Quantum communication and computation are emerging fields with the potential to launch new technologies to control, propagate and process information. Amongst candidate systems for transporting quantum information, photons are the most promising as they can both maintain coherence over long distances, and interact strongly with electrons to generate nonlinear effects and allow transfer of information between subsystems. As a result, use of photons as ‘qubits’ has led to ground-breaking demonstrations of quantum entanglement, quantum teleportation and quantum cryptography. However in many of the devices being developed for use in quantum photonics, particularly solid-state devices such as single photon sources, decoherence suffered by the participating electrons is a key limiting factor, reducing the interaction strength and randomizing the quantum state of the photons. In order to minimise the effect of electron decoherence, such devices must generally be operated under cryogenic conditions; even then, in many cases, other noise mechanisms are revealed which limit device functionality. As a result of these practical obstacles and performance limitations, single photon sources have yet to find widespread use and photonic quantum information is largely confined to laboratory demonstrators.
The WASPS project seeks to overcome these major bottlenecks in the technology by taking a revolutionary approach. Namely, we plan to exploit the potential of cavity quantum electrodynamics in the bad emitter limit where decoherence is mostly due to the artificial atom. In this limit, preliminary results show that cavity filtering properties and the Purcell effect can be used to engineer the electron-photon interaction, thereby turning electron decoherence into an advantage rather than an obstacle. We will use this strategy to develop a new generation of single photon source devices based on colour centres in diamond placed in optical microcavities. Devices targeted will be a high speed single photon source, an indistinguishable single photon source, and a spin-photon interface. Emphasis will be on practically useful devices with features such as wavelength tunability, room temperature operation, and robust, highly portable assembly. The team comprises six leading European groups in the fields of diamond photonics, solid state cavity quantum electrodynamics and quantum information processing. Within this three year research project we aim to develop and field-test the devices, to bring a valuable new capability to the growing quantum information community.
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