Single-photon detection in few-layer NbSe2 superconducting nanowires
Lucio Zugliani, Alessandro Palermo, Bianca Scaparra, Aniket Patra, Fabian Wietschorke, Pietro Metuh, Athanasios Paralikis, Domenico De Fazio, Christoph Kastl, Rasmus Flaschmann, Battulga Munkhbat, Kai Müller, Jonathan James Finley, Matteo Barbone
Abstract Superconducting Nanowire Single-Photon Detectors (SNSPDs) are key building blocks for photonic quantum technologies due to their ability to detect single photons with ultra-high efficiency, low dark counts and fast temporal resolution. Superconducting materials exhibiting high uniformity, large absorption cross-section and atomic-scale thickness are desirable to extend single-photon detection from the near-infrared up to the terahertz regime, where existing material choices are especially constrained. Substrate independence would further open the way to integrating detectors onto functional materials and heterostructures, enhancing performance and enabling proximal readout of a wide range of individual excitations. Here, we pattern the prototypical two-dimensional superconductor niobium diselenide (NbSe 2 ) into few-layer nanowires less than 100 nm wide and demonstrate single-photon detection at 780 nm and 1550 nm. At the same time, the dark-count rate remains below 1 Hz up to the switching current and we achieve a timing jitter below 50 ps. We estimate via a diffusive hot-spot model that materials and geometric parameters would allow a theoretical cut-off wavelength in the millimetre range, assuming state-of-the-art device parameters. Our results open up routes toward quantum-limited detectors integrated into quantum-photonic circuits and quantum devices, with the potential for novel detection capabilities and unprecedented energy sensitivity.
Abstract Superconducting Nanowire Single-Photon Detectors (SNSPDs) are key building blocks for photonic quantum technologies due to their ability to detect single photons with ultra-high efficiency, low dark counts and fast temporal resolution. Superconducting materials exhibiting high uniformity, large absorption cross-section and atomic-scale thickness are desirable to extend single-photon detection from the near-infrared up to the terahertz regime, where existing material choices are especially constrained. Substrate independence would further open the way to integrating detectors onto functional materials and heterostructures, enhancing performance and enabling proximal readout of a wide range of individual excitations. Here, we pattern the prototypical two-dimensional superconductor niobium diselenide (NbSe 2 ) into few-layer nanowires less than 100 nm wide and demonstrate single-photon detection at 780 nm and 1550 nm. At the same time, the dark-count rate remains below 1 Hz up to the switching current and we achieve a timing jitter below 50 ps. We estimate via a diffusive hot-spot model that materials and geometric parameters would allow a theoretical cut-off wavelength in the millimetre range, assuming state-of-the-art device parameters. Our results open up routes toward quantum-limited detectors integrated into quantum-photonic circuits and quantum devices, with the potential for novel detection capabilities and unprecedented energy sensitivity.
Single photon detection advanced rapidly in the last decade. The superconducting nanowire single-photon detector (SNSPD) is an emerging technology, which offers low dark count rates, broadband sensitivity from visible to mid-infrared wavelengths and very high quantum efficiency. All these features are appealing for future emerging applications in remote gas sensing, quantum key distribution and quantum information processing. By enclosing the detector in an optical cavity, tuned to the operating wavelength, the total system detection of the SNSPD is improved. Based on the cavity design, the detector absorption is boosted at the desired experimental wavelength. Devices have been fabricated and tested, in this thesis, with enhanced detection efficiency at near-infrared, infrared and mid-infrared wavelengths. NbTiN detectors fabricated on Ta2O5 / SiO2 distributed Bragg reflectors (DBR) for front-side coupling exhibit a system detection efficiency of ≈ 90% at λ = 940 nm for the best device measured. SNSPDs were also fabricated in NbTiN on metallic mirrors for back-side coupling for 1550 and 2333 nm experimental wavelengths. The first design exhibited a system detection efficiency of ≈ 84.5%, at λ = 1550 nm for the best device measured. The second exhibited low system detection efficiency since the device suffered from unexpectedly high dark count rate mainly due to blackbody radiation at 2.2 K. However, it was possible to measure the timing jitter of this device at 350 mK indicating a FWHM of 84 ps. Another technique to improve the total system detection efficiency of the SNSPD, is by fabricating a hairpin-shaped nanowire atop a single mode waveguide. In this design, photons travel through the waveguide and via evanescent coupling are absorbed in the nanowire. These SNSPD devices have been designed to thread along single mode Si ridge waveguides using a hairpin-shaped nanowire structure, which offers enhanced coupling and absorption efficiency via evanescent coupling. These ultra-thin superconducting MoSi detectors are precisely patterned on top of a single mode Si waveguide (600 nm) with alignment error less than 40 nm. Low temperature electrical and nano-optical characterization was carried out using a two-stage pulse tube (PT) coldhead, using an additional 4He / 3He sorption pump, low vibration characterization of SNSPD devices at 350 mK was carried out. Characterised devices exhibit low dark count rate <5 counts per second and timing jitter of ≈ 83 ps full width half maximum (FWHM) at wavelength (λ) = 1550 nm and at critical current ≈ 30 µA.
