Phase shifter based on an ultrathin superconducting bilayer with a through-hole for a superconducting device

Applying a radian phase shift other than 2π is a key issue for superconducting circuits, such as flux qubits. Magnetic flux is useful when generating a phase shift. However, to apply a quantized magnetic flux to a phase shifter, a fine geometrical design is required. The magnetic flux generated by an external field generates noise. In this study, we propose a compact phase bias system that does not require an external field during operation. We confirm the phase shift of a direct current superconducting interference device (SQUID) placed on an ultrathin superconducting Nb bilayer with a through-hole by cooling it to a temperature below the superconducting transition temperature with an external field. Although the cause of the phase shift in our system is unclear, we believe that it may be caused by a fractional quantum in the bilayer. When the SQUID is replaced by a qubit, the phase shift can be applied to a phase bias.