Quantum Opus’ SNSPDs generate high-quality single-photon signals that Swabian Instruments’ Time Taggers can measure with picosecond precision, ultra-low jitter, and multi-channel flexibility. Together, they enable precise and efficient Photon Number Resolution, reliably distinguishing single- and two-photon events.
The ability to accurately determine the exact number of photons in an event, namely photon number resolution (PNR), is crucial for quantum networking, communication, and sensing. While pseudo-PNR approaches rely on multiplexing, true PNR depends on the ability of the detector and electronics to efficiently discriminate electrical signals under different count rates, optical, and electrical conditions. This work explores a fidelity and accuracy assessment and discrimination methods from peak separation PNR methods. The signals generated by Quantum Opus SNSPDs were acquired and analyzed with picosecond resolution via Swabian Instruments Time Taggers. Experimental data reveal the tradeoffs between photon-number distinguishability acquisition and processing methods. Both mathematical analysis methods (a Poisson-weighted or independent exponentially modified Gaussian) agree on the optimum threshold voltage, but vary in practical deployment, robustness against parameter degeneracy, and further capabilities. Both timing acquisition methods allow for PNR, but self-referenced rise-time measurement sacrifices some distinguishability for increased optical flexibility.
Single-photon detectors based on superconducting nanowires (SNSPDs) are promising technologies with good comprehensive performance, especially their excellent temporal resolution for applications in quantum precision measurements and time-varying ultimate detection. The response time of an SNSPD can be characterized by aspects of hotspot thermal relaxation and electrical relaxation, which are also responsible for the time jitter of the SNSPD. The factors affecting the temporal resolution of an SNSPD, the underlying physical mechanism, the intrinsic limit, and possible optimization methods are reviewed. The poor energy resolution and lack of photon number resolution for conventional SNSPDs can be overcome by using high-impedance readouts, novel device structures, characterization methods and, most importantly, SNSPD arrays, which can simultaneously further improve the temporal resolution. The study of the temporal and photon number resolution of SNSPDs helps reveal the underlying physics and is valuable for their new application in various practical engineering areas.
Since their first demonstration in 2001 [Gol’tsman et al., Appl. Phys. Lett. 79, 705–707 (2001)], superconducting-nanowire single-photon detectors (SNSPDs) have witnessed two decades of great developments. SNSPDs are the detector of choice in most modern quantum optics experiments and are slowly finding their way into other photon-starved fields of optics. Until now, however, in nearly all experiments, SNSPDs were used as “binary” detectors, meaning that they could only distinguish between 0 and >=1 photons, and photon number information was lost. Recent research has demonstrated proof-of-principle photon-number resolution (PNR) SNSPDs counting 2–5 photons. The photon-number-resolving capability is highly demanded in various quantum-optics experiments, including Hong–Ou–Mandel interference, photonic quantum computing, quantum communication, and non-Gaussian quantum state preparation. In particular, PNR detectors at the wavelength range of 850–950 nm are of great interest due to the availability of high-quality semiconductor quantum dots (QDs) [Heindel et al., Adv. Opt. Photonics 15, 613–738 (2023)] and high-performance cesium-based quantum memories [Ma et al., J. Opt. 19, 043001 (2017)]. In this paper, we demonstrate NbTiN-based SNSPDs with >94% system detection efficiency, sub-11 ps timing jitter for one photon, and sub-7 ps for 2 photons. More importantly, our detectors resolve up to 7 photons using conventional cryogenic electric readout circuitry. Through theoretical analysis, we show that the PNR performance of demonstrated detectors can be further improved by enhancing the signal-to-noise ratio and bandwidth of our readout circuitry. Our results are promising for the future of optical quantum computing and quantum communication.
Single-photon sources and detectors are key enabling technologies for photonics in quantum information science and technology (QIST). QIST applications place high-level demands on the performance of sources and detectors; it is therefore essential that their properties can be characterized accurately. Superconducting nanowire single-photon detectors (SNSPDs) have spectral sensitivity from visible to beyond 2 μm in wavelength, picosecond timing resolution (Jitter <100 ps FWHM) and the capacity to operate ungated with low dark counts (<1 kHz). This facilitates data acquisition at high rates with an excellent signal-to-noise ratio. We report on the construction and characterization of a two-channel SNSPD system. The detectors are mounted in a closed-cycle refrigerator, which eliminates reliance on liquid cryogens. Our specification was to deliver a system with 1% efficiency in both channels at a wavelength of 1310 nm with 1 kHz dark count rate. A full width at half maximum timing jitter of less than 90 ps is achieved in both channels. The system will be used to detect individual photons generated by quantum-optical sources at telecom wavelengths. Examples include single-photon sources based on quantum dots (emitting at 1310 nm). The SNSPD system's spectral sensitivity and timing resolution make it suited to characterization of such sources, and to wider QIST applications.
Two decades after their demonstration, superconducting nanowire single-photon detectors (SNSPDs) have become indispensable tools for quantum photonics as well as for many other photon-starved applications. This invention has not only led to a burgeoning academic field with a wide range of applications but also triggered industrial efforts. Current state-of-the-art SNSPDs combine near-unity detection efficiency over a wide spectral range, low dark counts, short dead times, and picosecond time resolution. The present perspective discusses important milestones and progress of SNSPDs research, emerging applications, and future challenges and gives an outlook on technological developments required to bring SNSPDs to the next level: a photon-counting, fast time-tagging imaging, and multi-pixel technology that is also compatible with quantum photonic integrated circuits.
Precise time measurement and event correlation have gained a prominent role in a large variety of quantum photonics applications, including quantum communication, quantum simulation, and quantum computing. The increasing complexity and scale of quantum photonic systems, particularly those capable of generating, manipulating, and detecting single photons, necessitate advanced electronic timing systems that can accurately capture coincidence events across multiple channels. A highly effective approach for measuring the time of arrival of a photon, detected by single-photon detectors such as single-photon avalanche diodes (SPADs) or superconducting nanowires, is the cascading of a time-to-amplitude converter (TAC) with an analog-to-digital converter (ADC), a configuration distinguished by its high precision and linearity [1].