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International Journal of Quantum Information

Generating quantum entanglement of phonons assisted by hybrid systems

Jiuming Li, Shao-Ming Fei

Published Mar 28, 2025• 0 citations
Publisher

Abstract

As a result of study on surface acoustic waves (SAWs), we propose protocols for generating the quantum entanglement on phonons. In the protocol of phonon–photon entanglement generation, the hybrid system is composed of a surface acoustic wave resonator (SAWR), a superconducting resonator (SR) and a nitrogen-vacancy-center ensemble (NVE). For the generation of three phonon modes entanglement, the SAWRs are coupled to the corresponding NVEs, while the NVEs interact with the same SR. Both protocols exploit the resonant interaction and the dispersive coupling. By considering the decoherence of the corresponding systems, the fidelities of the phonon–photon entanglement and three phonon modes entanglement reach 99.35% and 91.01%, respectively. Generalizing the approaches, we also present the protocol of multiple phonon modes entanglement.

DOI
10.1142/s0219749925500091

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As a result of study on surface acoustic waves (SAWs), we propose protocols for generating the quantum entanglement on phonons. In the protocol of phonon–photon entanglement generation, the hybrid system is composed of a surface acoustic wave resonator (SAWR), a superconducting resonator (SR) and a nitrogen-vacancy-center ensemble (NVE). For the generation of three phonon modes entanglement, the SAWRs are coupled to the corresponding NVEs, while the NVEs interact with the same SR. Both protocols exploit the resonant interaction and the dispersive coupling. By considering the decoherence of the corresponding systems, the fidelities of the phonon–photon entanglement and three phonon modes entanglement reach 99.35% and 91.01%, respectively. Generalizing the approaches, we also present the protocol of multiple phonon modes entanglement.
Exploiting multiple modes in a quantum acoustic device could enable applications in quantum information in a hardware-efficient setup, including quantum simulation in a synthetic dimension and continuous-variable quantum computing with cluster states.We develop a multimode surface acoustic wave (SAW) resonator with a superconducting quantum interference device (SQUID) integrated in one of the Bragg reflectors.The interaction with the SQUID-shunted mirror gives rise to coupling between the more than 20 accessible resonator modes.We exploit this coupling to demonstrate two-mode squeezing of SAW phonons, as well as four-mode multipartite entanglement.Our results open avenues for continuous-variable quantum computing in a compact hybrid quantum system.
In this paper, we propose a system that consists of two acoustic wave resonators (AWRs) coupled to a nitrogen-vacancy-center ensemble (NVE) for constructing Greenberger–Horne–Zeilinger (GHZ) states and controlled-phase (c-phase) gate according to the recent study of surface acoustic waves. The two AWRs are fabricated on a diamond surface in perpendicular way, and the NVE is placed at the center of the crossing. By using the resonant interactions and microwave pulses, we present the protocols of constructing the GHZ states and the c-phase gate in the phonon–spin system. The numerical simulation shows that the fidelities of the two-excitation Bell state, three-excitation Bell state and the c-phase gate can reach 99.19[Formula: see text], 99.46[Formula: see text] and 98.62[Formula: see text], respectively, by considering the decoherence of the system.
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.
Phonons, and in particular surface acoustic wave phonons, have been proposed as a means to coherently couple distant solid-state quantum systems. Individual phonons in a resonant structure can be controlled and detected by superconducting qubits, enabling the coherent generation and measurement of complex stationary phonon states. We report the deterministic emission and capture of itinerant surface acoustic wave phonons, enabling the quantum entanglement of two superconducting qubits. Using a 2-millimeter-long acoustic quantum communication channel, equivalent to a 500-nanosecond delay line, we demonstrate the emission and recapture of a phonon by one superconducting qubit, quantum state transfer between two superconducting qubits with a 67% efficiency, and, by partial transfer of a phonon, generation of an entangled Bell pair with a fidelity of 84%.
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.
A hybrid quantum device consisting of three ensembles of nitrogen-vacancy centers (NVEs) whose spins are collectively coupled to a superconducting coplanar waveguide resonator is shown to enable the generation of controllable tripartite macroscopic entangled states. The density matrix of such NVEs can be encoded to recast a three-qubit system state, which can be characterized in terms of the entanglement witnesses in relation to the Greenberger-Horne-Zeilinger (GHZ) states. We identify the parameter space within which the generated entangled states can have an arbitrarily large overlap with GHZ states, indicating an enhanced entanglement in the system.