超导量子比特系统的特殊光学性质与其对量子信息的应用

Superconducting qubits are the fundamental elements in superconducting circuits to realize quantum storage and computation. Under the framework of circuit quantum electrodynamics, they are regarded as quasi two-level atomic systems. However, superconducting qubits are not exactly equivalent to two-level atoms, since they possess the special properties such as tunable energy spacings in a single-qubit system and controllable geometric spacings between qubits in a multi-qubit system. This project aims to develop special optical theories to cater to such properties peculiar to superconducting qubit systems and to clarify the effects endued when applying these optical properties to quantum information. The research contents cover three general aspects: .(1) study the relations between high-order susceptibilities and the systems parameters such as level spacings, relaxation times, and decoherence rates for a single superconducting qubit; compute the response of the qubit to its interaction with multi-photon processes; and develop the nonlinear optics based on circuit quantum electrodynamics..(2) study the cooperative effects in multi-qubit systems, deduce the relationship between the exciton-polariton collective excitations and the inter-qubit spacings, and develop the mesoscopic quantum optics for superconducting circuits..(3) based on the two aspects above, study the peculiar entanglement properties of the quantum states that exist in superconducting qubit systems..The ultimate goal of the project is to propose versatile designs for quantum information processing devices, through the understanding of these optical and entanglement properties.

超导量子比特是在超导电路上实现量子存贮和计算的基础元件。在电路量子电动力学的框架下，它多被作为一个类二能级原子系统来考虑。不过，超导量子比特不完全等价于二能级原子，它拥有单个量子比特能隙可调，多个量子特比间间距可控等特殊物理性质。本课题旨在发展出一套适用于超导量子比特系统的特殊光学理论，并阐明这类光学性质对量子信息的应用所产生的影响。课题的主要内容有三大方面：（1）研究单个超导量子比特的高阶磁化率与能隙、弛豫时间、退相干率等系统参数的关系，计算它对多光子相互作用的响应，发展基于电路量子电动力学的非线性光学理论。（2）研究多量子比特系统的合作现象，计算系统内激子极化子等与间距的关系，发展超导电路上的介观量子光学理论。（3）以前两方面为依据，研究超导量子比特系统上量子态的特殊纠缠性质。本课题的目标在于通过对这些特殊光学和纠缠性质的认识，提出多样化量子信息处理器件的设计方案。

超导量子比特是在超导电路上实现量子存贮和计算的基础元件。在多数研究框架下，它被看待成一个二能级原子，不过超导量子比特不完全等价于二能级原子，它拥有能隙可调，间距可控等特殊物理性质。本课题研究了基于这些特殊性的量子光学理论，并阐明了这类光学性质对量子信息的应用产生的影响。其中突出的重要结果有以下三个。.（1）构建了量子比特准晶格概念，发展了准晶格内量子比特纠缠并发度的计算方法。成果发表在《欧洲物理快报》上。.（2）证明了两超导量子比特可以通过相互与一单玻色模的耦合，将量子纠缠在时态演化上从一方传到另一方。成果发表在《物理评论》上。.（3）实验上证明了超导量子比特的能级被驱动场劈裂后，其辐射与再吸收的过程可以产生无粒子数翻转情况下的信号放大。成果发表在《物理评论快报》上。