In the field of quantum technologies, the superconducting nanowire single photon detector(SNSPD) is nowadays well recognized as a key enabling device. SNSPDs combine high detectionefficiency in the visible and near IR spectral ranges, timing jitter as low as 10 ps, low dark count rate(<100 s−1) and cut-off frequency above 100 MHz. These features make it particularly attractive e.g. forfundamental quantum optics experiments and quantum communications.Plug-and-play SNSPDs with fibered optical access, as shown in Figure 1, are based on a meandernanowire defined by patterning an ultrathin (<10 nm) superconducting film. The device is designedso that absorption of a single photon is enough to brake locally the superconducting order, and toinduce a measurable change of the wire’s resistance. Until recently, such devices displayed two mainlimitations: (1) their efficiency did not exceed ~40% due to the limited optical absorption of the thinfilm; and (2) their response was strongly polarization-sensitive, due to the optical anisotropy of thenanowire. I will present two different approaches which enable to get very high (>90% [1]) andpolarization-insensitive [2,3] detection efficiency. We consider designs based on the integration of thenanowire within an optical microcavity (compatible with the plug-and-play configuration) or on topof an optical waveguide (preferred approach for integration in photonic circuits). I will finally discussnovel application prospects of such detectors, with emphasis on photon-number resolution.
Superconducting nanowire single-photon detectors are widely used for detecting individual photons across various wavelengths from ultraviolet to near-infrared range. Recently, there has been increasing interest in enhancing their sensitivity to single photons in the mid-infrared spectrum, driven by applications in quantum communication, spectroscopy, and astrophysics. Here, we present our efforts to expand the spectral detection capabilities of U-shaped NbTiN-based superconducting nanowire single-photon detectors, fabricated in a 2-wire configuration on a silicon-on-insulator substrate, into the mid-infrared range. We demonstrate saturated internal detection efficiency extending up to a wavelength of 3.5 μm for a 5 nm thick and 50 nm wide NbTiN nanowire with a dark count rate less than 10 counts per second at 0.9 K and a rapid recovery time of 4.3 ns. The detectors are engineered for integration on waveguides in a silicon-on-insulator platform for compact, multi-channel device applications.
Ever since superconducting nanowire single-photon detectors (SNSPDs or SSPDs) were demonstrated, they have attracted a considerable attention due to the detectors’ promising performance that includes high detection efficiency (DE), low dark count rate (DCR), broadband sensitivity, and low timing jitter. The system detection efficiency (SDE) has been improved to be over 90% with a wavelength of 1550 nm in a fiber-coupled system by embedding the SNSPD in optical cavities. However, the implementation of optical cavity usually reduces the bandwidth of SNSPDs. As a result, there are some recent works on increasing the bandwidth of SNSPD. Furthermore, the size of the active area of meandered nanowires has to be compatible with the core size of an optical fiber such that good optical coupling can be achieved; this setup requires a long nanowire with a large kinetic inductance, thus resulting in a small counting rate and a large timing jitter, particularly for multi-mode fiber-coupled devices. Nevertheless, a particularly impressive waveguide-coupled SNSPD has been developed in recent years. By placing an SNSPD atop an optical waveguide that has been fabricated on various substrate materials, photons propagating in the waveguide have been found to be evanescently absorbed by nanowires that are only a few tens of microns long. The on-chip DE of this device has been estimated to be over 90%, thus indicating that it has both high absorptance and high intrinsic DE. If the waveguide and the nanowire are correctly dimensioned, the absorptance of this device can reach over 90% for a wavelength range of more than 700 nm. Furthermore, the length of the nanowire is shorter than that of the fiber-coupled SNSPD, thus leading to a higher count rate and lower timing jitter (~18 ps). However, unsatisfactory coupling losses between the optical fiber and the waveguide in such devices can decrease its SDE (~10%), thus limiting its applicability to quantum photonic integrated circuits (QPIC). Recently, we proposed a type of SNSPD that was coupled with microfibers (MFs), and simulations for this SNSPD