Harnessing non-Hermiticity for efficient quantum state transfer

TL;DR

This paper explores how non-Hermitian Hamiltonians can enhance quantum state transfer fidelity, surpassing classical limits and Hermitian models, especially in broken phases of specific non-Hermitian spin chains.

Contribution

It derives a general fidelity expression for U(1)-symmetric non-Hermitian systems and demonstrates improved quantum state transfer in non-Hermitian models like PT-symmetric XX and SSH.

Findings

Non-Hermitian models can exceed classical fidelity thresholds.

Broken phase of SSH model supports near-unit fidelity transfer.

Correspondence established between non-Hermitian and Hermitian regimes.

Abstract

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.