Hybrid semiconductor-superconductor photonic quantum circuits

• Applicants: Professor Dr. Peter Michler; Professor Dr. Michael Siegel
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2015 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 279609524

The aim of this project is the realization of an integrated platform of quantum optical devices for the demonstration of a CNOT functionality on a semiconductor chip. This implies in the proposed case, the realization of single-photon sources, of low-loss single-mode waveguide structures and on-chip cavities combined with superconductor nanowire single-photon detectors (SNSPD). The realization of this architecture was not demonstrated so far and would be a major step towards a miniaturized application in the photonic quantum technologies. It can only be achieved in a detailed understand-ing of the physical principles of the photon detection and generation process in the integrated envi-ronment. The platform consists of GaAs waveguides where InAs quantum dots (QD) were embed-ded as light emitters and NbN nanowires are evanescent coupled to these waveguides.To realize this goal, different intermediate steps have to be performed. Next to the realization of the waveguide, splitter, emitter and detector structures, we have to study the emission coupling into the waveguide in detail. For the targeted functionality, the created photons in different waveguide arms have to be indistinguishable. Therefore, different resonant excitation processes have to be applied in combination with the electrical adjustment of the different QD transition energies to one pre-selected energy via the Stark shift. Combinations of waveguide couplers with different splitting rati-os determine the photonic integrated circuit. Waveguide beam splitters adjusted to the single photon wavelength are the core of the circuit and will as well be used to prove the indistinguishability of the photons of the two different InAs QDs by two-photon interference measurements. Parallel to the examination of the emitter, the detector implementation will be studied. The super-conducting nanowires have to be optimized to allow a close to 100% detection efficiency of the sin-gle photons at 920 nm wavelength of QD emission on GaAs wafers. Thus, all the key parameters of nanowire such as coupling efficiency, absorption, intrinsic detection efficiency, as well as timing jitter have to be determined and analyzed in detail in dependence of different detector configura-tions for their optimization. Additionally, the SNSPDs and the readout electronics have to be devel-oped to allow photon number resolving detection in integrated systems. Finally, all components have to be implemented in one chip including filter elements for suppression of the resonant QD excitation and the quantum optical functionality will be demonstrated. These challenging goals can only be realized by the present cooperation of the leading groups in the fabri-cation and characterization of these kinds of high quality single-photon detectors, semiconductor material and single-photon sources.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Michael Jetter