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arXiv:1509.02858 · Physical Review A

Photon-induced self-trapping and entanglement of a bosonic Josephson junction inside an optical resonator

Paolo Rosson, G. Mazzarella, Gergely Szirmai, Luca Salasnich

Published Dec 1, 2015• 3 citations
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Abstract

We study the influence of photons on the dynamics and the ground state of the atoms in a bosonic Josephson junction inside an optical resonator. The system is engineered in such a way that the atomic tunneling can be tuned by changing the number of photons in the cavity. In this setup the cavity photons are a means of control, which can be utilized both in inducing self-trapping solutions and in driving the crossover of the ground state from an atomic coherent state to a Schr\"odinger cat state. This is achieved, for suitable setup configurations, with interatomic interactions weaker than those required in the absence of a cavity. This is corroborated by the study of the entanglement entropy. In the presence of a laser, this quantum indicator attains its maximum value (which marks the formation of the catlike state and, at a semiclassical level, the onset of self-trapping) for attractions smaller than those of the bare junction.

DOI
10.1103/physreva.92.063604

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We study the influence of photons on the dynamics and the ground state of the atoms in a bosonic Josephson junction inside an optical resonator. The system is engineered in such a way that the atomic tunneling can be tuned by changing the number of photons in the cavity. In this setup the cavity photons are a means of control, which can be utilized both in inducing self-trapping solutions and in driving the crossover of the ground state from an atomic coherent state to a Schr"odinger cat state. This is achieved, for suitable setup configurations, with interatomic interactions weaker than those required in the absence of a cavity. This is corroborated by the study of the entanglement entropy. In the presence of a laser, this quantum indicator attains its maximum value (which marks the formation of the catlike state and, at a semiclassical level, the onset of self-trapping) for attractions smaller than those of the bare junction.
We study the interplay between the dynamics of a Bose-Einstein condensate in a double-well potential and that of an optical cavity mode. The cavity field is superimposed to the double-well potential and affects the atomic tunneling processes. The cavity field is driven by a laser red detuned from the bare cavity resonance; the dynamically changing spatial distribution of the atoms can shift the cavity in and out of resonance. At resonance the photon number is hugely enhanced and the atomic tunneling becomes amplified. The Josephson-junction equations are revisited and the phase diagram is calculated. We find solutions with finite imbalance and at the same time find a lack of self-trapping solutions due to the emergence of a new separatrix resulting from enhanced tunneling.
In this paper, we investigate the dynamical synchronization of atomic populations in two Bosonic Josephson junctions(BJJs). The two BJJs are placed in two optical cavities, respectively. When there is no coupling between the two optical cavities, the dynamical evolution of the two BJJs is independent, and they can be in macroscopic quantum self-trapping regime or Josephson oscillation regime by controlling the strength of the interatomic interactions, respectively. However, when there is a coupling between the two optical cavities, we can adjust an external driving field to a specific value so that the two BJJs are dynamically synchronized even though the parameters of the two subsystems are different. We also found that it is possible to control the transition of the BJJ from the Josephson oscillation regime to the macroscopic quantum self-trapping regime by controlling the strength of the external driving field.
We investigate the self-trapping of a Bose Josephson junction, which is dispersively coupled to a driven optical cavity. The cavity-induced nonlinearity is presented analytically, and its effect results in the appearance of the self-trapping for the Bose-Einstein condensates in the Josephson oscillation regime. In addition, there exists competition between the nonlinearities induced by the interatomic interaction and by the driven cavity for the emergences of self-trapping. Our results show that the driven cavity can be utilized as a possible tool to produce the self-trapping for the condensates with weak interatomic interaction.
We study the behavior of ultracold bosonic atoms held in an optical lattice. We first show how a self-trapping transition can be induced in the system either by increasing the number of atoms occupying a lattice site or by raising the interaction strength above a critical value. We then investigate how applying a periodic driving potential to the self-trapped state can be used to coherently control the emission of a precise number of correlated bosons from the trapping site. This allows the preparation and transport of entangled bosonic states, which are of great relevance to novel technologies such as quantum-information processing.
We discuss the generation of entangled states of two two-level atoms inside an optical resonator. When the cavity decay is continuously monitored, the absence of photon counts is associated with the presence of an atomic entangled state. In addition to being conceptually simple, this scheme can be demonstrated with presently available technology. We describe how such a state is generated through conditional dynamics, using quantum jump methods, including both cavity damping and spontaneous emission decay, and evaluate the fidelity and relative entropy of entanglement of the generated state compared with the target entangled state.
This thesis summarizes the research work we did in the past years, which focuses on the theoretical study of quantum effects of ordered atomic structures interacting with the quantum electric field of an optical resonator. Within this work we investigated the quantum properties of the light at the cavity output, emitted by this kind of system, and the quantum state of the atoms confined by the light fields of the cavity mode. Following one possible partition, we have organized the thesis in two parts. The first part of the thesis is devoted to the quantum properties of the light at the output of optical cavities, in which atoms are confined. After a brief introduction on the basics of atom-photon interactions, we show theoretically, that two atomic dipoles in a resonator can behave as a quantum non-linear medium, whose response can be controlled through the interactomic distance of the atoms inside the resonator. We identify the parameter regime, for which the system operates as a parametric amplifier, based on the atoms' collective dipole cascade emission. Moreover we also determine the corresponding field squeezing spectrum at the cavity output. These dynamics could be observed as a result of self-organization processes of laser-cooled atoms in resonators. The second part of the thesis studies the quantum ground state of an ultracold atomic gas trapped inside an optical resonator by the mechanical effects of atom-photon interactions. Due to the strong coupling regime, the ultracold atomic gas feels a quantum potential, where the fluctuations at the single photon level may be relevant in determining the trapping conditions. This potential depends on the atomic distribution, which at the same time determines the intracavity field amplitude. Here, after a brief introduction on ultracold atoms in optical lattices, we study the low temperature physics of an ultracold atomic gas in the quantum potential formed inside a pumped cavity, by mapping the dynamics to an effective Bose-Hubbard model. We predict the existence of non-compressible states of the atomic gas, and determine a phase diagram as a function of the cavity parameters. Novel effects are encountered, such as the existence of overlapping stability regions corresponding to competing insulator-like states when the laser pumps the cavity, to provide one example out of many. At the end of the thesis a concluding chapter presents some general outlooks to this thesis work.