Abstract: Techniques are described for performing two-qubit gates on logical qubits. The two-qubit gates may be performed in a manner that is fault tolerant and/or that produces an indication of whether or not an error occurred during the gate. The robustness of the described techniques against errors is provided at the hardware level by engineering a system in which an ancilla qubit acts as flag states for certain errors. As such, manipulating the state of the system to counteract an error may not be necessary; rather, when errors occur the result of a gate may be filtered out, or performed again. In other cases, the error state may simply be recorded as an indication of quality of the state of the system. The techniques for performing two-qubit gates described herein may also be compatible with different bosonic encodings of logical qubits, of which illustrative examples are described.

Abstract: Systems and methods for performing fault tolerant quantum operations for the 4-legged cat code are provided. The quantum systems include an ancilla qubit dispersively coupled to a first logical qubit, and the quantum system may be operated at least in part by: generating and applying a first drive waveform to the ancilla qubit, the first drive waveform comprising a first comb of 7t-pulses having selective frequencies corresponding to a first selection of even and odd cavity resonance frequencies of the first logical qubit; and reading out a state of the ancilla qubit.

Abstract: Systems and methods for performing fault tolerant quantum operations for the 4-legged cat code are provided. The quantum systems include an ancilla qubit dispersively coupled to a first logical qubit. and the quantum system may be operated at least in part by: generating and applying a first drive waveform to the ancilla qubit. the first drive waveform comprising a first comb of 7t-pulses having selective frequencies corresponding to a first selection of even and odd cavity resonance frequencies of the first logical qubit: and reading out a state of the ancilla qubit.