Josh Nunn

Multi-pulse addressing of a Raman quantum memory: Configurable beam splitting and efficient readout

We address an optical quantum memory with multiple pulses, enabling unit efficiency readout and programmable beam splitting. The resulting coherent processor with built-in storage is universal for scalable photonic quantum information processing.

A cavity-enhanced room-temperature broadband Raman memory

Quantum memories enable the synchronisation of photonic operations. Raman memories are a promising platform, but are susceptible to four-wave mixing noise. We present a demonstration of a cavity-enhanced Raman memory, showing suppression of four-wave mixing.

High efficiency Raman memory by suppressing radiation trapping

Raman interactions in alkali vapours are used in applications such as atomic clocks, optical signal processing, generation of squeezed light and Raman quantum memories for temporal multiplexing. To achieve a strong interaction the alkali ensemble needs both a large optical depth and a high level of spin-polarisation. We implement a technique known as quenching using a molecular buffer gas which allows near-perfect spin-polarisation of over in caesium vapour at high optical depths of up to a factor of 4 higher than can be achieved without quenching. We use this system to explore efficient light storage with high gain in a GHz bandwidth Raman memory.

Applications of Raman Scattering in Quantum Technologies

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A noiseless quantum optical memory at room temperature

A quantum optical memory (QM) is a device that can store and release quantum states of light on demand. Such a device is capable of synchronising probabilistic events, for example, locally synchronising non-deterministic photon sources for the generation of multi-photon states, or successful quantum gate operations within a quantum computational architecture [1], as well as for globally synchronising the generation of entanglement over long distances within the context of a quantum repeater [2]. Desirable attributes for a QM to be useful for these computational and communicational tasks include high end-to-end transmission (including storage and retrieval efficiency), large storage-time-bandwidth product, room temperature operation for scalability and, of utmost importance, noise free performance for true quantum operation.

Photonic Networked Quantum Information Technologies

Hybrid light-matter networks offer the promise for delivering robust quantum information processing technologies, from sensor arrays to quantum simulators. New sources, detectors and memories illustrate progress towards build a resilient, scalable photonic quantum network.

Bad Cavities for Good Memories: Suppression of Four-Wave Mixing in Raman Memories

Quantum memories enable the synchronisation of photonic operations. Raman memories are a promising platform, but are susceptible to four-wave mixing noise. We present a demonstration of a cavity-enhanced Raman memory, showing suppression of four-wave mixing.

Quantum memories and large-scale quantum coherence based on Raman interactions

Applied research into quantum technologies and fundamental research into the foundations of quantum mechanics run hand in hand, since our understanding of quantum correlations both advances, and is advanced by, our ability to control large quantum systems. The off-resonant Raman interaction of light with material systems provides a powerful tool both for quantum information processing, and for accessing macroscopic non-classical states of matter. We describe a recent demonstration of entanglement between the motion of separated diamond crystals at room temperature, and the implementation of quantum memories in cesium vapour that can store and retrieve photons on demand with a time-bandwidth product exceeding 2000, both based on Raman scattering.

Synchronizing single photons with quantum memories

Without deterministic single photon sources, multiphoton rates fall exponentially with the number of photons required, making practical photonics unfeasible. We show how quantum memories improve multiphoton rates by many orders of magnitude.

Entangling the motion of diamonds at room temperature

We demonstrate entanglement between the vibrational mode of two macroscopic, spatially-separated diamonds at room temperature with ultrashort pulses and a far-off-resonant Raman interaction.