Waveguide-QED with Rydberg atoms

The interaction of matter and light confined within cavities (cavity QED), has a long and fruitful history achieving a number of high precision tests of quantum theory and more recently a platform for the manipulation of quantum information. In recent times a related area of research, waveguide QED, has attracted significant attention. Waveguide-QED is centred around the coupling of atoms (real or artificial) to a continuum of electromagnetic modes constrained to prop- agate in a single dimension. Moving from cavities to a 1D continuum presents opportunities which may be exploited for quantum information processing. The atoms can have a significant effect on photon transport properties through the waveguide. This has lead to potential uses in photon routing and the generation of non-classical light e.g bunching and anti bunching. The waveguide may also act to mediate long range interactions between atoms. Due to the spontaneous emission being confined to a single dimension the interaction strength does not decay with distance as is the case for atoms in free space. By placing atoms at positions of identical electric field within the mode the atoms can col- lectively interact with the continuum as if they were a single entity, a situation described by the Dicke Hamiltonian. This leads to super/sub-radiance, where spontaneous emission is strongly enhanced or suppressed respectively. Sub- radiant states in particular are of interest for quantum information processing. Their highly suppressed interaction with the waveguide is due to interference effects forbidding them to decay. The sub-radiant states form a decoherence-free subspace (DFS), a partition of the total atomic Hamiltonian which is decoupled from the environment. In this project high-n Rydberg states in helium will be used to explore waveguide-QED phenomenon. Rydberg atoms are ideally suited to this task due to their exaggerated properties, such as large transition dipole moments and, particularly in circular states, extended lifetimes. The wide range of transition frequencies makes them a flexible technology capable of coupling to a wide range of other quantum computing systems which operate in the GHz region, in particular super-conducting qubits. Initial studies will be performed in 3D waveguide structures before transitioning to co-planar waveg- uides. Realising waveguide-QED phenomena in co-planar waveguide structures would represent a large step towards hybrid quantum computing schemes with Rydberg atoms.

Quantum technologies promise a transformation of the fields of measurement, communication and information processing. They present a particular opportunity since they are disruptive technologies: not only do they offer a chance for rapid growth but they also allow lesser participants in a field (such as the UK in IT) to become major players through appropriate risk-taking and manpower development. Students graduating from the InQuBATE Skills Hub will have the right mindset to work in the industries where quantum technologies will be applied, and help to break down the traditional barriers between those sectors to make this transformation happen. They will have all the necessary technical and transferable skills, plus a network of contacts with our partners, their fellow cohort members and the academic supervisors.

Our commercial partners are keen to help our students realise their potential and achieve the impact we expect of them, through the training they offer and their contributions to the centre's research. They include companies who have already developed quantum technologies to products in quantum communication (Toshiba) and optimization (D-Wave), large corporates who are investing in quantum technology because they see its potential to transform their businesses in aerospace, defence, instrumentation and internet services (Lockheed Martin, Google,) and government agencies with key national responsibilities (NPL). We want to see the best communication of our students' research, so our students will benefit from the existing training programme set up with a leading scientific publisher (Nature Publishing Group); we also want to see more of the future companies that lead this field based the UK, so we have partnered with venture capital group DFJ Esprit to judge and mentor the acceleration of our students' innovations toward the market.