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arXiv:2606.22099

Transient Information Partition in Coherent Exciton-Phonon-Photon Dynamics

Kunio Ishida

quant-phcond-mat.otherSubmitted Jun 20, 2026• Announced Jun 23, 2026
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Abstract

We study transient information partition in a coherent exciton-phonon-photon system using subsystem-resolved quantum mutual information (QMI). By employing a model with excitonic, phononic, and photonic degrees of freedom, we analyze the dynamics in the $J$-$ν$ plane, where $J$ characterizes excitonic delocalization and $ν$ denotes the exciton-phonon coupling strength. By comparing time-averaged QMI maps with the absorbed photon number, we show that optical activity alone does not determine the character of the light-induced transient state. The exciton-centered information partition identifies a broad crossover between polariton-like and polaron-like transient responses, depending on whether excitonic information is mainly shared with the photon or phonon subsystem. In contrast, the phonon-centered partition reveals a sharper boundary-adjacent redistribution ridge near the boundary between the zero- and one-exciton ground-state sectors. This ridge is absent from both the ground-state sector map and the photon-absorption map, indicating that it is neither a static sector boundary nor an enhancement of optical absorption. A variational strength-function analysis connects the ridge to a region-II-like finite-energy polaronic excitation whose dominant spectral weight lies near the one-phonon energy, and thus the ridge represents a hidden transient correlation structure in which a limited amount of phonon-related information is preferentially shared with the photon subsystem before being predominantly allocated to exciton-phonon dressing. These results show that QMI-based information partition provides a correlation-based framework for characterizing coherent light-induced transient states in which optical and material degrees of freedom jointly participate quantum mechanically.

