Supercurrent parity meter in a nanowire Cooper-pair transistor*

Semiconductor nanowires coupled with superconductors are a promising platform to construct Majorana zero modes as well as to build up topological fault-tolerant quantum computers. In semiconductor nanowire/superconductor hybridized island, charging energies are introduced and thus even/odd fermion parity of two Majorana zero modes work as a two-level quantum system. By embedding such hybridized islands into superconducting circuit, not only can trivial Andreev bound states and Majorana bound states be distinguished via the supercurrent phase of the island, but also topological-qubit readout and operation can be performed by supercurrent measurements. Here, we insert an InSb-Al hybridized island into a NbTiN superconducting circuit forming a superconducting interference device. In such a device, we find that the switching current of the InSb-Al island depends on its parity and the corresponding superconducting phase also shows parity-dependent behaviours. In this way, the parity of bound states residing in the hybridized island can be read out, which paves the way for parity read out of Majorana superconducting qubits.