arXiv subjects

Towsif Taher

Publications and source records attributed to Towsif Taher.

7 recordsLinked to original sources

arXiv2026

Entanglement distribution and quantum storage of more than 8000 modes over a metropolitan network

Entanglement generation between telecommunication photons and matter is central to fibre-based quantum repeaters. Achieving practical communication rates requires multiplexing, which multimode quantum memories can provide. Rare-earth-ion ensembles offer large temporal multimode storage by exploiting the numerous spectral channels within their absorption spectrum. Here, we report on a quantum repeater node comprised of a $^{171}$Yb$^{3+}$:Y$_2$SiO$_5$ multimode quantum memory, featuring a 250 MHz bandwidth and a $76.6~\mu\mathrm{s}$ lifetime, and a bandwidth-matched entangled photon-pair source. We introduce and validate a quantitative measure of the effective temporal mode capacity using a Schmidt decomposition. With this platform, we demonstrate entanglement between a telecom photon propagating through a 25.3 km fiber spool and a 979 nm photon stored for $125~\mu\mathrm{s}$ across 16340 temporal modes. Finally, we report a field deployment distributing entanglement over 5.66 km through the Geneva metropolitan fibre network while storing 8235 modes for $63~\mu\mathrm{s}$.

quant-ph↗

arXiv2026

Certification of the genuine resolution of photon number resolving detectors

Photon-number-resolving (PNR) detectors are essential components of photonic quantum technologies, yet thus far, no practical metric exists to certify how many photons they can genuinely resolve in a single measurement. Here we introduce an operational framework for quantifying the capability of a PNR detector to distinguish between different numbers of photons, i.e. its genuine resolution. In turn, we develop a practical and scalable protocol for certifying the genuine resolution of a detector, which is based on coherent state probes. We apply the method to a 28-pixel photon-number-resolving superconducting nanowire single-photon detector (PNR-SNSPD) and certify genuine four-outcome resolution. Our work highlights the critical requirements in terms of detector efficiency towards achieving high genuine resolution. This approach provides an operational benchmark for PNR detectors and fills a crucial gap in the characterization of photonic quantum devices.

quant-ph↗

arXiv2026

Phase-correlation-free quantum key distribution source operating at gigahertz rates

Phase randomization is essential for the security of practical decoy-state quantum key distribution (QKD) systems. Commonly, implementations rely on laser sources which are either actively phase-randomized, or gain-switched. However, at high repetition rates these show correlations, which can ultimately compromise security and performance. We present a 1.25 GHz phase-randomized QKD source based on a super-luminescent light emitting diode (SLED) operating in the C-band as a compact and cost-effective alternative. The source generates $\sim100$ ps optical pulses with $400$ ps pulse-to-pulse separation, compatible with high-speed time-bin encoding. Interferometric measurements demonstrate $>99\%$ visibility between adjacent time bins, confirming strong first-order coherence within the same quantum signals, while the spontaneous-emission-driven nature of the SLED ensures intrinsic global phase randomization between adjacent signals. This work establishes a scalable SLED-based platform for high-speed prepare-and-measure QKD systems.

quant-ph↗

arXiv2025

Electrical thermography via centimetre-scale fiber-based distributed temperature sensing

We present a Raman-based Distributed Temperature Sensor (RDTS) with centimetre-scale resolution for thermographic analysis of electronic circuits. Temperature is measured along a single-mode fiber routed across a custom printed circuit board (PCB) with 1 cm$^2$ heating elements, using optical time-domain reflectometry of Raman signals detected by superconducting nanowire single-photon detectors (SNSPDs). This approach enables two-dimensional thermal mapping of the PCB under heating configurations with multiple hotspots. A spatial resolution of 3 cm and a temperature accuracy of 2 {\deg}C are achieved with an integration time of 5 minutes. Thermography can be performed down to 77 K, revealing that the PCB thermal resistance decreases by nearly an order of magnitude compared to room temperature, due to enhanced convective cooling in liquid nitrogen. These results establish centimetre-scale RDTS as a robust technique for real-time, spatially resolved thermography of electronic circuits, particularly in regimes where infrared imaging is ineffective, such as at low temperatures or within volumetric electronic architectures.

quant-ph↗

arXiv2025

Towards High-Efficiency Particle Detection Using Superconducting Microwire Arrays

We present a detailed study of an 8-channel $1\times1$ mm$^{2}$ WSi superconducting microwire single photon detector (SMSPD) array exposed to 120 GeV hadron beam and 120 GeV muon beam at the CERN Super Proton Synchrotron H6 beamline. Following up on our first detailed characterization of the efficiency and response of an SMSPD fabricated on a 3 nm WSi film, we report measurements of enhanced particle detection efficiency using a sensor fabricated from a thicker 4.7nm-thick WSi film. We also report the first SMSPD detection efficiency measurement made for muons. Measurements are enabled by a silicon tracking telescope providing 10 $\mu$m in-situ spatial resolution. The results show a fill factor-normalized detection efficiency of 75% and a time resolution of about 130 ps across pixels. These findings represent a significant advancement toward developing high-efficiency SMSPD charged particle tracking systems with simultaneous precision timing, with potential applications in future accelerator-based experiments such as the FCC-ee and Muon Collider.

physics.ins-det↗

arXiv2024

Enhanced Detection Rate and High Photon-Number Efficiencies with a Scalable Parallel SNSPD

Since their inception, superconducting nanowire single-photon detectors have been enabling quantum optical applications and the rise of the photonic quantum industry. The evolution in the detector design and read-out strategies has led to the introduction of devices with a plurality of independent pixels, which have been able to operate with high system detection efficiency at high speed while also supporting photon number resolution capabilities. However, this comes at the cost of a complex readout that requires one coaxial cable for each pixel of the array. Here, we report a 28-pixel SNSPD with a dedicated parallel architecture that, while maintaining a simple readout with a single coaxial line, enables the detector to operate at high speed with low-performance degradation. The device shows a maximum single-photon efficiency of 88% and is able to maintain its efficiency above 50%, coupled with a timing jitter lower than 80 ps, up to a detection rate of 200 million counts per second. The detector also provides state-of-the-art photon-number-resolving performances with a 2-photon efficiency of 75% and a 3-photon efficiency of 62%.

quant-ph↗

arXiv2022

Unveiling photon statistics with a 100-pixel photon-number-resolving detector

Single-photon detectors are ubiquitous in quantum information science and quantum sensing. They are key enabling technologies for numerous scientific discoveries and fundamental tests of quantum optics. Photon-number-revolving detectors are the ultimate measurement tool of light. However, few detectors to date can provide high-fidelity photon number resolution at few-photon levels. Here, we demonstrate an on-chip detector that can resolve up to 100 photons by spatiotemporally multiplexing an array of superconducting nanowires along a single waveguide. The unparalleled photon number resolution paired with the high-speed response exclusively allows us to unveil the quantum photon statistics of a true thermal light source for the first time, which is realized by direct measurement of high-order correlation function g^(N) with N up to 15, observation of photon-subtraction-induced photon number enhancement, and quantum-limited state discrimination against a coherent light source. Our detector provides a viable route towards various important applications, including photonic quantum computation and quantum metrology.

quant-ph↗