Quantum state tomography across the exceptional point in a single dissipative qubit
Quantum state tomography across the exceptional point in a single dissipative qubit
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DOI：
10.1038/s41567-019-0652-z
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发表时间：
2019-12-01
期刊：
影响因子：
19.6
通讯作者：
Murch, K. W.
中科院分区：
文献类型：
--
作者：
Naghiloo, M.;Abbasi, M.;Murch, K. W.
开放的物理系统可以用有效的非厄米哈密顿量来描述，它描述了系统中能量或粒子数的获得或损失。报道了光学(1-7)和机械(8-13)非厄米系统的实验实现，展示了激光(14-16)、拓扑特征(7，17-19)、最佳能量传递(20，21)和增强传感(22，23)等功能。这种实现仅限于经典(波)系统，在该系统中只测量幅度信息，而不测量相位。因此，一个系统接近一个特异点--这种非厄米哈密顿量的简并，在那里本征值和相应的本征模合并(24-29)--对它的量子演化的影响仍然没有被探索。在这里，我们使用后选择对一个三能级超导跨量子电路进行了单个耗散量子比特在其例外点附近的量子态层析成像。我们观察到零失谐时的时空反射对称性破缺跃迁(30)(，)(31)，有限失谐时的退相干增强，以及量子比特弛豫态例外点的量子特征。我们的实验显示了与非厄米物理相关的现象，如在完全量子区域内本征态的非正交性，这可能为探索和利用量子信息处理的例外点简并提供一条途径。
Open physical systems can be described by effective non-Hermitian Hamiltonians that characterize the gain or loss of energy or particle numbers from the system. Experimental realization of optical(1-7) and mechanical(8-13) non-Hermitian systems has been reported, demonstrating functionalities such as lasing(14-16), topological features(7,17-19), optimal energy transfer(20,21) and enhanced sensing(22,23). Such realizations have been limited to classical (wave) systems in which only the amplitude information, not the phase, is measured. Thus, the effects of a systems's proximity to an exceptional point-a degeneracy of such non-Hermitian Hamiltonians where the eigenvalues and corresponding eigenmodes coalesce(24-29)-on its quantum evolution remain unexplored. Here, we use post-selection on a three-level superconducting transmon circuit to carry out quantum state tomography of a single dissipative qubit in the vicinity of its exceptional point. We observe the spacetime reflection symmetry-breaking transition(30)(,)(31) at zero detuning, decoherence enhancement at finite detuning and a quantum signature of the exceptional point in the qubit relaxation state. Our experiments show phenomena associated with non-Hermitian physics such as non-orthogonality of eigenstates in a fully quantum regime, which could provide a route to the exploration and harnessing of exceptional point degeneracies for quantum information processing.