Observation of quantum state collapse and revival due to the single-photon Kerr effect
Observation of quantum state collapse and revival due to the single-photon Kerr effect
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DOI：
10.1038/nature11902
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发表时间：
2013-03-14
期刊：
影响因子：
64.8
通讯作者：
Schoelkopf, R. J.
中科院分区：
文献类型：
--
作者：
Kirchmair, Gerhard;Vlastakis, Brian;Schoelkopf, R. J.
为了创建和操纵量子信息协议的非经典光态，需要单光子水平上的强非线性相互作用。产生合适相互作用的一种方法是将光子与原子耦合，如空腔量子电动力系统的强耦合机制(1,2)。然而，在这些系统中，光的量子态只能通过操纵原子来间接控制(3)。直接的光子-光子相互作用发生在所谓的克尔介质中，这种介质通常仅引起微弱的非线性，但代价是显着的损失。到目前为止，还不可能达到单光子克尔状态，其中单个光子之间的相互作用强度超过损失率。在这里，我们使用三维电路量子电动力学架构(4)，设计了一种人造克尔介质，它可以进入这种状态并允许观察新的量子效应。我们实现了一个 gedanken 实验（5），其中可以观察到相干态的崩溃和复活。这种时间演化是腔内光场量子化和单个光子之间非线性相互作用的结果。在演化过程中，形成了相干态的非经典叠加（即多分量“薛定谔猫”态）。我们通过测量 Husimi Q 函数来可视化这种演化，并通过腔态断层扫描确认这些瞬态的非经典特性。在这种高质量因子光子模式下创建和操纵相干态叠加的能力为将连续变量（6）物理与超导电路相结合开辟了前景。单光子克尔效应可用于光子的量子非破坏测量（7）、单光子生成（8）、自主量子反馈方案（9）和量子逻辑运算（10）。
To create and manipulate non-classical states of light for quantum information protocols, a strong, nonlinear interaction at the single-photon level is required. One approach to the generation of suitable interactions is to couple photons to atoms, as in the strong coupling regime of cavity quantum electrodynamic systems(1,2). In these systems, however, the quantum state of the light is only indirectly controlled by manipulating the atoms(3). A direct photon-photon interaction occurs in so-called Kerr media, which typically induce only weak nonlinearity at the cost of significant loss. So far, it has not been possible to reach the single-photon Kerr regime, in which the interaction strength between individual photons exceeds the loss rate. Here, using a three-dimensional circuit quantum electrodynamic architecture(4), we engineer an artificial Kerr medium that enters this regime and allows the observation, of new quantum effects. We realize a gedanken experiment(5) in which the collapse and revival of a coherent state can be observed. This time evolution is a consequence of the quantization of the light field in the cavity and the nonlinear interaction between individual photons. During the evolution, non-classical superpositions of coherent states (that is, multi-component 'Schrodinger cat' states) are formed. We visualize this evolution by measuring the Husimi Q function and confirm the non-classical properties of these transient states by cavity state tomography. The ability to create and manipulate superpositions of coherent states in such a high-quality-factor photon mode opens perspectives for combining the physics of continuous variables(6) with superconducting circuits. The single-photon Kerr effect could be used in quantum non-demolition measurement of photons(7), single-photon generation(8), autonomous quantum feedback schemes(9) and quantum logic operations(10).