/9808078. Bibcode:1999PhRvL..82.3190A. doi:10.1103/PhysRevLett.82.3190. S2CID 119348960.
Cohen, D.; Imry, Y. (1999). "Dephasing at low temperatures". Physical Review B. 59 (17): 11143–11146. arXiv:cond-mat/9807038. Bibcode:1999PhRvB..5911143C. doi:10.1103/PhysRevB.59.11143. S2CID 51856292.
Golubev, D. S.; Schön, G.; Zaikin, A. D. (2003). "Low-temperature dephasing and Renormalization in model systems". Journal of the Physical Society of Japan. 72 (Suppl. A): 30–35. arXiv:cond-mat/0208548. Bibcode:2003JPSJ...72S..30S. doi:10.1143/JPSJS.72SA.30. S2CID 119036267.
Saminadayar, L.; Mohanty, P.; Webb, R. A.; Degiovanni, P.; Bäuerle, C. (2007). "Electron coherence at low temperatures: The role of magnetic impurities". Physica E. 40 (1): 12–24. arXiv:0709.4663. Bibcode:2007PhyE...40...12S. doi:10.1016/j.physe.2007.05.026. S2CID 13883162.
Mohanty, P. (2001). "Of decoherent electrons and disordered conductors". In Skjeltorp, A. T.; Vicsek, T. (eds.). Complexity from Microscopic to Macroscopic Scales: Coherence and Large deviations. Kluwer. arXiv:cond-mat/0205274. Bibcode:2002cond.mat..5274M.
Frasca, M. (2003). "Saturation of dephasing time in mesoscopic devices produced by a ferromagnetic state". Physical Review B. 68 (19): 193413. arXiv:cond-mat/0308377. Bibcode:2003PhRvB..68s3413F. doi:10.1103/PhysRevB.68.193413. S2CID 119498061.
January 01, 1970
dephasing, this, article, multiple, issues, please, help, improve, discuss, these, issues, talk, page, learn, when, remove, these, template, messages, this, article, includes, list, references, related, reading, external, links, sources, remain, unclear, becau. This article has multiple issues Please help improve it or discuss these issues on the talk page Learn how and when to remove these template messages This article includes a list of references related reading or external links but its sources remain unclear because it lacks inline citations Please help improve this article by introducing more precise citations February 2020 Learn how and when to remove this message This article may lack focus or may be about more than one topic Please help improve this article possibly by splitting the article and or by introducing a disambiguation page or discuss this issue on the talk page February 2012 Learn how and when to remove this message In physics dephasing is a mechanism that recovers classical behaviour from a quantum system It refers to the ways in which coherence caused by perturbation decays over time and the system returns to the state before perturbation It is an important effect in molecular and atomic spectroscopy and in the condensed matter physics of mesoscopic devices Cavity loses coherence due to dephasing The reason can be understood by describing the conduction in metals as a classical phenomenon with quantum effects all embedded into an effective mass that can be computed quantum mechanically as also happens to resistance that can be seen as a scattering effect of conduction electrons When the temperature is lowered and the dimensions of the device are meaningfully reduced this classical behaviour should disappear and the laws of quantum mechanics should govern the behavior of conducting electrons seen as waves that move ballistically inside the conductor without any kind of dissipation Most of the time this is what one observes But it appeared as a surprise to whom to uncover that the so called dephasing time that is the time it takes for the conducting electrons to lose their quantum behavior becomes finite rather than infinite when the temperature approaches zero in mesoscopic devices violating the expectations of the theory of Boris Altshuler Arkady Aronov and David E Khmelnitskii 1 This kind of saturation of the dephasing time at low temperatures is an open problem even as several proposals have been put forward The coherence of a sample is explained by the off diagonal elements of a density matrix An external electric or magnetic field can create coherences between two quantum states in a sample if the frequency corresponds to the energy gap between the two states The coherence terms decay with the dephasing time or spin spin relaxation T2 After coherence is created in a sample by light the sample emits a polarization wave the frequency of which is equal to and the phase of which is inverted from the incident light In addition the sample is excited by the incident light and a population of molecules in the excited state is generated The light passing through the sample is absorbed because of these two processes and it is expressed by an absorption spectrum The coherence decays with the time constant T2 and the intensity of the polarization wave is reduced The population of the excited state also decays with the time constant of the longitudinal relaxation T1 The time constant T2 is usually much smaller than T1 and the bandwidth of the absorption spectrum is related to these time constants by the Fourier transform so the time constant T2 is a main contributor to the bandwidth The time constant T2 has been measured with ultrafast time resolved spectroscopy directly such as in photon echo experiments What is the dephasing rate of a particle that has an energy E if it is subject to a fluctuating environment that has a temperature T In particular what is the dephasing rate close to equilibrium E T and what happens in the zero temperature limit This question has fascinated the mesoscopic community during the last two decades see references below See also editDephasing rate SP formulaReferences edit Altshuler B L Aronov A G Khmelnitsky D E 1982 12 30 Effects of electron electron collisions with small energy transfers on quantum localisation Journal of Physics C Solid State Physics 15 36 7367 7386 Bibcode 1982JPhC 15 7367A doi 10 1088 0022 3719 15 36 018 ISSN 0022 3719 Other edit Imry Y 1997 Introduction to Mesoscopic Physics Oxford University Press And references therein Aleiner I L Altshuler B L Gershenson M E 1999 Comment on Quantum Decoherence in Disordered Mesoscopic Systems Physical Review Letters 82 15 3190 arXiv cond mat 9808078 Bibcode 1999PhRvL 82 3190A doi 10 1103 PhysRevLett 82 3190 S2CID 119348960 Cohen D Imry Y 1999 Dephasing at low temperatures Physical Review B 59 17 11143 11146 arXiv cond mat 9807038 Bibcode 1999PhRvB 5911143C doi 10 1103 PhysRevB 59 11143 S2CID 51856292 Golubev D S Schon G Zaikin A D 2003 Low temperature dephasing and Renormalization in model systems Journal of the Physical Society of Japan 72 Suppl A 30 35 arXiv cond mat 0208548 Bibcode 2003JPSJ 72S 30S doi 10 1143 JPSJS 72SA 30 S2CID 119036267 Saminadayar L Mohanty P Webb R A Degiovanni P Bauerle C 2007 Electron coherence at low temperatures The role of magnetic impurities Physica E 40 1 12 24 arXiv 0709 4663 Bibcode 2007PhyE 40 12S doi 10 1016 j physe 2007 05 026 S2CID 13883162 Mohanty P 2001 Of decoherent electrons and disordered conductors In Skjeltorp A T Vicsek T eds Complexity from Microscopic to Macroscopic Scales Coherence and Large deviations Kluwer arXiv cond mat 0205274 Bibcode 2002cond mat 5274M Frasca M 2003 Saturation of dephasing time in mesoscopic devices produced by a ferromagnetic state Physical Review B 68 19 193413 arXiv cond mat 0308377 Bibcode 2003PhRvB 68s3413F doi 10 1103 PhysRevB 68 193413 S2CID 119498061 Retrieved from https en wikipedia org w index php title Dephasing amp oldid 1116054178, wikipedia, wiki, book, books, library,
