EXPLORING NONLINEAR QUANTUM DYNAMICS WITH SUPERCONDUCTING CIRCUITS
Lead Research Organisation:
University of Nottingham
Department Name: Sch of Physics & Astronomy
Abstract
Circuit quantum electrodynamics (QED) devices typically consist of 'artificial atoms' containing Josephson junctions (JJ) coupled to modes of the electromagnetic field confined within a microwave cavity. Such systems facilitate strong interactions between the microwave electromagnetic field and the artificial atoms, whilst at the same time suppressing decoherence. Circuit QED has already proved an extremely fruitful tool for exploring quantum physics, opening up exciting new avenues of research in areas as diverse as many-body quantum physics, ultra-strong light-matter coupling the production of highly non-classical states and quantum vacuum fluctuations. This project aims to develop theoretical models for a new class of circuit-QED devices in which a JJ is embedded within a microwave cavity and a dc bias voltage applied rather than ac control fields, leading to the flow of a current of charges through the device. Such systems bring together two important subfields of physics: the quantum transport of charge (i.e. Cooper pairs) and the quantum optics of photons in the microwave cavity. Furthermore, the interactions between charges and photons are highly nonlinear and can be made exceptionally strong. The project will explore the fascinating physics of such systems and their connections with other driven-dissipative quantum systems.
Organisations
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| EP/N50970X/1 | 01/10/2016 | 30/09/2021 | |||
| 1940674 | Studentship | EP/N50970X/1 | 01/10/2017 | 23/06/2021 | William Morley |
| Description | We chose to study the specific case of superharmonic resonance in a Josephson junction (JJ) cavity system. In this case two cooper pairs must tunnel to create a single photon in the cavity which had never been studied in any detail before. This proved difficult as the normal approximation to make the system time independent, known as the Rotating Wave Approximation (RWA), was found to fail in this regime. To combat this we used an extension of the approximation, the second order RWA, which proved effective. As far as we are aware this is the first time anyone has use this method on these classes of systems. We found that the superharmonic resonance displayed a rich variety of behaviours. At very weak driving we observed a crossover of dynamical behaviour from a response at the drive frequency to that of the natural frequency, indicating a change in the dominate tunnelling behaviour. This was describable only with a semi-classical description and not with the second order RWA. In the strong drive regime we observed strong photon anti bunching, the photon emission was no longer thermal, indicating that the system had entered a squeezed quantum state. To further explore this we the link between the coupling strength between the JJ and the cavity and how it affected this photon anti bunching. We observed, both analytically and numerically, a position where the system should have perfect photon anti bunching, or very close. This is not uncommon in these types of systems, however, in the linked JJ-cavity system this is the lowest value of the coupling it has ever been predicted at and is very close to experimentally realisable values. |
| Exploitation Route | The fact that this particular system predicts very strong ant bunching at a value of the coupling that is very close to the already experimentally realisable values lends itself to much further research. This system would lend its self to groups that are already interested in the production of anti-bunched photons as a very simple to fabricate on chip source of these. This effect could also be used as a Control for charge transport across the junction in a similar manor. |
| Sectors | Digital/Communication/Information Technologies (including Software) |