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Applied Physics Letters

Single photon detection in NbRe superconducting microstrips

Mikkel Ejrnaes, C. Cirillo, Daniela Salvoni, Federico Chianese, Ciro Bruscino, Pasquale Ercolano, A. Cassinese, C. Attanasio, Giovanni Piero Pepe, L. Parlato

Published Dec 26, 2022• 27 citations
Publisher

Abstract

Detection of single infrared photons in superconducting microstrips of 4 nm thick disordered Nb0.15Re0.85 has been investigated. Microstrips with a critical temperature of 5.15 K and widths from 1.0 to 2.5 μm have been fabricated by optical lithography. We demonstrate single photon detection sensitivity at 1.5 μm wavelength at a temperature of 1.79 K. By investigating the detection process at this temperature, we find that the current bias threshold is at 21% of the depairing current. This threshold is similar to what should be observed in typical amorphous superconductors, which confirms that ultrathin disordered Nb0.15Re0.85 is an interesting material for superconducting microstrip single photon detectors that operate above 1 K.

DOI
10.1063/5.0131336

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Applied Physics Letters•Oct 26, 2020•32 citations
Detection of single infrared photons in superconducting microstrips of 4 nm thick disordered Nb0.15Re0.85 has been investigated. Microstrips with a critical temperature of 5.15 K and widths from 1.0 to 2.5 μm have been fabricated by optical lithography. We demonstrate single photon detection sensitivity at 1.5 μm wavelength at a temperature of 1.79 K. By investigating the detection process at this temperature, we find that the current bias threshold is at 21% of the depairing current. This threshold is similar to what should be observed in typical amorphous superconductors, which confirms that ultrathin disordered Nb0.15Re0.85 is an interesting material for superconducting microstrip single photon detectors that operate above 1 K.
Superconducting microstrip single photon detectors (SMSPDs) are increasingly attracting the interest of the scientific community as a new platform for large area detectors with unprecedented advantaged in terms of fabrication. However, while their operativity at the telecommunication wavelength was achieved, working beyond 1.55 µm is challenging. Here, we experimentally demonstrate single-photon operation of NbRe microstrips at wavelengths of 1.55 and 2 µm. The devices are structured as pairs of parallel microstrips with widths ranging from 1.4 to 2.2 μm and lengths from 5 to 10 μm. This innovative design may assure large sensitive areas, without affecting the kinetic inductance, namely the time performance of the detectors. The results are discussed in the framework of the hot-spot two-temperature model.
Abstract Superconducting microstrip single photon detectors (SMSPDs) received great interest since they are expected to combine the excellent performance of superconducting nanostrip single photon detectors with the possibility to cover large active areas using low-cost fabrication techniques. In this work, we fabricated SMSPDs based on NbRe to investigate the role of vortices in the dark counts events in this innovative material and in devices with micrometer size. We realized devices with different layouts, namely single microstrips and pairs of parallel microstrips. The energy barriers related to the motion of single vortices or vortex–antivortex pairs, responsible of detection events, have been determined and compared with the ones of similar devices based on different materials, such as MoSi, WSi and NbN. The analysis confirms the high potential of NbRe for the realization of superconducting single photon detectors with large areas.
In this paper, we present a large-area niobium titanium nitride (NbTiN) superconducting microstrip single-photon detector (SMSPD) fabricated using a photolithography process. We fabricated a 1-μm-wide NbTiN-SMSPD covering 420 × 420 μm2active area with a filling factor of 20% using an i-line stepper. The detector is cooled down to approximately 2.2 K, and its performance is evaluated at the wavelengths from visible to near-infrared. The detector operates stably without a shunt resistor and shows single-photon sensitivity for photons with a wavelength of 1550 nm. The bias current dependence of the detection count rate is measured at the wavelengths from 406 to 1550 nm. The saturation of the detection count rate with increasing the bias current was successfully observed at wavelengths below 850 nm, suggesting an internal detection efficiency approaching 100%. Furthermore, we evaluated the timing jitter performance using the femtosecond pulse laser with a wavelength of 1550 nm. Consequently, we achieved a system timing jitter of 85 ps for a light spot diameter of 100 μm.
Superconducting microstrip single-photon detectors (SMSPDs) with near-infrared sensitivity have significant advantages in terms of high quantum efficiency and low dark counts in a large active area. Hole-patterned superconductor microstrips have been reported for fast and efficient single-photon detection. In this work, we fabricated and characterized hole-patterned microstrips with different hole diameters on 5 nm thick MoSi films and an area of 500 × 500 μm2. We observed that the count rate curves of detectors 2 and 3 with holes tend to saturate slightly, whereas those of detector 1 without holes do not. Furthermore, the dark count is similar between detector 1 without holes and detector 2 with small holes and much lower than that of detector 3 with large holes. These experiments indicate that a proper hole is beneficial for efficiency without increasing the dark count rate.
The effective and convenient detection of single photons via advanced detectors with a large active area is becoming significant for quantum and classical applications. This work demonstrates the fabrication of a superconducting microstrip single-photon detector (SMSPD) with a millimeter-scale active area via the use of ultraviolet (UV) photolithography. The performances of NbN SMSPDs with different active areas and strip widths are characterized. SMSPDs fabricated by UV photolithography and electron beam lithography with small active areas are also compared from the aspects of the switching current density and line edge roughness. Furthermore, an SMSPD with an active area of 1 mm × 1 mm is obtained via UV photolithography, and during operation at 0.85 K, it exhibits near-saturated internal detection efficiency at wavelengths up to 800 nm. At a wavelength of 1550 nm, the detector exhibits a system detection efficiency of ∼5% (7%) and a timing jitter of 102 (144) ps, when illuminated with a light spot of ∼18 (600) µm in diameter, respectively.
Superconducting Nanowire Single Photon Detectors (SNSPDs) based on Nb0.15Re0.85 disordered nanowires are developed. The devices have a meander structure of wires 50–100 nm wide and cover a circular detection area with a diameter of about 10–16 μm. The main figures of merit of the detectors are extracted from a flood illumination process at 2.8 K, featuring a saturated internal efficiency up to λ= 1301 nm, recovery times between about 8 and 19 ns, and a jitter of about 35 ps. These results confirm that Nb0.15Re0.85 is a promising candidate for the realization of fast SNSPDs, as recently suggested.