Demonstrating an erasure-detected entangling gate between dual-rail cavity qubits - part 1

Dual-rail qubits encoded in 3D superconducting cavities are a promising approach for realizing error-detected qubits [1]. Detecting errors on physical qubits allows them to be converted to erasure errors, dramatically easing the task of quantum error correction and improving near-term error-detected algorithms. To this end, it is crucial to be able to detect hardware errors, even when they occur during the qubit operations themselves. This has been achieved for most of the required operations such as state-preparation and measurement [2], single qubit gates [3, 4], and erasure-checks [5].

In part 1 of this talk, we focus on the remaining missing ingredient -- an entangling gate between two dual-rail cavity qubits. Following the proposal in [6], we show how entangling ZZ-gates can be implemented with just a beamsplitter operation between two of the four cavities, and an ancilla transmon that is dispersively coupled to only one of the cavities. We detail the gate operation and show how it can detect the dominant first-order errors in the cavities and transmon, and enables lower gate infidelities that scale as (T_gate/T_coherence)^2 when no errors are flagged.

​​​​​​​[1] Teoh et al., PNAS 120 (41), e2221736120, 2023 

[2] Chou et al., arXiv:2307.03169, 2023 

[3] Lu, Maiti et al., Nat Comm 14, 5767, 2023 

[4] Chapman, de Graaf et al., PRX Quantum 4, 020355, 2023 

[5] Koottandavida, Tsioutsios et al. in prep. 

[6] Tsunoda, Teoh et al., PRX Quantum 4, 020354, 2023