An error-detectable logical measurement of two bosonic modes

Encoding information in the long-lived bosonic modes of high-Q superconducting cavities allows one to perform the first layer of quantum error correction in a single device. For example, storing logical information in Schrodinger cat states enables protection against single photon loss. In this encoding, measurements of the joint photon number parity of two cavities (a logical-ZZ measurement) have been performed by coupling them to a common transmon ancilla, but are limited by decay and dephasing errors in the lossier transmon. In this talk, we demonstrate a measurement of the joint photon number parity that relies on a transmon ancilla coupled to just one cavity plus a tunable beamsplitter interaction between cavities, and that detects both ancilla dephasing and decay errors. We further show how this measurement can be used as an error-detectable entangling operation for a variety of bosonic codes.