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International Journal of Quantum Chemistry

Quantum‐phase and information‐entropy dynamics of dimers interacting with a single‐mode coherent field: The difference between one‐ and two‐exciton models

Masayoshi Nakano, Kizashi Yamaguchi

Published Jan 1, 2001• 2 citations
Publisher

Abstract

Abstract We develop a numerically exact approach to the quantum‐phase and information‐entropy dynamics of a molecular aggregate interacting with quantized fields. It is well known that a peculiar quantum nature, i.e., collapses and revivals, is observed in monomer and noninteracting aggregate models. In this article, we investigate the intermolecular interaction effects on the collapse‐revival behavior using several dimer models (composed of two‐state monomers with different intermolecular distances) interacting with a single‐mode coherent photon field. The intermolecular interaction is taken into account by using the dipole‐dipole interaction. Also, one‐ and two‐exciton dimer models are considered in order to elucidate the exciton contributions to collapse‐revival behavior. This quantum behavior is analyzed from the viewpoint of the dynamics of Pegg–Barnett photon‐phase and information‐entropy of dimers, which closely relate to the time evolution of quantum coherency between the ground and the excited dimer states and the degree of the entanglement between dimer and photon, respectively. It is found that the intermolecular interaction and the two‐exciton generation provide remarkable changes in the collapse‐revival behavior through their significant influence on the quantum‐phase dynamics and the photon‐dimer entanglement. From the dimer entropy dynamics, intermediate intermolecular interaction is found to cause the momentary decrease in the photon‐dimer correlation in the early time region. This feature leads to the enhancement of off‐diagonal density (quantum coherency) between two dimers. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001

