Readout of superconducting qubits with a Josephson photomultiplier

A Josephson photomultiplier (JPM) formed from a current-biased Josephson junction is the centerpiece of an alternative method for measuring the state of a superconducting qubit in a microwave cavity compared to conventional linear amplification followed by heterodyne readout. This approach, which involves mapping the qubit state onto the cavity photon occupation followed by photon detection with the JPM, reduces the requirements on bulky microwave hardware and amplifiers in the cryostat. We will discuss the implementation of superconducting microwave cavities and transmon qubits tailored for this readout technique. Furthermore, we will present steps towards the readout of multiple qubits in a common cavity with the JPM-based protocol.