Strong Light-Matter Coupling

The following sections are included:

• Preface
• Contents

The following sections are included:

• Foreword
• Introduction
• A spin and a spring
• Ideal QND measurement of the photon number: The quantum jumps of light
• Monitoring the decoherence of mesoscopic quantum superpositions
• An experiment on quantum feedback
• Reservoir engineering
• Conclusion and perspectives
• References

In these lecture notes I shall review excitons and polaritons in bulk semiconductors and in systems with electron and photon confinement. Emphasis will be on a proper definition of exciton-photon coupling, on the effects of reduced electron and photon dimensionality, and on the conditions for the occurrence of the strong-coupling regime of radiation-matter interaction. In addition to bulk semiconductors, I shall treat exciton-photon interaction in two-dimensional systems like quantum well excitons in planar microcavities and in waveguide-embedded photonic crystals. I shall also consider quantum dots in three-dimensional cavities, comparing the strong-coupling regime in zero dimensions with exciton-polariton physics in higher dimensions.

Superconducting qubits are electrical circuits that behave as artificial two-level systems when cooled at low temperatures; they have allowed the implementation of basic quantum information protocols with up to three entangled qubits. Modern ways of manipulating and reading out these qubits all involve strongly coupling them to superconducting resonators, giving rise to the field of circuit quantum electrodynamics (circuit QED).

An overview of the theory of Markov quantum open systems as commonly met in quantum optics is presented. Following a review of background material, the quantum trajectory formalism is developed from a consideration of photoelectron counting for output fields.

In the last 25 years a new understanding has evolved of the role of information in quantum mechanics. At the same time there has been tremendous progress in atomic/optical physics and condensed matter physics, and particularly at the interface between these two formerly distinct fields, in developing experimental systems whose quantum states are long-lived and which can be engineered to perform quantum information processing tasks. These lecture notes will present a brief introduction to the basic theoretical concepts behind this ‘second quantum revolution.’ These notes will also provide an introduction to ‘circuit QED.’ In addition to being a novel test bed for non-linear quantum optics of microwave electrical circuits which use superconducting qubits as artificial atoms, circuit QED offers an architecture for constructing quantum information processors.

Polaritons are mixed light-matter particles arising from the strong coupling between excitons and photons confined in a two-dimensional semiconductor microcavity. Their bosonic nature along with the possibility to directly manipulate them in a semiconductor chip makes them an excellent workbench to study non-linear properties of interacting degenerate bosons in a dissipative system. In this chapter we review the basic properties of semiconductor microcavities in the strong coupling regime including the methods used to achieve polariton condensation and to observe quantum fluid effects. We then describe how the engineering of the planar cavity using different technological approaches allows confining polaritons in low dimensional structures with a large variety of geometries. We illustrate the fascinating physics that arise from these low dimensional microstructures choosing a few examples: periodically modulated wires, coupled micropillars and polariton lattices. Cavity polaritons thus appear as a versatile platform to implement non-linear Hamiltonians and to study non-linear topological excitations.

Robust techniques to achieve and manipulate strong coupling between individual quantum emitters and single photons are a critical resource for quantum information processing and single-photon nonlinear optics. Despite remarkable theoretical and experimental progress, however, such techniques remain elusive. Here, we describe a novel approach of “quantum plasmonics” that has been introduced in recent years, in which quantum emitters interact strongly with the large fields of tightly confined, nanoscale surface plasmons. We present an overview of the underlying theoretical concepts of plasmonics and of strong coupling, describe examples of how plasmonic systems can be used for quantum information processing protocols, and provide an outlook for the field.

The excitonic polariton concept was introduced already in 1958 by J.J. Hopfield. Although its description was based on a full quantum theory including light quantization, the investigation of the optical properties of excitons developed mainly independently of quantum optics. In this chapter we shall review exciton polariton quantum optical effects by means of some recent works and results appeared in the literatures on both bulk semiconductors and in cavity embedded quantum wells…

Owing to the very strong confinement of the optical field, nonlinear effects in photonic crystal cavities and waveguides are enhanced drastically. All optical processing, relying on these effects, is now feasible in integrated photonic devices, meeting specifications in terms of power consumption, speed and size for applications in signal processing.