DOI
10.1002/qua.1407

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Abstract We develop a numerically exact approach to the quantum‐phase and information‐entropy dynamics of a molecular aggregate interacting with quantized fields. It is well known that a peculiar quantum nature, i.e., collapses and revivals, is observed in monomer and noninteracting aggregate models. In this article, we investigate the intermolecular interaction effects on the collapse‐revival behavior using several dimer models (composed of two‐state monomers with different intermolecular distances) interacting with a single‐mode coherent photon field. The intermolecular interaction is taken into account by using the dipole‐dipole interaction. Also, one‐ and two‐exciton dimer models are considered in order to elucidate the exciton contributions to collapse‐revival behavior. This quantum behavior is analyzed from the viewpoint of the dynamics of Pegg–Barnett photon‐phase and information‐entropy of dimers, which closely relate to the time evolution of quantum coherency between the ground and the excited dimer states and the degree of the entanglement between dimer and photon, respectively. It is found that the intermolecular interaction and the two‐exciton generation provide remarkable changes in the collapse‐revival behavior through their significant influence on the quantum‐phase dynamics and the photon‐dimer entanglement. From the dimer entropy dynamics, intermediate intermolecular interaction is found to cause the momentary decrease in the photon‐dimer correlation in the early time region. This feature leads to the enhancement of off‐diagonal density (quantum coherency) between two dimers. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
It is well-known that the interaction among atoms/molecules and quantized electromagnetic fields with a small number of photons provides a peculiar quantum nature, i.e., collapses and revivals in the Rabi oscillations. In this study, we investigate the intermolecular interaction (dipole–dipole interaction) effect on the collapse-revival behavior using several dimer models (composed of two kinds of two-state monomers with slightly different excitation energies) with different intermolecular distances in the presence of a two-mode squeezed coherent field, in which each mode is initially correlated. It is found that although the collapse-revival behavior is fairly overlapped and indistinct in the case of a noninteracting dimer under the present two-mode squeezed coherent field, the decrease in the intermolecular distance (the increase in the intermolecular interaction) resurrects relatively distinct collapse-revival behavior with longer collapse and revival times. By analyzing the quantum behavior from the viewpoint of the dynamics of two-mode Pegg–Barnett photon-phase distributions and off-diagonal dimer density matrices, this feature is found to closely relate to a significant change in the degree of contribution between one- and two-photon processes caused by the variation in the intermolecular interaction.
We investigate the intermolecular-interaction (dipole–dipole interaction) effects on the quantum dynamics of dimer density matrices and photon-phase distributions using several dimer models with different intermolecular distances in the presence of a two-mode squeezed vacuum field. In this photon field, each mode is initially correlated and the reduced one-mode photon distribution is equivalent with that of a thermal field. For comparison, we perform parallel studies, in which the initial fields are two types of noncorrelated two-mode fields, i.e., a two-mode coherent field and a two-mode thermal field. It is found that although the two-mode squeezed vacuum field causes the random oscillations of dimer populations in the noninteracting dimer, the periodic oscillations like the collapse–revival behavior emerge as the intermolecular distance decreases (the intermolecular interaction increases). Similar and dissimilar features among quantum dynamics caused by these three types of fields are investigated by analyzing the dynamical behavior of two-mode Pegg–Barnett photon-phase distributions and off-diagonal dimer density matrices, which indicate the coherency between dimer states. In addition to the quantum statistical properties of initial photon field, the change in the degree of contribution between one- and two-photon processes caused by the intermolecular interaction is found to be important to determine these features.
We investigate the quantum dynamics for a molecular-state-model system interacting with a resonant two-mode squeezed coherent field, in which each mode is initially correlated. As an example, we consider a three-state molecular model, which mimics the electronic excited states of trans-octatetraene obtained by a full-configuration-interaction calculation using the Pariser-Parr-Pople Hamiltonian, interacting with a two-mode squeezed coherent field. For comparison, we also perform parallel studies, in which the initial fields are prepared in uncorrelated two-mode states, i.e., a two-mode coherent state and a two-mode thermal state. It is well known that the case of two-mode coherent field leads to the usual collapse-revival phenomena of the Rabi oscillations, while the case of a two-mode thermal state leads to an irregular evolution of them. Although the two-mode squeezed coherent field exhibits similar collapse-revival behavior to that for the two-mode coherent field, some differences are detected in the amplitudes and periods of collapse-revival oscillations. Further, the dynamics of off-diagonal molecular density matrices between the ground and second excited states for these two fields are found to be distinctively different from each other. Such attractive behavior is found to be closely associated with the two-mode photon-phase dynamics obtained by the Pegg-Barnett phase operator and the initial quasiprobability (Q function) distribution of photons. These differences in phase properties are also shown to significantly affect the dynamics of the information entropy for a molecule, i.e., molecular entropy, which represents the degree of entanglement between the molecule and photons.
From the viewpoints of photon-phase and information-entropy dynamics, we investigate the dynamical behavior of initially one-mode amplitude- and phase-squeezed photon fields interacting with a two-state molecular system. A peculiar behavior of these systems is known to be the collapses and revivals of Rabi oscillation of the molecular population. As shown in previous studies, significant differences are observed in the amplitude and the period of the collapse−revival behavior for these fields. These differences are found to be well-described by the dynamical behavior of the photon phase (the Pegg−Barnett phase and the quasiprobability ( Q function) distributions). The features of these photon-phase dynamics are also found to provide significant influence on the time evolution of the information entropy of the molecule, which characterizes the degree of the entanglement between the molecule and the field.
Abstract We investigate the quantum dynamics of a dissipative molecular system interacting with a single‐mode coherent field (with an initial average photon number 8) using the Monte Carlo wave function (MCWF) method. As quantum dissipation, we consider cavity relaxation (the dissipation of an internal single mode to outer mode) and molecular population relaxation and molecular coherent (phase) relaxation caused by nuclear vibration. In this study, we elucidate the effects of these dissipations on the unique quantum dynamic behaviors of this coupled system, e.g., collapse–revival behavior of Rabi oscillations, using the diagonal and off‐diagonal molecular density matrices. It is found that although slight cavity relaxation suppresses the revival of molecular population similarly to other relaxation effects with larger decay rates the cavity relaxation hardly suppresses the increase in the off‐diagonal molecular density matrix (representing the degree of coherency between the ground and excited states) in the quiescent region, the feature of which is related to the generation of the Schrödinger cat state, in contrast to molecular phase and population relaxations. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
We perform numerically exact calculations of quantum dynamics for a two-state molecular model system interacting with initially single-mode strongly amplitude- and strongly phase-squeezed fields (average photon number 〈n̂〉=8). The second-order correlation function for these fields are taken to be 2, which is equivalent to that for the chaotic field with the identical average photon number. Although the responses of the molecule for these two squeezed fields are relatively similar to those for the chaotic field as shown in a previous paper, there are found to be some significant differences among these fields in the dynamical behavior of quantum-phase distributions of photons, i.e., the Pegg–Barnett phase and the Q function distributions. These differences are also elucidated by the dynamics of the information entropy for the molecule, i.e., molecular entropy, which represents the degree of entanglement between the molecule and the photon field.