Characterizing quantum operations between superconducting cavity qubits with an erasure-detecting ancilla

Superconducting microwave cavities have emerged as promising platforms for quantum memories, achieving single-photon coherence times on the order of tens of milliseconds [1]. However, leveraging these long photon lifetimes to realize high-fidelity two-qubit gates is limited by the noisy, non-linear ancilla qubit used to control the cavities. Detecting and converting dominant ancilla errors into erasures can improve the post-selected gate fidelity and significantly benefit quantum error correction codes.

Here, we present a novel ancilla qubit for controlling cavity qubits, allowing the conversion of dominant ancilla errors into detectable erasures.We characterize the ancilla qubit and describe the building blocks for realizing high-fidelity quantum gates on cavity qubits.

[1] Milul, Guttel et al., PRX Quantum 4, 030336, 2023