Feedback control of superconducting quantum circuits

Feedback control of superconducting quantum circuits

Ristè, D.

Kouwenhoven, L.P. (promotor)

Applied Sciences

Quantum Nanoscience

2014-10-17

Superconducting circuits have recently risen to the forefront of the solid-state prototypes for quantum computing. Reaching the stage of robust quantum computing requires closing the loop between measurement and control of quantum bits (qubits). This thesis presents the realization of feedback control of superconducting qubits based on projective measurement, with initial applications. The first application is a reset operation which initializes a qubit in the ground state fast and on demand. In a second experiment, we transform a cavity into a two-qubit parity meter, which is capable of generating entanglement starting from an unentangled superposition state. We then employ feedback to turn the generation of entanglement from probabilistic to deterministic, thus combining two key ingredients - parity measurement and feedback - of quantum error correction. As a third application, we transform a superconducting qubit into a charge-parity detector to investigate the limits of quasiparticle tunneling to qubit coherence. We find room for at least a tenfold increase in qubit coherence times before quasiparticles become the bottleneck. Finally, we present our latest results towards implementing the bit-flip error correction code in a five-qubit processor and discuss the role of feedback control in the future development of superconducting quantum circuits.

quantum feedback
quantum measurement
superconducting qubits
quasiparticles
entanglement

https://doi.org/10.4233/uuid:787bc488-96b2-4e03-abbe-0a9fba2c4d75

9789085931966

Institutional Repository

doctoral thesis

(c) 2014 Ristè, D.