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Physical Review A

Controllable quantum state transfer and entanglement generation between distant nitrogen-vacancy-center ensembles coupled to superconducting flux qubits

Qiong Chen, Wan Li Yang, Mang Feng

Published Aug 24, 2012• 35 citations
Publisher

Abstract

We investigate the dissipative dynamics of a hybrid system consisting of two inductively coupled superconducting flux qubits (FQs), each of which couples magnetically with a nitrogen-vacancy-center spin ensemble (NVE). The system displays a series of damped oscillations under various experimental situations, where we obtain analytically the time-dependent populations associated with arbitrary values of the FQ-FQ inductively coupling strength $g$ and the FQ-NVE magnetically coupling strength $G$ in the one-excitation case. Our results show that a reliable high-fidelity quantum state transfer between the two distant NVEs can be realized by modulating the parameters $g$ and $G.$ Furthermore, we also present a potentially practical idea to entangle the two separate NVEs, which is within reach due to the currently available technology.

DOI
10.1103/physreva.86.022327

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We investigate the dissipative dynamics of a hybrid system consisting of two inductively coupled superconducting flux qubits (FQs), each of which couples magnetically with a nitrogen-vacancy-center spin ensemble (NVE). The system displays a series of damped oscillations under various experimental situations, where we obtain analytically the time-dependent populations associated with arbitrary values of the FQ-FQ inductively coupling strength ggg and the FQ-NVE magnetically coupling strength GGG in the one-excitation case. Our results show that a reliable high-fidelity quantum state transfer between the two distant NVEs can be realized by modulating the parameters ggg and G.G.G. Furthermore, we also present a potentially practical idea to entangle the two separate NVEs, which is within reach due to the currently available technology.
We explore controllable quantum dynamics of a hybrid system, which consists of an array of mutually coupled superconducting resonators (SRs) with each containing a nitrogen-vacancy center spin ensemble (NVE) in the presence of inhomogeneous broadening. We focus on a three-site model, which compared with the two-site case, shows more complicated and richer dynamical behavior, and displays a series of damped oscillations under various experimental situations, reflecting the intricate balance and competition between the NVE-SR collective coupling and the adjacent-site photon hopping. Particularly, we find that the inhomogeneous broadening of the spin ensemble can suppress the population transfer between the SR and the local NVE. In this context, although the inhomogeneous broadening of the spin ensemble diminishes entanglement among the NVEs, optimal entanglement, characterized by averaging the lower bound of concurrence, could be achieved through accurately adjusting the tunable parameters.
We propose a system for quantum state transfer (QST) between two nitrogen-vacancy center ensembles (NVEs) coupled to two transmission line resonators (TLRs) via flux qubits (FQs). We study the transfer of an arbitrary quantum state by various system's controlling parameters i.e. , the coupling between nitrogen vacancy ensembles g , the coupling strength between resonators λ for both the resonant and non-resonant interactions in the presence of decoherence. Furthermore, we investigate the dynamics of QST for three different cases, i.e. , g ≫ λ , g ≃ λ and g ≪ λ in detail. It is found that the quantum state can be efficiently transferred between NVEs for suitable values of controlling parameters. We observe that the fidelity of quantum state transfer is about 99 % in all cases for short operational time ( 0.45 μ s ) while in the presence of decoherence fidelity is above 96 % . This reveals that decoherence has no prominent effect on quantum state transfer.
We propose an effective scheme for realizing a Jaynes-Cummings model with the collective nitrogen-vacancy-center ensemble (NVE) bosonic modes in a hybrid system. Specifically, the controllable transmon qubit can alternatively interact with one of the two NVEs, which results in the production of NNN-particle entangled states. Arbitrary NNN-particle entangled states, NOON states, NNN-dimensional entangled states, and entangled coherent states are demonstrated. Realistic imperfections and decoherence effects are analyzed via numerical simulation. Since no cavity photons or excited levels of the NV center are populated during the whole process, our scheme is insensitive to cavity decay and the spin dephasing effect of the NVE. The idea provides a scalable way to realize NVE-circuit cavity quantum information processing with current technology.
Exploration of macroscopic quantum entanglement is of great interest in both fundamental science and practical application. We investigate a hybrid quantum system that consists of two nitrogen-vacancy centers ensembles (NVE) coupled to a superconducting coplanar waveguide resonator (CPWR). The collective magnetic coupling between the NVE and the CPWR is employed to generate macroscopic entanglement between the NVEs, where the CPWR acts as the quantum bus. We find that, this NVE-CPWR hybrid system behaves as a system of three coupled harmonic oscillators, and the excitation prepared initially in the CPWR can be distributed into these two NVEs. In the nondissipative case, the entanglement of NVEs oscillates periodically and the maximal entanglement always keeps unity if the CPWR is initially prepared in the odd coherent state. Considering the dissipative effect from the CPWR and NVEs, the amount of entanglement between these two NVEs strongly depends on the initial state of the CPWR, and the maximal entanglement can be tuned by adjusting the initial states of the total system. The experimental feasibility and challenge with currently available technology are discussed.
Abstract We propose a potentially practical scheme for creating macroscopic entangled coherent state between two separate nitrogen-vacancy center spin ensembles placed near a superconducting flux qubit. Through the collective magnetic coupling and the in situ tunability of the flux qubit, the arbitrary entangled coherent states of spin ensembles can be achieved with high success possibilities under the influence from decoherence of the flux qubit and spin ensembles. The experimental feasibility and challenge are justified using currently available technology.
We study a hybrid quantum system consisting of spin ensembles and superconducting flux qubits, where each spin ensemble is realized using the nitrogen-vacancy centers in a diamond crystal and the nearest-neighbor spin ensembles are effectively coupled via a flux qubit. We show that the coupling strengths between flux qubits and spin ensembles can reach the strong and even ultrastrong coupling regimes by either engineering the hybrid structure in advance or tuning the excitation frequencies of spin ensembles via external magnetic fields. When extending the hybrid structure to an array with equal coupling strengths, we find that in the strong-coupling regime, the hybrid array is reduced to a tight-binding model of a one-dimensional bosonic lattice. In the ultrastrong-coupling regime, it exhibits quasiparticle excitations separated from the ground state by an energy gap. Moreover, these quasiparticle excitations and the ground state are stable under a certain condition that is tunable via the external magnetic field. This may provide an experimentally accessible method to probe the instability of the system.