Using PT-symmetric Qubits to Break the Tradeoff Between Fidelity and the Degree of Quantum Entanglement

TL;DR

This paper demonstrates that active PT-symmetric systems can overcome the traditional trade-off between entanglement degree and fidelity, enabling rapid, high-fidelity multi-qubit entanglement generation even with imperfect gain-loss balance.

Contribution

The study introduces a method using active PT-symmetric systems to achieve maximal entanglement with high fidelity and speed, surpassing limitations of dissipation and post-selection.

Findings

Active PT-symmetric systems enable faster entanglement preparation.

High fidelity entanglement is achievable despite gain-loss imbalance.

The approach is effective for bipartite and tripartite entanglement.

Abstract

A noteworthy discovery is that the minimal evolution time is smaller for parity-time ($\mathcal{PT}$) symmetric systems compared to Hermitian setups. Moreover, there is a significant acceleration of two-qubit quantum entanglement preparation near the exceptional point (EP), or spectral coalescence, within such system. Nevertheless, an important problem often overlooked for quantum EP-based devices is their fidelity, greatly affected by the process of dissipation or post-selection, creating an inherent trade-off relation between the degree of entanglement and fidelity. Our study demonstrates that this limitation can be effectively overcome by harnessing an active $\mathcal{PT}$-symmetric system, which possesses balanced gain and loss, enabling maximal entanglement with rapid speed, high fidelity, and greater resilience to non-resonant errors. This new approach can efficiently prepare multi-qubit entanglement and use not only bipartite but also tripartite entanglement, as illustrative examples, even when the precise gain-loss balance is not strictly maintained. Our analytical findings are in excellent agreement with numerical simulations, confirming the potential of truly $\mathcal{PT}$-devices as a powerful tool for creating and engineering diverse quantum resources for applications in quantum information technology