报告题目: Semiconductor sources and superconductor detectors for quantum photonics
报告摘要: In this talk, I will start by discussing experiments in which ultrafast methods are used to prepare and study individual spins in single III-V quantum dot (QD) nanostructures. Results confirm the long held belief that electron spin dynamics are governed by the hyperfine field of the nuclear spin bath and its long-time evolution due to quadrupolar interactions between nuclear spins [1,2]. For electrons, we obtain T2 ~1ns consistent with the findings of other groups, due to the slow dephasing of the electron spin that occurs over microsecond timescales [2-4]. In contrast, for holes, we measure much longer timescales (several hundred ns) due to the weaker hyperfine interaction with the nuclear spin system. Our focus will shift to the on-demand generation of quantum light. Here, we have recently shown that for resonantly excited two-level systems, emission of the photon during the presence of the excitation laser pulse and subsequent re-excitation results in a degradation of the obtainable single-photon purity [4,5]. While this can be exploited to generate photon pairs on demand, we investigate a scheme based on two-photon excitation of the biexciton and demonstrate that it yields superior performance with an ultra-low multi-photon probability [5-7]. We show how coherent quantum state preparation [8] can be combined with coherent triggering of photon emission to suppress unwanted re-excitation processes, that lead to multi-photon errors, while precisely timed stimulation pulses reduce the timing jitter of emitted photons [6]. In this way, we simultaneously obtain 𝑔(0) < 10 and photon indistinguishability exceeding ~90% by coherently triggering single photon emission. Finally, our attention will turn from quantum light sources to superconducting nanowire single-photon detectors (SNSPDs) that nowadays provide near-unity detection quantum efficiency, negligible dark count rates and picosecond timing resolution. We have developed single and multi-pixel SNSPDs and explored how local He-ion irradiation can be used to significantly enhance photon detection efficiency [9]. Such methods provide much perspective for multi-pixel and focal-plane detectors with photon number resolving capabilities.
[1] A. Bechtold et al., Nature Physics (2015). DOI: 10.1038/nphys3470, [2] A. Bechtold et al. Phys. Rev. Lett. 116, 027402 (2016), [3] K. A. Fischer et al. New J. Phys. 18, 113053 (2016), [4] K. A. Fischer et al. Nature Physics doi:10.1038/nphys4052, (2017), [5] L. Hanschke et al. Physical Review Letters 125 (17), 170402, (2020), [6] F. Sbrezny et al. Phys. Rev. Lett. 128, 093603 (2022), [7] E. Schöll et al. Phys. Rev. Lett. 125, 233605 (2020), [8] V. Villafane et al. Phys. Rev. Lett. 130, 083602, (2023), [9] S. Strohauer et al. arXiv:2305.14175, to appear in Adv. Q. Tech (2023)
报告人简介：Prof. Finley studied at the Universities of Manchester and Sheffield in the U.K., completing his Ph.D. in 1997 under the guidance of M. S. Skolnick (FRS) working on the spectroscopy of III-V nanostructures. In 1998 he moved to the Technical University of Munich (TUM) with a fellowship of The Royal Society. At this time, he started to work on the physics of quantum dots and other semiconductor nanostructures. After a brief hiatus at the University of Sheffield (1999-2002), he returned to Munich in 2002 where he was Junior Group leader at the Max Planck Institut for Quantum Optics (2002), before being appointed as a tenured associate (C3) professorship in 2003. Since 2013 he has been a Full Professor at TUM (W3), where he leads the chair for Semiconductor Nanomaterials and Quantum Systems.
主持联系人：许秀来(Tel: 62750683)
科学前沿报告会(619)