indicated that its absorption would be as high as 90%. Microfibers and nanofibers, tapered adiabatically from standard fibers, with diameters close to or smaller than the wavelength of the guided light were demonstrated to have low transmittance losses by Tong et al. in 2003. MFs have been shown to have many interesting properties, such as strong evanescent fields, tight optical confinement, wideband abilities, and small masses; these properties are appealing for applications such as optical sensing and coupling. MFs also provide seamless connections with high transmittance from standard fibers; therefore, MF-coupled SNSPDs can achieve both high SDEs and wideband compatibility. We proposed and demonstrated the MF-coupled SNSPDs successfully. The simulation results indicate that with optimal device structure, the optical absorption with efficiency < 90% can be realized over a wavelength range of 350 nm to 2150 nm. The fabricated MF-coupled SNSPD, shows unparalleled broadband system detection efficiencies (SDEs) of more than 50% from 630 nm to 1500 nm. The SDEs reach 66% at 785 nm and 45% at 1550 nm. These results pave the way for ultra-broadband weak light detection with quantum-limit sensitivity.
High Resolution Image Download MS PowerPoint Slide We present superconducting nanowire photodetectors based on hBN-encapsulated, few-layer NbSe 2, showing signatures of single-photon sensitivity. The top-down fabrication process preserves the superconducting properties of NbSe 2, as confirmed by low-temperature transport measurements showing comparable results to unpatterned sheets, and it maintains a contact and wiring resistance down to ∼30 Ω at T = 4 K. Meandered NbSe 2 nanowires exhibit high responsivity (up to 4.9 × 10 4 V/W) over a spectral range of 650–1550 nm in a closed-cycle cryostat at 4 K, outperforming samples with different geometries in this work. The meander achieves a recovery time of (135 ± 36) ns, a system timing jitter of (1103 ± 7) ps, and a detection efficiency of ∼0.01% at 0.95 I c . A linear increase of the count rate with the number of photons between the noise level and the latching threshold offers a signature of single-photon sensitivity at 1100 nm.
Superconducting nanowire single-photon detectors (SNSPDs) are the leading technology for low noise, high efficiency infrared single-photon detection. The basic SNSPD consists of a nanowire patterned in an ultrathin superconducting thin film, which is cooled below its critical temperature and biased close to its critical current. The absorption of a single-photon creates a resistive region, triggering a fast output voltage pulse which can be readily amplified and registered. The excellent performance of SNSPDs at near-infrared and telecommunications wavelengths has led to their adoption in important applications such as quantum secure communications, single-photon spectroscopy and single-photon LIDAR. A clear challenge for the SNSPD community is to extend the spectral range of SNSPDs into the mid infrared, and to improve material uniformity to enable the realization of large area arrays for multimode or free space coupling. The aim of this work is to evaluate potential materials for next generation mid-infrared SNSPD arrays. In this work, thin films of polycrystalline NbN and amorphous MoSi have been optimized to test the uniformity of a multipixel array configuration composed of 8 nanowire meander structures covering 10 um x 10 um area, 100 nm width and 50% filling factor. The 8-pixels SNSPD arrays have been patterned on 8 nm thickness NbN grown on high resistivity silicon (HR Si) substrate at room temperature and at 800 °C exhibiting respectively 4.4 K and 7.3 K as mean critical temperature across the pixels. The 8- pixels SNSPD array patterned on 8 nm thickness MoSi cooling the HR Si substrate to -180 °C has exhibited a mean critical temperature of 3.2 K across the pixels. Optical properties have been measured by an attenuated 1550 nm laser diode source delivered by single mode optical fibre at a controlled distance from the chip in order to broadly illuminate the array. The optical properties have been studied only for the 8 nm thickness NbN SNSPD array grown at room temperature has demonstrated uniform optical properties across pixels exhibiting similar saturation of the internal efficiency over a large bias, similar dark count rate and similar timing jitter (about 137 ps) across pixels. In the single photon regime at 1550 nm, pixels 4 and 6 of the 8 nm thickness NbN SNSPD array exhibit 28.4% and 4.7% pixel detection efficiency as measured at the bias current 95% of their respective critical current at 2.2 K.