Quantum dot single-photon sources with ultra-low multi-photon probability

Abstract

High-quality sources of single photons are of paramount importance for quantum communication, sensing and metrology. To these ends, resonantly excited two-level systems based on self-assembled quantum dots have recently generated widespread interest. Nevertheless, we have recently shown that for resonantly excited two-level systems, emission of a photon during the presence of the excitation laser pulse and subsequent re-excitation results in a degradation of the obtainable single-photon purity. Here, we demonstrate that generating single photons from self-assembled quantum dots with a scheme based on two-photon excitation of the biexciton strongly suppresses the re-excitation. Specifically, the pulse-length dependence of the multi-photon error rate reveals a quadratic dependence in contrast to the linear dependence of resonantly excited two-level systems, improving the obtainable multi-photon error rate by several orders of magnitude for short pulses. We support our experiments with a new theoretical framework and simulation methodology to understand fewphoton sources.

Effective second-order correlation function and single-photon detection

“…The notion of very low multi-photon projection from low g (2) -measurements has been an important aspect of research, see e.g. [28,29]. At this point, it is worth comparing with the results from [26].…”

Generation of Non‐Classical Light Using Semiconductor Quantum Dots

“…d) Level scheme with optical transitions of an uncharged QD with (left) and without (right) symmetry. (b) Adapted under a Creative Commons Attribution 4.0 international license . Copyright 2018, The Author, Published by Springer Nature.…”

“…[], (c) adapted from ref. [] under the terms of a Creative Commons Attribution license. Copyright 2016, 2018, The Author(s); Published by IOP Publishing Ltd on behalf of Deutsche Physikalische Gesellschaft, and Springer Nature, respectively.…”

“…Recently, another scheme was used to demonstrate very pure single photon generation with values . In this scheme (Figure 4d), a two‐photon excitation process coherently prepares the system in the 2 X state .…”

“…Single photons can then be obtained by frequency filtering either on the X or 2 X transition. Since re‐excitation is only possible after the radiative cascade has returned the system to the ground state it is largely suppressed . The dependence of g (2) [0] on the pulse length is presented in Figure 5c for a resonantly driven two‐level system (black) and two‐photon excitation of a three‐level system (red) for exciting with square pulses.…”