laboratoire pierre aigrain
électronique et photonique quantiques
laboratoire pierre aigrain

Séminaire - 14 Décembre 2009

Alexia AUFFEVES<br class='autobr' />Institut Néel, Grenoble - CNRS
Broadband emitter in a high Q cavity : a new regime for cavity quantum electrodynamics

Cavity Quantum Electrodynamics aims to describe light-matter interaction when light and matter reduce to canonical systems, namely, when light is modeled by a single mode of the electromagnetic field, and matter by a two-level system. Achieving this situation allows to implement fundamental tests of quantum mechanics, and paves the road towards quantum information processing. Historically, first CQED evidences where demonstrated with atoms coupled to microwave and optical cavities. These systems are characterized by a very long radiation lifetime of the uncoupled emitter, which in the spectral domain corresponds to a narrow emitter coupled to a broad cavity. This picture has been the usual paradigm for CQED so far.

CQED experiments can now be conducted with solid-state emitters and cavities. Strong coupling has been reached for for the excitonic transition of quantum dots, nanocrystals coupled to optical semi-conducting cavities, as well as for superconducting qubits coupled to microwave cavities. In these systems, the quality factor of the cavities can be very high. At the same time, solid state emitters are intrinsically coupled to the matrix they are embedded in, thus undergo decoherence that unavoidably broadens any transition between the discrete states of these so-called "artificial atoms". These new conditions open an unexplored regime for CQED so far, where the emitter’s linewidth can be of the same order of magnitude, or even broader than the cavity linewidth. Usual results can be deeply modified, in particular, the emission properties of an emitter-cavity system are strongly affected by the emitter’s linewidth as it has been observed for quantum dots coupled to detuned semi-conducting cavities. Various mechanisms contribute to the broadening of the transitions of solid-state emitters, such as phonon-assisted mechanisms, or spectral diffusion. If spectral diffusion happens on a timescale much shorter than the spontaneous emission timescale (motional narrowing regime), it can safely be modeled by a simple pure dephasing channel in the master equation describing the dynamics of the system. Because of its evident simplicity, the scheme of a two-level system undergoing pure dephasing appears as a generic tool to explore this new field for cavity QED, as well as a nice effective model to describe solid-state emitters.

In this talk we will describe the emission properties of a two-level system undergoing pure dephasing, coupled to a cavity mode, under different excitation schemes, namely, in the spontaneous emission (SE) picture, and in the incoherent pumping regime. We will show that decoherence can be seen as a supplementary degree of freedom with respect to isolated atoms, offering appealing perspectives to achieve advanced nanophotonic devices controlled by decoherence [1]. Moreover, we will evidence that one can define an effective atom-cavity coupling that sheds new light on the dynamics of a solid-state emitter coupled to a cavity. In particular, this coupling allows to define a generalized Purcell factor, taking into account the influence of pure dephasing. Finally we study the influence of pure dephasing on the lasing properties of the device.

[1] A. Auffèves, J.M. Gérard, J.P. Poizat, "Pure dephasing : a resource for advanced solid-state single photon sources", Phys. Rev. A 79, 053838 (2009).