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Experimental investigation of the detection mechanism in WSi nanowire superconducting single photon detectors

Gaudio, R., Renema, J.J., Zhou, Z., Verma, V.B., Lita, A.E., Shainline, J., Stevens, M.J., Mirin, R.P., Sae Woo Nam, Martin P. van Exter, Dood, M.J.A. de, Fiore, A.

Published Jan 1, 2016• 17 citations
OpenAlex

Abstract

We use quantum detector tomography to investigate the detection mechanism in WSi nanowire superconducting single photon detectors (SSPDs). To this purpose, we fabricated a 250nm wide and 250nm long WSi nanowire and measured its response to impinging photons with wavelengths ranging from $\lambda$ = 900 nm to $\lambda$ = 1650 nm. Tomographic measurements show that the detector response depends on the total excitation energy only. Moreover, for energies Et > 0.8eV the current energy relation is linear, similar to what was observed in NbN nanowires, whereas the current-energy relation deviates from linear behaviour for total energies below 0.8eV.

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We use quantum detector tomography to investigate the detection mechanism in WSi nanowire superconducting single photon detectors (SSPDs). To this purpose, we fabricated a 250nm wide and 250nm long WSi nanowire and measured its response to impinging photons with wavelengths ranging from λ\lambdaλ = 900 nm to λ\lambdaλ = 1650 nm. Tomographic measurements show that the detector response depends on the total excitation energy only. Moreover, for energies Et > 0.8eV the current energy relation is linear, similar to what was observed in NbN nanowires, whereas the current-energy relation deviates from linear behaviour for total energies below 0.8eV.
We use quantum detector tomography to investigate the detection mechanism in WSi nanowire superconducting single photon detectors. To this purpose, we fabricated a 250 nm wide and 250 nm long WSi nanowire and measured its response to impinging photons with wavelengths ranging from λ = 900 nm to λ = 1650 nm. Tomographic measurements show that the detector response depends on the total excitation energy only. Moreover, for total absorbed energies >0.8 eV the current–energy relation is linear, similar to what was observed in NbN nanowires, whereas the current–energy relation deviates from linear behavior for total energies below 0.8 eV.
Using detector tomography, we investigate the detection mechanism in NbN-based superconducting single photon detectors (SSPDs). We demonstrate that the detection probability uniquely depends on a particular linear combination of bias current and energy, for a large variation of bias currents, input energies and detection probabilities, producing a universal detection curve. We obtain this result by studying multiphoton excitations in a nanodetector with a sparsity-based tomographic method that allows factoring out of the optical absorption. We discuss the implication of our model system for the understanding of meander-type SSPDs.
Superconducting single photon detectors consist of a narrow and thin wire of superconductor and can detect single photons with high efficiency and high speed. Simultaneous optimization of the detection efficiency and detector response time is difficult because the response time is set by the dimensions of the wire (cross section and length) while the detection efficiency is determined by both the internal detection mechanism and the dimensions of the wire. Wider and shorter wires are easier to fabricate, are more robust and lead to shorter detector reset time, but are generally less efficient. Experiments employing detector tomography provide important insights into the photon detection mechanism and indicate a detection mechanism where the edges of the wire are more efficient. This leads to a position dependent local detection efficiency that can be explained in the context of a photon-assisted-vortex-entry model and predicts an optimum wire width ~70 nm. A 50 nm wide silicon nanowire deposited on top of a 150 nm wide NbN nanowire directs light at 1550 nm wavelength to the edges and improves both the total absorption efficiency and the internal detection efficiency of the wire. The total absorption efficiency can be enhanced by 30% while the internal detection efficiency is increased by 70%. Assuming that the wire covers a similar area the detector response time is reduced 4-fold compared to the standard design using a 70 nm wide wire.
In this paper, we study the response properties of multi-photon of NbN superconductor nanowire in superconducting single photon detector (SSPD). We measure the NbN nanowire device's DC characteristics and detection probability for single and multi-photon light pulse signal at a temperature of 3.5 K. The measured results show that the superconducting transition current of superconductor nanowire decreases as light irradiation intensity increases. The photon number detected by SSPD is derived from the slope of detection probability versus light intensity. We find that the detected photon number increases as superconducting nanowire bias current decreases. Moreover, based on quantum optics and hotspot theory, we analyze the mechanism of the multi-photon response of superconducting nanowire semi-quantitatively. This result may be of benefit to understanding SSPD and developing the SSPD with the capability of resolving photon number.
We report the fabrication and characterization of a niobium titanium nitride (NbTiN)-based superconducting nanowire single-photon detector (SSPD or SNSPD) on the Si waveguide toward the realization of waveguide-coupled SSPD. The device consists of a silicon optical waveguide fabricated using a silicon-on-insulator (SOI) substrate and a 100-nm-wide NbTiN nanowire constructed on the waveguide, with an inductor to prevent latch operation. For the fabricated device, the observed superconducting critical temperature and critical current were 7.85 K and 34.4 μA at 0.3 K, respectively. We investigated the optical response of the fabricated device and found that the device exhibited a single-photon response by measuring of the input power dependence of the output count rate. Furthermore, the fabricated device showed a clear bias current dependence of the output counts similar to conventional SSPDs, and the pulse-generation probability is estimated to be 90.1% based on two assumptions: a sigmoidal model to the detection efficiency and the device has a 100% pulse-generation probability at the saturated region.
Superconducting nanowire single-photon detectors (SNSPDs) have attracted considerable attention owing to their excellent detection performance; however, the underlying physics of the detection process is still unclear. In this study, we investigate the wavelength dependence of the intrinsic detection efficiency (IDE) for NbN SNSPDs. We fabricate various NbN SNSPDs with linewidths ranging from 30 nm to 140 nm. Then, for each detector, the IDE curves as a function of bias current for different incident photon wavelengths of 510–1700 nm are obtained. From the IDE curves, the relations between photon energy and bias current at a certain IDE are extracted. The results exhibit clear nonlinear energy–current relations for the NbN detectors, indicating that a detection model only considering quasiparticle diffusion is unsuitable for the meander-type NbN-based SNSPDs. Our work provides additional experimental data on SNSPD detection mechanism and may serve as an interesting reference for further investigation.