The intrinsic mechanism of absorbing photons in superconductors reveals the interaction between photons and Cooper pairs, which is of great significance for developing new superconducting nanowire single photon detectors (SNSPDs). Here we propose a photon-assisted phase slip model to describe the interaction mechanism between photons and superconductors. In this model, incident photons destroy large quantities of Cooper pairs and reduce the free-energy barrier of the phase slip, resulting in proliferation in the phase slip events and leading to superconducting transition. The switching rates from the superconducting state of a niobium nitride nanowire under various photon irradiation and temperatures are calculated through the distribution of switching currents in the experiment. The experimental data can be well fitted by our deduced expression of phase slip rate after eliminating the influence of external noise.
Integration of photon number resolving superconducting nanowire single-photon detectors (PNR-SNSPDs) with nanophotonic waveguides is a key technology that enables a broad range of quantum technologies on chip-scale platforms. However, all on-chip integrated SNSPDs are fabricated above the waveguide layer, which makes the characteristics of the detector’s photoresponsive film material only depend on the waveguide material, thus lowering the waveguide selectivity. Here, we report an on-chip integrated SNSPD based on optimized topology that the nanowire is sandwiched between the waveguide and the substrate. This device maintains the film characteristics with different waveguides and the light transmitted from the upper waveguide to the substrate is absorbed by the film, which not only increases the selectivity of the waveguide, but also improves light absorption of SNSPD. As an example, SiO2 waveguide with the lower optical transmission loss was fabricated in an integrated PNR-SNSPD. We proposed a multi-channel photon response amplitude superposition multiplexing scheme, which realized photon detection by integrating SNSPD on the optical transmission waveguide in the photonic integrated circuit. The solution not only can effectively read the photon responses of multiple SNSPDs through a readout port, but also can distinguish the number of photons and the corresponding response channels through the amplitude of the readout circuit, thereby realizing a photonic integrated circuit with multiple modes. Finally, we prepared a 4-channel integrated PNR-SNSPD, which resolved the number of photons and corresponding photon response positions through 16 different signal amplitudes. This result is compatible of a wide range of waveguide materials, overcoming the limitation of single photon detector integrated on waveguide for quantum photonic integrated circuit.
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