A quantum electrodynamical matter field theory for quantum nanoplasmonics

• Applicant: Dr. Fouad Ballout
• Subject Area: Theoretical Condensed Matter Physics
• Term: from 2014 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 253375095

One of the main purposes of quantum nanoplasmonics is the creation of a nanophotonic, chip-integrated quantum circuit which enables an electro-optical or even all-optical control of quantum information at the single quantum level. There are already some rudimentary systems that are designed for simple quantum optical applications. They are composites of a two-state quantum optical system (qubit) and a metallic nanowire or nanoparticle. By means of the so called surface plasmon-polariton (SPP), which couples the photon emitted by the qubit with the collective electronic excitations at the metal surface, these systems feature an unprecedented level of bandwidth and compactness. Even though they don't represent a quantum computing network, they give a good impression of the challenge one has to take on the way there, which is the storage and maintenance of quantum coherence and quantum correlations over relatively long spatial and temporal distances in the presence of internal and dissipative losses. A promising strategy is to increase the coupling strength to the point where a coherent, reversible flow of information between the system and the environment occurs allowing a persistent transmission of quantum signals. In devising the details of such a strategy we cannot draw on the current quantum plasmonic theories as they are content with a phenomenological treatment of the material response of the plasmonic system and they make use of approximations, which limits their scope to the weak coupling case.The new contribution of the proposed research is the formulation of a quantum theory of plasmodynamics which takes account of the many-body nature of the plasmonic environment and to exactly depict the interaction between the qubit and the plasmonic environment in order to cope with internal losses and strong couplings, respectively. In the course of deriving such a quantum field theory I will arrive at a quantum propagator for the SPP field which interrelates the participating quantum fields and the surface topology of the metallic host sustaining the SPP. The presence of the plasmonic environment modifies the photonic density of states available to the qubit for spontaneous emission. This change in the mode density, which affects the strength of the coupling between the qubit and the plasmonic environment is controlled by the geometric configuration of this environment. I will embed the SPP quantum propagator into a nonperturbative master equation of qubit-SPP coupling to identify the exact geometrical settings under which strong coupling can be enforced. In conclusion, I will extend the nonperturbative single-qubit master equation to the two-qubit case to see what kinds of non-classical qubit-qubit correlations the two-qubit state exhibits and over which space-temporal scale they can be sustained in the case of strong system-environment coupling.

• DFG Programme: Research Fellowships
• International Connection: United Kingdom
• Host: Professor Dr. Ortwin Hess