Tungsten Transition-edge Sensors Research Articles

NUCLEUS: Exploring Coherent Neutrino-Nucleus Scattering with Cryogenic Detectors

The NUCLEUS experiment aims for the detection of coherent elastic neutrino-nucleus scattering at a nuclear power reactor with gram-scale, ultra-low-threshold cryogenic detectors. This technology leads to a miniaturization of neutrino detectors and allows to probe physics beyond the Standard Model of particle physics. A 0.5 g NUCLEUS prototype detector, operated above ground in 2017, reached an energy threshold for nuclear recoils of below 20 eV. This sensitivity is achieved with tungsten transition edge sensors which are operating at temperatures of 15 mK and are mainly sensitive to non-thermal phonons. These small recoil energies become accessible for the first time with this technology, which allows collecting large-statistics neutrino event samples with a moderate detector mass. A first-phase cryogenic detector array with a total mass of 10 g enables a 5-sigma observation of coherent scattering within several weeks. We identified a suitable experimental site at the Chooz Nuclear Power Plant and performed muon and neutron background measurements there. The operation of a NUCLEUS cryogenic detector array at such a site requires highly efficient background suppression. NUCLEUS plans to use an innovative technique consisting of separate cryogenic anticoincidence detectors against surface backgrounds and penetrating (gamma, neutron) radiation. We present first results from prototypes of these veto detectors and their operation in coincidence with a NUCLEUS target detector.

Photon-Number-Resolving Transition-Edge Sensors for the Metrology of Quantum Light Sources

Low-temperature photon-number-resolving detectors allow for direct access to the photon number distribution of quantum light sources and can thus be exploited to explore the photon statistics, e.g., solid-state-based non-classical light sources. In this work, we report on the setup and calibration of a detection system based on fiber-coupled tungsten transition-edge sensors (W-TESs). Our stand-alone system comprises two W-TESs, read out by two 2-stage-SQUID current sensors, operated in a compact detector unit that is integrated in an adiabatic demagnetization refrigerator. Fast low-noise analog amplifiers and digitizers are used for signal acquisition. The detection efficiency of the single-mode fiber-coupled detector system in the spectral region of interest (850–950 nm) is determined to be larger than 87 %. The presented detector system opens up new routes in the characterization of quantum light sources for quantum information, quantum-enhanced sensing and quantum metrology.

Quasiparticle Diffusion in CRESST Light Detectors

CRESST-II is a direct dark matter experiment that uses scintillating calorimeters to detect WIMP-induced nuclear scatter processes. Heat and light signals are read out with tungsten transition edge sensors (TESs) that are optimized toward their sensitivity to non-thermal phonons. The usage of superconducting thin film structures (e.g., aluminum) serving as phonon collectors to increase the collection area for this signal component is an approach to improve the sensitivity of the TES. The performance of the phonon collectors depends on the material properties and the quality achieved in the production process. We optimized the size of the phonon collectors for the given quality of CRESST-II light detectors. The diffusion lengths measured in this work are $$\mathcal {O}$$ (1 mm) and show a strong correlation to the Residual Resistivity Ratio of the respective films. First tests of CRESST-II light detectors with larger as well as thicker phonon collectors individually show improvements in the measured pulse height of 30 %.

Quantum Efficiency Characterization and Optimization of a Tungsten Transition-Edge Sensor for ALPS II

The ALPS II experiment, Any Light Particle Search II at DESY in Hamburg, will look for sub-eV mass new fundamental bosons (e.g., axion-like particles, hidden photons, and other weakly interacting sub-eV particles) in the next years by means of a light-shining-through-wall setup. The ALPS II photosensor is a tungsten transition-edge sensor (W-TES) optimized for 1064 nm photons. This TES, operated at 80 mK, has already allowed single infrared photon detections as well as non-dispersive spectroscopy with very low background rates. The demonstrated quantum efficiency for such TES is up to 95 % (1064 nm) as has been already demonstrated by the US National Institute of Standards and Technology. A back-to-back measurement of the ALPS TES quantum efficiency using a calibrated charge-coupled device camera has lead to a first estimation of 30 %. Improvement methods are discussed.

Quasiparticle Transport in Thick Aluminum Films Coupled to Tungsten Transition Edge Sensors

We have fabricated and characterized test devices of a new geometry for cryogenic dark matter search superconducting sensors. The modified design uses the same photolithography masks used to fabricate earlier-generation devices, but with the Al and W films deposited in reverse order. This inverted film geometry (Al over W instead of our conventional W over Al) offers a simplified and robust way to dramatically increase the thickness of Al energy-collecting fins coupled to thin W-TESs—tungsten-transition edge sensors. Data are presented from experiments with inverted geometry test devices exposed to X-rays from a NaCl fluorescence source. The results are compared to data obtained with similar devices fabricated in the standard, non-inverted geometry.

Measurement of quasiparticle transport in aluminum films using tungsten transition-edge sensors

We report on experimental studies of phonon sensors which utilize quasiparticle diffusion in thin aluminum films connected to tungsten transition-edge-sensors (TESs) operated at 35 mK. We show that basic TES physics and a simple physical model of the overlap region between the W and Al films in our devices enables us to accurately reproduce the experimentally observed pulse shapes from x-rays absorbed in the Al films. We further estimate quasiparticle loss in Al films using a simple diffusion equation approach. These studies allow the design of phonon sensors with improved performance.

