Path integral approach to the quantum fidelity amplitude

Jiøí Vaníček, Doron Cohen

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


The Loschmidt echo is a measure of quantum irreversibility and is determined by the fidelity amplitude of an imperfect time-reversal protocol. Fidelity amplitude plays an important role both in the foundations of quantum mechanics and in its applications, such as time-resolved electronic spectroscopy.We derive an exact path integral formula for the fidelity amplitude and use it to obtain a series of increasingly accurate semiclassical approximations by truncating an exact expansion of the path integral exponent. While the zeroth-order expansion results in a remarkably simple, yet non-trivial approximation for the fidelity amplitude, the first-order expansion yields an alternative derivation of the so-called -dephasing representation,- circumventing the use of a semiclassical propagator as in the original derivation. We also obtain an approximate expression for fidelity based on the second-order expansion, which resolves several shortcomings of the dephasing representation. The rigorous derivation from the path integral permits the identification of sufficient conditions under which various approximations obtained become exact.

Original languageEnglish
Article number20150164
JournalPhilosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
Issue number2069
StatePublished - 13 Jun 2016


  • Dephasing representation
  • Loschmidt echo
  • Path integral
  • Quantum fidelity

ASJC Scopus subject areas

  • Mathematics (all)
  • Engineering (all)
  • Physics and Astronomy (all)


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