On-chip microlaser driven sources of indistinguishable photons for quantum networks
In many of our projects we have investigated Bragg-reflection waveguides as a probable candidate for such a source. The large effective optical nonlinearity of AlGaAs semiconductor devices allows for bright emission of photon pairs at a wavelength around 1550nm via parametric down-conversion. This process, however, has a large disadvantage in its probabilistic nature. As such, it can never be a true on-demand single photon source. While this can be overcome by heralding of one of the photons of a pair and clever algorithms, the overall device efficiency will still suffer.
In contrast, quantum dots act as artificial atoms within a semiconductor structure. Hence, their emission consists of single photons (aside from loss and background mechanisms). Furthermore, by incorporating a micro-laser on the same device as the quantum dots, it is possible to tune and excite them electrically. However, typically quantum dots in this material platform emit photons at a wavelength around 800-900nm, which is not compatible with the current telecommunication standard. A lot of effort is being put into tuning their emission wavelength via strain or electricity, which typically decreases the quality of the emitted photons.
Funding
The Austrian Science Fund funds our D-A-CH project "On-chip microlaser driven sources of indistinguishable photons for quantum networks" (I-5061, together with Tobias Huber, University of Würzburg and Stephan Reizenstein, University of Berlin)