Towards strong coupling of a single spin with a superconducting circuit: Flux qubits in 3D cavities.
The flux qubit is often considered as a major design for the future of quantum integrated circuits and its properties have triggered intense interest in the last decade [1-2]. This superconducting circuit behaves as a two-level system, each level being characterized by the direction of a macroscopic permanent current flowing in the loop of the qubit. The permanent current, typically of the order of several hundreds of nAs, generates a large magnetic dipole, which offers interesting prospects for hybrid quantum circuits . However, the flux qubit suffers from limited and irreproducible lifetimes which prevent these potential applications. Recently, a novel architecture where qubits are placed in a three dimensional cavity was introduced for transmon qubit . It was shown that coherence properties can be greatly improved.
I will present the first measurements of flux qubits in a three dimensional cavity and show that they can reach long and more reproducible T1. The qubits were fabricated on a sapphire substrate and were measured by coupling them inductively to an on-chip superconducting resonator embedded in a three dimensional copper cavity. All the measured flux qubits exhibit an intrinsic T1 comprised between 5 and 13 us.
These long and reproducible depolarization times are a key element to reach the strong coupling limit with a single spin as suggested in . I will describe our current experimental efforts towards this long term objective.
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