SwePub - sökning: WFRF:(Mahashabde Sumedh 1985)

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1.	de Graaf, Sebastian Erik, 1986, et al. (författare) Quantifying dynamics and interactions of individual spurious low-energy fluctuators in superconducting circuits 2021 Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 103:17 Tidskriftsartikel (refereegranskat)abstract Understanding the nature and dynamics of material defects in superconducting circuits is of paramount importance for improving qubit coherence and parameter stability and much needed for implementing large-scale quantum computing. Here we present measurements on individual highly coherent environmental two-level systems (TLS). We trace the spectral diffusion of specific TLS and demonstrate that it originates from the TLS coupling to a small number of low energy incoherent fluctuators. From the analysis of these fluctuations, we access the relevant parameters of low energy fluctuators: Dipole moments, switching energies, and, more importantly, interaction energies. Our approach opens up the possibility of deducing the macroscopic observables in amorphous glassy media from direct measurements of local fluctuator dynamics at the microscopic level- A route towards substantiating commonly accepted, but so far phenomenological, models for the decohering environment.
2.	de Graaf, S. E., et al. (författare) Two-level systems in superconducting quantum devices due to trapped quasiparticles 2020 Ingår i: Science advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 6:51 Tidskriftsartikel (refereegranskat)abstract A major issue for the implementation of large-scale superconducting quantum circuits is the interaction with interfacial two-level system (TLS) defects that lead to qubit parameter fluctuations and relaxation. Another major challenge comes from nonequilibrium quasiparticles (QPs) that result in qubit relaxation and dephasing. Here, we reveal a previously unexplored decoherence mechanism in the form of a new type of TLS originating from trapped QPs, which can induce qubit relaxation. Using spectral, temporal, thermal, and magnetic field mapping of TLS-induced fluctuations in frequency tunable resonators, we identify a highly coherent subset of the general TLS population with a low reconfiguration temperature similar to 300 mK and a nonuniform density of states. These properties can be understood if the TLS are formed by QPs trapped in shallow subgap states formed by spatial fluctutations of the superconducting order parameter. This implies that even very rare QP bursts will affect coherence over exponentially long time scales.
3.	Dodkins, Rupert H., et al. (författare) First principle simulator of a stochastically varying image plane for photon-counting high contrast applications 2020 Ingår i: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 132:1016, s. 1-12 Tidskriftsartikel (refereegranskat)abstract Optical and near-infrared Microwave Kinetic Inductance Detectors, or MKIDs are low-temperature detectors with inherent spectral resolution that are able to instantly register individual photons with potentially no false counts or readout noise. These properties make MKIDs transformative for exoplanet direct imaging by enabling photon-statistics-based planet-discrimination techniques as well as performing conventional noise-subtraction techniques on shorter timescales. These detectors are in the process of rapid development, and as such, the full extent of their performance enhancing potential has not yet be quantified. MKID Exoplanet Direct Imaging Simulator, or MEDIS, is a general-purpose end-to-end numerical simulator for high-contrast observations with MKIDs. The simulator exploits current optical propagation libraries and augments them with a new MKIDs simulation module to provide a pragmatic model of many of the degradation effects present during the detection process. We use MEDIS to demonstrate how changes in various MKID properties affect the contrast-separation performance when conventional differential imaging techniques are applied to low-flux, short duration observations. We show that to improve performance at close separations will require increasing the maximum count rate or pixel sampling when there is high residual flux after the coronagraph. We predict that taking pixel yield from the value achieved by current instruments of 80% and increasing it to 100% would result in an improvement in contrast of a factor of ∼4 at 3λ/D and ∼8 at 6λ/D. Achieving better contrast performance in this low flux regime would then require exploiting the information encoded in the photon arrival time statistics.
