Fig. 1: Superconducting resonator coupled to singlet-triplet two-level system (TLS) in a crystal-phase nanowire (NW).
a Optical microscope image of the device showing a half-wave NbTiN resonator with a characteristic impedance of 2.1 kΩ. In the middle of the center conductor, a dc bias line is connected via a meandered inductor. b False-colored scanning electron micrograph of the crystal-phase NW device (image is rotated by − 90° with respect to a). The NW is placed at the position indicated in (a), and the purple gate line is galvanically connected to the resonator at its voltage anti-node. Tunnel barriers are highlighted in red. Using the gate voltages VL and VR, the device is operated with an even electron filling as depicted schematically. The spin-orbit gap ΔSO corresponds to the indicated spin-rotating tunnel transition, which forms the TLS. The in-plane magnetic field angle α is varied during the experiments using a vector magnet that controls the magnetic field B. c Level diagram for an even electron occupation as a function of the electrostatic detuning ε in the presence of strong SOI and finite magnetic field exhibiting singlet (S) and triplet (T) states. Subscripts denote the filling of the left and right dots, and the superscript denotes the spin quantum number of the triplet states (see methods). The avoided crossing between the spin-polarized triplet state T+ and the low-energy singlet state at ε = ε0 is detected using the resonator.
