基于网络分析仪的3D Transmon相干测量方法

3D Transmon是目前已知退相干时间较长的一种超导量子比特,在超导量子计算、量子光学、腔量子电动力学等方面具有重要的应用.拉比振荡是表征量子系统退相干时间的重要方法,也是体现量子系统能够进行能级演化的基本实验.对3D Transmon进行拉比振荡测试,需要进行严格的时序控制,测试调试的过程较为繁琐.本文制备了3D Transmon样品,对其基本参数进行了测试表征,创新性地提出了一种基于网络分析仪的拉比振荡测试方法,基于该方法的测试系统搭建简单,可作为迅速验证3D Transmon是否具备量子特性的一种手段,该方法也可推广至其他量子系统进行时域特性的初步验证.

Three-dimensional transmon coherence measurement method based on network analyser

Three-dimensional(3D)transmon is a kind of superconducting qubit with long decoherence time,which has important applications in superconducting quantum computation,quantum optics,cavity quantum electrodynamics,et al.Rabi oscillation is a vital method to characterize the decoherence time of quantum system,and it is also a basic experiment to demonstrate the energy level evolution of quantum system.In order to test the Rabi oscillation of 3D transmon,strict timing control is necessary,and the process of testing and debugging is complicated.In this paper,3D transmon samples are fabricated and their basic parameters EC=348.74 MHz and EJ=11.556 GHz are tested and characterized.The coupling coefficient g2/D between qubit and the 3D cavity is 43 MHz,which is located in the dispersive regime.The qubit’s first transition frequency f01=9.2709 GHz,and the second transition frequency f12=9.0100 GHz.The 3D resonator is fabricated by the material 6061T6 aluminum,the loaded quality factor is 4.8×105,and the bare frequency of the resonator is 8.108 GHz.Through comparison,it is found that the Rabi oscillation time obtained by the proposed method is shorter than by the Jaynes-Cummings method.The main reasons are as follows.First,the measurement of network analyzer is a continuous measurement,and the test signal always affects the decoherence process of 3D transmon.Second,the quantum bit is in the ground state after decoherence,and the ground state measured by the network analyzer accounts for a relatively high proportion,which causes the curve measured by the network analyzer to be one-sided attenuation oscillation.Third,the dispersive readout method is related to the quality factor of the superconducting cavity.The storage time of microwave photons in the superconducting cavity is longer than the decoherence time of 3D transmon,so the quantum information is partially decohered before leaving the superconducting cavity,which will shorten the Rabi oscillation time.An innovative Rabi oscillation test method based on network analyzer is presented.The test system based on this method is simple to build and can be used as a new way to quickly verify whether 3D transmon has quantum characteristics.This method can also be extended to other quantum systems for preliminarily verifying the time domain characteristics.