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Studia Universitatis Babeș-Bolyai Physica

COLLECTIVE BEHAVIOR OF COUPLED QUANTUM MECHANICAL OSCILLATORS

Larissa Davidova, Sandor BORBÉLY, Z. NÉDA

Published Jun 30, 2015• 0 citations
OpenAlex

Abstract

A simple model of coupled oscillators is investigated from the perspective of quantum mechanics. The classical model of two oscillators connected by a common platform can be easily solved analytically, but the quantum system requires a numerical approach. We assume that both the oscillators and the platform are quantum objects in their respective ground states at start and they evolve in time as a connected system. By following numerically this time-evolution we investigate the dynamics of the oscillators and calculate an order parameter that characterizes their correlated time-evolution. We study the order parameter as a function of the oscillators initial state and compare the findings with the equivalent classical system. Interestingly, for a given parameter region we found an enhanced collective behavior in the quantum mechanical system.

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A simple model of coupled oscillators is investigated from the perspective of quantum mechanics. The classical model of two oscillators connected by a common platform can be easily solved analytically, but the quantum system requires a numerical approach. We assume that both the oscillators and the platform are quantum objects in their respective ground states at start and they evolve in time as a connected system. By following numerically this time-evolution we investigate the dynamics of the oscillators and calculate an order parameter that characterizes their correlated time-evolution. We study the order parameter as a function of the oscillators initial state and compare the findings with the equivalent classical system. Interestingly, for a given parameter region we found an enhanced collective behavior in the quantum mechanical system.
We study the time evolution of an ideal system composed of two harmonic oscillators coupled through a quadratic Hamiltonian with arbitrary interaction strength. We solve its dynamics analytically by employing tools from symplectic geometry. In particular, we use this result to completely characterize the dynamics of the two oscillators interacting in the ultrastrong-coupling regime with additional single-mode squeezing on both oscillators, as well as higher-order terms. Furthermore, we compute quantities of interest, such as the average number of excitations and the correlations that are established between the two subsystems due to the evolution. We find that this model predicts a second-order phase transition and we compute the critical exponents and the critical value. We also provide an exact decoupling of the time evolution in terms of simple quantum optical operations, which can be used for practical implementations and studies. Finally, we show how our techniques can be extended to include more oscillators and higher-order interactions.
We study the time evolution of driven quantum systems using analytic, algebraic, and numerical methods. First, we obtain analytic solutions for driven free and oscillator systems by shifting the coordinate and phase of the undriven wave function. We also factorize the quantum evolution operator using the generators of the Lie algebra comprising the Hamiltonian. We obtain coupled ODE's for the time evolution of the Lie algebra parameters. These parameters allow us to find physical properties of oscillator dynamics. In particular we find phase-space trajectories and transition probabilities. We then search for chaotic behavior in the Lie algebra parameters as a signature for dynamical chaos in the quantum system. We plot the trajectories, transition probabilities, and Lyapunov exponents for a wide range of the following physical parameters: strength and duration of the driving force, frequency difference, and anharmonicity of the oscillator. We identify conditions for the appearance of chaos in the system.
The statistical properties of systems of coupled quantum-mechanical harmonic oscillators are analyzed. The Hamiltonian for the system is assumed to be an inhomogeneous quadratic form in the creation and annihilation operators, and is allowed to have an explicit time dependence. The relationship to classical theory is emphasized by expressing pure states in terms of the coherent-state vectors, and density operators by means of the PPP representation and an analogous representation involving the Wigner function. The state which evolves from an initially coherent state of the system is found, and equations governing the time evolution of the Wigner function and the weight function for the PPP representation are derived, in differential and integral form, for arbitrary initial states of the system. The results remain valid for couplings which do not preserve the vacuum state, and for cases in which the time dependence of the coupling parameters gives rise to large-scale amplification of the initial field intensities. The analysis is performed by first treating general linear inhomogeneous canonical transformations on the oscillator variables, and then specializing to the case in which these transformations represent the solutions for the Heisenberg operators in terms of their initial values. The results are illustrated within the context of a model of parametric amplification.
We consider a system composed of two linearly mutually interacting, identical Kerr-like nonlinear oscillators.Assuming that the system initially is in a coherent state, we discuss the system's dynamics and concentrate on the field's mutual correlations.As a measure of such correlations, we apply the normalized first-and second-order coherence functions.We derive the analytical formulas for such functions showing that their time-evolution strongly depends on the linear coupling parameter.
Abstract The non-analyticity induced by exceptional points (EPs) has manifestations not only in non-Hermitian but also in Hermitian systems. In this work, we focus on a minimal Hermitian bosonic Kitaev model to reveal the dynamical demonstration of EPs in a Hermitian system. It is shown that the EPs separate the parameter space into four regions, in which the systems are characterized by different equivalent Hamiltonians, including the harmonic oscillator, the inverted harmonic oscillator, and their respective counterparts. We employ the second-order intensity correlation to characterize a nonequilibrium quantum phase transition by calculating the time evolution of a trivial initial state. The results indicate that the concept of the EP can be detected in a small Hermitian bosonic system.