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IEEE Transactions on Applied Superconductivity

Photon Number Resolving Mo/AuPd Transition Edge Sensors for Visible up to NIR Wavelength

Matthias Schmelz, Vitaly Shvab, Katja Peiselt, Jürgen Kunert, Gabriel Zieger, V. Zakosarenko, G. Oelsner, Ronny Stolz

Published May 14, 2026• 0 citations
Publisher

Abstract

We present results of the development of transition-edge sensors (TES) based on Mo/AuPd thermistors aiming for photon number resolution in the visible up to NIR wavelength. TES are deposited on an oxidized solid Silicon substrate and make use of electron-phonon decoupling at mK-temperatures generating a weak link for thermal relaxation. The Mo/AuPd bilayers have a tuned critical temperature of approximately 180 mK and are being read out by making use of a series SQUID array, both implemented in a setup in an adiabatic demagnetization refrigerator. Optical pulses, generated via gated laser sources at room temperature, are fed via an optical single mode fiber to the TES. Their absorption is measured as a TES pulse response with a SQUID array. By means of pulse amplitude histograms (PAH), single photon resolution in the visible to NIR has been achieved. We've proven TES pulse response originating from single photon absorption in the TES via fitting the PAH with a Poissonian distribution. For 405 nm laser wavelength, we've achieved an energy resolution of about 0.7 eV, determined via analysis of the raw measurement data using PAH.

DOI
10.1109/tasc.2026.3693297

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IEEE Transactions on Applied Superconductivity•Jan 12, 2026•2 citations
We present results of the development of transition-edge sensors (TES) based on Mo/AuPd thermistors aiming for photon number resolution in the visible up to NIR wavelength. TES are deposited on an oxidized solid Silicon substrate and make use of electron-phonon decoupling at mK-temperatures generating a weak link for thermal relaxation. The Mo/AuPd bilayers have a tuned critical temperature of approximately 180 mK and are being read out by making use of a series SQUID array, both implemented in a setup in an adiabatic demagnetization refrigerator. Optical pulses, generated via gated laser sources at room temperature, are fed via an optical single mode fiber to the TES. Their absorption is measured as a TES pulse response with a SQUID array. By means of pulse amplitude histograms (PAH), single photon resolution in the visible to NIR has been achieved. We've proven TES pulse response originating from single photon absorption in the TES via fitting the PAH with a Poissonian distribution. For 405 nm laser wavelength, we've achieved an energy resolution of about 0.7 eV, determined via analysis of the raw measurement data using PAH.
Single photon detectors are fundamental tools for quantum metrology, e.g. to calibrate both detectors and sources, as for quantum information. One of the most promising detectors able to resolve single photons is the transition-edge sensor (TES). We report our last results obtained with Ti/Au TES deposited on SiN substrate. Photon counting measurements, obtained by using pulsed sources, in the NIR-visible wavelength range, show the ability to resolve up to fourteen photons with an energy resolution of 0.44 eV at 690 nm (1.80 eV) and 0.38 eV at 1310 nm (0.95 eV), with a good linearity. A preliminary measurement obtained by using a parametric down conversion (PDC) heralded single photon source, at 812 nm (1.53 eV), is also reported.
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.
Transition-edge sensor (TES) microcalorimeters are promising for application in the field of quantum information and quantum computation thanks to their outstanding single photon detection capabilities. Good energy resolution and photon number discrimination at visible and near-infrared wavelengths make them extensively used as single photon detectors. In this work we report details on the fabrication of Pd/Ti TESs deposited by e-beam evaporation on silicon nitride substrates. We use Pd as alternative to Au layer thanks to its stronger influence on the Ti layer, that allows to obtain the same temperature reduction with thinner layers. The transition temperatures Tcof the devices range from 83 to 110 mK with a transition width DeltaTc=0.5 mK. Thermal and electric characteristics of Pd/Ti TESs at different temperatures and its capability as single photon sensor are reported.
Abstract Optical transition-edge sensors (TESs) have shown an energy resolution for resolving the number of incident photons at the telecommunication wavelength. However, a higher energy resolution is required for biological imaging and microscopic spectroscopy. In this study, we tested an Au/Ti (10/20 nm) bilayer TES that showed a high energy resolution. The high energy resolution was achieved by lowering the critical temperature T c to 115 mK, and the resultant energy resolution was 67 meV full width at half maximum (FWHM) at 0.8 eV. When T c was reduced to 115 mK, the theoretical resolution would scale up to 30 meV FWHM, considering that the typical energy resolution of optical TESs was 150 meV and T c was 300 mK. To investigate the difference between the theoretical expectation (30 meV) and the measured value (67 meV), we measured the complex impedance and current noise of the TES. We found excess Johnson noise in the TES; the excess Johnson noise term M was 1.5 at a bias point where the resistance was 10% of the normal resistance. For reference, the above mentioned TES was compared with a TES showing typical energy resolution (156 meV FWHM). We also discussed factors that improved or inhibited the energy resolution.
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.
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%.