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Complexity in Engineering (COMPENG)

On the effect of the number of photons on the generation and transfer of entangled states between toroidal cavities via artificial atoms

Emilio H. S. Sousa, A. Vidiella-Barranco, José Antonio Roversi

Published Jul 18, 2022• 0 citations
Publisher

Abstract

We present an efficient scheme for the generation of entangled states of two spatially separated whispering-gallery-mode (WGM) micro-resonators which are coupled via 2 two-level atoms. Using an atom chain as bridges, we explore the possibility of generation, transfer as well as distributing quantum entanglement between the two cavities. We show that, for an initial preparation with the system having only one photon, the atoms can become periodically (and maximally) entangled while the intra-cavity modes in each cavity become periodically (partially) entangled. Interestingly, if the cavities are initially prepared with two photons, the dynamics can be tuned in such a way that the intra-cavity modes in each cavity become periodically entangled, reaching maximum entanglement, while the atoms remain unentangled during all time.

DOI
10.1109/compeng50184.2022.9905461

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We present an efficient scheme for the generation of entangled states of two spatially separated whispering-gallery-mode (WGM) micro-resonators which are coupled via 2 two-level atoms. Using an atom chain as bridges, we explore the possibility of generation, transfer as well as distributing quantum entanglement between the two cavities. We show that, for an initial preparation with the system having only one photon, the atoms can become periodically (and maximally) entangled while the intra-cavity modes in each cavity become periodically (partially) entangled. Interestingly, if the cavities are initially prepared with two photons, the dynamics can be tuned in such a way that the intra-cavity modes in each cavity become periodically entangled, reaching maximum entanglement, while the atoms remain unentangled during all time.
We investigate the entanglement dynamics of a system comprising a pair of two-level dipole-dipole interacting atoms coupled to a microtoroidal resonator. Each atom is individually coupled with the two counter-propagating whispering gallery modes of the resonator through their evanescent fields. The atom-atom entanglement shown for several parameter sets of the system was obtained using the negativity. For ideal resonators, it is seen that the entanglement is correlated to the dipole-dipole interaction and the average number of photons when the modes of the resonator are prepared in a thermal state even at high temperatures. Further, for the non-ideal resonator case, where there is a small structural deformation of the microtoroidal structure that allows a direct coupling between the modes, a counter-intuitive result is presented. The imperfections also offer the advantage of generating maximally entangled states for a two-atom subsystem with maximum fidelity.
We present an efficient scheme for the generation of entangled states of two spatially separated nitrogen-vacancy (NV) centers with two whispering-gallery-mode (WGM) microresonators, which are coupled either by an optical fiber-taper waveguide or by the evanescent fields of the WGM. We show that the steady state of the two NV centers can be steered into a singletlike state through a dissipative quantum dynamical process, where the cavity decay plays a positive role and can help drive the system to the target state. The protocol may open up promising perspectives for quantum communication and computation with this solid-state cavity quantum electrodynamic system.
We propose a dissipative scheme to prepare maximally entangled steady states in cavity QED setup, consisting of two two-level atoms interacting with the two counter-propagating whispering-gallery modes (WGMs) of a microtoroidal resonator. Using spontaneous emission and cavity decay as the dissipative quantum dynamical source, we show that the steady state of this system can be steered into a two-atom single state as well as into a two-mode single state. We probed the compound system with weak field coupled to the system via a tapered fiber waveguide, finding it is possible to determine whether the two atoms or two modes are driven to a maximally entangled state. Through the transmission and reflection measurements, without disturbing the atomic state, when the cavity modes are being driven, or without disturbing the cavity field state, when a single atom being driven, one can get the information about the maximal entanglement. We also investigated for both subsystem, two-atom and two-mode states, the entanglement generation and under what conditions one can transfer entanglement from one subsystem to the other. Our scheme can be selectively used to prepare both maximally entangled atomic state as well as maximally entangled cavity-modes state, providing an efficient method for quantum information processing.
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We theoretically investigate how the initial state influence the entanglement dynamics between two and three two-level atoms with dipole-dipole interaction (DDI) coupled to a whispering-gallery-mode (WGM) microtoroidal cavity. Two different cases, where the two atoms are coupled symmetrically or asymmetrically to the two WGMs through evanescent fields, are discussed in detail. Considering two types of initial states between the atoms and the symmetric regime, we show that for the initial entangled state, the sudden death and birth, as well as the freezing of the entanglement, can be obtained by adjusting both the scattering strength between the modes and the DDI, differently from the initial product state. Moreover, we note that the atomic entanglement generation is more susceptible to the scattering strength variation between the modes than to the DDI. In addition, for the asymmetric regime, the entanglement generation is strongly dependent on the atomic location and the scattering strength. Similar results are obtained for the case of three atoms coupled to a microtoroidal cavity, even in the presence of losses.
The generation of entanglement between two identical coupled cavities, each containing a single three-level atom, is studied when the cavities exchange two coherent photons and are in the N=2,4N=2,4N=2,4 manifolds, where NNN represents the maximum number of photons possible in either cavity. The atom-photon state of each cavity is described by a qutrit for N=2N=2N=2 and a five-dimensional qudit for N=4N=4N=4. However, the conservation of the total value of NNN for the interacting two-cavity system limits the total number of states to only 4 states for N=2N=2N=2 and 8 states for N=4N=4N=4, rather than the usual 9 for two qutrits and 25 for two five-dimensional qudits. In the N=2N=2N=2 manifold, two-qutrit states dynamically generate four maximally entangled Bell states from initially unentangled states. In the N=4N=4N=4 manifold, two-qudit states dynamically generate maximally entangled states involving three or four states. The generation of these maximally entangled states occurs rather rapidly for large hopping strengths. The cavities function as a storage of periodically generated maximally entangled states.