Comments
13 pages, 8 figures

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We study transient information partition in a coherent exciton-phonon-photon system using subsystem-resolved quantum mutual information (QMI). By employing a model with excitonic, phononic, and photonic degrees of freedom, we analyze the dynamics in the JJJ-ννν plane, where JJJ characterizes excitonic delocalization and ννν denotes the exciton-phonon coupling strength. By comparing time-averaged QMI maps with the absorbed photon number, we show that optical activity alone does not determine the character of the light-induced transient state. The exciton-centered information partition identifies a broad crossover between polariton-like and polaron-like transient responses, depending on whether excitonic information is mainly shared with the photon or phonon subsystem. In contrast, the phonon-centered partition reveals a sharper boundary-adjacent redistribution ridge near the boundary between the zero- and one-exciton ground-state sectors. This ridge is absent from both the ground-state sector map and the photon-absorption map, indicating that it is neither a static sector boundary nor an enhancement of optical absorption. A variational strength-function analysis connects the ridge to a region-II-like finite-energy polaronic excitation whose dominant spectral weight lies near the one-phonon energy, and thus the ridge represents a hidden transient correlation structure in which a limited amount of phonon-related information is preferentially shared with the photon subsystem before being predominantly allocated to exciton-phonon dressing. These results show that QMI-based information partition provides a correlation-based framework for characterizing coherent light-induced transient states in which optical and material degrees of freedom jointly participate quantum mechanically.
Time-resolved photoluminescence (PL) of excitonic molecules in GaAs quantum wells (QW's) reveals an initial transient characterized by a finite rise and an extremely fast nonexponential decay [H. Wang, J. Shah, and T. C. Damen et al., Solid State Commun. 98, 807 (1996)]. The transient is attributed to coherent quantum evolution towards the molecule ground state of two optically correlated excitons, ${\ensuremath{\sigma}}^{+}$ and ${\ensuremath{\sigma}}^{\ensuremath{-}},$ which undergo the Coulombic attraction. In the present paper, we develop a theory of the transient PL and fit the experimental data. The radiative decay of a quasi-two-dimensional (2D) excitonic molecule is analyzed with the giant oscillator strength model adapted to QW's and with the bipolariton model. Within the 2D bipolariton model, the main ``hidden'' channel of the radiative decay of an excitonic molecule is the resonant dissociation into two outgoing interface (surface) polaritons rather than the observable decay into the bulk radiative modes. We conclude that quasi-2D molecules dissociate already within the initial transient of PL, while the following exponential decay of the molecule-mediated PL is due to the escape of secondary interface polaritons into the bulk modes. According to the 2D bipolariton model, the sequence ``two incoming $\mathrm{photons}\ensuremath{\rightarrow}\mathrm{two}$ virtual $\mathrm{excitons}\ensuremath{\rightarrow}2\mathrm{D}$ $\mathrm{molecule}\ensuremath{\rightarrow}\mathrm{two}$ outgoing interface polaritons'' is a completely coherent process. The fit of the time-resolved molecule-mediated PL provides us with numerical estimates of the exciton-photon coupling in GaAs QW's.
The three-dimensional confinement created by the ultrasmall semiconductor structures known as quantum dots greatly modifies the optical properties of the spatially localized carriers. These systems are presently of great interest to the research community, both for the improved understanding of the physics of confined structures, and for the potential applications of these systems to areas such as optoelectronics and quantum computing. Here, the techniques of transient coherent nonlinear optical spectroscopy are applied to the investigation of excitons confined within InAs/GaAs self-assembled quantum dots. These methods provide a powerful tool for the study of dynamic processes in these novel materials. The nonlinear measurements are based on the differential transmission experimental geometry, and utilize ultrafast pulsed lasers in order to temporally resolve the carrier dynamics after excitation. The experiments performed here are resonant with the ground state absorption of the quantum dots, as evidenced by comparison with the photoluminescence measurements which are used to characterize the sample. The incoherent relaxation dynamics of the population of photoexcited excitons are examined, allowing for a determination of both the lifetime of the excitons and the time scale for relaxation between the two polarization eigenstates of the system. The three-dimensional quantum confinement results in the suppression of these relaxation processes, as predicted. The use of coherent spectroscopic techniques allows for the first unambiguous demonstration of an optically-induced nonradiative Raman coherence in these quantum dots. Simultaneous excitation of both polarization states of the exciton results in a coherent superposition state, whose temporal evolution is observed through the homodyne-detection scheme. In these transient experiments, this is manifested as a beating in the nonlinear response, which allows us to directly measure the fine-structure splitting between the polarization states. Utilizing optical pulse shaping techniques, transient spectral hole burning is performed, which allows for the nonlinear response to be spectrally resolved. As expected for the strongly confined quantum dot excitons, the results show that diffusion among the localized states is not a significant effect. Temperature dependent measurements show that at elevated temperatures, extra dephasing processes, potentially related to acoustic phonon scattering, become important. Finally, this technique allows for the first direct observation of the induced absorption from the exciton to biexciton transition in these InAs quantum dots, and a measurement of the associated binding energy. These results lay the foundation for future studies in this material system, and for the possible development of quantum logic devices utilizing quantum dots.
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The phonon scattering assisted luminescence of semiconductor quantum well excitons after short pulse excitation is investigated. The presented analysis is based on the low-density limit of a set of equations for quantum correlation functions for electrons, phonons, and photons. The dynamics of the correlation functions describes the optical excitation and the decay of the coherent exciton polarization as well as the generation of an incoherent exciton occupation and its luminescence decay. Numerical solutions of the equations of motion demonstrate strong competition effects of the exciton-phonon and the exciton-photon interaction on a picosecond time scale and lead to a nonmonotonous temperature dependence of the time-resolved spontaneous emission. The angle resolved emission resembles the generation and decay dynamics of the exciton density for different in-plane momenta.
A semiconductor quantum dot (QD) embedded within an optical microcavity is a system of fundamental importance within quantum information processing. The optimization of quantum coherence is crucial in such applications, requiring an in-depth understanding of the relevant decoherence mechanisms. We provide herein a critical review of prevalent theoretical treatments of the QD-cavity system coupled to longitudinal acoustic phonons, comparing predictions against a recently obtained exact solution. Within this review we consider a range of temperatures and exciton-cavity coupling strengths. Predictions of the polaron Nakajima-Zwanzig (NZ) and time-convolutionless (TCL) master equations, as well as a variation of the former adapted for adiabatic continuous wave excitation (CWE), are compared against an asymptotically exact solution based upon Trotter's decomposition (TD) theorem. The NZ and TCL implementations, which apply a polaron transformation to the Hamiltonian and subsequently treat the exciton-cavity coupling to second order, do not offer a significant improvement accuracy relative to the polaron transformation alone. The CWE adaptation provides a marked improvement, capturing the broadband features of the absorption spectrum (not present in NZ and TCL implementations). We attribute this difference to the effect of the Markov approximation, and particularly its unsuitability in pulsed excitation regime. Even the CWE adaptation, however, breaks down in the regime of high temperature (50K50K50K) and strong exciton-cavity coupling (g≳0.2g \gtrsim 0.2g≳0.2 meV). The TD solution is of comparable computational complexity to the above-mentioned master equation approaches, yet remains accurate at higher temperatures and across a broad range of exciton-cavity coupling strengths (at least up to g=1.5g=1.5g=1.5 meV).