4.	Gunbina, A. A., et al. (författare) A 90 GHz SINIS detector with 2 GHz readout 2021 Ingår i: IEEE Transactions on Applied Superconductivity. - 1558-2515 .- 1051-8223. ; 31:5 Tidskriftsartikel (refereegranskat)abstract A superconductor-insulator-normal metal-insulator-superconductor (SINIS) detector integrated in a planar 90 GHz band twin-slot antenna with a 2 GHz superconducting resonator readout was fabricated and experimentally studied. In order to achieve high pixel count, the traditional dc readout of the SINIS detector is replaced by NbN coplanar 13.850 mm long superconducting resonator. SINIS detectors have traditionally dc Junction Field Effect Transistor (JFET) room-temperature readout. Such readout requires individual wiring for each pixel, while the microwave readout is far less cluttered as only one coaxial line is needed for hundreds of devices. Such readout operates similar to frequency domain multiplexing (FDM) for microwave kinetic inductance detectors (MKID). The planar twin slot antenna has two parallel slots in a metal ground plane which are excited coherently by short sections of a coplanar waveguide (CPW) line with a SINIS detector at the center. One section of the CPW is extended past the slot in a long superconducting section which functions as a quarter wavelength resonator. This resonator is short circuited to the ground plane at the far end, with the expected open circuited end terminated by the SINIS detector in the antenna. We measured the response of sample to black body radiation temperatures 6 K and 9 K. The corresponding dynamic resistance maximum drops from 50 k down to 30 k. An RF readout channel comprising a coplanar coupler and a coplanar resonator has a resonant frequency of 1.8 GHz. Unloaded Q factor (without incoming irradiation) is 200. The signal spectral characteristics and the response to the black body radiation have shown design values as expected.
5.	Gunbina, A. A., et al. (författare) Spectral Response of Arrays of Half-wave and Electrically Small Antennas with SINIS Bolometers 2020 Ingår i: Physics of the Solid State. - 1063-7834 .- 1090-6460. ; 62:9, s. 1604-1611 Tidskriftsartikel (refereegranskat)abstract Two types arrays of annular half-wave and electrically small antennas with typical sizes of the elements corresponding to 1/10 of the wavelength at SubTHz band with integrated superconductor-insulator-normal metal-insulator-superconductor (SINIS) bolometers have been developed, fabricated and experimentally studied. We performed numerical modeling of the full structure and use additional reference channels in experimental studies to enhance the accuracy of the spectral response estimations of receiving arrays. In experiments three reference channels were used for normalization of the spectral response: a pyroelectric detector outside the cryostat, and two cold channels-a RuO(2)bolometer and on-chip thermometer comprising series array of NIS-junctions.
6.	Kern, S., et al. (författare) Reflection-enhanced gain in traveling-wave parametric amplifiers 2023 Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 107:17 Tidskriftsartikel (refereegranskat)abstract The operating principle of traveling-wave parametric amplifiers is typically understood in terms of the standard coupled mode theory, which describes the evolution of forward propagating waves without any reflections, i.e., for perfect impedance matching. However, in practice, superconducting microwave amplifiers are unmatched nonlinear finite-length devices, where the reflecting waves undergo complex parametric processes, not described by the standard coupled mode theory. Here, we present an analytical solution for the TWPA gain, which includes the interaction of reflected waves. These reflections result in corrections to the well-known results of the standard coupled mode theory, which are obtained for both three-wave and four-wave mixing processes. Due to these reflections, the gain is enhanced and unwanted nonlinear phase modulations are suppressed. Predictions of the model are experimentally demonstrated on two types of unmatched TWPA, based on coplanar waveguides with a central wire consisting of (i) a high kinetic inductance superconductor, and (ii) an array of 2000 Josephson junctions.
7.	Lemzyakov, S., et al. (författare) Experimental study of a SINIS detector response time at 350 GHz signal frequency 2018 Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 969:1 Konferensbidrag (refereegranskat)abstract Response time constant of a SINIS bolometer integrated in an annular ring antenna was measured at a bath temperature of 100 mK. Samples comprising superconducting aluminium electrodes and normal-metal Al/Fe strip connected to electrodes via tunnel junctions were fabricated on oxidized Si substrate using shadow evaporation. The bolometer was illuminated by a fast black-body radiation source through a band-pass filter centered at 350 GHz with a passband of 7 GHz. Radiation source is a thin NiCr film on sapphire substrate. For rectangular 10÷100 μs current pulse the radiation front edge was rather sharp due to low thermal capacitance of NiCr film and low thermal conductivity of substrate at temperatures in the range 1-4 K. The rise time of the response was ∼1-10 μs. This time presumably is limited by technical reasons: high dynamic resistance of series array of bolometers and capacitance of a long twisted pair wiring from SINIS bolometer to a room-Temperature amplifier.
