Progress towards fault tolerant error mapping in pair coherent states (1/2)

The stabilization of Bosonic qubits in microwave cavities is a promising step toward implementing quantum error correction codes. The pair cat code, which utilizes a two-mode entangled state, assures significant advantages over the previously implemented one-mode cat code for autonomous quantum error correction schemes [1]. A pair coherent state (PCS) forms the basis of this pair cat code where the error syndrome can be measured from the photon number difference (PND) between the two modes [2]. Measuring the PND of the system can be made first-order fault tolerant by achieving negative matching of the dispersive shift values for the two storage modes. We achieve this by utilizing a fluxonium qubit, with a local flux application to avoid storage lifetime degradation and utilize 3D architectures, as an ancilla due to the large anharmonicity. We use the large straddling regime of this qubit with a small external drive [3] to account for deviations in fabrication to achieve the negative dispersive shift matching.