Fully On-Chip Single-Photon Hanbury-Brown and Twiss Experiment on a Monolithic Semiconductor–Superconductor Platform

Abstract

Photonic quantum technologies such as quantum cryptography [1], photonic quantum metrology [2][3][4], photonic quantum simulators and computers [5][6][7] will largely benefit from highly scalable and small footprint quantum photonic circuits. To perform fully on-chip quantum photonic operations, three basic building blocks are required: single-photon sources, photonic circuits and single-photon detectors [8].Highly integrated quantum photonic chips on silicon and related platforms have been demonstrated incorporating only one [9] or two [10] of these basic building blocks.Previous implementations of all three components were mainly limited by laser stray light, making temporal filtering necessary [11] or required complex manipulation to transfer all components onto one chip [12]. So far, a monolithic, simultaneous implementation of all elements demonstrating single-photon operation remains elusive.Here, we present a fully-integrated Hanbury-Brown and Twiss setup on a micron-sized footprint, consisting of a GaAs waveguide embedding quantum dots as single-photon sources, a waveguide beamsplitter and two superconducting nanowire single-photon detectors. This enables a second-order correlation measurement at the single-photon level under both continuous-wave and pulsed resonant excitation.Up to now, most quantum waveguide (WG) circuits have been fabricated from glass-based and Si-based materials. Both material platforms do not allow monolithic integration of deterministic single-photon sources. The used InGaAs/GaAs material system benefits from the capability of directly integrating on-demand non-classical light sources, namely semiconductor quantum dots (QDs) [13]. These emitters reach state-of-the-art performances in terms of single and indistinguishable photon emission, typically via a resonant excitation scheme [14]. Within this platform, single-photon emission in combination with single-mode WGs and beamsplitters (BSs) was demonstrated with and without resonant excitation [15][16][17][18][19][20]. Moreover, the implementation of superconducting nanowire single-photon detectors (SNSPDs) was successfully demonstrated on this material system [11,21,22]. These detectors represent the most suitable choice for working at the single photon level due to their potential near-unity detection efficiency (93 % [23]), low dark count rate and very high time resolution with intrinsic timing jitters in the ps range [24,25].On the other hand, for silicon and silicon-related quantum photonic platforms a high degree of device complexity was reached, but efficient on-demand non-classical light sources are still missing [10]. By using parametric down conversion sources, only probabilistic singlephoton emission is possible and the amount of stray light coming from the intense pump laser prevented so far the implementation of single-photon detectors on the same chip.Electrically-driven sources may solve this issue [12,26], but the used non-resonant excitation scheme typically leads to the emission of photons with a limited degree of i...

Advanced Technologies for Quantum Photonic Devices Based on Epitaxial Quantum Dots

“…; The work by Schwartz et al. provides an outstanding example, where single‐photon detectors are monolithically integrated, such an approach imposes a challenging trade‐off between the achievable on‐chip light‐matter interaction and photonic losses . The former factor regards the ability to couple quantum dot emission into manageable optical modes (e.g., a single on‐chip waveguide or cavity mode), and can be substantially enhanced in carefully designed III–V semiconductor geometries; the latter regards the ability to transport and interfere emitted photons on‐chip with minimum photon losses (e.g., in a large interferometric network that implements a unitary transformation), and is in general difficult to be minimized in etched III–V geometries.…”

Characterization of a Photon-Number Resolving SNSPD Using Poissonian and Sub-Poissonian Light

“…Integrated quantum photonic circuits are the next natural step to increase the complexity and ease of use of quantum photonic circuits [6]. The realization of a fully integrated Hanbury Brown and Twiss (HBT) [7] experiment on the single-photon level has recently been demonstrated on GaAs [8] as logic photonic building block. This allows the investigation of the brightness and the normalized 2nd order correlation (two-photon correlation) of the integrated singlephoton source [9] by the use of a 50/50 beam splitter in combination with two single-photon detectors.…”

“…The detector is illuminated from the top by external photon sources. Top illumination allows for a well controlled, spatial homogeneous, photon flux on the detector area in contrast to waveguide coupling [21] and also the use of a resonantly excited QD single-photon source without introducing stray light [8]. This ensures an accurate characterization of the optical properties of the detector.…”

“…For optical characterization the device was mounted inside a helium flow cryostat and kept at a temperature about 4 K. The detector was excited from the top by photons passing through an optical window of the cryostat. The exciting photons at a wavelength λ = 900 nm(these photons are of energy typical for emission of resonantly excited In(Ga)As/GaAs quantum dots[8],[23]-[25]) were selected from radiation of a thermal halogen light source using a monochromator with a spectral resolution of 10 nm. The bias current dependence of count rate (a) Count-rate dependence on the counter threshold voltage for different mean numbers of photons per pulse µ.…”

Silicon photonic add-drop filter for quantum emitters

“…For example, several works have demonstrated the integration of solid-state quantum emitters with SiO2 [9], SiN [10][11][12][13][14], and Si photonic chips [15,16]. Moreover, recent advances in developing on-chip single-photon detectors [17][18][19] have paved the way for quantum photonic circuits that are fully chip-integrated (i.e., the photons do not leave the chip from generation to detection).…”