Hybrid Cavity-QED with Rydberg Atoms and Microwave Circuits

Atoms and molecules in highly-excited Rydberg states can exhibit very large electric dipole moments, on the order of 1000 Debye. These large dipole moments make them very well suited to studies of light-matter interactions at microwave frequencies, and long-range dipolar interactions in free-space and close to surfaces. They also make samples in high Rydberg states states very amenable to manipulation and trapping using inhomogeneous electric fields.

The recent development of a new chip-based experimental architecture which exploits these large electric dipole moments to control the translational motion and internal quantum states of Rydberg atoms and molecules close to surfaces has opened up new opportunities in (i) the development of hybrid approaches to quantum information processing in which gas-phase and solid-state systems are combined, (ii) studies of long-range interactions between Rydberg atoms/molecules and surfaces, and (iii) the preparation and study of gas-phase molecular samples at low temperatures. In the work described in this proposal it is planned to exploit, and further develop, this architecture, in a manner which encompasses the first two of these areas, to perform experiments in a setting which can be described as a hybrid between traditional cavity-quantum-electrodynamics (cavity-QED), involving three-dimensional resonators and two-level quantum systems in the gas-phase, and purely solid-state circuit-QED.

To achieve this helium atoms will be prepared in long-lived, circular Rydberg states. These states will then be coupled to microwave fields in the vicinity of chip-based co-planar microwave waveguides to study their coherence times and long-range Rydberg-atom--surface interactions. The off-resonant interaction of these atomic samples with chip-based superconducting microwave resonators will then be exploited for the realisation of new chip-based devices for non-destructive detection of the Rydberg samples.

In the long term it is foreseen to use the gas-phase Rydberg atoms in this hybrid system as long-coherence-time quantum memories which are coupled via the chip-based microwave resonators to superconducting circuits in which fast operations can be performed. In this way, the challenges associated with exploiting each system individually for applications in quantum information processing will be circumvented.

The research described here involves bringing together gas-phase and solid-state quantum systems for fundamental studies of atom/molecule-surface interactions and the development of new chip-based devices for the non-destructive detection of atoms and molecules. This work represent the stepping stones toward the future implementation of hybrid approaches to quantum information processing in which gas-phase atoms are used as long-coherence time quantum memories that are coupled via chip-based microwave resonators to superconducting circuits in which fast operations can be performed. Hybrid approaches, of this kind, to quantum information processing seek to combine two complimentary quantum systems to overcome potential limitations associated with each individual system in terms of their coherence times, scalability, or the rate at which operations can be preformed. From this perspective the research described will contribute to the UK-based development of new quantum technologies. As outlined in the outcome of the 'EPSRC Grand Challenges Survey', in addition to the economic benefit arising from the development of new high-tech industries based upon quantum technologies, there is significant potential for impact in society given the role that electronic devices play in our lives today.

Further impact of this research is associated with the education and training of undergraduate and graduate students, and postdoctoral researchers in the skills necessary to make a significant contribution to, and lead, future developments in the UK (i) in academic research, (ii) in research and development in industry, in particular in the identification and manufacture of new quantum devices, and (iii) in analysis and risk assessment in the financial services sector. With the growing importance of new quantum technologies in society today, the training of personnel with appropriate skills to contribute to and support this area in the UK, in government research laboratories and in the industrial sector, is essential.

The unusual and often surprising properties of quantum systems, of the kind which will be investigated through this grant, form a wonderful platform form which to generate interest among the general public in the physical sciences. To continue the efforts I have made in the past to share the excitement of scientific research with the public, both in Switzerland and in the UK, we plan to participate in several outreach activities throughout the period of this grant. These include lecturing to A-level students at The Science Center at UCL, working with the UCL public engagement unit to take part in outreach programs directed toward school children, and participating in public open days. By doing this it is hoped that we will inspire young students to develop an interest in the physical sciences, and support the government's effort to prioritise the increased uptake in STEM (Science, Technology, Engineering and Mathematics) subjects by young people.