8.	Mahashabde, Sumedh, 1985, et al. (författare) A distributed-absorber cold-electron bolometer single pixel at 95GHz 2015 Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 107:9 Tidskriftsartikel (refereegranskat)abstract We describe a Frequency Selective Surface (FSS) based distributed-absorber Cold-Electron Bolometer (CEB) pixel at 95GHz integrated in a multi-moded horn. The FSS provides a resonant interaction with incident mm and sub-mm radiation and defines the bandwidth of the array while the horn provides the matching of the beam to the telescope optics. CEB detectors with matched impedance are integrated within the periodic elements of the FSS and generate a voltage response proportional to the incident optical power in the bandwidth of the FSS. A prototype pixel was designed, fabricated, and characterized at a temperature of 280 mK. We present optical response to blackbody radiation and fit it to the CEB model. For an absorbed power of 50 pW, we estimate an optical responsivity of 1.2×108V/W and a readout dominated Noise Equivalent Power (NEP) of 1.8×10-15 W Hz - 1 / 2. A measured bandwidth of 9GHz of this detector array confirms the frequency selective nature. This prototype represents a possible solution as a detector for the 95GHz channel of the SWIPE instrument on the LSPE balloon-borne telescope. This kind of FSS based mm-wave architecture can be easily scaled to other frequency ranges and used on any other balloon-borne telescope focal planes.
9.	Mahashabde, Sumedh, 1985, et al. (författare) A Frequency Selective Surface based focal plane receiver for the OLIMPO balloon-borne telescope 2015 Ingår i: IEEE Transactions on Terahertz Science and Technology. - 2156-342X .- 2156-3446. ; 5:1, s. 145-152 Tidskriftsartikel (refereegranskat)abstract We describe here a focal plane array of Cold-Electron Bolometer (CEB) detectors integrated in a Frequency Selective Surface (FSS) for the 350 GHz detection band of the OLIMPO balloon-borne telescope. In our architecture, the two terminal CEB has been integrated in the periodic unit cell of the FSS structure and is impedance matched to the embedding impedance seen by it and provides a resonant interaction with the incident sub-mm radiation. The detector array has been designed to operate in background noise limited condition for incident powers of 20 pW to 80 pW, making it possible to use the same pixel in both photometric and spectrometric configurations. We present high frequency and dc simulations of our system, together with fabrication details. The frequency response of the FSS array, optical response measurements with hot/cold load in front of optical window and with variable temperature black body source inside cryostat are presented. A comparison of the optical response to the CEB model and estimations of Noise Equivalent power (NEP) is also presented.
10.	Mahashabde, Sumedh, 1985, et al. (författare) Fast Tunable High-Q-Factor Superconducting Microwave Resonators 2020 Ingår i: Physical Review Applied. - 2331-7019. ; 14:4 Tidskriftsartikel (refereegranskat)abstract We present fast tunable superconducting microwave resonators fabricated from planar NbN on a sapphire substrate. The 3 lambda/4 wavelength resonators are tuning fork shaped and tuned by passing a dc current that controls the kinetic inductance of the tuning fork prongs. The lambda/4 section from the open end operates as an integrated impedance converter that creates a nearly perfect short for microwave currents at the dc terminal coupling points, thus preventing microwave energy leakage through the dc lines. We measure an internal quality factor Q(int) > 10(5) over the entire tuning range. We demonstrate a tuning range of greater than 3% and tuning response times as short as 20 ns for the maximum achievable detuning. Because of the quasifractal design, the resonators are resilient to magnetic fields of up to 0.5 T.
