Towards an ensemble bismuth dopant-based quantum memory with tunable superconducting microresonators*

Despite recent improvement, the limited coherence time remains a major impediment to implementation for modern superconductor quantum processors. Yet often in large-scale quantum algorithms, most logic qubits spend most of their lifetimes waiting in idle, while incurring dear expenses for error correction. Such incongruity invites exploration of possibilities for a heterogeneous architecture where a dedicated memory unit serves exclusively to store the idle quantum information. Rid of the requirement for a universal gate set, we may extend the scope of candidate host qubits to the lower end of the versatility spectrum.

In this talk, we present a new design towards microwave quantum memories based on ensemble bismuth dopants in silicon – superconductor hybrid systems, where coherence time as long as 300 ms is demonstrated [1]. We attempt to address the key issue of overall photon conversion deficiency with a catch-and-release protocol. A pair of parametrically coupled superconducting resonators buffers between the spin ensemble and the incoming photon with dynamically tunable virtual bandwidth and resonance frequency, which promotes not only the capture efficiency of the flying qubit, but also that of the ensemble photon absorption to near unit cooperativity.

[1] Ranjan, V., et al. PRL, 125(21), 210505