TY - JOUR

T1 - Local ergodicity as a probe for chaos in quantum systems

T2 - Application to the Henon-Heiles system

AU - Ramachandran, B.

AU - Kay, Kenneth G.

PY - 1987

Y1 - 1987

N2 - Classical chaos is usually accompanied by "local" ergodicity - ergodic behavior in regions of phase space that are generally smaller than, but of the same dimensionality as, the energy surface. If there are strong bottlenecks in phase space impeding the relaxation to statistical equilibrium in the full region of ergodicity, it is often possible to define an approximate form of ergodic behavior in a smaller subregion where relaxation occurs temporarily but quickly. Such "pseudoergodicity" is also a symptom of chaos. We use the presence of quantum behavior that mimics local ergodicity and pseudoergodicity as a probe for the influence of classical chaos on quantum dynamics. We show that the quantum analog of a pseudoergodic region in phase space is generally formed by superpositions of energy eigenstates. The superposition states spanning a given pseudoergodic zone have similar expectation values and small off-diagonal elements to other states with similar energy for a certain class of operators. We perform calculations which identify the ergodic regions for two versions of the quantum Henon-Heiles system. For the "more classical" of these systems we find good agreement between the proportion of quantum states in pseudoergodic zones and the proportion of classical phase space occupied by chaotic trajectories. We also find that the quantum pseudoergodic regions can be identified with classical vague tori of the precessing and librating types. Different ergodic regions are separated from one another by what appear to be the quantum analogs of the precessor-librator separatrix and other classical bottlenecks. For the "less classical" of the systems, we find that classical chaos is reflected in the quantum dynamics to a smaller, but still noticeable, degree.

AB - Classical chaos is usually accompanied by "local" ergodicity - ergodic behavior in regions of phase space that are generally smaller than, but of the same dimensionality as, the energy surface. If there are strong bottlenecks in phase space impeding the relaxation to statistical equilibrium in the full region of ergodicity, it is often possible to define an approximate form of ergodic behavior in a smaller subregion where relaxation occurs temporarily but quickly. Such "pseudoergodicity" is also a symptom of chaos. We use the presence of quantum behavior that mimics local ergodicity and pseudoergodicity as a probe for the influence of classical chaos on quantum dynamics. We show that the quantum analog of a pseudoergodic region in phase space is generally formed by superpositions of energy eigenstates. The superposition states spanning a given pseudoergodic zone have similar expectation values and small off-diagonal elements to other states with similar energy for a certain class of operators. We perform calculations which identify the ergodic regions for two versions of the quantum Henon-Heiles system. For the "more classical" of these systems we find good agreement between the proportion of quantum states in pseudoergodic zones and the proportion of classical phase space occupied by chaotic trajectories. We also find that the quantum pseudoergodic regions can be identified with classical vague tori of the precessing and librating types. Different ergodic regions are separated from one another by what appear to be the quantum analogs of the precessor-librator separatrix and other classical bottlenecks. For the "less classical" of the systems, we find that classical chaos is reflected in the quantum dynamics to a smaller, but still noticeable, degree.

UR - http://www.scopus.com/inward/record.url?scp=7044278259&partnerID=8YFLogxK

U2 - 10.1063/1.452704

DO - 10.1063/1.452704

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AN - SCOPUS:7044278259

SN - 0021-9606

VL - 86

SP - 4628

EP - 4647

JO - Journal of Chemical Physics

JF - Journal of Chemical Physics

IS - 8

ER -