Quantum Memories at Room-Temperature

Supervisors: Dr Dylan Saunders (Primary) and Prof. Ian Walmsley

Local Supervisor: Prof. Myungshik Kim (Imperial)

Background: Photonics is an exciting platform for exploring quantum phenomena at room-temperature. However, photon loss and the probabilistic operation of quantum operations prohibit the scaling of experiments to a regime where large numbers of photons can be prepared in quantum-correlated states.

Here at the Ultrafast Quantum Optics Group (UFQO) at the University of Oxfordwe have been exploring the use of two-photon interactions in warm Alkali vapours as a potential solution to this scaling problem. The solution we areproposing is to synchronise the output of multiple non-deterministic photonic operations using quantum memories [1]. Briefly, a quantum memory is a device that maps flying photons onto atoms, encoding the state of the light field into a “hologram” formed by superpositions of excited atoms across an ensemble ofwarm atoms at room temperature in a robust simple package. The photons can be recalledon demand after a programmable delay: a light-matter beam-splitter.

For the Master’s project, we are proposing an investigation into a new noise-suppression technique in our lambda Raman quantum memory. This will be demonstration of a new protocol: a quantum Zeno noise suppression technique to kill a noise-process prohibits quantum operation, a process known as four-wave-mixing. We will suppress two-mode-squeezing via incoherent Hamiltonian engineering. This work, and the PhD work, would be undertaken at the University of Oxford, in the quantum memories sub-team within the UFQO.

For the PhD Project,you would continue to develop the quantum Zeno noise suppression technique, incorporating it into our recently demonstrated Cavity enhanced quantum memory [2] and interface with a novel new photon source [3]. Moving onto a demonstration of coherent Hamiltonian engineering to suppress noise we will use the Zeno effect to select either the beam-splitter or two-mode squeezing interactions as shown in the figure. As the project matures we will interface our new memory in a compact miniaturised form in the following experiments: light-matter Hong-Ou-Mandel interference: to certify the quality of the memory operation;and the manipulation of time-frequency modes [4], a completely new concept for compact information storage in a light beam.

References:

[1] J. Nunn et. al. Enhancing Multiphoton Rates with Quantum Memories PRL 110, 133601 (2013)

[2] D. Saunders et. al. Cavity-Enhanced Room-Temperature Broadband Raman Memory PRL 116, 090501 (2016)

[3]. B. Brecht et al.A versatile design for resonant guided-wave parametric down-conversion sources for quantum repeaters,Appl. Phys. B 122: 116 (2016)

[4] B. Brecht et al. Photon Temporal Modes: A Complete Framework for Quantum Information SciencePRX, 5, 041017 (2015).