11.	Mahashabde, Sumedh, 1985, et al. (författare) Focal plane array of thermo-electric bolometers 2010 Ingår i: 21st International Symposium on Space Terahertz Technology 2010, ISSTT 2010; Oxford; United Kingdom; 23 March 2010 through 25 March 2010. - 9781617823626 ; , s. 257- Konferensbidrag (refereegranskat)abstract Novel concepts of the parallel and series array of Thermo-Electric Bolometers (TEB) with Superconductor-Insulator-Normal (SIN) Tunnel Junctions [1] have been proposed and realized for a distributed focal plane antenna. The arrays are developed for a pixel design based on arrays of TEBs coupled to a distributed slot antenna or dipole antenna [2] similar to array of Cold-Electron Bolometers (CEB) [3,4].
12.	Mahashabde, Sumedh, 1985 (författare) Frequency Selective Cold-Electron Bolometer Arrays 2015 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract This work presents the integration of the Cold-Electron Bolometer (CEB) in Frequency Selective Surface (FSS) based arrays targeting balloon-borne telescope missions with high incident power requirements (typically tens of pW). FSS are planar frequency sensitive structures typically consisting of repeating pattern of a simple motif like square, circle, etc. This creates an array structure that is impedance matched to incident electromagnetic radiation. We investigated the integration of CEB detectors in these arrays and their response to incident millimeter/submillimeter radiation. The inherent frequency sensitive characteristics of the FSS allow these kinds of arrays to be designed for a wide range of frequency bands with coupling efficiencies approaching unity. A prototype 23 pixel CEB array at 345 GHz was developed for the OLIMPO telescope for performing photometric and spectroscopic observations of the Sunyaev– Zel'dovich effect from clusters of galaxies. Measurements from test pixel indicate a responsivity up to 2x10^8 V/W at low background powers. Spectral measurements indicate a bandwidth of about 20 GHz. Using room temperature commercial amplifiers, the Noise Equivalent Power (NEP) was estimated as 2x10^-16 W\sqrt{Hz} ,which is larger than the theoretically modelled value by a factor of 4-5. Prototype pixels which could possibly be used for the 145 GHz and 95 GHz channels on the SWIPE instrument in the LSPE balloon-borne telescope have also been developed and characterised. The spectral response of the 95 GHz pixels closely matches RF simulations with a bandwidth of about 8 GHz. An efficiency greater than 70% is estimated from analysis of measured data with responsivity approaching 1x10^{8} V/W at a background power of 60 pW.
13.	Mahashabde, Sumedh, 1985, et al. (författare) Planar Frequency Selective Bolometric Array at 350 GHz 2015 Ingår i: IEEE Transactions on Terahertz Science and Technology. - 2156-342X .- 2156-3446. ; 5:1, s. 37-43 Tidskriftsartikel (refereegranskat)abstract In this paper we describe a bolometric focal plane array consisting of the Cold Electron Bolometer integrated in a Frequency Selective Surface fabricated on a Silicon substrate with a backshort. This array is formed by a periodic pattern of conducting annular square and ring shapes and the two-terminal CEB is embedded directly in the element. The CEBs impedance has been matched to the FSS which provides resonant interaction with incident sub-millimetre radiation. A further degree of freedom for the tuning is via varying the thickness of the substrate. We've been able to design the FSS at 350 GHz with peak coupling of more than 90% as is common for FSS based filters. A prototype of such a detector has been fabricated and optical response to blackbody radiation has been measured, indicating responsivities of 210^9 V/W and higher at 185 mK and 310^8 V/W and higher at 300 mK. The details of this new concept, together with numerical simulations and optical measurements are presented.
