Shi-Lei Su

Shortcuts to adiabatic passage for multiqubit controlled-phase gate

We propose an alternative scheme of shortcuts to a quantum controlled phase gate in a much shorter time based on the approach of Lewis-Riesenfeld invariants in cavity quantum electrodynamics systems. This scheme can be used to perform a one-qubit phase gate, a two-qubit controlled phase gate, as well as a multiqubit controlled phase gate. The strict numerical simulations demonstrate that the total operation time for implementing controlled phase gates is much shorter than previous schemes and very robust against decoherence.

Adiabatic passage for three-dimensional entanglement generation through quantum Zeno dynamics.

We propose an adiabatic passage approach to generate two atoms three-dimensional entanglement with the help of quantum Zeno dynamics in a time-dependent interacting field. The atoms are trapped in two spatially separated cavities connected by a fiber, so that the individual addressing is needless. Because the scheme is based on the resonant interaction, the time required to generate entanglement is greatly shortened. Since the fields remain in vacuum state and all the atoms are in the ground states, the losses due to the excitation of photons and the spontaneous transition of atoms are suppressed efficiently compared with the dispersive protocols. Numerical simulation results show that the scheme is robust against the decoherences caused by the cavity decay and atomic spontaneous emission. Additionally, the scheme can be generalized to generate N-atom three-dimensional entanglement and high-dimensional entanglement for two spatially separated atoms.

Simplified scheme for entanglement preparation with Rydberg pumping via dissipation

Department of Physics, College of Science, Yanbian University, Yanji, Jilin 133002, ChinaInspired by recent work [A. W. Carr and M. Saffman, Phys. Rev. Lett. 111, 033607 (2013)], weproposed a simplified scheme to prepare the two-atom maximally entangled states via dissipative Ry-dberg pumping. Compared with the previous scheme, the simplified one only requires one Rydbergstate rather than two in each atom. Thus, the four Rydberg interactions in the previous scheme aresimplified to one and the asymmetric Rydberg interactions are avoided. And the required numberof classical laser fields are reduced to two. Master equation simulations demonstrate the maximallyentangled state fidelity F = 0.999 in theory under certain conditions. Furthermore, we generalizethe scheme to prepare the three-dimensional entangled state, and the numerical simulations showthat the fidelity of the desired three-dimensional entanglement could be higher than 0.997.

Dissipative preparation of three-atom entanglement state via quantum feedback control

Two schemes are presented for generating steady three-atom Greenberger–Horne–Zeilinger and W states in a strongly dissipative cavity via quantum feedback control. The quantum feedback control is only applied to a single atom based on quantum-jump detection to improve the fidelity of the target state. Thus, cavity decay plays a key role in obtaining the target state. The required interaction time need not be accurately controlled.

Environment-assisted entanglement restoration and improvement of the fidelity for quantum teleportation

Three environment-assisted schemes are proposed to suppress the amplitude damping decoherence for entanglement distribution via weak measurement reversal. Based on the measurement of environment and appropriate weak measurement reversal operations, the initial entangled state can be recovered between two separated participants with high success probability and fidelity. In some specific cases, the restored optimal concurrence could reach up to 1 without requirement of the reversing measurement. Moreover, we concretely show that the proposed environment-assisted entanglement restoration can be applied to quantum teleportation to significantly improve the fidelity of the teleported state.

Preparation of entanglement between atoms in spatially separated cavities via fiber loss

We propose a scheme to prepare a maximally entangled state for two Λ-type atoms trapped in separate optical cavities coupled through an optical fiber based on the combined effect of the unitary dynamics and the dissipative process. Our work shows that the fiber loss, as well as the atomic spontaneous emission and the cavity decay, is no longer undesirable, but requisite to prepare the distributed entanglement, which is meaningful for the long distance quantum information processing tasks. Originating from an arbitrary state, the desired state could be prepared without precise time control. The robustness of the scheme is numerically demonstrated by considering various parameters.Graphical abstract

Quantum information processing in collective-rotating decoherence-free subspace

Using the atomic state encoded in the collective-rotating decoherence-free subspace (CRDFS), two methods to construct the hybrid-controlled-phase-flip gate between photon and the single logic qubit are presented assisted by the cavity input–output process. Then, ways to realize the common single-qubit operations in CRDFS are given out. Based on the former gate and single-qubit operations, methods to construct the parity gate and controlled-phase gate in CRDFS are discussed. Next, two ways to realize the Bell-state measurement and the approach to realize quantum information transfer in CRDFS are proposed. Final discussion and numerical simulation reveal that our work is feasible and useful for quantum information processing tasks in CRDFS.