Fibre-integrated ORCA quantum memory

Photonic quantum networks would enable quantum computing, guaranteed-secure communications and enhanced sensing capabilities, running at high bandwidths in ambient conditions

To exploit the full potential of photonic networks, the capability to switch and re-time optical signals is required. But this has proved challenging for quantum signals, since amplification adds noise at the quantum level, and so passive losses must be carefully eliminated. Conventional photonic switching and storage solutions based on electro-optical phase modulation and bulk non-linearities are too lossy or not suitable for operation at the level of individual light quanta.

A promising route to fast, low-loss, quantum-compatible fibre-integrated switching devices is the incorporation of atomic vapour into hollow fibres. This is the focus of the proposed PhD project.

In recent work at Oxford, GHz bandwidth photons were stored in, and retrieved from, a warm alkali vapour, via off-resonant cascaded absorption (ORCA) [Kaczmarek et al. Phys. Rev. A 97.4 042316 (2018)]. The same protocol has since been implemented at the Weizmann Institute [Finkelstein et al. Science advances 4.1 eaap8598 (2018)] and at the University of Adelaide [Perella et al. unpublished communication (2018)]. In parallel work at Bath, in partnership with NQIT and TMD Ltd., we have explored the use of hollow-fibre vapour cells for magnetometry and atomic clocks. In this project, the student will further develop this initial work, with the aim of splicing fibre vapour cells directly into single-mode fibres, and demonstrating fibre-integrated light storage via ORCA at the quantum level.

The work will proceed in close collaboration with the group of Dr. Pete Mosley (CPPM director) and forms part of the UK Quantum Technology Programme, under the aegis of the Phase II Hub in Quantum Simulation and Quantum Computation, in which Bath Physics is participating.

On the specifics of the project: the first task will be to build a pulsed laser system to enable storage and retrieval in Rb vapour via the ORCA protocol. Next, a vacuum system to load Rb into hollow fibre will be built. We will then look at splicing our hollow fibres to single-mode fibre, using an intermediate mode conversion fibre to match the core diameters. Finally we will investigate performing the splice after Rb loading, under helium overpressure, so that Rb is sealed into the hollow fibre. The ultimate aim of the project, time permitting, is to demonstrate the storage and retrieval of pulses inside a fibre-integrated memory.