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IEEE Transactions on Applied Superconductivity

Characterization of Optical Fast Transition-Edge Sensors With Optimized Fiber Coupling

L. Lolli, E. Taralli, M. Rajteri, Takayuki Numata, Daiji Fukuda

Published Feb 20, 2013• 25 citations

Abstract

Energy resolution (ΔE), recovery time (τeff), and quantum efficiency (QE) are some of the most important single photon-counting detector parameters. New applications in the quantum optics field place extreme demand on detector performances that go beyond the capabilities of established single-photon detectors. Unfortunately, it is hard to reach best results for all these parameters at the same time. Concerning transition-edge sensors (TESs) as single photon detectors, ΔEand τeffare directly and inversely proportional to the transition temperatureTc, respectively. Moreover, the geometrical optical coupling between illuminating fiber and detector, the device material and the characteristics of the optical cavity or the antireflection coating, drastically influence theQEand in some cases also the ΔE. Previous TESs fabricated by Istituto Nazionale di Ricerca Metrologica were characterized by very high energy resolution (0.18 eV) but high τeffand lowQE. In this work, we present a Ti/Au TES with higherTc(300 mK) that, using the optical alignment system implemented by AIST, shows an optimization of these important parameters, energy resolution of 0.26 eV, recovery time of 186 ns, and a quantum efficiency of 50% without using any optical structure deposited on the detector.

DOI: 10.1109/tasc.2013.2238981

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Transition-Edge Sensors (TESs) are superconducting photon detectors offering high quantum efficiency, energy resolution, and photon-number discrimination, making them attractive for quantum sensing applications. We report on the design, fabrication, and characterization of a Ti/Au/Ti TES optimized for multimode fiber coupling in NV-center experiments. The device integrates a bi-layer anti-reflective coating optimized for 700 nm, the emission wavelength range of NV centers in which we are interested. Optical characterization in a cryogenic setup demonstrated an energy resolution below 2 eV and photon-number resolution capability. A dedicated calibration setup was used to evaluate the system detection efficiency (SDE), yielding

0.85 \pm 0.02

. These results confirm the suitability of large-area TESs for efficient multimode fiber coupling and highlight their potential for improving the performance of NV-center-based quantum sensing experiments.

This study developed transition-edge sensors (TESs), which can achieve high detection efficiency and fast response time through an optimized optical cavity design. Their suitability for optical quantum information processing was confirmed. Furthermore, we developed TESs with two different sensitive area sizes—8 × 7 ţm2, 12 × 11 ţm2—and systematically evaluated their performances. By employing a titanium (Ti)/gold (Au) bilayer with a relatively high transition temperature as the sensitive element, we achieved a fast total response time—defined as the sum of the rise and decay times—of ∼160 ns. Furthermore, the optical cavity structure—predicted by simulations to achieve a photon absorptance of 99.9% at 1550 nm—yielded measured system detection efficiencies of 94.7% ± 0.62% for the 8 × 7 ţm2 TES and 99.0% ± 0.60% for the 12 × 11 ţm2 TES. Photon response measurements indicate an energy resolution of 0.20 eV for the 8 × 7 ţm2 TES and 0.37 eV for the 12 × 11 ţm2 TES. These results establish that the proposed TESs are the fastest and most efficient devices reported to date. The proposed devices offer a high detection efficiency, high count rate, and accurate photon-number resolution. Therefore, they provide a breakthrough platform for scalable fault-tolerant quantum information processing and enable significant advances in experimental quantum optics.

Superconducting transition-edge sensors (TESs), working as single-photon detectors with high quantum efficiency, low dark count rate, and photon number resolving capability, have been successfully used in quantum information experiments as well as astronomical transient object observations. Aiming to achieve high count rate, we are developing titanium-based superconducting TES single-photon detectors with a critical temperature of ~300 mK. Ti-based TESs with active area from 10 × 10 μm to 40 × 40 μm are first fabricated on silicon substrate coated with SiOx. The fabricated TES devices show a thermal conductance scaling with the active area and an effective time constant of ~4 μs from pulsed laser diode illumination. In order to get high quantum efficiency, we further design and fabricate a 1550-nm optical cavity based on dielectric mirror and antireflection layer, and study its absorption with an IR spectrometer. Ti TES devices on the dielectric mirror are then fabricated and the superconducting transition is measured.