Efficient, ever-ready quantum memory at room temperature for single photons

—by Till Weinhold and Sarah Lau

EQUS researchers have demonstrated a quantum memory that stores and recalls information with comparable performance to the current best laboratory demonstrations, operates continuously, and may be implemented with minimal technical effort.

Quantum technologies have the potential to revolutionise our society, but creating the networks of quantum resources to support these future technologies is challenging.  One potential solution is a quantum repeater with a quantum memory.  Many high-performing quantum memories have been demonstrated under laboratory conditions, but these memories are not suitable for large-scale use.

The EQUS team have demonstrated a simple, readily usable quantum memory, which operates continuously, at room temperature and without vacuum, and can store and recall quantum states with comparable performance to the laboratory demonstrations.  We used hot rubidium gas in a glass cell as our memory medium, and single particles of light (photons) as the quantum states.

Memory operation and storage results: timing for the magnetic field gradient (a) and control field switching (b); and experimental coincidence data of the input states (c), and of a single photon state (d) and corresponding coherent state (e) stored and recalled after 4 μs, overlaid with simulated results.

With this set-up, we successfully stored photons and could recall them 84% of the time—comparable to the current best quantum memories.  However, because our memory does not require any state preparation steps, it operates continuously.  Moreover, because it operates outside of a vacuum and at room temperature, it can be implemented with minimal technical effort for quantum technology applications.  This is in contrast to other quantum memories, which require long preparation times between operation, and complex and expensive technology for implementation.

Looking forward, we hope to implement our quantum memory in a quantum communication channel to synchronise communication between two stations and extend feasible communication distances.  Specifically, communication to satellites suffers from a Doppler shift because of the movement of the satellite, which creates a problem when linking to different ground stations.  Our memory has a proven capability of changing the frequency of the stored light and we're looking to use it to compensate for the Doppler shift.

Read the full paper here: https://arxiv.org/abs/2203.12108.  Sarah is an EQUS PhD student, currently working at Finisar in Sydney; Till is an EQUS Research Fellow at the University of Queensland.  This work is a collaboration between EQUS and the ARC Centre of Excellence for Quantum Computation and Communication Technology (CQC2T).  It forms part of EQUS' Quantum Engines and Instruments research program.


Left, the set-up of the quantum memory. Right, the down-conversion crystal being pumped.

Major funding support

Australian Research Council

The Australian Research Council Centre of Excellence for Engineered Quantum Systems (EQUS) acknowledges the Traditional Owners of Country throughout Australia and their continuing connection to lands, waters and communities. We pay our respects to Aboriginal and Torres Strait Islander cultures and to Elders past and present.