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Optics Express

Achieving maximum entanglement between two nitrogen-vacancy centers coupling to a whispering-gallery-mode microresonator

Siping Liu, Jiahua Li, Rong Yu, Ying Wu

Published Feb 4, 2013• 26 citations
Publisher

Abstract

We investigate the entanglement generation between two nitrogen-vacancy (NV) centers in diamond nanocrystal coupled to a high-Q counterpropagating twin whispering-gallery modes (WGMs) of a microtoroidal resonator. For looking into the degree and dynamics of the entanglement, we calculate the concurrence using the microscopic master equation approach. The influences of the coupling strength between the WGMs (or the size of the two spherical NV centers), the distance between two NV centers, the frequency detuning between the NV center and microresonator, and the initial state of the system on the dynamics of concurrence are discussed in detail. It is found that the maximum entanglement between the two NV centers can be created by properly adjusting these controllable system parameters. Our results may provide further insight into future solid-state cavity quantum electrodynamics (CQED) system for quantum information engineering.

DOI
10.1364/oe.21.003501

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We investigate the entanglement generation between two nitrogen-vacancy (NV) centers in diamond nanocrystal coupled to a high-Q counterpropagating twin whispering-gallery modes (WGMs) of a microtoroidal resonator. For looking into the degree and dynamics of the entanglement, we calculate the concurrence using the microscopic master equation approach. The influences of the coupling strength between the WGMs (or the size of the two spherical NV centers), the distance between two NV centers, the frequency detuning between the NV center and microresonator, and the initial state of the system on the dynamics of concurrence are discussed in detail. It is found that the maximum entanglement between the two NV centers can be created by properly adjusting these controllable system parameters. Our results may provide further insight into future solid-state cavity quantum electrodynamics (CQED) system for quantum information engineering.
We explore the entanglement generation and the corresponding dynamics between two separate nitrogen-vacancy (NV) centers in diamond nanocrystal coupled to a photonic molecule consisting of a pair of coupled photonic crystal (PC) cavities. By calculating the entanglement concurrence with readily available experimental parameters, it is found that the entanglement degree strongly depends on the cavity-cavity hopping strength and the NV-center-cavity detuning. High concurrence peak and long-lived entanglement plateau can be achieved by properly adjusting practical system parameters. Meanwhile, we also discuss the influence of the coupling strength between the NV centers and the cavity modes on the behavior of the concurrence. Such a PC-NV system can be employed for quantum entanglement generation and represents a building block for an integrated nanophotonic network in a solid-state cavity quantum electrodynamics platform. In addition, the present theory can also be applied to other similar systems, such as two single quantum emitters positioned close to a microtoroidal resonator with the whispering-gallery-mode fields propagating inside the resonator.
The solid-state qubits based on diamond nitrogen-vacancy centers (NVC) are promising for future quantum information processing. We investigate the dynamics of entanglement among three NVCs coupled to a microtoroidal cavity supporting two counter-propagating whispering-gallery-modes (WGMs) in the presence of Rayleigh scattering. Our results indicate that the maximal entanglement among all the NVCs could be achieved through adjusting several key parameters, such as the scattering-induced coupling between the WGMs, the distance between the NVCs, and the NVC-WGM coupling strengths, as well as the frequency detuning between the NVC and cavity. We show that entanglement of the NVCs displays a series of damped oscillations under various experimental situations, which reflects the intricate interplay and competition between the Rayleigh scattering and the NVC-WGM coupling. The quantum dynamics of the system is obtained via solutions to the corresponding microscopic master equation, which agrees well with the numerical simulation results using the phenomenological master equation. The feasibility of our proposal is supported by the application of currently available experimental techniques.
