Quantum Random Access Memory Architectures Using 3D Superconducting Cavities

Quantum random access memory (QRAM) is a common architecture resource for algorithms with many proposed applications, including quantum chemistry, windowed quantum arithmetic, unstructured search, machine learning, and quantum cryptography. Here, we propose two bucket -brigade QRAM architectures based on high -coherence superconducting resonators, which differ in their realizations of the conditional -routing operations. In the first, we directly construct cavity -controlled controlled - SWAP ( CSWAP ) operations, while in the second, we utilize the properties of giant -unidirectional emitters (GUEs). For both architectures, we analyze singleand dual -rail implementations of a bosonic qubit. In the singlerail encoding, we can detect first -order ancilla errors, while the dual -rail encoding additionally allows for the detection of photon losses. For parameter regimes of interest, the postselected infidelity of a QRAM query in a dual -rail architecture is nearly an order of magnitude below that of a corresponding query in a single -rail architecture. These findings suggest that dual -rail encodings are particularly attractive as architectures for QRAM devices in the era before fault tolerance.