Sergey Pereverzev

Record-Low NEP in Hot-Electron Titanium Nanobolometers

We are developing hot-electron superconducting transition-edge sensors (TES) capable of counting THz photons and operating at . We fabricated superconducting Ti nanosensors with Nb contacts with a volume of on planar Si substrates and have measured the thermal conductance in the material, G=4times10-3 W/K at 0.3 K, caused predominantly by the weak electron-phonon coupling. The corresponding phonon-noise NEP=3times10-19 W/Hz1/2 . Detection of single optical photons (1550 nm and 670 nm wavelength) has been demonstrated for larger devices and yielded the thermal time constants of 30 mus at 145 mK and of 25 mus at 190 mK. This hot-electron direct detector (HEDD) is expected to have a small enough energy fluctuation noise for detecting individual photons with v>THz where NEP~3times10-20 W/Hz1/2 is needed for spectroscopy in space.

Energy-resolved detection of single infrared photons with λ = 8 μm using a superconducting microbolometer

We report on the detection of single photons with λ = 8 μm using a superconducting hot-electron microbolometer. The sensing element is a titanium transition-edge sensor with a volume ∼0.1 μm3 fabricated on a silicon substrate. Poisson photon counting statistics including simultaneous detection of 3 photons was observed. The width of the photon-number peaks was 0.11 eV, 70% of the photon energy, at 50–100 mK. This achieved energy resolution is one of the best figures reported so far for superconducting devices. Such devices can be suitable for single-photon calorimetric spectroscopy throughout the mid-infrared and even the far-infrared.

Energy resolution of terahertz single-photon-sensitive bolometric detectors

We report measurements of the energy resolution of ultrasensitive superconducting bolometric detectors. The device is a superconducting titanium nanobridge with niobium contacts. A fast microwave pulse is used to simulate a single higher-frequency photon, where the absorbed energy of the pulse is equal to the photon energy. This technique allows precise calibration of the input coupling and avoids problems with unwanted background photons. Present devices have an intrinsic full-width at half-maximum energy resolution of approximately 23 THz, near the predicted value due to intrinsic thermal fluctuation noise.

Development of the nano-HEB array for low-background far-IR applications

We present an overview of the recent progress made in the development of a far-IR array of ultrasensitive hot-electron nanobolometers (nano-HEB) made from thin titanium (Ti) films. We studied electrical noise, signal and noise bandwidth, single-photon detection, optical noise equivalent power (NEP), and a microwave SQUID (MSQUID) based frequency domain multiplexing (FDM) scheme. The obtained results demonstrate the very low electrical NEP down to 1.5×10-20 W/Hz1/2 at 50 mK determined by the dominating phonon noise. The NEP increases with temperature as ~ T3 reaching ~ 10-17 W/Hz1/2 at the device critical temperature TC = 330-360 mK. Optical NEP = 8.6×10-18 W/Hz1/2 at 357 mK and 1.4×10-18 W/Hz1/2 at 100 mK respectively, agree with thermal and electrical data. The optical coupling efficiency provided by a planar antenna was greater than 50%. Single 8-μm photons have been detected for the first time using a nano-HEB operating at 50-200 mK thus demonstrating a potential of these detectors for future photon-counting applications in mid-IR and far-IR. In order to accommodate the relatively high detector speed (~ μs at 300 mK, ~ 100 μs at 100 mK), an MSQUID based FDM multiplexed readout with GHz carrier frequencies has been built. Both the readout noise ~ 2 pA/Hz1/2 and the bandwidth > 150 kHz are suitable for nano-HEB detectors.

Noise Measurements in Hot-Electron Titanium Nanobolometers

We are presenting experimental results on the electrical noise in small titanium hot-electron nanobolometers with the critical temperature above 300 mK. The noise data demonstrate good agreement with the conventional bolometer theory prediction. The noise is dominated by the thermal energy fluctuations (phonon noise) when the operating temperature is set just a few mK below the superconducting transition. The corresponding noise equivalent power (NEP) is about 3 times 10-18 W/Hz1/2 for the smallest measured device. The relative NEPs for the two devices measured scale roughly as the square root of the device volume as one would expect from the theory. Therefore an additional factor of 2-3 reduction of NEP may be feasible if the length and width of our device are further reduced. The demonstrated combination of the low NEP and the relatively high operating temperature is attractive for submillimeter low-background applications.

Characterization of Terahertz Single-Photon-Sensitive Bolometric Detectors Using a Pulsed Microwave Technique

We describe a technique for characterizing bolometric detectors that have sufficient sensitivity to count single terahertz photons. The device is isolated from infrared blackbody radiation and a single terahertz photon is simulated by a fast microwave pulse, where the absorbed energy of the pulse is equal to the photon energy. We have employed this technique to characterize bolometric detectors consisting of a superconducting titanium nanobridge with niobium contacts. Present devices have T_c = 0.3K and a measured intrinsic energy resolution of approximately 6 terahertz full‐width at half‐maximum, near the predicted value due to intrinsic thermal fluctuation noise, with a time constant of 2 μs. An intrinsic energy resolution of 1 terahertz should be achievable by reducing the volume of the titanium nanobridge. Such a detector has important applications in future space‐based terahertz astronomy missions.

Ultra-sensitive hot-electron nanobolometers for THz astrophysics

The background-limited spectral imaging of the early Universe requires terahertz (THz) detectors with the sensitivity 2-3 orders of magnitude better than that of the state-of-the-art bolometers. To realize this sensitivity without sacrificing the operating speed, the sensing element of a bolometric detector should have an exceptionally high thermal isolation from the environment combined with an ultrasmall heat capacity. We have demonstrated that this goal can be achieved by realizing a superconducting hot-electron nanobolometer whose design blocks photon and phonon energy exchange through its contact leads. The remaining coupling due to electron-phonon interaction provides thermal control at a level of one thousandth of the quantum of thermal conductance GQ ap 1 [pW/K] times T. These hot-electron nanobolometers with a heat capacity of ~ 0.1 aJ/K will be sufficiently sensitive for registration of single THz photons. These devices are very promising for submillimeter astronomy and other applications based on quantum calorimetry and photon counting.