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arXiv:2509.02810 · Physical Review A

Hybrid quantum memory leveraging slow light and gradient echo duality

Stanisław Kurzyna, Mateusz Mazelanik, Wojciech Wasilewski, Michal P. Parniak

Published May 27, 2026• 1 citation
arXivHTMLPDF

Abstract

We demonstrate a hybrid quantum memory that combines Gradient Echo Memory (GEM) and Electromagnetically Induced Transparency (EIT) protocols for reversible mapping between light and atomic coherence. By leveraging GEM and EIT complementarity, we realize time-to-frequency and frequency-to-time conversion mechanisms for spectro-temporal modes. This capability provides a versatile tool for quantum communication, where coherent frequency-time conversion enhances network interoperability. In addition, the protocol may enable fundamental studies of atomic coherence, including investigations of Rydberg polaritons and mapping of single Rydberg excitations and ionic impurities.

DOI
10.1103/8wzh-jk9z

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Gradient echo memory (GEM) is a protocol for storing optical quantum states of light in atomic ensembles. The primary motivation for such a technology is that quantum key distribution (QKD), which uses Heisenberg uncertainty to guarantee security of cryptographic keys, is limited in transmission distance. The development of a quantum repeater is a possible path to extend QKD range, but a repeater will need a quantum memory. In our experiments we use a gas of rubidium 87 vapor that is contained in a warm gas cell. This makes the scheme particularly simple. It is also a highly versatile scheme that enables in-memory refinement of the stored state, such as frequency shifting and bandwidth manipulation. The basis of the GEM protocol is to absorb the light into an ensemble of atoms that has been prepared in a magnetic field gradient. The reversal of this gradient leads to rephasing of the atomic polarization and thus recall of the stored optical state. We will outline how we prepare the atoms and this gradient and also describe some of the pitfalls that need to be avoided, in particular four-wave mixing, which can give rise to optical gain.
Spectrotemporal encoding of optical quantum information is emerging as a powerful tool in quantum information technology. Processing of spectrotemporal information has recently been demonstrated in multi-mode quantum memories, based on extensions to memory protocols. We simulate one such process, the fractional Fourier transform, in a system based on a dual quantum memory composed of successive gradient echo memory and electromagnetically-induced transparency operations. We demonstrate the potential of electromagnetically-induced transparency systems for spectrotemporal processing.
We propose a quantum memory protocol based on dynamically changing the resonance frequency of an ensemble of two-level atoms. By sweeping the atomic frequency in an adiabatic fashion, photons are reversibly transferred into atomic coherences. We present a polaritonic description for this type of storage, which shares some similarities with electromagnetically induced transparency based quantum memories. On the other hand the proposed memory is also linked to the gradient echo memory due to the effective spatial gradient that pulses experience in the medium. We discuss a possible implementation of the protocol in hollow-core photonic crystal fibers.