Photonic Chip with Three Components

Illustration of a photonic circuit in which single photons are emitted, guided and split into two waveguide-arms. The detection is done on-chip via integrated detectors at the end of the two waveguides arms. (Source: M. Schwartz, Univ. Stuttgart)

Quantum computers one day should be able to solve certain computing problems much faster than a classical computer. One of the most promising approaches is based on the utili­zation of single photons to carry and process quantum infor­mation. Scientists of the Univer­sity of Stuttgart and the Karls­ruhe Institute of Tech­nology (KIT) were now able to integrate three necessary main components – single-photon source, beam­splitters and single-photon detectors – on a single chip and operate it on the single-photon level. This experiment demon­strates the func­tionality of the basic components for a scalable system for photon-based quantum infor­mation processes.

In contrast to the wide­spread silicon tech­nology, the experiment was imple­mented on a gallium arsenide (GaAs) platform, allowing the direct inte­gration of nanometer-sized quantum dots (QDs), which can serve as efficient on-demand sources of single photons. In addition, GaAs allows guiding these single photons to optical logic circuits and to special on-chip detectors made of super­conducting nanowires. In the experiment, single photons emitted by an opti­cally pumped quantum dot were guided inside a photonic waveguide and divided by an on-chip beam­splitter into two waveguide-arms, each equipped with a detector.

“One of the challenges so far in this type of fully on-chip experiment was the close proximity of the exci­tation laser to the on-chip detectors”, explains Mario Schwartz. The PhD student from the Institute of Semi­conductor Optics and Functional Inter­faces (IHFG), Univer­sity of Stuttgart, was working over the last years on the reali­zation of a proof-of-principle experiment to show the feasi­bility of combining all main components on one single photonic chip. The project was realized in close colla­boration with the PhD student Ekkehart Schmidt from the KIT, who is an expert for the design and imple­mentation of the on-chip detectors. “The detectors cannot distinguish photons coming from the laser and photons coming from the quantum dot, leading to unde­sirable detection events”, Schmidt further points out.

The scientists were able to signi­ficantly reduce the influence of the laser photons by imple­menting reflecting metal layers on the chip. This idea allowed the veri­fication of the quantum nature of the QD emission by using only the on-chip components. “The suc­cessful experiment is an important step forward and demon­strates the potential of fully inte­grated photonic circuits with all main components being imple­mented on a single chip. We foresee clear possi­bilities of increasing the device complexity in the near future” says Peter Michler, director of the IHFG. (Source: Univ. Stuttgart)

Reference: M. Schwartz et al.: Fully On-Chip Single-Photon Hanbury-Brown and Twiss Experiment on a Monolithic Semiconductor–Superconductor Platform, Nano Lett. 186892 (2018); DOI: 10.1021/acs.nanolett.8b02794

Link: Center for Integrated Quantum Science and Technology, University of Stuttgart, Stuttgart, Germany

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