On-chip, photon-number-resolving, telecommunication-band detectors for scalable photonic information processing

Integration is currently the only feasible route towards scalable photonic quantum processing devices that are sufficiently complex to be genuinely useful in computing, metrology, and simulation. Embedded on-chip detection will be critical to such devices. We demonstrate an integrated photon-number resolving detector, operating in the telecom band at 1550 nm, employing an evanescently coupled design that allows it to be placed at arbitrary locations within a planar circuit. Up to 5 photons are resolved in the guided optical mode via absorption from the evanescent field into a tungsten transition-edge sensor. The detection efficiency is 7.2 \pm 0.5 %. The polarization sensitivity of the detector is also demonstrated. Detailed modeling of device designs shows a clear and feasible route to reaching high detection efficiencies.

The Cryogenic Dark Matter Search (CDMS) experiment: Results and prospects

Weakly Interacting Massive Particles (WIMPs) are a strong candidate for the Cold Dark Matter of the Universe. CDMS-II is a direct-search WIMP search experiment, operating at 50 mK and housed at the Soudan mine, Minnesota. The 250 gram Ge detectors utilize athermal phonon sensors where tungsten transition edge sensors are operated in negative electrothermal feedback. The search at Soudan is ongoing with an expected final reach of CDMS-II by the end of 2008 of a WIMP-nucleon cross-section sensitivity of 2.1 x10-44 cm2, at a WIMP mass of 60 GeV/c2. To proceed further, we have proposed the SuperCDMS program.

Energy Collection Efficiency of Tungsten Transition-Edge Sensors in the Near-Infrared

Single-photon detectors operating at visible and near-infrared wavelengths with high detection efficiency and low noise are a requirement for many quantum-information applications. Detection of visible and near-infrared light at the single-photon level and discrimination between one- and two-photon absorption events place stringent requirements on TES design in terms of heat capacity, thermometry, and optical detection efficiency. Energy loss in the conversion of the photon energy in tungsten TESs to heat degrades the performance of these devices. By fabricating TESs on surface-micromachined Si3N4 membranes we improved the energy collection efficiency by a factor of two, to ∼80% energy efficiency.

Low-temperature optical photon detectors for quantum information applications

There is increasing interest in using high-performance cryogenic optical photon detectors in a variety of applications in quantum information science and technology. These applications require detectors that have extremely low dark count rates, high count rates, high quantum efficiency, and moderate energy resolution for IR to optical photons. We describe three applications, quantum key distribution, quantum optics with spontaneous parametric down converters, and linear optical quantum computing. We also describe preliminary results using a superconducting tungsten transition-edge sensor in a quantum key distribution system and a quantum optics experiment with spontaneous parametric down converters.

Near-unity absorption of near-infrared light in tungsten films

The number-resolving ability and extremely low dark-count rate of tungsten transition-edge sensors make them excellent candidates to replace avalanche photodiodes in quantum information experiments such as quantum key distribution and quantum computing at the telecommunication wavelengths, 1330 and 1550nm. Increasing the absorption of these devices from the current value of 20% to near unity would make these detectors even more desirable for these applications. By incorporating the tungsten in a stack of elements including a mirror and an anti-reflective coating, we have demonstrated room-temperature absorption of greater than 97% in films of tungsten.

Transition edge sensors as single photon detectors

We have recently demonstrated wideband detection of individual photons from the mid infrared (IR), through the optical, and into the near ultraviolet (UV). We use thin film tungsten transition edge sensors about 20 /spl mu/m on a side to detect single photon events above a noise threshold of 0.3 eV (4 /spl mu/m wavelength), with an energy resolution of 0.12 eV FWHM (full width at half maximum). The observed events have a risetime (falltime) of 0.5 /spl mu/s (30 /spl mu/s). In this paper we present a summary of recent calibration data and resolution measurements as well as two proof-of-principle experiments to show the ability of TES detectors to extract both time and energy information from photons arriving at the detector during astronomical observations.

Detection of single infrared, optical, and ultraviolet photons using superconducting transition edge sensors

We have demonstrated the use of superconducting transition edge sensors for the wide-band detection of individual photons from the mid infrared (IR), through the optical, and into the far ultraviolet (UV). These tungsten transition edge sensors are squares about 18 μm on a side and detect single photon events above a threshold of 0.3 eV (4 μm wavelength), with an energy resolution of 0.15 eV full width at half maximum, and with a risetime (falltime) of .5 μs (60 μs). The calibration data extend up to the UV cutoff of the fiber optic feed at 3.5 eV (350 nm).

Advances in Stanford phonon-mediated elementary particle detectors

We have demonstrated a new phonon sensor design based on aluminum phonon collection pads connected to tungsten transition-edge sensors (TES). The device is patterned onto a silicon crystal and phonons produced by events in the Si are absorbed into the aluminum films where about half of the energy is converted into long-lived quasiparticle excitations. These diffuse until they encounter the lower gap W regions where they deposit their potential energy to the electron system in the W. With the Si crystal at ∼ 40 mK, the W is kept near the center of its resistive transition ( ∼ 90 mK) using voltage bias and Joule self-heating. Current changes induced by particle events are measured with a high-bandwidth SQUID amplifier readout. We have demonstrated an energy resolution of ∼ 360 eV FWHM and a position sensitivity of ∼ 0.2 mm for 55Fe X-rays. We have also completed a new analysis of the nuclear recoil versus electron recoil ballistic phonon production experiments which used our earlier generation Ti TES on Si crystals. The new results set an upper limit on the distinction between the two phonon spectra and provide a better understanding of the phonon sensor response.