14.	Mukhin, Anton, 1988, et al. (författare) Sensitivity and Noise of Cold-Electron Bolometer Arrays 2017 Ingår i: Radiophysics and Quantum Electronics (English Translation of Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika). - : Springer Science and Business Media LLC. - 0033-8443 .- 1573-9120. ; 59:8-9, s. 754-762 Tidskriftsartikel (refereegranskat)abstract We perform experimental and theoretical studies of the series-parallel arrays of the cold-electron bolometers integrated into a cross-slot antenna and composed with an immersion silicon lens. This work is aimed at determining the efficiency of radiation absorption by bolometers, their volt-watt sensitivity, and equivalent noise power. The absorbed power was found using two independent methods, which ensured a better reliability of the results. The first method is based on comparing the experimental current-voltage characteristics of bolometers with the model based on the heat-balance equation. The second approach involves simulation of the electromagnetic properties of the system including the antenna, the lens, the bandpass filters, and the radiation source. The discrepancy among the results obtained using various methods does not exceed 30%. Optimization of the experimental setup is proposed to reach the photon-noise detection regime.
15.	Salatino, Maria, 1983, et al. (författare) Cold-electron bolometers for future mm and sub-mm sky surveys 2014 Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819496218 ; 9153, s. Art. no. 91530A- Konferensbidrag (refereegranskat)abstract Future sky surveys in the mm/sub-mm range, like the forthcoming balloon-borne missions LSPE, OLIMPO, SPIDER etc., will need detectors insensitive to cosmic rays (CRs) and with a NEP of the order of 10-17 ¥ 10-18 W/sqrt(Hz). The Cold-Electron Bolometers (CEBs) technology is promising, having the required proper-ties, since the absorber volume is extremely small and the electron system of the absorber is thermally insulated from the phonon system. We have developed an experimental setup to test the optical performance and the CRs insensitivity of CEBs, with the target of integrating them in the OLIMPO and LSPE focal planes.
16.	Salatino, Maria, 1983, et al. (författare) Sensitivity to Cosmic Rays of Cold Electron Bolometers for Space Applications 2014 Ingår i: Journal of Low Temperature Physics. - : Springer Science and Business Media LLC. - 0022-2291 .- 1573-7357. ; 176:3-4, s. 323-330 Tidskriftsartikel (refereegranskat)abstract An important phenomenon limiting the sensitivity of bolometric detectors for future space missions is the interaction with cosmic rays. We tested the sensitivity of Cold Electron Bolometers (CEBs) to ionizing radiation using gamma-rays from a radioactive source and X-rays from an X-ray tube. We describe the test setup and the results. As expected, due to the effective thermal insulation of the sensing element and its negligible volume, we find that CEBs are largely immune to this problem.
17.	Tan, B. K., et al. (författare) Investigation of the performance of an SIS mixer with Nb-AlN-NBN tunnel junctions in the 780-950 GHz frequency band 2018 Ingår i: 2018 29th IEEE International Symposium on Space Terahertz Technology, ISSTT 2018. ; , s. 139-142 Konferensbidrag (refereegranskat)abstract In this paper, we present preliminary measured performance of an SIS mixer employing a Nb/AIN/NbN tunnel junction in the frequency range of 780-950 GHz range. The mixer design is an upgrade of the Carbon Heterodyne Array of the Max-Planck-Institute Plus (CHAMP+) mixer, coupled with an easy to fabricate smooth-walled horn. The noise temperature of the mixer is measured using the standard Y-factor method, but all the RF optics is enclosed in the cryostat. We use a rotating mirror in the cryostat to switch between a room temperature load and a 4 K blackbody load. With this method, we have measured a noise temperature of 330 K around 850 GHz, corrected for a mismatch between a reduced height rectangular waveguide at the input of the mixer block and a full height waveguide at the output of the horn. To remove this mismatch we now plan to redesign a new mixer chip with a full-height waveguide back-piece. The expected performance of the new mixer chip is also reported.
