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IEEE Transactions on Applied Superconductivity

Mathematical Analysis of Multiplexing Techniques for SNSPD Arrays

Sonja Engert, Olaf Wetzstein, M. Hofherr, K. Ilin, M. Siegel, H.‐G. Meyer, Hannes Toepfer

Published Mar 12, 2013• 7 citations
Publisher

Abstract

Superconducting nanowire single photon detectors (SNSPDs) are distinguished by a very high sensitivity, a broad spectral range and a sparse dark count rate. Therefore, arrays of SNSPDs enable novel ultrasensitive imaging applications. The goal is to realize large arrays in the near future. Hence, in order to improve detector systems, there is the necessity to develop multiplexing techniques to keep the number of wires in the cryogenic environment as low as possible. We realized a readout circuit with rapid single flux quantum electronics. All detector output signals were merged to a single output channel. This leads to a loss of spatial resolution of the information provided by the single pixels. In order to overcome this effect, this work describes a theoretical analysis of time and code multiplexing technique for arrays of SNSPDs and a comparison concerning their applicability in different cases. We developed rules for the usability of each multiplexing technique and verified the results with measurements of a 4-pixel SNSPD array.

DOI
10.1109/tasc.2013.2247455

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Superconducting nanowire single photon detectors (SNSPDs) are distinguished by a very high sensitivity, a broad spectral range and a sparse dark count rate. Therefore, arrays of SNSPDs enable novel ultrasensitive imaging applications. The goal is to realize large arrays in the near future. Hence, in order to improve detector systems, there is the necessity to develop multiplexing techniques to keep the number of wires in the cryogenic environment as low as possible. We realized a readout circuit with rapid single flux quantum electronics. All detector output signals were merged to a single output channel. This leads to a loss of spatial resolution of the information provided by the single pixels. In order to overcome this effect, this work describes a theoretical analysis of time and code multiplexing technique for arrays of SNSPDs and a comparison concerning their applicability in different cases. We developed rules for the usability of each multiplexing technique and verified the results with measurements of a 4-pixel SNSPD array.
Superconducting nanowire single-photon detectors (SNSPDs) have emerged as essential devices that push the boundaries of photon detection with unprecedented sensitivity, ultrahigh timing precision, and broad spectral response. Recent advancements in materials engineering, superconducting electronics integration, and cryogenic system design are enabling the evolution of SNSPDs from single-pixel detectors toward scalable arrays and large-format single-photon time tagging cameras. This perspective article surveys the rapidly evolving technological landscape underpinning this transition, focusing on innovative superconducting materials, advanced multiplexed read-out schemes, and emerging cryo-compatible electronics. We highlight how these developments are set to profoundly impact diverse applications, including quantum communication networks, deep-tissue biomedical imaging, single-molecule spectroscopy, remote sensing with unprecedented resolution, and the detection of elusive dark matter signals. By critically discussing both current challenges and promising solutions, we aim to articulate a clear, coherent vision for the next generation of SNSPD-based quantum imaging systems.
Detecting spatial and temporal information of individual photons is a crucial technology in today's quantum information science. Among the existing single-photon detectors, superconducting nanowire single-photon detectors (SNSPDs) have been demonstrated with a sub-50 ps timing jitter, near unity detection efficiency1, wide response spectrum from visible to infrared and ~10 ns reset time. However, to gain spatial sensitivity, multiple SNSPDs have to be integrated into an array, whose spatial and temporal resolutions are limited by the multiplexing circuit. Here, we add spatial sensitivity to a single nanowire while preserving the temporal resolution from an SNSPD, thereby turning an SNSPD into a superconducting nanowire single-photon imager (SNSPI). To achieve an SNSPI, we modify a nanowire's electrical behavior from a lumped inductor to a transmission line, where the signal velocity is slowed down to 0.02c (where c is the speed of light). Consequently, we are able to simultaneously read out the landing locations and arrival times of the photons from the output electrical pulses using only two connections. We have demonstrated single-photon imaging by using a 19.7 mm long SNSPI, which is meandered into an imaging area of 286 {\mu}m*193 {\mu}m. The nanowire has a temporal resolution of 50 ps for detecting 1.5 {\mu}m photons. The 2D spatial resolution is 13.0 {\mu}m in the vertical direction and 5.6 {\mu}m in the horizontal direction. The maximum number of resolvable locations (i.e., the effective number of pixels) in such a long nanowire is calculated to be 590. Rather than operating an individual detector in a scanning mode or using SPD arrays, this SNSPI gives an alternative approach to taking large-scale single-photon images and measuring temporal and spatial correlation.
Integrated arrays of Superconducting Nanowire Single Photon Detectors (SNSPDs) have shown capabilities such as Photon Number Resolution, single photon imaging and coincidences detection, and can be effectively used also in other different applications related to quantum optics. The growing complexity of such applications requires the use of multiplexing schemes for the simultaneous readout of different detectors. A simple multiplexing scheme can be realized by arranging a series of SNSPDs elements, shunted by appropriate resistances. The goal of this work is to investigate and optimize this scheme, developing a general method able to identify the optimal sets of shunting resistences for any different application. The methodology obtained is very general, and can be extended to other detection systems.
We present the development of key technologies for realization of superconducting nanowire single photon detector array system, which enables high counting rates, and allow spatial and pseudo photon number resolution. Toward the realization of practical large-scale SSPD array system, primary issue is how to avoid heat flow into cryocooler system. One of the challenging tasks is the development of their readout electronics. In the conventional readout technique used for single pixel devices, the number of high-frequency coaxial cables increases proportionally with the number of arrays. This causes a significant increase in the heat load from room temperature, which makes the implementation of the SSPD arrays in a compact refrigerator difficult. To overcome this problem, we proposed applying readout electronics with superconducting single-flux-quantum (SFQ) logic circuitsWe show the implementation and successful operation of four pixels SSPD array connected to SFQ readout electronics with parallel bias scheme in a 0.1W GM cryocooler system.
A two-dimensional single-photon imaging system with high sensitivity and high time resolution is the ultimate camera and useful in a wide range of fields. A superconducting nanowire single-photon detector (SSPD or SNSPD) is one of the best candidates for realizing such an ultimate camera due to its high detection efficiency in a wide spectral range, low dark count rate without after-pulsing, and excellent time resolution. Here we propose a new readout scheme to realize a large-scale imaging array based on SSPD, where a row-column readout architecture is combined with a digital signal processor based on a single-flux-quantum (SFQ) circuit. A 16-pixel row-column readout SSPD array is fabricated and measured with an SFQ digital signal processor. We successfully acquired spatial information as encoded digital bit codes with the temporal information of the photon detection. The system timing jitter was measured as <80 ps for all 16 pixels even through the SFQ signal processor, indicating the potential for an imaging array with an extremely high time resolution.
We propose an efficient multiplexing technique for superconducting nanowire single-photon detectors based on an orthogonal detector bias switching method enabling the extraction of the average count rate of a set of detectors by one readout line. We implemented a system prototype where the SNSPDs are connected to an integrated cryogenic readout and a pulse merger system based on rapid single flux quantum (RSFQ) electronics. We discuss the general scalability of this concept, analyze the environmental requirements which define the resolvability and the accuracy and demonstrate the feasibility of this approach with experimental results for a SNSPD array with four pixels.