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Laser Physics

Properties of hybrid entanglement among two flux qubits and a nitrogen-vacancy-center ensemble

Qinghong Liao, Lin Chen, Xin Liu, Nanrun Zhou

Published Jun 27, 2018• 0 citations
Publisher

Abstract

Abstract We investigate hybrid flux-nitrogen-vacancy (NV) entanglement in the system consisting of two flux qubits and an NV-center ensemble (NVE). The influence of the initial entanglement degree of the flux qubit C, the coupling strength between two flux qubits, the coupling strength between the flux qubit M and the NVE on the bipartite entanglement and the tripartite entanglement is discussed. The maximally bipartite entangled state and the maximally tripartite entangled state can be obtained under certain conditions. In addition, it is shown that the time of disentanglement of the hybrid quantum system can be controlled by adjusting the coupling strength between two flux qubits and the coupling strength between the flux qubit M and the NVE.

DOI
10.1088/1555-6611/aac7de

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Abstract We investigate hybrid flux-nitrogen-vacancy (NV) entanglement in the system consisting of two flux qubits and an NV-center ensemble (NVE). The influence of the initial entanglement degree of the flux qubit C, the coupling strength between two flux qubits, the coupling strength between the flux qubit M and the NVE on the bipartite entanglement and the tripartite entanglement is discussed. The maximally bipartite entangled state and the maximally tripartite entangled state can be obtained under certain conditions. In addition, it is shown that the time of disentanglement of the hybrid quantum system can be controlled by adjusting the coupling strength between two flux qubits and the coupling strength between the flux qubit M and the NVE.
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 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.
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.
Quantum entanglement is a kernel of quantum computation and quantum communication. We introduce a theoretical scheme to achieve the entanglement between two separated quantum nodes in a hybrid system. The proposed hybrid system based on diamond nitrogen-vacancy (NV) center spin ensemble is coherently coupled to a superconducting quantum circuit consisting of two quantum nodes and a quantum channel. Each node in our setup is composed of an NV center spin ensemble magnetically coupled to a superconducting coplanar resonator. The NV center spin ensemble composed of N identical and non-interacting NV spins, is placed in the magnetic field antinode of the superconducting coplanar resonator where the coupling is maximized. An array of superconducting quantum interference devices (SQUIDs) is inserted in the central conductor of resonator to make its frequency tunable with the magnetic flux threading through the SQUID loops. This flux is generated by passing current through an on-chip wire, so that the resonator can be brought in resonance with the NV center spins without changing their Zeeman splitting. Quantum qubits encoded into two separate nodes are connected by a vacuum superconducting coplanar resonator that is used as a quantum channel. This setup can potentially take the best elements of each individual system:NV center spin ensemble with longer coherence time capable of preparing, storing and releasing photonic quantum information, and the superconducting quantum circuits are easy to manipulate externally and can perform quantum logic gates to control quantum information rapidly. In order to realize the entanglement between two separated quantum nodes, firstly, we make a canonical transformation and obtain the Hamiltonian of the system that is reduced to two NV center spin ensembles resonantly coupled to a single mode of the superconducting coplanar resonator. Then we put forward the hybrid NV center spin-photon qubit encoding. In this hybrid encoding, the NV center spin and photon degrees of freedom enter on an equal footing into the definition of the qubit, in which case, quantum channel will switch on when three superconducting coplanar resonators are in resonance with each other, and all the manipulations can perform simply by tuning the frequencies of the superconducting coplanar resonators. Under the precise control of the evolution time, high fidelity entanglement between two separated quantum nodes is achieved. We show that this proposal can provide high fidelity quantum entanglement under realistic conditions, both in the resonant and the dispersive interaction cases. This hybrid quantum system will exhibit long coherence time and possess features like easy fabrication, integratability, and potential scalability. Furthermore, the quantum node composed of an NV center spin ensemble magnetically coupled to a superconducting coplanar resonator can be respectively integrated, which has practical applications in the realization of quantum information transmission and quantum entanglement among multiple quantum nodes.
We propose how to realize high-fidelity quantum storage using a hybrid quantum architecture including two coupled flux qubits and a nitrogen-vacancy center ensemble (NVE). One of the flux qubits is considered as the quantum-computing processor and the NVE serves as the quantum memory. By separating the computing and memory units, the influence of the quantum-computing process on the quantum memory can be effectively eliminated, and hence the quantum storage of an arbitrary quantum state of the computing qubit could be achieved with high fidelity. Furthermore, the present proposal is robust with respect to fluctuations of the system parameters, and it is experimentally feasible with currently available technology.
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.