Breaking the entanglement-fidelity tradeoff in P T-symmetric quantum systems

A noteworthy discovery is that the minimal evolution time is smaller for parity-time ( \({PT}\) )-symmetric systems compared to Hermitian setups. Moreover, there is a significant acceleration of two-qubit quantum entanglement preparation near an exceptional point (EP), or spectral coalescence, within such a system. Nevertheless, an important problem often overlooked for quantum EP-based devices is their fidelity, greatly affected by the process of dissipation. We identify an inherent trade-off relation between the degree of entanglement and fidelity, and demonstrate that this limitation can be effectively overcome by harnessing an active \({PT}\) -symmetric system, which possesses balanced gain and loss, enabling maximal entanglement with rapid speed, high fidelity, and greater resilience to non-resonant and coupling strength errors. Two- to six-partite entanglement is prepared as the concrete example to show (i) how to break this inherent fidelity-entanglement trade-off even with non-balanced gain and loss, and its resilience against non-resonant errors, in contrast to passive \({PT}\) -symmetric dynamics; (ii) achieving speedups of many orders of magnitude, in contrast to conventional Hermitian dynamics. We use this approach to prepare 10-qubit entanglement to show the generality of this method. These findings highlight the potential of truly \({PT}\) -symmetric devices as a versatile platform for generating and manipulating diverse quantum resources, with implications for advancing quantum information technologies.