基于超导电路QED系统的多稳态开放系统量子模拟

In order to effectively control quantum systems, one method is to isolate the quantum system from the environment and control its coherent properties. The other method is to design dissipation-driven mechanism for coupling the quantum system to the environment, using the dissipation as useful resources, which arouses a great deal of research interest in recent years. For controlled dissipation-driven mechanism, the common used method is to engineer dissipation-induced irreversible dynamics and thus to make the system with arbitrary initial states evolve to a unique steady state. But the realized steady state through existing methods is a mixed state, thus it does not implement the quantum gate deterministically. In order to solve this problem, it is required to engineer dissipation-driven mechanism similar to the unitary evolution, which controls the system in a specific initial state to evolute under the domination of dissipation-induced multiple steady state dynamics, and implement the gate deterministically. The project studies the dissipative system with the driven superconducting qubits coupling to the superconducting cavities, engineers the open system with multiple steady states dynamics mechanism, and thus realizes quantum simulation for deterministic preparation of many-body quantum states and implementation of logic computation operation and also the exploration of novel phase transition behavior that is induced by steady state transition. The engineered multiple steady state dynamics evolution is dependent on the system's controlling parameters; it is independent on the dissipative parameters but protected by the dissipation. Therefore, the operation process is insensitive to the environmental fluctuation, relaxing the requirements for experimental implementation.

为了有效地控制量子系统，一种做法是把量子系统与环境隔绝并控制它的相干特性；另一种做法是设计系统与环境耦合的驱动耗散机制，把耗散作为有用的资源并加以利用，近年来引起了广泛研究兴趣。对于驱动耗散的控制机制，通常的做法是构造耗散诱导的不可逆动力学，使任意初态的系统演化到一个独特的稳态。但是利用现有方法所实现的稳态是个混态，因此并非确定性地构建了量子门操作。为了解决这个问题，必须构建类似于幺正演化的驱动耗散机制，使特定初态的系统，经过耗散诱导的多稳态动力学演化，执行确定性的门操作。本课题研究受驱动超导比特与超导腔耦合的耗散系统，构建开放体系多稳态的动力学机制，来进行确定性的多体量子态制备和逻辑计算操作以及稳态跃迁诱导的新奇相变行为探索等量子模拟。所构建的多稳态动力学演化只取决于系统的控制参量而并不依赖于耗散参量，但是通过耗散来得到保护。因此操作过程对环境的起伏不敏感，放宽了对实验实施的要求。

为了有效地控制量子系统，一种做法是把量子系统与环境隔绝并控制它的相干特性；另一种做法是设计系统与环境耦合的驱动耗散机制，把耗散作为有用的资源并加以利用。本项目首先研究了单个驱动超导比特与耗散超导腔的耦合体系，构造出特定的可控耗散环境以制备单比特布诺赫球面态，该方法可直接适用于耗散量子网络中任意格点多比特的初始化，并且初始化的效率并不依赖于比特数目；研究了超导电路耦合腔QED系统，利用耦合腔模的集体光子衰竭来辅助实现耦合腔链网络中任意两个节点间的稳态制备；研究通过构建驱动耗散谐振子以及耦合谐振子的多暗态稳态产生机制，实现了基于谐振子相干态的普适量子计算操作；研究单个比特与一个零温玻色库的耦合，发现比特的几何相位可不通过对库自由度的求迹来获得，并且在马尔科夫和非马尔科夫域会呈现出有趣的震荡行为，进一步研究发现，类似的行为存在于纠缠的多比特与多个零温玻色库的耦合系统中；研究单个驱动超导比特在参量空间的演化，发现其驱动动力学幺正演化过程中态与拓扑数之间存在非常紧密的关联，并模拟再现了参量空间中的“磁单极子”，研究并揭示了其“磁场”强度与系统量子态之间的关系。进一步研究发现，比特系统在参量空间中的演化与几何微空间中的类引力波演化呈现及其类似的行为。这些研究及后续的跟进研究将不断丰富开放量子系统特别是超导电路QED系统的研究内容，对相关领域将有一定的借鉴意义。