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Advanced Photon Counting Techniques

Progress in the realization of multi-channels waveguide-integrated photon number resolving detectors

Oliver P. Page, Iurii Konyshev, Vincent Spreter, Roland Jaha, Erik Jung, Simone Ferrari, Wolfram H. P. Pernice

Published Jun 7, 2024• 1 citation
Publisher

Abstract

We present our progress in the realization of a waveguide-integrated, near-infrared, 20-channel pseudo photon number resolving architecture realized on the silicon nitride platform. Each channel consists of a space multiplexing network directing to 8 superconducting nanowire single-photon detectors connected in series. Our design focusses on minimizing splitting losses, ensuring robust response across different wavelengths in the near-infrared range and achieving low noise electrical readout. Specifically, we will report on the design of wavelength-independent splitting elements operating in the near-infrared, the realization of low-loss fiber-to-chip coupling and detail the implementation of the cryogenic biasing and readout scheme. Our work constitutes a significant advancement towards practical multi-channel photon number resolving detectors, serving as a promising building block for scalable and high-performance quantum information processing systems.

DOI
10.1117/12.3016388

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We present our progress in the realization of a waveguide-integrated, near-infrared, 20-channel pseudo photon number resolving architecture realized on the silicon nitride platform. Each channel consists of a space multiplexing network directing to 8 superconducting nanowire single-photon detectors connected in series. Our design focusses on minimizing splitting losses, ensuring robust response across different wavelengths in the near-infrared range and achieving low noise electrical readout. Specifically, we will report on the design of wavelength-independent splitting elements operating in the near-infrared, the realization of low-loss fiber-to-chip coupling and detail the implementation of the cryogenic biasing and readout scheme. Our work constitutes a significant advancement towards practical multi-channel photon number resolving detectors, serving as a promising building block for scalable and high-performance quantum information processing systems.
We present enhancements in the spectral sensitivity and scalability of superconducting nanowire single-photon detectors based on U-shaped NbTiN nanowires. Designed on a silicon-on-insulator photonic platform, our detectors exhibit near-unity internal detection efficiency under flood illumination across wavelengths from 1550nm to 3502nm. Additionally, we demonstrate arrays of waveguide-integrated superconducting nanowire single-photon detectors optimized for operation at 1550nm. Cryogenic light coupling to the arrays is achieved through a photonic wire bonding technique, enabling low-loss coupling and high-density integration, thereby facilitating the scaling of detector counts per cryostat for near-infrared applications.
Superconducting nanowire single-photon detectors are an enabling technology for modern quantum information science and are gaining attractiveness for the most demanding photon counting tasks in other fields. Embedding such detectors in photonic integrated circuits enables additional counting capabilities through nanophotonic functionalization. Here, we show how a scalable number of waveguide-integrated superconducting nanowire single-photon detectors can be interfaced with independent fiber optic channels on the same chip. Our plug-and-play detector package is hosted inside a compact and portable closed-cycle cryostat providing cryogenic signal amplification for up to 64 channels. We demonstrate state-of-the-art multi-channel photon counting performance with average system detection efficiency of (40.5 ± 9.4)% and dark count rate of (123 ± 34) Hz for 32 individually addressable detectors at minimal noise-equivalent power of (5.1 ± 1.2) · 10−18 W/Hz. Our detectors achieve timing jitter as low as 26 ps, which increases to (114 ± 17) ps for high-speed multi-channel operation using dedicated time-correlated single photon counting electronics. Our multi-channel single photon receiver offers exciting measurement capabilities for future quantum communication, remote sensing, and imaging applications.
