Kavli Institute of Nanoscience, Delft University of Technology, The Netherlands.
Phys Rev Lett. 2012 Aug 3;109(5):050507. doi: 10.1103/PhysRevLett.109.050507.
We demonstrate initialization by joint measurement of two transmon qubits in 3D circuit quantum electrodynamics. Homodyne detection of cavity transmission is enhanced by Josephson parametric amplification to discriminate the two-qubit ground state from single-qubit excitations nondestructively and with 98.1% fidelity. Measurement and postselection of a steady-state mixture with 4.7% residual excitation per qubit achieve 98.8% fidelity to the ground state, thus outperforming passive initialization.
我们通过在 3D 电路量子电动力学中对两个超导量子比特的联合测量来演示初始化。通过约瑟夫森参量放大对腔传输进行同相检测，以非破坏性且保真度为 98.1%的方式从单量子比特激发中区分出双量子比特基态。对具有每个量子比特 4.7%残余激发的稳态混合物进行测量和后选择，实现了对基态的 98.8%保真度，从而优于被动初始化。
