A SNAIL-mediated Cascaded Random Access Quantum Memory (Part 1)

Multimode cavities are a promising, hardware-efficient platform for quantum memories: they host several long-lived modes and enable universal, random-access control via coupling to a nonlinear element within the framework of circuit QED. The simplest architecture for such a memory involves a multimode cavity directly coupled to a control circuit (e.g., a transmon). However, this leaves the memory vulnerable to ancilla-induced mode nonlinearities and interactions, additional decoherence, and backaction from ancilla errors. The Cascaded Random Access Quantum Memory (C-RAQM) [1] addresses these issues by coupling the multimode memory to an intermediate buffer cavity via a tunable coupler that transfers states between the memory and the buffer. The buffer serves as a cache memory, where operations are executed using a coupled transmon, while providing an additional layer of protection for the memory from ancilla errors.

We introduce a C-RAQM device comprising seamless flute cavities, a SNAIL coupler, and a transmon ancilla. In part one of this two-part talk, we will discuss the device design and core capabilities, the optimization of flux delivery for biasing the SNAIL, and decoherence limits for SNAIL-activated beam-splitter operations.

[1] Z. Li, et al., arXiv:2503.13953 (2025).