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Laser Physics

Robust state transfer and entanglement distribution in the quantum spin channel via non-Hermitian operation

Fei Chen, Lan Xu, Yun-Hui Zhao, Zhi He, Qiong Wang

Published Jun 10, 2021• 9 citations
Publisher

Abstract

Abstract Using the non-Hermitian operation approach, robust state transfer and entanglement distribution can be realized in the quantum spin chain channel. We derive the exact analytical expressions of the quantum fidelity and entanglement and in detail investigate the influence of non-Hermitian operator parameters on the quantum fidelity and entanglement. Compared with pure decoherence process (without non-Hermitian operator process), we find that the non-Hermitian operator process can obvious enhance and preserve the quantum fidelity and entanglement.

DOI
10.1088/1555-6611/ac0637

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Using the weak measurement (WM) and quantum measurement reversal (QMR) approach, robust state transfer and entanglement distribution can be realized in the spin-12\frac{1}{2}21​ Heisenberg chain. We find that the ultrahigh fidelity and long distance of quantum state transfer with certain success probability can be obtained using proper WM and QMR, i.e., the average fidelity of a general pure state from 8080%80 to almost 100100%100, which is almost size independent. We also find that the distance and quality of entanglement distribution for the Bell state and the general Werner mixed state can be obviously improved by the WM and QMR approach.
The non-Hermitian Hamiltonian describes the effective dynamics of a system coupled to a continuously measured bath, and can exhibit anti-unitary symmetries that give rise to exceptional points and broken phases with complex eigenvalues, features unique to non-Hermitian systems. Going beyond conventional Hermitian physics, we analyze the impact of non-Hermiticity in the quantum state transmission by employing a non-Hermitian spin chain that functions as a quantum data bus. By deriving a general expression for the fidelity of quantum state transfer for a U(1)-symmetric non-Hermitian Hamiltonian, we analyze PT-symmetric XX and SSH models, complemented by a numerical study of the RT-symmetric iXY model. We demonstrate that, in several parameter regimes, the transfer fidelity in the non-Hermitian setting exceeds the classical threshold and can even exceed the performance of the corresponding Hermitian models. In particular, for the SSH model with dominant inter-cell coupling, the broken phase supports near-unit-fidelity quantum state transfer, a level of performance that the corresponding Hermitian model fails to attain. Moreover, we establish a correspondence between the non-Hermitian and Hermitian descriptions by identifying related parameter regions in which the fidelity fails to surpass the classical bound.
Abstract Decoherence suppression from disturbance of the environment is an essential task in quantum information processing. Using the non-Hermitian operation approach, decoherence suppression of a qubit system interacting with a zero-temperature reservoir with both spontaneous emission and dephasing is investigated. We derive the exact analytical expressions of the quantum fidelity and find that quantum coherence can be significantly enhanced by controlling the non-Hermitian operator parameters. In particular, the non-Hermitian is more effective in the case of strong decay rates and show better inhibition effect on dephasing process than the spontaneous emission process.
Abstract The enhancement of qubit–qubit entanglement is systematically investigated by employing local non-Hermitian operations. Special attention is paid to the comparison of prior and post non-Hermitian cases. We derive the exact expressions of concurrence quantifying entanglement to arrive at an exact solution model, consisting of two qubits interacting with an independent structured reservoir. The results show that qubit–qubit entanglement can obviously be enhanced by means of either local prior or post non-Hermitian operations. In particular, we find that the effect of the prior non-Hermitian operator process of the double damping channels is superior to the post non-Hermitian process, while the effect of the single damping channel case shows the opposite trend.
The study of non-Hermitian systems has attracted more and more attention, because physical properties in many real systems should be described by non-Hermitian Hamiltonians. Due to the existence of absorption and dissipation, transmission and transformation of entangled states with high fidelity are very difficult to realize in the non-Hermitian systems. How to realize transmission and transformation of entangled states with high fidelity in these dissipative systems becomes an open problem. Here we provide an inverse design scheme for topologically protected channels to solve such a problem. From our scheme, topologically protected channels can be designed according to the requirements for the overlap integrals among the initial states, target states, and eigenstates of the system. As a result, robust transmission and transformation of entangled states with high fidelity can be achieved in the non-Hermitian systems. Our proposed scheme has been demonstrated experimentally using the constructed non-Hermitian quantum walk platform. This work interconnects topology, quantum physics, and non-Hermitian systems, and opens up an avenue for quantum engineering in real systems.