Performing quantum computing robustly requires closing the loop between measurement and qubit rotations to correct for errors in real time. Here, I present our development of feedback control of superconducting qubits and its first applications. Building on a nondemolition qubit readout with 99% single-shot fidelity, we implement a digital feedback loop to initialize a qubit fast and on demand. Moving to the multi-qubit setting, we transform the cavity into a qubit parity meter. Applying a parity measurement on a two-qubit superposition state, we first create entanglement probabilistically by postselection on either parity result, then deterministically using feedback to target the same Bell state every time. The entanglement fidelity is limited by measurement backaction, in the form of stochastic qubit phase kickbacks. Turning to an equivalent single-qubit scenario, we counteract such kickbacks using analog feedback. Finally, we report progress towards the implementation of the bit-flip error-correction code in a 5-qubit planar architecture.
A coffee break will be served at 11h00. The seminar will be given in English.
Kavli Institute of Nanoscience