Random-access quantum memory using chirped pulse phase encoding

TL;DR

This paper presents a novel quantum memory protocol using chirped pulse phase encoding that enables high-density, random access storage with extended lifetime, demonstrated in the microwave regime with potential optical applications.

Contribution

Introduces a chirped pulse encoding protocol for quantum memories that achieves random access and improved lifetime without dedicated cavities per qubit.

Findings

Stored and retrieved up to four microwave pulses on-demand

Memory lifetime extended up to 2 milliseconds

Suppressed superradiant emission critical near unit cooperativity

Abstract

As in conventional computing, key attributes of quantum memories are high storage density and, crucially, random access, or the ability to read from or write to an arbitrarily chosen register. However, achieving such random access with quantum memories in a dense, hardware-efficient manner remains a challenge, for example requiring dedicated cavities per qubit or pulsed field gradients. Here we introduce a protocol using chirped pulses to encode qubits within an ensemble of quantum two-level systems, offering both random access and naturally supporting dynamical decoupling to enhance the memory lifetime. We demonstrate the protocol in the microwave regime using donor spins in silicon coupled to a superconducting cavity, storing up to four multi-photon microwave pulses in distinct memory modes and retrieving them on-demand up to 2~ms later. A further advantage is the natural suppression of superradiant echo emission, which we show is critical when approaching unit cooperativity. This approach offers the potential for microwave random access quantum memories with lifetimes exceeding seconds, while the chirped pulse phase encoding could also be applied in the optical regime to enhance quantum repeaters and networks.