Squeezed and correlated states of quantum systems

V. V. Dodonov

V. V. Dodonov, A. V. Klimow, Vladimir I. Man’ko

Alina-Mihaela Stoica, Аурелиан Исар

Abstract Hellinger geometric quantum discord and interferometric power are investigated for an open system consisting of two bosonic modes interacting with four different environments: vacuum, squeezed vacuum, thermal and squeezed thermal, taking the initial state of the system either a single-mode squeezed state, which presents no correlations, or a squeezed vacuum state. The description of the evolution of the correlations is formulated in the framework of the theory of open systems, based on completely positive quantum dynamical semigroups, using the Gorini-Kossakowski-Lindblad-Sudarshan master equation. We show that both quantum correlations can be generated from an initial factorized state and even amplified, while also studying the back and forth impact of the squeezing parameters on the considered correlations; specifically, for the squeezed vacuum environment, the competition between the influences exerted by the squeezing of the initial state and the squeezing of the environment leads to the decreasing, and even destruction of the correlations, or to their enhancement. In the case of an initial squeezed vacuum state in interaction with the squeezed vacuum environment, for specific conditions one can achieve decoherence-free states (DFS), while for the interaction with a thermal environment there exist regimes of enhancing or decreasing the considered correlations, depending on the parameters of both open system and environment.

Sofia Arranz Regidor, Matthew Kozma, Stephen Hughes

Squeezed light states have a special place in quantum optics with potentially profound applications in emerging quantum technologies. We present a numerically-exact matrix product states (MPS) approach to model quantum pulses of squeezed light, at the few-photon level, interacting with a two-level system in a waveguide environment. We represent the squeezed state as a coherent superposition of Fock states and explore the nonlinear population dynamics as well as multi-photon correlation functions that emerge. We show how the squeezed pulse can create quantum correlations that are unique to squeezed pulses, including $\langle b(t) b(t+t')\rangle$ for transmitted fields as well as $\langle b^\dagger(t) b^\dagger(t+t') b(t+t') b(t) \rangle$. We also demonstrate how $\langle b(t) b(t+t') \rangle$, a first-order correlation function, shows nonlinear photon correlations that are similar to those known and measured for two-photon scattering states. Finally, we also study the squeezed spectra of the pulse before and after interacting with the two-level system, and highlight the role of the spectral bandwidth of the incident pulse. The MPS theory allows the modeling of arbitrary bandwidth squeezing without making any Markov and Born approximations for the light-matter interaction processes, and can easily be extended to waveguide systems with multiple emitters and time-delayed feedback.

Kaoru Shimizu, Daisuke Hashimoto

This paper characterizes a quantum correlation formed in an ensemble of atomic two-level systems that stores a narrow-band squeezed state of light by coherently trapping an electron in an atomic superposed state $a|1⟩+b|0⟩$. In the storage process, a photonic quantum correlation in the squeezed light is transformed into an atomic quantum correlation between $N$ atoms in an adiabatic way. If we regard the atomic superposed state as a 1/2-spin state and adopt the framework of a pairwise spin entanglement to analyze the atomic quantum correlation, we can identify a certain entangled state of a spin pair as the atomic signature of the squeezed light. The pairwise spin entangled state reflects all the physical properties of the squeezed light. By following the dissipative time evolution in the pairwise entangled state, we can describe the degraded properties of the squeezed light in retrieval.

V. V. Dodonov, A. B. Klimov, Vladimir I. Man’ko