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Seminars

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  • Title:Quantum Radiation and Vacuum Fluctuations
  • Start Date/Time:2020-01-15 / 12:30
  • End Date/Time :2020-01-15 / 13:30
    • Speaker:Prof. Bei-Lok Hu (Univ of Maryland)
    • Place:P512 of NCTS, 5F, 3rd General Building, Nat'l Tsing Hua Univ.
    • Host:Prof. Chong-Sun Chu (NTHU)
    • Abstract:From the 70s recurring confusion appears in two aspects of quantum radiation from/in an atom. They are:
      (A) The claim that one can explain phenomena associated with vacuum fluctuations by radiation reaction and vice versa [1].  (B) Unruh effect [2] says that a uniformly accelerated atom will get hot, but is there emitted radiation from it in the nature of Lamor?  (None. Proven in 1+1 dimension [3]). Issue B is particularly relevant to experimental tests of Unruh/Hawking radiation. In this talk we shall focus on Aspect A because it brings out several important issues at the interfaces of quantum, stochastic, semiclassical and classical.   Misconception in Issue A could generate more confusion because it is often used by “classicists” as an example that one can always find a classical explanation for any quantum phenomena, which is wrong.  We reiterate what was said in [4] before:  What holds the `duality relation’ with vacuum fluctuations is not radiation reaction, but quantum dissipation.  These two entities belong to two different worlds: vacuum fluctuations are quantum in nature but radiation reaction already exists at the classical level. A charge, be it moving or stationary, feels the effect of vacuum fluctuations, as would any physical object in all circumstances, but radiation reaction is absent for a uniformly accelerated (UA) charge. We use the simplest example of a stationary atom to illustrate the relation between vacuum fluctuations, quantum dissipation and quantum radiation. While the fluctuation-dissipation relation [5] describes the balance between vacuum fluctuations and quantum dissipation in all situations, we show that delicate cancelation of the interference between emitted radiation from the atom and the local fluctuations in the free field at the observation point is what accounts for the absence of quantum radiation. Continued work for a UA atom in 3+1 D will resolve the mystery of Issue B: Whether there is emitted quantum radiation in Unruh effect.

       

      *Based on J. T. Hsiang and B. L. Hu,  Physics 1, 430–444 (2019) arXiv:1910.11527 

      [1] Milonni, P.W. The Quantum Vacuum: An Introduction to Quantum Electrodynamics; Academic Press: Cambridge, MA, 1993.  Different ways of looking at the electromagnetic vacuum. Phys. Scr. T12, 102 (1988).

      [2] Unruh, W.G. Notes on black-hole evaporation. Phys. Rev. D14, 870 (1976).
      [3] Raine, D.J.; Sciama, D.W.; Grove, P., Does a uniformly accelerated quantum oscillator radiate? Proc. R. Soc. Lond. A435, 205 (1991). Hu, B.L.; Raval, A. Is there emitted radiation in Unruh effect? arXiv:quant-ph/0012134. Lin, S.-Y.; Hu, B.L. Accelerated detector–quantum field correlations: From vacuum fluctuations to radiation flux. Phys. Rev. D 73, 124018 (2006)
       
      [4] Johnson, P.R.; Hu, B.L., Phys. Rev. D65, 065015 (2002). Johnson, P.R.; Hu, B.L., Unruh effect in a uniformly accelerated charge: From quantum fluctuations to classical radiation. Found. Phys. 35, 1117 (2005)
      [5] Ford, G.W. The fluctuation-dissipation theorem. Contemp. Phys. 58, 244 (2017).
      Hsiang, J.-T.; Hu, B.L.; Lin, S.-Y. Fluctuation-dissipation and correlation-propagation relations from the nonequilibrium dynamics of detector-quantum field systems. Phys. Rev. D 100, 025019 (2019). Hsiang, J.-T.; Hu, B.L.; Lin, S.-Y.; Yamamoto, K. Fluctuation-dissipation and correlation-propagation relations in (1+3)D moving detector-quantum field systems. Phys. Lett. B 795, 694 (2019).
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