Prof. Ioan Pop (KIT) - Superconducting qubits in high magnetic field

Abstract: Superconducting qubits equipped with quantum non-demolishing readout and active feedback can be used as information engines to probe and manipulate microscopic degrees of freedom, whether intentionally designed or naturally occurring in their environment. In the case of spin systems, the required magnetic field bias presents a significant challenge for superconductors and Josephson junctions. Using a nano-Josephson junction, of only 20 nm cross-section, and superconducting granular Aluminum films with critical field above 5 Tesla, we operate a flux qubit in magnetic field of up-to 1.2 Tesla. Remarkably, the spectrum and coherence of the qubit remain stable in this entire range, and we can observe the freezing of a paramagnetic spin ensemble coupled to the qubit.