Since the project 3-5-FIRST was initiated in March 2016, we have been working hard to implement the prime objectives and work was performed in both involved disciplines, atomic physics and semiconductor physics.
On the atomic physics side, we have demonstrated a quantum memory in warm Rb vapor with on-demand storage and retrieval, based on electromagnetically induced transparency, and with an acceptance bandwidth of δf = 0.66 GHz. This memory is suitable for single photons emitted by semiconductor quantum dots. In this regime, vapor cell memories offer an excellent compromise between storage efficiency, storage time, noise level, and experimental complexity.
On the semiconductor physics side we have demonstrated a fast, bandwidth-tunable single-photon source based on an epitaxial GaAs quantum dot. Exploiting spontaneous spin-flip Raman transitions, single photons at Rb compatible wavelengths are generated on-demand and with tailored spectral and temporal profiles. This allowed the generation of quantum dot photons with linewidths as low as 0.2 GHz, narrow compared to the 1.1 GHz natural of the quantum dot and well within the acceptance bandwidth of the atomic quantum memory. These experiments are crucial step towards the development of an optimized hybrid semiconductor-atom interface as needed for high-speed quantum networks.
Despite these efforts and successes, the brightness of the developed single photon source is still too small to be combined with the developed atomic quantum memory at its present level of performance. Until brighter quantum dot sources are available, the memory can be tested with single photons generated by an alternative single photon source, namely a source based on cavity-enhanced spontaneous parametric down conversion (SPDC). During a secondment of the ER to Humboldt-Universität Berlin first steps towards the construction of such a source were carried out and first results are expected soon. In parallel, efforts are ongoing to improve the performance of the atomic quantum memory.
Results dissemination
The work on the “simple atomic quantum memory suitable for semiconductor quantum dot single photons” was published in Physical Review Letters 19, 060502 (2017) and discussed by an article in the Basel University News (Uni News) in 9/2017.
The work on the “on-demand semiconductor source of 780 nm single photons with controlled temporal wave packets” has been accepted for publication in Physical Review B and is available as preprint arXiv:1710.02490.
The results were presented at several international conferences and workshops, most prominent are:
1. Presentation – J. Wolters, “Cold atom-semiconductor hybrid quantum system,” Spring meeting of the German physical society, Hannover, February/March 2016.
2. Presentation ¬– J. Wolters, “Towards an atom-semiconductor quantum interface,” SPS Annual Meeting, Lugano, August 2016
3. Presentation – J. Wolters, “Towards an atom-semiconductor quantum interface,” International Conference on Quantum Communication, Measurement and Computing (QCMC), Singapore, July 2016.
4. Presentation – J. Wolters, “Towards an atom-semiconductor quantum interface,” Single Photons Single Spins (SPSS) Meeting, Oxford, September 2016.
5. Presentation – J. Wolters, “Generation of single photons with tailored waveforms using a quantum dot emitting near the Rb D2 line,” Spring meeting of the German physical society, Mainz, March 2017.
6. Presentation – J. Wolters, “An atomic memory suitable for semiconductor quantum dot single photons,” Spring meeting of the German physical society, Mainz, March 2017.
7. Presentation – J. Wolters, “An atomic memory suitable for semiconductor quantum dot single photons,” Spring meeting of the German physical society, Dresden, March 2017.
8. Presentation – J. Wolters, “An atomic memory suitable for semiconductor quantum dot single photons,” CLEO Europe, Munich, June 2017.
9. Presentation – J. Wolters, “Towards storage of quantum dot single photons in a rubidium quantum memory for quantum networks,” Single Photons Single Spins (SPSS) Meeting, Troyes, August/September 2017.
