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IEEE Transactions on Applied Superconductivity

Investigation of Ti/Pd Bilayer for Single Photon Detection

E. Taralli, Chiara Portesi, Roberto Rocci, M. Rajteri, E. Monticone

Published Jun 1, 2009• 16 citations
Publisher

Abstract

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.

DOI
10.1109/tasc.2009.2019561

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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.
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 Sensors (TESs) are microcalorimeters that measure the energy of incident single photons by the resistance increase of a superconducting film biased within the superconducting-to-normal transition. TES are able to detect single photons from IR to X-ray with an intrinsic energy resolution and photon-number discrimination capability. Metrology, astronomy and quantum \ncommunication are the fields where these properties can be particularly useful. In this work, we report about characterization of different TESs based on Ti films. Single photons have been detected from 200nm to 800 nm working at transition temperature Tc ∼ 100 mK. Using a pulsed laser at 690nm we have demonstrated the capability to resolve up to five photons.
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.
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%.
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.
We are developing single-photon detectors employing superconducting-transition-edge sensors (TESs). TESs are fabricated both with Ti and proximity bilayers of Ti / Au and the characterisitcs of the two films are compared. In the visible-near infrared spectral region, the photon absorption occurs directly in the film and the quantum efficiency of the detector is limited by the reflection losses at the film surface, which are around 60%. For many applications, like quantum cryptography, these losses are too high. In a previous paper [Nucl. Instr. Meth. A559(2) (2006) 757–759], we presented a way to reduce the detector reflectance for two projects based on the deposition of a few layers of amorphous silicon-nitrogen alloys. In this paper, we report some experimental data at low temperature relative to those projects. We will also show how to minimize the detector reflectance simultaneously for three telecommunication wavelengths and for a new continuum band.