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IEEE Transactions on Applied Superconductivity

Fabrication and Characterization of Fast TESs With Small Area for Single Photon Counting

Chiara Portesi, E. Taralli, L. Lolli, M. Rajteri, E. Monticone

Published Nov 20, 2014• 20 citations
Publisher

Abstract

Transition edge sensors (TESs) with high energy resolution (ΔE) at telecommunication wavelengths have been realized in the last years for application to experiments of quantum optics and quantum information. In these fields, lasers with repetition rate of the order of 50 MHz are usually applied and hence TES with recovery times lower than 20 ns would be desirable. To this aim, Ti TESs with area ranging between 1 μm × 1 μm and 2 μm × 2 μm are fabricated and characterized, to study the effects of the different sizes of active areas and critical temperatures on the energy resolutions and on the response times. Titanium TESs have been fabricated by thermal evaporation and Electron Beam Lithography technique on Si/SiN substrates, and they have been electrically and optically characterized. The experimental data have been analyzed and correlated to the detector geometrical parameters. The superconducting transitions of TESs with areas down to 1 μm × 1 μm result to be affected by lateral proximity effects of Nb wirings. Ti TESs with critical temperature of 470 mK show response time of about 150 ns and energy resolution of 0.16 eV.

DOI
10.1109/tasc.2014.2367455

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Transition edge sensors (TESs) with high energy resolution (ΔE) at telecommunication wavelengths have been realized in the last years for application to experiments of quantum optics and quantum information. In these fields, lasers with repetition rate of the order of 50 MHz are usually applied and hence TES with recovery times lower than 20 ns would be desirable. To this aim, Ti TESs with area ranging between 1 μm × 1 μm and 2 μm × 2 μm are fabricated and characterized, to study the effects of the different sizes of active areas and critical temperatures on the energy resolutions and on the response times. Titanium TESs have been fabricated by thermal evaporation and Electron Beam Lithography technique on Si/SiN substrates, and they have been electrically and optically characterized. The experimental data have been analyzed and correlated to the detector geometrical parameters. The superconducting transitions of TESs with areas down to 1 μm × 1 μm result to be affected by lateral proximity effects of Nb wirings. Ti TESs with critical temperature of 470 mK show response time of about 150 ns and energy resolution of 0.16 eV.
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.
Transition-edge sensors (TESs) have shown the capability of both energy resolution and resolving photon numbers. In this work, we present the fabrication and characterization of high detection efficiency Ti optical TESs with the critical temperatureTc= 213 mK and the photon-number resolving capability at telecommunication wavelength 1550 nm. The Ti superconducting film is prepared by a DC magnetron sputtering technique. An optical cavity comprised of 5-layers antireflection and 15-layers high-reflection Ta2O5/SiO2is enclosed with the Ti film by an ion beam assisted deposition method to improve detection efficiency, which brings the absorption of 99.74%. The energy resolution for the Ti TES with sensitive area 20 μm × 20 μm is 0.45 eV and the detection efficiency is 97% ± 1%.
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.
A transition edge sensor (TES) is one of superconducting photon detectors, which has a photon number resolving ability in light pulses. The TES device is a kind of calorimeters operated at an extremely low temperature, and the energy of the photons is measured as a resistance change in a superconducting transition region of the TES. The advantages of the TESs are an excellent energy resolution and a high quantum efficiency. However a response speed is limited due to slow thermal recovery time. To overcome this, we fabricated new TES devices which are based on a titanium superconductor. The critical temperature of our titanium films is around 410 mK, which greatly improves the thermal recovery time. The observed decay time constant of response signals to the light pulses is around several hundreds of ns, that make it possible to operate the devices at a counting rate over 1 MHz. The photon number resolving power is 0.35 eV(FWHM) for a 5 μm size device even at the high operating temperature. The system quantum efficiency is 65 % by embedding the TES films in an optical structure with a high reflection dielectric mirror and an anti-reflection coatings fabricated by an ion beam assisted sputtering method. These features are very promising for high speed photon number resolving applications in the quantum information field.
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.
Transition-edge sensor (TES) microcalorimeters are extensively used as single photon detectors from infrared to x-ray. Their good energy resolution and photon number resolving capability at visible and near-infrared wavelengths make them powerful tools for quantum information and quantum computation. In this work we report details on the fabrication of Ti/Pd TESs deposited by e-beam evaporation on silicon nitride substrates. By the proximity effect between Ti and Pd, the Ti critical temperature was tuned down to 100 mK, usual working temperature for these devices. Sharp transition of two-three mK and reproducible Tc were obtained. The Pd material can be a valid alternative to widely used Au proximity material thanks to its stronger influence on the Ti layer, that allows to obtain the same temperature reduction with thinner layers. Thermal and electrical characteristics of Ti/Au and Ti/Pd bilayers are compared in view of single photon detection.