Decoherence and equilibration under nondestructive measurements

Lawrence S. Schulman

남궁민

Vladimir B. Braginskii, Sergey P. Vyatchanin

Thomas Vanderbruggen, Ralf Kohlhaas, Andréa D Bertoldi +3 more

We consider the decoherence of a pseudospin ensemble under collective random rotations and study, both theoretically and experimentally, how a nondestructive measurement combined with real-time feedback correction can protect the state against such a decoherence process. We theoretically characterize the feedback efficiency with different parameters---coherence, entropy, fidelity---and show that a maximum efficiency is reached in the weak measurement regime, when the projection of the state induced by the measurement is negligible. This article presents in detail the experimental results published previously [T. Vanderbruggen et al., Phys. Rev. Lett. 110, 210503 (2013)], where the feedback scheme stabilizes coherent spin states of trapped ultracold atoms and nondestructively probes them with dispersive optical detection. In addition, we study the influence of several parameters, such as atom number and rotation angle, on the performance of the method. We analyze the various decoherence sources limiting the feedback efficiency and propose a way to mitigate their effect. The results demonstrate the potential of the method for the real-time coherent control of atom interferometers.

Yang Xiao, Yi‐Hao Kang, Ri‐Hua Zheng +4 more

Abstract In this paper, a robust and accurate protocol is proposed to realize nondestructive parity measurement of artificial atoms using a superconducting resonator and homodyne measurement. With the help of an additional microwave driving field, the cavity field evolves into a coherent state or remains in a vacuum state according to the parity of the atoms. Consequently, the parity information of atoms can be read out by a homodyne measurement on the cavity. Parity information can be obtained without destroying the original state of the system, which means that the state can be further applied to other quantum information processing tasks after a parity measurement. The numerical simulation results show that the protocol is robust against systematic error, random noise, and decoherence. Therefore, this protocol can provide a feasible viewpoint for nondestructive parity measurement.

Yu Ning, Yi‐Hao Kang, Zhi‐Cheng Shi +2 more

Abstract In this paper, we put forward a protocol for the complete and nondestructive Bell-state measurement of trapped ions. We show that the four different Bell states of two information carriers can be distinguished using two auxiliary ions with the initial Bell states unchanged after the procedures. The parameter selections are discussed based on the experimentally available parameters, and the robustness against the errors and decoherence are analyzed. The results show that the protocol works well with the selected parameters, and possesses robustness against errors and decoherence. Since the laser pulses to drive the transitions of ions in the procedures are designed via reverse engineering, the control parameters can be flexibly selected under certain boundary conditions, which provides the possibility to find corrective parameters to compensate the errors caused by the decoherence. We hope the protocol can be useful for the Bell-state based quantum information tasks.