超导量子比特的弱测量及其量子力学时间对称性的研究

Superconducting qubits have become the most promising candidate of quantum computing and quantum information processing, for its scalability and the easiness to control and read, etc. Here, we will use a Josephson Parametric Amplifier to conduct nearly single microwave photon readout of the 3D transmon, which is also defined as the weak measurement. This measurement will not completely destroy the coherence of the quantum system and only acquire partial information of the system. In quantum mechanics, a measurement at a time t, can be predicted by the quantum state before the measurement, which is the Born prediction. However, this measurement can also be predicated by both the quantum states before and after the measurement, which is the ABL prediction. It is accepted that the ABL prediction behaves better than the Born prediction. Yakir Aharqnov,et al. think half of the information, which determines a measurement at t comes from before the measurement and the other half comes from after the measurement, because of the past and future symmetry in the formula of ABL prediction. In this project, we will first conduct weak measurement using superconducting qubits and circuits and then, perform necessary statistical analysis of the obtained data, while others did not do, in order to compare the Born prediction with the ABL prediction .We will also systematically study the difference between causality and correlation in statistics in order to answer whether the future could influence the measurement in the past.

超导量子比特，由于良好的可扩展性、易于调控读写等优点已成为制备量子计算机和量子信息处理系统的重要候选者。我们将利用约瑟夫参数放大器对三维transmon进行单光子级别的读取。这种读取不完全破坏系统的量子态，而部分获得系统的信息，定义为弱测量。量子力学中，某刻的测量结果，可以由测量前的量子态预测，也可以由测量前和测量后的量子态共同预测。这俩种预测分别是波恩和ABL预测。文献认为ABL预测优于波恩预测。由于ABL预测中，过去和未来的信息的对称性，Yakir Aharqnov等提出在量子力学中对测量结果的影响一半来之过去，一半来之于未来。本项目将进行超导量子比特弱测量,通过统计的方法分析数据,区分波恩和ABL预测。本项目还将研究统计上因果关系和相关性的差别，望能回答量子力学中未来是否会影响过去等重要问题。

最近，量子计算硬件获得了世界性的关注和取得了巨大的成就。由于低耗散，钇铁石榴石薄膜的自旋波模式（磁子）可用来进行可靠量子信息处理。量子器件和钇铁石榴石薄膜的相干耦合还没有被报道。这里，我们提出一种能够获得超导磁通量子比特和钇铁石榴石薄膜磁子的强耦合方案。不像和其他自旋系综的基特尔模式耦合，有一个√N 的增强系数，当自旋的总数为N的时候，和有限波长的磁子模式进行有效磁耦合的时候，有一个额外的以空间坐标为函数的相位需要考虑。为了避免由于对称边界条件引起的不必要的耦合系数相消，一个薄的CoFeB薄层被加在钇铁石榴石薄膜的一边来破坏对称性。我们的数值模拟证明了劈裂和有效的量子信息传递在磁通量子比特和钇铁石榴石薄膜之间的。我们证明了钇铁石榴石薄膜可以用来作为俩个磁通量子比特之间可调控的开关，磁通量子比特形状做了稍微的改变为了减小俩比特之间的互感耦合。我们结果证明了可以耦合俩个磁通量子比特而减小二者之间不必要的串扰。