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Physical Review A

Phase-space dynamics of a single-atom laser: Nonclassicality and bistability

Alexander B. Mikhalychev, Svetlana V. Vlasenko, S. Ya. Kilin

Published Jun 30, 2022• 2 citations
Publisher

Abstract

We investigate the dynamics of a single-qubit single-mode laser with continuous incoherent pumping of a qubit, the field mode being initially prepared in a coherent state. Analysis of partial differential equations for quasiprobability distributions helps us distinguish two stages of evolution (coherent and incoherent ones) with their characteristic features. The system can exhibit bistabilitylike behavior, similar to that reported for a single-atom laser with continuous coherent pumping, and is capable of generating Schr\"odinger cat states. Quantitative analysis of the field state nonclassicality shows that its maximum is reached at intermediate stages of evolution.

DOI
10.1103/physreva.105.063723

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We investigate a single-atom nondegenerate cascade laser model, based on a coherently pumped three-level atom coupled to two independently damped cavity modes. We show that while many features predicted within a recently proposed N-atom superradiant laser model [F. Haake et al., Phys. Rev. Lett. 71, 995 (1993)] can readily be obtained in the single-atom case, some of the quantum noise properties are significantly different. The influence of spontaneous decay and nonadiabatic effects due to the finite spectral width of the lower cavity mode are discussed. Finally, we show that the present model has a large potential for the stationary preparation of various nonclassical states of the atom-field system.
We investigate the quantum evolution of the pump field in second-harmonic generation under strong pump depletion. Starting from a coherent state, the pump develops a nonclassical phase-space structure resembling a Schrödinger cat state. This behavior originates from phase instability induced by vacuum fluctuations of the harmonic mode. A rigorous quantum analysis has been performed for mean photon numbers up to ⟨n^⟩=100\langle \hat n \rangle = 100⟨n^⟩=100 in pump mode. For larger photon numbers, up to ⟨n^⟩=107\langle \hat n \rangle = 10^{7}⟨n^⟩=107, the dynamics have been analyzed using a classical trajectory method with sampled initial conditions that reproduces the main features of the quantum evolution. The results indicate that nonlinear frequency conversion can generate macroscopic superposition-like states of the pump field. Although the resulting state is not pure due to correlations with the second-harmonic wave, it remains non-classical with negative zones of Wigner function. These results indicate that strongly nonlinear frequency conversion can provide a scalable route toward macroscopic nonclassical states of light.
In this paper, we study the interaction between two two-level atoms and two nondegenerate cavity modes when the atoms and the field are initially in the atomic superposition states and the pair-coherent state (PCS), respectively. We investigate the atomic inversions, tangles and joint probability distribution. We show that the system can generate long-living entanglement by controlling the values of the interaction parameters. Also we show generally that for obtaining a large amount of entanglement from two qubits interacting with a maximally entangled two-mode state one has to prepare the qubits initially in the decoupled states. Moreover, the system – at certain values of interaction parameters – can generate different types of nonclassical states, such as the mth-photon PCS, statistical mixtures of PCSs and superposition of PCS.
We study atomic center of mass motion and field dynamics of a single-atom laser consisting of a single incoherently pumped free atom moving in an optical high-Q resonator. For sufficient pumping, the system starts lasing whenever the atom is close to a field antinode. If the field mode eigenfrequency is larger than the atomic transition frequency, the generated laser light attracts the atom to the field antinode and cools its motion. Using quantum Monte Carlo wave function simulations, we investigate this coupled atom-field dynamics including photon recoil and cavity decay. In the regime of strong coupling, the generated field shows strong nonclassical features such as photon antibunching, and the atom is spatially confined and cooled to sub-Doppler temperatures.