Single Photon : Manipulation

People :

Experiment : Gilles Nogues, Jean-Philippe Poizat, Signe Seidelin, PhD Student : Inah Yeo ; Technical staff : Edouard Wagner

Theory : Alexia Auffèves ; Post-doc : Stefano Portolan, PhD students, Igor Diniz, Daniel Valente.

Principle

We aim at realizing a CNOT gate between single photons, which is a necessary step towards the implementation of a photonic computer. The table truth of such a gate is the following :

The first bit is the control bit, the second bit the target bit. If the control bit is 0, the target bit remains the same, if the control bit is 1, the target bit is inverted. If 0 and 1 represent the number of photons in a given mode of the electromagnetic field, such a gate can be realized by using a giant optical non-linear medium, sensitive at the single photon level.

A two-level atom in a symmetric Fabry-Perot cavity (ie made of two identical mirrors) whose radiation diagram is directional provides a giant Kerr medium, the non-linearity being due to the saturation of the emitter by a single photon. We have theoretically studied the optical response of this medium when it is probed by a tunable laser field with controllable intensity (see figure 2 et ref.[1]).

At resonance and if the cavity is empty, the transmission is 1. The presence of an emitter in the cavity induces the total reflexion of the probe laser field if the probe is weak (fig. 2a). If the probe is strong, the emitter cannot block the light and one recovers the transmission of an empty cavity. The transmission of the medium depends thus on the power of the probe laser, the switch happening at a typical power of 1 photon per lifetime of the emitter, which corresponds to a giant non-linear effect (fig. 2b).

Implementation

We plan to use solid-state atoms and cavities, namely semiconductor quantum dots and micropillars. A micropillar is a microscopic Fabry-Perot cavity, the directivity of the emitted light being ensured by the geometry of the cavity (fig. 3). We envisage to realize such logical gates using photonic crystal cavities designed at the Institut des Nanotechnologies de Lyon, and waveguides from CEA/INAC in Grenoble. In the long term, these efforts hold the promise to realize integrated photonic circuits of increasing complexity.

Purcell factor measurements

We have studied in detail the Purcell factor measurement, which is an important factor of merit of cavity cavity quantum electrodynamics, in the case of a quantum dot embedded in a pillar microcavity [2]. In addition to the standard direct lifetime measurement, we have developed method that can be implemented with continuous wave lasers. The main advantage of this technique is that it does not rely on the timing resolution of the experimental set-up.

PhD thesis Mathieu Munsch : “Étude du régime de Purcell pour une boîte quantique unique dans une microcavité semiconductrice. Vers une non-linéarité optique géante. “,

References

[1] A.Auffèves-Garnier, C.Simon, J.M.Gérard and J.P.Poizat, “Giant optical nonlinearity induced by a single two-level system interacting with a cavity in the Purcell regime”, Phys. Rev. A 75, 053823 (2007).

[2] M. Munsch, A. Mosset, A. Auffèves, S. Seidelin, and J. P. Poizat, J.M. Gérard, A. Lemaître, I. Sagnes, and P. Senellart, “Continuous-wave versus time-resolved measurements of Purcell factors for quantum dots in semiconductor microcavities”, Phys. Rev B 80, 115312 (2009)

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