We theoretically investigate a cavity quantum electrodynamics system in which a high-QQQ whispering-gallery-mode (WGM) microresonator interacts with multiple diamond nanocrystals each containing a single nitrogen-vacancy (NV) center. With a tapered fiber waveguide coupling the WGMs, the transmission spectrum of the system exhibits a twofold-splitting phenomenon, where the first fold of splitting originates from the nanocrystals' Rayleigh scattering and the second fold stems from the NV center dipole coupling with the WGMs. The interacting system can serve as a platform to generate quantum entanglement between two NV centers embedded in distant diamond nanocrystals. Our further study reveals that the Rayleigh scattering of the nanocrystals plays a positive role in generating entanglement in some cases. The analytical results show that the relatively strong scattering leads to a larger concurrence for the fixed dipole-cavity detunings. This investigation may hold potential for solid-state quantum information processing applications.
For cavity quantum electrodynamics systems (cavity-QED) to play a role in quantum information processing applications and in quantum networks, they must be robust and scalable in addition to having a suitable method for the generation, processing and storage of quantum bits. One solution is to develop a composite system that couples a nitrogen vacancy (NV) center in diamond to a whispering gallery mode supported by a fused silica microsphere. Such a system is motivated by the optical and electron-spin properties of the NV center. The NV center is the leading spin-qubit and exhibits atomic like linewidths at cryogenic temperatures and has spin coherence times greater than milliseconds at room temperature. These long coherence times, coupled with nanosecond scale spin readout and manipulation times, allow for millions of quantum operations to be processed. Silica whispering gallery resonators are the only class of microresonators with quality factor high enough to reach the strong coupling regime, which is necessary for some quantum information processing applications. \n \nIntegrating these two components into a system that could position a diamond nanopillar near the surface of a deformed-double stemmed microsphere system, with nanometer precision, at 10 K was a major achievement of this research. Cavity resonances in deformed microspheres can be excited with a free-space coupling technique which simplifies their integration into cryogenic environments. In these intentionally deformed resonators, an enhanced evanescent field decay length was observed at specific locations along the ray orbit. The double-stem arrangement enables the cavity resonance to be tuned over 450 GHz, with sub-10 MHz resolution, at 10 K. These two features, the enhanced decay length and broad range tuning with high resolution, are indispensible tools for cavity-QED studies with silica microspheres. \n \nDiamond nanopillars were fabricated from single crystal diamond with diameters as small as 140 nm in order to maintain a high quality factor. Studies were conducted on NV centers in nanopillars and bulk diamond to determine their suitability for cavity-QED applications. In an attempt to increase the light-matter interaction between NV centers and whispering gallery modes, diamond substrates were optically characterized that were irradiated with nitrogen ions.
Abstract We theoretically investigate an efficient scheme for quantum state transfer (QST) between two nitrogen-vacancy (N-V) centers coupled to the whispering gallery modes (WGM) of a micro-resonator. We analyze the impact of mode coupling and the distance between two N-V centers on the dynamics of state transfer. Specifically, we explore QST under three coupling regimes:comparable coupling (J ≃ g), strong mode coupling J ≫ g, and weak mode coupling J ≪ g, also incorporating system decay factors (WGM decay Γ and N-V dephasing γ) at different interparticle distances. Our study shows that by adjusting the system control parameters, quantum information can be transferred between N-V centers with high efficiency. Additionally, the fidelity of QST reaches approximately 99% in all cases, with an oscillatory pattern, reflecting the intricate interplay between NV-resonator and mode coupling strengths. These findings underscore the importance of interparticle distance and mode coupling in the realization of solid-state qubit-based quantum information processing devices.
We propose an efficient scheme for the realization of quantum information transfer and entanglement with nitrogen-vacancy (N-VVV) centers coupled to a high-QQQ whispering-gallery mode (WGM) microresonator. We show that based on the effective dipole-dipole interaction between the N-VVV centers mediated by the WGM, quantum information can be transferred between the N-VVV centers through Raman transitions combined with laser fields. This protocol may open up promising possibilities for quantum communications with the solid-state quantum electrodynamic cavity system.