📝 SummarXiv

Abstract

For a truly $\mathcal{PT}$-symmetric quantum system, the conventional non-Hermitian Hamiltonian is $H = H_{\rm drive} -i\gamma|1\rangle\langle1| + i\gamma|0\rangle\langle0|$, where $\Omega$ and $\gamma$ are real parameters. The three terms respectively represent coherent coupling, loss (on state $|1\rangle$), and gain (on state $|0\rangle$). However, realizing the gain term $+i\gamma|0\rangle\langle0|$ has remained an outstanding challenge for quantum system, especially on ground state -- no theoretical or experimental schemes have definitively demonstrated its achievement. While systems omitting this gain term can exhibit a passively $\mathcal{PT}$-symmetric energy spectrum (featuring a parallel imaginary shift) and display related phenomena, they fail to capture the full physical behavior and unique properties inherent to truly $\mathcal{PT}$-symmetric systems. In this manuscript, we propose a method to achieve effective gain on the ground state $|0\rangle$ ($+i\gamma|0\rangle\langle0|$) after averaging all trajectories, by integrating the S{\o}rensen-Reiter effective operator method with the Wiseman-Milburn master equation for continuous measurement and instantaneous feedback control after averaging the evolution over all trajectories. This approach provides a possible pathway to efficiently construct truly $\mathcal{PT}$-symmetric quantum devices, offering a powerful platform for engineering quantum resources vital for quantum information technology applications.