Sheng-Li Ma

Dissipative preparation of entangled states between two spatially separated nitrogen-vacancy centers

We present a novel 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 singlet-like 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 communications and computations with this solid-state cavity quantum electrodynamic system.

Optimal fidelity of teleportation with continuous variables using three tunable parameters in a realistic environment

We introduce three tunable parameters to optimize the fidelity of quantum teleportation with continuous-variable in nonideal scheme. Using the characteristic function formalism, we present the condition that the teleportation fidelity is independent of the amplitude of input coherent states for any entangled resource. Then we investigate the effects of tunable parameters on the fidelity with or without the presence of environment and imperfect measurements, by analytically deriving the expression of fidelity for three different input coherent state distributions. It is shown that, for the linear distribution, the optimization with three tunable parameters is the best one with respect to single- and two-parameter optimization. Our results reveal the usefulness of tunable parameters for improving the fidelity of teleportation and the ability against the decoherence.

Dissipative production of controllable steady-state entanglement of two superconducting qubits in separated resonators

We propose an efficient method for dissipative preparation of controllable steady-state entanglement of two superconducting qubits coupled to spatially separated transmission line resonators, which are linked by an additional superconducting qubit acting as a tunable coupler. The quantum-state production process is based on a form of reservoir engineering, i.e., the dissipation of the coupler is utilized to steer the system into the desired state at stationary state. The distinct feature of our scheme is that neither initial state preparation nor unitary dynamics are required. These make the present protocol more feasible in the experimental implementation.

One-step generation of Greenberger–Horne–Zeilinger states of multi solid-state spin qubits

We propose a one-step scheme for the generation of Greenberger–Horne–Zeilinger states of multi solid-state qubits and the implementation of quantum phase gates in a system consisting of N spatially separated nitrogen-vacancy centers coupled to the whispering-gallery mode (WGM) of a microsphere cavity. The proposed scheme is based on the effective electronic dipole–dipole interaction between electron spins associated with the NV centers, which is mediated by the WGM and applying external driving laser fields. As the spontaneous emission of the excited states of the NV centers is highly suppressed and the cavity mode is only virtually excited, the scheme is insensitive to decoherence.

Preparing entangled states between two NV centers via the damping of nanomechanical resonators

We propose an efficient scheme for preparing entangled states between two separated nitrogen-vacancy (NV) centers in a spin-mechanical system via a dissipative quantum dynamical process. The proposal actively exploits the nanomechanical resonator (NAMR) damping to drive the NV centers to the target state through a quantum reservoir engineering approach. The distinct features of the present work are that we turn the detrimental source of noise into a resource and only need high-frequency low-Q mechanical resonators, which make our scheme more simple and feasible in experimental implementation. This protocol may have interesting applications in quantum information processing with spin-mechanical systems.

Quantum microwave-optical interface with nitrogen-vacancy centers in diamond

We propose an efficient scheme for a coherent quantum interface between microwave and optical photons using nitrogen-vacancy (NV) centers in diamond. In this setup, an NV center ensemble is simultaneously coupled to an optical and a microwave cavity. We show that, by using the collective spin excitation modes as an intermediary, quantum states can be transferred between the microwave cavity and the optical cavity through either a double-swap scheme or a dark-state protocol. This hybrid quantum interface may provide interesting applications in single microwave photon detections or quantum information processing.

Two-mode squeezing generation in hybrid chains of superconducting resonators and nitrogen-vacancy-center ensembles

We consider a hybrid quantum system consisting of two independent chains of nearest-neighbor linearly interacting superconducting transmission-line resonators, each of which a nitrogen-vacancy-center ensemble (NVE) is magnetically coupled to. In addition, the first-beginning pair of the resonators is locally driven by a two-mode microwave squeezed bath. We show that in the steady state a series of NVE pairs in the up and down chains is in a two-mode spin squeezed state. In the low excitation limit, collective excitation modes of the up- and down- NVE pairs are in the two-mode squeezed state of the driven field, i.e., realizing a perfect squeezed state replication.

Quantum information transfer with hybrid NV center-photon qubit encoding

We propose a scheme to perform quantum information transfer based on hybrid spin-photon qubit encoding in superconducting quantum circuits. The hybrid qubit consists of a nitrogen-vacancy center spin ensemble coherently coupled to a microwave photon confined in a frequency tunable superconducting co-planar waveguide cavity. The spin ensemble-cavity hybrid system forms quantum nodes capable of sending, receiving, storing, and releasing photonic quantum information by the hybrid encoding. Quantum information transfer between distinct nodes is achieved by the coherent exchange of a single photon. We show the faithful transfer of an arbitrary superposition hybrid quantum state between two separate identical nodes via coherent control on the system’s dynamics. The protocol may have interesting applications in quantum networking with this hybrid spin-photon structure.

Generation and swapping of multi-qubit entangled state in a coupled superconducting resonator array

An efficient method is proposed for the generation and swapping of multi-qubit entangled state in an array of linearly coupled superconducting resonators, each of which is coupled to N superconducting qubits. With the external driving fields to adjust the desired qubit–resonator interaction, we firstly show that the multipartite entangled state of superconducting qubits hosted in two nearest-neighbor interacting resonators can be deterministically realized. Furthermore, by utilizing the produced entangled state, we put forward a protocol for the swapping of quantum entangled state in the coupled resonator array based on measurement, i.e., the multi-particle entangled state can be achieved for the qubits in long-distance separated resonators. The numerical simulation suggests that our scheme is feasible with current circuit QED technology.

Simulating the Lipkin-Meshkov-Glick model in a hybrid quantum system

We propose an efficient scheme for simulating the Lipkin-Meshkov-Glick (LMG) model with nitrogen-vacancy (NV) center ensembles in diamond magnetically coupled to superconducting coplanar waveguide cavities. With the assistance of external microwave driving fields, we show that the interaction of the NV spins can be easily controlled, and several types of the LMG model can be realized by tuning the different parameters. Under the thermal dynamical limit, the distinct non-equilibrium second order quantum phase transition of the spin ensemble can be achieved at the critical point. Furthermore, we show that the spin squeezed state can be generated by tailoring the LMG Hamiltonian to possess the two-axis counter-twisting form in this hybrid quantum system.