18.	Tarasov, M.A., et al. (författare) Power load dependencies of cold electron bolometer optical response at 350 ghz 2014 Ingår i: 25th International Sympsoium on Space Terahertz Technology, ISSTT 2014; Moscow; Russian Federation; 27 April 2014 through 30 April 2014. ; , s. 35-41 Konferensbidrag (refereegranskat)abstract Cold electron bolometers integrated with twin-slot antennas have been designed and fabricated. Optical response was measured in 0.06-0.6 K temperature range using black body radiation source at temperature 2-15 K. The responsivity of 0.3109 V/W was measured at 2.7 K radiation temperature. The estimated ultimate dark responsivity at 100 mK can approach Sv=1010 V/W and reduces down to 1.1108 V/W at 300 mK for the sample with absorber volume of 510-20 m3. At high power load levels and low temperatures the changes of tunneling current, dynamic resistance and voltage response have been explained by non-thermal energy distribution of excited electrons. Distribution of excited electrons in such system is of none-Fermi type, electrons with energies of the order of 1 K tunnel from normal metal absorber to superconductor instead of relaxing down to thermal energy kTe. This effect can reduce quantum efficiency of bolometer from hf/kTph in ideal case down to single electron per signal quantum in the high power case.
19.	Tarasov, Mikhail, et al. (författare) Arrays of Annular Antennas With SINIS Bolometers 2020 Ingår i: IEEE Transactions on Applied Superconductivity. - 1558-2515 .- 1051-8223. ; 30:3 Tidskriftsartikel (refereegranskat)abstract For improving the dynamic range and sensitivity at high power load, we have integrated superconductor-insulator-normal metal-insulator-superconductor (SINIS) bolometers with a frequency selective surface (FSS)-based distributed absorber formed by a series and parallel array consisting of 25 annular antenna elements, each containing two SINIS bolometers. By using a design with 50 bolometers, we reduce incident power load on each bolometer, increase sensitivity and saturation power which is important for ground-based and balloon-borne telescopes with high background power loads. Our main detector pixel is optimized for a frequency band centered at 345GHz. The detectors are matched to incoming telescope beam by a back-to-back horn with a back reflector. Such a configuration improves both the efficiency and the bandwidth of the receiver. Measured voltage responsivity approaches 210(9) VW with an amplifier-limited voltage noise of 20nVHz(12), which corresponds to a NEP 10(-17) WHz(12). The linear voltage response for incoming power is observed for absorbed power of about 5 pW. The current responsivity for parallel array is 210(4) AW and the shot noise limited intrinsic noise equivalent power is NEP 510(-18)WHz(12). The noise equivalent temperature difference is NETD 100 KHz(12) at 2.7-K background radiation temperature.
20.	Tarasov, Mikhail, 1954, et al. (författare) Electrical and optical properties of a bolometer with a suspended absorber and tunneling-current thermometers 2017 Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 110:24 Tidskriftsartikel (refereegranskat)abstract We have developed a bolometer with a suspended normal-metal absorber connected to superconducting leads via tunneling barriers. Such an absorber has reduced heat losses to the substrate, which greatly increases the responsivity of the bolometer to over 10(9) V/W at 75 mK when measured by dc Joule heating of the absorber. For high-frequency experiments, the bolometers have been integrated in planar twin-slot and log-periodic antennas. At 300GHz and 100 mK, the bolometer demonstrates the voltage and current response of 3 x 10(8) V/W and 1.1 x 10(4) A/W, respectively, corresponding to the quantum efficiency of similar to 15 electrons per photon. An effective thermalization of electrons in the absorber favors the high quantum efficiency. We also report on how the in-plane-and transverse magnetic fields influence the device characteristics.
21.	Tarasov, Mikhail, 1954, et al. (författare) Nonthermal optical response of superconductor-insulator-normal metal-insulator-superconductor tunnel structures 2014 Ingår i: Journal of Experimental and Theoretical Physics. - : Pleiades Publishing Ltd. - 1090-6509 .- 1063-7761. ; 119:1, s. 107-114 Tidskriftsartikel (refereegranskat)abstract Bolometers, which are based on superconductor-insulator-normal metal-insulator-superconductor structures integrated into double slot antennas, are designed and fabricated. The change in the tunneling current in such structures during irradiation at a frequency of 330 GHz is experimentally studied at a temperature of about 0.1 K. It is found that, during irradiation, the energy distribution of electrons has a substantially nonequilibrium form, which differs from the Fermi distribution, and the main contribution to the addition to the tunneling current is made by the electrons that have no time to attain equilibrium within the electron system of the normal metal absorber. The characteristic electron and phonon relaxation times are estimated, and the estimates support the fact that the electron system is strongly nonequilibrium in the radiation field.
