Advanced quantum optical devices based on photonic wires – WIFO

Coupling a single light emitter to a single spatial mode of a propagating electromagnetic field is a key requirement to produce quantum state of light with high efficiency and to implement giant nonlinearities at the single photon level. This system is known as "one-dimensional atom", and is usually realized using resonant photonic structures such as micropillar or photonic crystal microcavities. This approach particularizes one single frequency. The present project deals with a quantum dot embedded in a photonic wire. This device is frequency independent, allowing the efficient coupling of the emitter with two frequency separated optical modes. This paves the road toward the production of entangled photon pairs, as well as the implementation of giant two-mode nonlinearity for quantum logical gates.

A photonic wire containing a semi-conducting quantum dot has been used recently by one of the partners to realize the most efficient single photon source so far. More than 90% of the photons were emitted within the guided mode and 72% collected within 0.75 numerical aperture optics, providing a promising realization of a one-dimensional atom. A noteworthy property of these photonic wires is that this performance is maintained over a broadband of 70 nm around the central wavelength of 950 nm. As a consequence, any emitting transitions within this range will benefit from this quasi one-dimensional photonic extraction. For example, both excitonic and biexcitonic lines can be efficiently addressed and collected.

The project builds on this record efficiency combined with broadband operation of a photonic wire containing self-assembled InAs/GaAs quantum dots. One of the two goals of this project is to realize a very efficient source of polarization entangled photons. Indeed since both excitonic and biexcitonic lines can be extracted efficiently, an entangled pair production efficiency of at least 0.72*0.72=0.52 is expected, more than four times the present state of the art. The other main goal is to take advantage of the possibility of addressing two different transitions of the quantum dot. First, we will prepare the quantum dot in a population inverted state and investigate the stimulated emission at the single photon level of this individual object. Second, we will use this device to probe two-mode giant non-linearity at the single photon level which will provide a new type of single photon transistor, wherein the property of a single control photon can change the transmission of a signal photon.