Several systems are under investigation for their potential use in the fields of quantum information and communication. Semiconductor quantum dots (QDs), also dubbed “artificial atoms”, are one of such systems, as they can be used both as sources and hosts of “quantum bits” and can be easily integrated into compact devices and photonic structures. However, unlike natural atoms, no two QDs are identical in terms of spectral features and optical quality - a major obstacle towards their actual application. After a short overview on the state-of-the-art, I will discuss two methods to obtain QDs via self-assembled growth: (i) the conventional Stranski-Krastanow growth-mode, which is used to obtain strained, high-quality InGaAs QDs with light-emission at wavelengths around 900 nm (see, e.g., [1]), and (ii) an alternative approach relying on self-assembled nanoholes [2-6] and leading to unstrained GaAs QDs with emission in the 700-800 nm spectral range. Recent experiments show that the latter QDs outperform conventional InGaAs QDs as sources of entangled photon pairs and show promising properties also in terms of photon indistinguishability [5,6]. In the second part of the talk I will show how elastic strain produced by novel piezoelectric actuators can be used to overcome problems arising from unavoidable fluctuations during QD growth and to reshape the QD electronic structure and excitonic emission after fabrication. In particular I will illustrate (on the InGaAs/GaAs material system) how any arbitrarily chosen QD can be employed as a wavelength-tunable source of entangled photon pairs, a first step towards the implementation of entanglement swapping with QD photons [7-9]. A discussion on future perspectives will conclude the talk.
[1] X. Ding et al. Phys. Rev. Lett. 116, 020401 (2016) [2] A. Rastelli et al. Phys. Rev. Lett. 92, 166104 (2004) [3] Y. Huo et al. Nature Phys. 10, 46 (2014) [4] H. Huang et al., ACS Photonics (2017), DOI:10.1021/acsphotonics.6b00935 [5] D. Huber et al., Nature Comm. (2017), in press (arXiv:1610.06889v1) [6] M. Reindl et al., arXiv:1701.07812v1 [7] J. Martín-Sánchez et al., Adv. Opt. Mater. 4, 682 (2016) [8] R. Trotta et al., Phys. Rev. Lett. 114, 150502 (2015) [9] R. Trotta et al., Nature Comm. 7, 10375 (2016)