22.	Tarasov, Mikhail, 1954, et al. (författare) Optical Response of a Cold-Electron Bolometer Array Integrated in a 345-GHz Cross-Slot Antenna 2011 Ingår i: IEEE Transactions on Applied Superconductivity. - 1558-2515 .- 1051-8223. ; 21:6, s. 3635-3639 Tidskriftsartikel (refereegranskat)abstract Two series/parallel arrays of ten cold-electronbolometers with superconductor–insulator–normal tunnel junctionswere integrated in orthogonal ports of a cross-slot antenna.To increase the dynamic range of the receiver, all single bolometersin an array are connected in parallel for the microwavesignal by capacitive coupling. To increase the output response,bolometers are connected in series for dc bias. With the measuredvoltage-to-temperature response of 8.8 μV/mK, absorbervolume of 0.08 μm3, and output noise of about 10 nV/Hz1/2,we estimated the dark electrical noise equivalent power (NEP)as NEP = 6∗ 10−18 W/Hz1/2. The optical response down toNEP = 2∗ 10−17 W/Hz1/2 was measured using a hot/cold loadas a radiation source and a sample temperature down to 100 mK.The fluctuation sensitivity to the radiation source temperature is1.3 ∗ 10−4 K/Hz1/2. A dynamic range over 43 dB was measuredusing a backward-wave oscillator, a variable polarization gridattenuator, and cold filters/attenuators.
23.	Tarasov, Mikhail, 1954, et al. (författare) Power Load and Temperature Dependence of Cold-Electron Bolometer Optical Response at 350 GHz 2014 Ingår i: IEEE Transactions on Applied Superconductivity. - 1558-2515 .- 1051-8223. ; 24:6, s. 1- Tidskriftsartikel (refereegranskat)abstract Cold-electron bolometers (CEBs) integrated with twin-slot antennas have been designed and fabricated. Optical response was measured at bath temperatures of 0.06 to 3 K using blackbody radiation source at temperatures of 3 to 15 K. The responsivity of 0.3 * 10(9) V/W was measured at 2.7-K blackbody temperature that is close to the temperature of the cosmic microwave background. Optical measurements indicate quasi-optical coupling efficiency of up to 60% at low phonon temperature and low signal level. Estimations for bolometer responsivity were made for practical range of bath temperatures and blackbody radiation temperatures. The estimated ultimate dark responsivity at 100-mK bath temperature can approach S-V = 10(10) V/W and reduces down to 1.1 * 10(8) V/W at 300 mK for a device with absorber volume of 5 * 10(-20) m(3).
24.	Tarasov, Mikhail, 1954, et al. (författare) Quantum Efficiency of Cold Electron Bolometer Optical Response 2015 Ingår i: IEEE Transactions on Terahertz Science and Technology. - 2156-342X .- 2156-3446. ; 5:1, s. 44-48 Tidskriftsartikel (refereegranskat)abstract In this paper we present the measurements of optical response dependence on power load of a Cold Electron Bolometer integrated in a twin slot antenna. These measurements are also compared to the models of the bolometer limit and the photon counter limit. The responsivity of 0.2210^9 V/W was measured at 0.22 pW radiation power from a black body at 3.5 K. According to our estimations, for optimized device the voltage responsivity at 100 mK electron temperature can approach Sv=10^10 V/W for power load below 0.1 pW and decreases down to 10^7 V/W at 300 mK for 5 pW signal power in a sample with absorber volume of 510^-20 m^3. In the case of low bath temperatures and high applied RF power the changes of tunneling current, dynamic resistance and voltage response are explained by non-thermal energy distribution of excited electrons. Distribution of excited electrons in such system at lower temperatures can be of non-Fermi type, hot electrons with energies of the order of 1 K tunnel from normal metal absorber to superconductor instead of relaxing down to thermal energy kTe in absorber before tunneling. This effect can reduce quantum efficiency of the bolometer at 350 GHz from hf/kTph>100 in ideal case down to single electron per absorbed photon (Q.Eff=1) in the high power case. Methods of preserving high quantum efficiency are discussed.
