Highly Uniform and Indistinguishable Scalable Single Photon Source Arrays—Towards Quantum Optical Circuits

Abstract

In the field of quantum information processing, realization of integrated quantum optical circuits towards quantum communication, quantum sensing, quantum cryptography, and quantum computation has been a long-sought goal. The biggest obstacle towards achieving such a goal is the lack of an ordered scalable array of on demand single photon sources (SPSs) having sufficient spectral uniformity, near unity brightness, single photon purity and indistinguishability meeting functional requirement for specific applications. In this talk, I will present our continued study of a unique class of mesa top single quantum dot (MTSQD) in an ordered array[1-3], which is grown using the substrate-encoded size reducing epitaxy (SESRE) approach where surface curvature induced surface stress gradient is exploited as the driving force to have adatoms preferentially migrate from mesa side wall towards pre-patterned nanomesa top. The planarized $ GaAs/In_{0.5}Ga_{0.5}As $ MTSQDs grown in a 5x8 array is shown to have high spectral uniformity with standard deviation σλ~2.8nm, within the local wavelength tunning range to bring different MTSQDs into resonance with each other. The highly spectrally uniform MTSQDs show near unity internal quantum efficiency, high single photon purity >99% $ (g^{(2)}(0)~0.015) $, and high two-photon interference (TPI) visibility of 0.83±0.03 (measured at 11.5K without Purcell enhancement) [4]. The TPI visibility is limited by phonon induced dephasing and can reach ~0.92 at 4K. The TPI visibility can be further improved to approach unity with MTSQDs integrated with appropriate photonic structure to provide Purcell enhancement. The reported TPI visibility is one of the best reported amongst various site-controlled QDs [4]. The MTSQDs also show highly uniform behavior in single photon emission purity and TPI visibility. Statistics on these will be discussed. Further work on establishing MTSQDs uniformity across larger arrays, i.e 10x10 and 50x50 is underway. Such planarized MTSQDs in an ordered array with near unity quantum efficiency, single photon purity, and indistinguishability, provide a highly promising platform towards realizing quantum optical circuits in a horizontal architecture using well established monolithic or hybrid integration approach that enable on-chip multiphoton interference and entanglement towards various quantum information applications. Work on the integration of MTSQDs to light manipulation units using waveguide and 2D photonic crystal approach is underway. The work is supported by the Air Force Office of Scientific Research (FA9550-17-1-0353) and the US Army Research Office (W911NF1910025) [1] J. Zhang et al., Jour. App. Phys. 120, 243103 (2016). [2] J. Zhang, et al., App. Phys. Lett 114, 071102 (2019). [3] J. Zhang, et al., APL photonics 5, 116106 (2020). [4] J. Zhang, et al., arXiv:2108.01428 (2021).