Integration of photon number resolving superconducting nanowire single-photon detectors (PNR-SNSPDs) with nanophotonic waveguides is a key technology that enables a broad range of quantum technologies on chip-scale platforms. However, all on-chip integrated SNSPDs are fabricated above the waveguide layer, which makes the characteristics of the detector’s photoresponsive film material only depend on the waveguide material, thus lowering the waveguide selectivity. Here, we report an on-chip integrated SNSPD based on optimized topology that the nanowire is sandwiched between the waveguide and the substrate. This device maintains the film characteristics with different waveguides and the light transmitted from the upper waveguide to the substrate is absorbed by the film, which not only increases the selectivity of the waveguide, but also improves light absorption of SNSPD. As an example, SiO2 waveguide with the lower optical transmission loss was fabricated in an integrated PNR-SNSPD. We proposed a multi-channel photon response amplitude superposition multiplexing scheme, which realized photon detection by integrating SNSPD on the optical transmission waveguide in the photonic integrated circuit. The solution not only can effectively read the photon responses of multiple SNSPDs through a readout port, but also can distinguish the number of photons and the corresponding response channels through the amplitude of the readout circuit, thereby realizing a photonic integrated circuit with multiple modes. Finally, we prepared a 4-channel integrated PNR-SNSPD, which resolved the number of photons and corresponding photon response positions through 16 different signal amplitudes. This result is compatible of a wide range of waveguide materials, overcoming the limitation of single photon detector integrated on waveguide for quantum photonic integrated circuit.
With recent advances in quantum technologies for applications such as communication, cryptography, computing, metrology and sensing, the performance and scalability of single-photon detection as a vital key component is becoming increasingly important. At the same time, ongoing efforts in the development of high-performance photonic integrated circuits (PIC) benefit the miniaturization and scalability of these quantum technologies. Waveguide-integrated superconducting nanowire single-photon detectors (WI-SNSPDs) allow to combine excellent performance metrics, such as high detection efficiency, low dark-count rates and low timing jitter below 20 ps with the scalability and functionality that PIC platforms such as Si3N4 provide. We have previously demonstrated broadband efficient single-photon detection with a single device over a range from visible to mid-infrared wavelengths and ultra-fast detector recovery times allowing for up to GHz count rates. Here, we present the utilization of WI-SNSPDs for discrete-variable quantum cryptography receivers with the complete photonic circuitry embedded together with the single-photon detectors on a single silicon chip, where the secret-key rates greatly benefit from the short recovery times of the detectors especially for metropolitan distances. We further realize a fully packaged 64 channel WI-SNSPD matrix for use in a wavelengthdivision multiplexed QKD setup.
Upcoming quantum technologies require scalable and cost-efficient technical solutions for widespread functionality. In order to exploit the quantum states of light, single-photon detectors are essential for application. Here, we present a low-footprint plug-and-play multi-channel single-photon detector system featuring integrated photonics that allows for ultra-fast quantum key distribution (QKD). Each channel comprises a superconducting nanowire single-photon detector (SNSPD) patterned from a niobium-titanium nitride (NbTiN) superconducting film atop silicon nitride waveguide structures. Subsequently, the on-chip photonics are interfaced by broadband 3D polymeric fiber-to-chip couplers to the ports of an 8x8 fiber array. The readout electronics allow for individual evaluation of up to 64 channels simultaneously. Integrated to a QKD experiment, a pair of the system's detection channels achieves secret key rates of up to 2.5 Mbit/s employing a coherent one-way protocol.
Quantum photonic integration circuits are a promising approach to scalable quantum processing with photons. Waveguide single-photon-detectors (WSPDs) based on superconducting nanowires have been recently shown to be compatible with single-photon sources for a monolithic integration. While standard WSPDs offer single-photon sensitivity, more complex superconducting nanowire structures can be configured to have photon-number-resolving capability. In this work, we present waveguide photon-number-resolving detectors (WPNRDs) on GaAs/Al0.75Ga0.25As ridge waveguides based on a series connection of nanowires. The detection of 0–4 photons has been demonstrated with a four-wire WPNRD, having a single electrical read-out. A device quantum efficiency of ∼24% is reported at 1310 nm for the transverse electric polarization.