25.	Tarasov, Mikhail, 1954, et al. (författare) SINIS bolometer with a suspended absorber 2018 Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 969:1 Konferensbidrag (refereegranskat)abstract We have developed a Superconductor-Insulator-Normal Metal-Insulator-Superconductor (SINIS) bolometer with a suspended normal metal bridge. The suspended bridge acts as a bolometric absorber with reduced heat losses to the substrate. Such bolometers were characterized at 100-350 mK bath temperatures and electrical responsivity of over 10 9 V/W was measured by dc heating the absorber through additional contacts. Suspended bolometers were also integrated in planar twin-slot and log-periodic antennas for operation in the submillimetre-band of radiation. The measured voltage response to radiation at 300 GHz and at 100 mK bath temperature is 3∗10 8 V/W and a current response is 1.1∗10 4 A/W which corresponds to a quantum efficiency of ∼15 electrons per photon. An important feature of such suspended bolometers is the thermalization of electrons in the absorber heated by optical radiation, which in turn provides better quantum efficiency. This has been confirmed by comparison of bolometric response to dc and rf heating. We investigate the performance of direct SN traps and NIS traps with a tunnel barrier between the superconductor and normal metal trap. Increasing the volume of superconducting electrode helps to reduce overheating of superconductor. Influence of Andreev reflection and Kapitza resistance, as well as electron-phonon heat conductivity and thermal conductivity of N-wiring are estimated for such SINIS devices.
26.	Trappe, N., et al. (författare) Next Generation Sub-millimetre Wave Focal Plane Array Coupling Concepts - An ESA TRP project to develop multichroic focal plane pixels for future CMB polarisation experiments 2016 Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9781510602076 ; 9914:Part 1, s. UNSP 991412- Konferensbidrag (refereegranskat)abstract The main objective of this activity is to develop new focal plane coupling array concepts and technologies that optimise the coupling from reflector optics to the large number of detectors for next generation sub millimetre wave telescopes particularly targeting measurement of the polarization of the cosmic microwave background (CMB). In this 18 month TRP programme the consortium are tasked with developing, manufacturing and experimentally verifying a prototype multichroic pixel which would be suitable for the large focal plane arrays which will be demanded to reach the required sensitivity of future CMB polarization missions. One major development was to have multichroic operation to potentially reduce the required focal plane size of a CMB mission. After research in the optimum telescope design and definition of requirements based on a stringent science case review, a number of compact focal plane architecture concepts were investigated before a pixel demonstrator consisting of a planar mesh lens feeding a backend Resonant Cold Electron Bolometer RCEB for filtering and detection of the dual frequency signal was planned for manufacture and test. In this demonstrator the frequencies of the channels was chosen to be 75 and 105 GHz in the w band close to the peak CMB signal. In the next year the prototype breadboards will be developed to test the beams produced by the manufactured flat lenses fed by a variety of antenna configurations and the spectral response of the RCEBs will also be verified.
27.	Yager, Thomas, 1987, et al. (författare) Express Optical Analysis of Epitaxial Graphene on SiC: Impact of Morphology on Quantum Transport 2013 Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 13:9, s. 4217-4223 Tidskriftsartikel (refereegranskat)abstract We show that inspection with an optical microscope allows surprisingly simple and accurate identification of single and multilayer graphene domains in epitaxial graphene on silicon carbide (SiC/G) and is informative about nanoscopic details of the SiC topography, making it ideal for rapid and noninvasive quality control of as-grown SiC/G. As an illustration of the power of the method, we apply it to demonstrate the correlations between graphene morphology and its electronic properties by quantum magneto-transport.

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