Extracting classical Lyapunov exponent from one-dimensional quantum mechanics

Abstract

The commutator $[x(t),p]$ in an inverted harmonic oscillator (IHO) in one-dimensional quantum mechanics exhibits remarkable properties. It reduces to a c-number and does not show any quantum fluctuations for arbitrary states. Related to this nature, the quantum Lyapunov exponent computed through the out-of-time-order correlator (OTOC) $⟨[x(t),p{]}^2⟩$ precisely agrees with the classical one. Hence, the OTOC may be regarded as an ideal indicator of the butterfly effect in the IHO. Since IHOs are ubiquitous in physics, these properties of the commutator $[x(t),p]$ and the OTOCs might be seen in various situations, too. In order to clarify this point, as a first step, we investigate OTOCs in one-dimensional quantum mechanics with polynomial potentials, which exhibit butterfly effects around the peak of the potential in classical mechanics. We find two situations in which the OTOCs show exponential growth reproducing the classical Lyapunov exponent of the peak. The first one, which is obvious, is using a suitably localized wave packet near the peak, and the second one is taking a limit akin to the large-$N$ limit in the noncritical string theories.

15 pages, 5 figures. Appendix moved to the main text,the version published in PRD

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Cited by in corpus (8)

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• Classical approach to equilibrium of out-of-time ordered correlators in mixed systems
• Relative asymptotic oscillations of the out-of-time-ordered correlator as a quantum chaos indicator
• Entanglement wedge method, out-of-time-ordered correlators, and pole skipping
• Out-of-Time-Order-Correlator for van der Waals potential
• Saturation of Chaos Bound in a Phenomenological Rotating Black Hole--Effective Matter System at Low-Temperature Limit
• Spectral chaos bounds from scaling theory of maximally efficient quantum-dynamical scrambling
• Out-of-Time-Order-Correlation in perturbed quantum wells