标题： 通过宇称-时间对称相变对外耦合较弱的量子比特进行色散读取 显示英文标题

标题： Dispersive readout of a weakly coupled qubit via the parity-time-symmetric phase transition

摘要： 对于某些腔量子电动力学系统（例如，单个电子自旋与被动腔耦合的系统），达到强耦合态是非常具有挑战性的。在弱耦合状态下，传统的色散读出技术无法用于分辨自旋的量子态。在此，我们提出了一种改进的色散读出方法，通过利用一个或两个线性耦合到包含量子比特的被动腔的辅助腔，来测量弱耦合量子比特的量子态。在两种情况下，适当参数下，排除量子比特的系统可以在例外点（EP）处表现出宇称时间对称相变。由于EP可以放大由量子比特引起的扰动，并且宇称时间对称性可以缩小被动腔传输光谱中峰值的线宽，因此可以通过该传输光谱测量弱耦合量子比特的量子态。由于量子比特与被动腔之间的弱耦合，在排除强耦合限制的情况下，与传统强耦合下的色散读出技术相比，量子比特测量带来的反作用也可以减少。 显示英文摘要

摘要： For some cavity-quantum-electrodynamics systems, such as a single electron spin coupled to a passive cavity, it is challenging to reach the strong-coupling regime. In such a weak-coupling regime, the conventional dispersive readout technique cannot be used to resolve the quantum states of the spin. Here we propose an improved dispersive readout method to measure the quantum states of a weakly coupled qubit by harnessing either one or two auxiliary cavities linearly coupled to the passive cavity containing the qubit. With appropriate parameters in both cases, the system excluding the qubit can exhibit a parity-time-symmetric phase transition at the exceptional point (EP). Because the EP can amplify the perturbation induced by the qubit and the parity-time symmetry can narrow the linewidths of the peaks in the transmission spectrum of the passive cavity, we can measure the quantum states of the weakly coupled qubit via this transmission spectrum. Owing to the weak coupling between the qubit and the passive cavity, the backaction due to the measurement of the qubit can also be reduced in comparison with the conventional dispersive readout technique in the strong-coupling regime.