Frank Wilhelm-Mauch, Universität des Saarlandes, Germany
Readout plays a central role in most quantum information protocols, notably in fault tolerance. While the readout of supercondcuting qubits operating in the microwave regime has reached exquisite performance using Josephson Parametric Amplifiers, these ask for large technological overhead that is difficult to scale down. We will show how a recently introduced microwave photon counter, the Josephson Photomultiplier JPM can be used for qubit readout with much less overhead and even elementary data processing on chip. As this detector does not respond to the phase of the microwaves, it can be used for direct one-shot parity measurement that is called for in the surface code or in variational eigensolvers for quantum chemistry. We will also highlights on limitations of the QNDness of such measurements based on the formation of dressed coherent states.