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Annalen der Physik

Accurate Parity Meter Based on Coherent State Measurement

Yang Xiao, Ri‐Hua Zheng, Yang Liu, Yi‐Hao Kang, Jie Song, Yan Xia

Published Dec 23, 2021• 6 citations
Publisher

Abstract

Abstract Parity meter is the core step of many quantum information works. In this paper, a robust and accurate protocol to construct a parity meter of two artificial atoms coupled to a cavity is proposed. Specifically, when the atomic system is in states with different parities, the cavity will evolve into different states. Then, the parity information of the atomic system can be distinguished by measuring the state of the cavity via the homodyne measurement. In addition, the influence of decoherence (including the cavity decay, the atomic spontaneous emission, and the dephasing) and systematic errors are numerically discussed. The results show that the protocol is robust against these negative factors. Therefore, this protocol may provide helpful perspectives for accurate parity meters.

DOI
10.1002/andp.202100461

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Abstract Parity meter is the core step of many quantum information works. In this paper, a robust and accurate protocol to construct a parity meter of two artificial atoms coupled to a cavity is proposed. Specifically, when the atomic system is in states with different parities, the cavity will evolve into different states. Then, the parity information of the atomic system can be distinguished by measuring the state of the cavity via the homodyne measurement. In addition, the influence of decoherence (including the cavity decay, the atomic spontaneous emission, and the dephasing) and systematic errors are numerically discussed. The results show that the protocol is robust against these negative factors. Therefore, this protocol may provide helpful perspectives for accurate parity meters.
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.
Parity meters, utilized to distinguish bipartite quantum states with even or odd parity, have many applications in quantum information processing. We propose a potentially practical scheme to construct the nondestructive Rydberg parity meter (NRPM) in ground-state subspace using Rydberg atoms. Based on the proposed NRPM, the parity of the qubit atoms could be known in a deterministic and nondestructive way, implying that the output state of the NRPM can be further used in the rest of the process for quantum information tasks. In addition, we study the applications of the proposed NRPM in entangled state fusion, entangled state analysis, and quantum teleportation, as well as quantum logic gate in a decoherence-free subspace regarding collective-dephasing errors. We analyze the performance of the NRPM under the influence of decoherence and consider more general situations for the feasibility of the scheme.
In this paper, we propose a robust and high-fidelity scheme to construct a nondestructive Rydberg parity meter by optimized inverse engineering, after which we can know the parity information of the bipartite state without destroying it, implying that the output bipartite state can be further used in the rest quantum information processing tasks. Specifically speaking, we build a model with two systematic Rydberg atoms and one auxiliary Rydberg atom and control them by utilizing optimized inverse engineering against systematic error. Also, since the accumulated time for the Rydberg atoms simultaneously being in Rydberg states is minimized, the mechanical effect and the further possible ionization are almost avoided. Moreover, numerical simulation shows that the present scheme is robust against the systematic error, the dephasing, and the thermal noise, demonstrating feasibility in the experiment.
We present a protocol for realizing parity detection of a bipartite system based on non-Hermitian spectral phase transition. The system comprises two superconducting qubits as information carriers and an auxiliary superconducting resonator. We derive a parity-dependent effective Hamiltonian, where the frequency of the resonator is shifted when the qubits are in even-parity states. The frequency shift results in a spectral phase transition in the non-Hermitian dynamical matrix in the Heisenberg picture, where the spectrum turns from purely imaginary to purely real. With a proper frequency shift, the spectral distinction between the even- and odd-parity cases leads to markedly different photon number dynamics, i.e., exponential growth for the odd-parity case, and bounded oscillations for the even-parity case. By measuring the photon number in the resonator after a fixed evolution time, the parity of the qubits can be reliably discriminated. Numerical simulations further demonstrate that the protocol is robust against systematic imperfections and decoherence, including the spontaneous emission and dephasing of the qubits, as well as cavity decay. These results establish a practical route to parity detection via non-Hermitian dynamics. This approach provides a scalable building block for superconducting-circuit quantum information processing.
We investigate an atomic entanglement purification protocol based on the coherent state input-output process by working in low-Q cavity in the atom-cavity intermediate coupling region. The information of entangled states are encoded in three-level configured single atoms confined in separated one-side optical micro-cavities. Using the coherent state input-output process, we design a two-qubit parity check module (PCM), which allows the quantum nondemolition measurement for the atomic qubits, and show its use for remote parities to distill a high-fidelity atomic entangled ensemble from an initial mixed state ensemble nonlocally. The proposed scheme can further be used for unknown atomic states entanglement concentration. Also by exploiting the PCM, we describe a modified scheme for atomic entanglement concentration by introducing ancillary single atoms. As the coherent state input-output process is robust and scalable in realistic applications, and the detection in the PCM is based on the intensity of outgoing coherent state, the present protocols may be widely used in large-scaled and solid-based quantum repeater and quantum information processing.
Abstract In this paper, a protocol for nondestructive parity meter (NPM) of two cat‐state qubits is proposed. The physical model contains two cavities and an auxiliary qubit. For each cavity, the quantum information is encoded on the odd and even cat state, forming a cat‐state qubit. By adjusting the strength of the driving field on the auxiliary qubit, an effective Hamiltonian for cavity‐selective transition is derived. Moreover, reverse engineering based on the effective Hamiltonian is applied to find the evolution path, and the systematic‐error‐sensitivity nullification method is used to select proper parameters of the evolution path. In this way, robust control fields are designed to combat the influence of the systematic errors. Furthermore, the effects of random noise and decoherence on the fidelity of the protocol are considered. Numerical simulations show that the protocol is insensitive to the experimental imperfection, including systematic errors, random noise and decoherence. Therefore, the protocol is expected to expand the vision of realizing NPM.