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Sekine, N., & Hosako, I. (2009). Intensity modulation of terahertz quantum cascade lasers under external light injection. Appl. Phys. Lett., 95, 201106(1–3).
Abstract: We investigated the light-current characteristics of terahertz (THz) quantum cascade lasers under external light injection, which excites interband transitions in the active materials. It was found that the amount of reduction in the THz power was constant for all injection currents above threshold, and the dependence of the reduction amount on the wavelength of the external light was observed to show a resonancelike feature. The dominant intensity modulation mechanism was found to be the loss change caused by interband transitions in the active region. Further, the effective coupling efficiency plays an important role in the intensity modulation.
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Ryabchun, S., Tong, C. - Y. E., Paine, S., Lobanov, Y., Blundell, R., & Goltsman, G. (2009). Temperature resolution of an HEB receiver at 810 GHz. IEEE Trans. Appl. Supercond., 19(3), 293–296.
Abstract: We present the results of direct measurements of the temperature resolution of an HEB receiver operating at 810 GHz, in both continuum and spectroscopic modes. In the continuum mode, the input of the receiver was switched between black bodies with different physical temperatures. With a system noise temperature of around 1100 K, the receiver was able to resolve loads which differed in temperature by about 1 K over an integration time of 5 seconds. This resolution is significantly worse than the value of 0.07 K given by the radiometer equation. In the spectroscopic mode, a gas cell filled with carbonyl sulphide (OCS) gas was used and the emission line at 813.3537060 GHz was measured using the receiver in conjunction with a digital spectrometer. From the observed spectra, we determined that the measurement uncertainty of the equivalent emission temperature was 2.8 K for an integration time of 0.25 seconds and a spectral resolution of 12 MHz, compared to a 1.4 K temperature resolution given by the radiometer equation. This relative improvement is due to the fact that at short integration times the contribution from 1/f noise and drift are less dominant. In both modes, the temperature resolution was improved by about 40% with the use of a feedback loop which adjusted the level of an injected microwave radiation to maintain a constant operating current of the HEB mixer. This stabilization scheme has proved to be very effective to keep the temperature resolution of the HEB receiver to close to the theoretical value given by the radiometer equation.
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Ozhegov, R. V., Okunev, O. V., Gol’tsman, G. N., Filippenko, L. V., & Koshelets, V. P. (2009). Noise equivalent temperature difference of a superconducting integrated terahertz receiver. J. Commun. Technol. Electron., 54(6), 716–720.
Abstract: The dependence of the noise equivalent temperature difference (NETD) of a superconducting integrated receiver (SIR) on the receiver noise temperature and the inputsignal level has been investigated. An unprecedented NETD of 13±2 mK has been measured at a SIR noise temperature of 200 K, intermediate-frequency bandwidth of 4 GHz, and time constant of 1 s. With a decrease in the input signal, an improvement in the NETD is observed. This effect is explained by a reduction in the influence of the instabilities of the receiver power supply and the amplification circuit that occur when the input signal is decreased.
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Benford, D., Moseley, H., & Zmuidzinas, J. (2009). Direct detectors for the Einstein inflation probe. In J. Phys.: Conf. Ser. (Vol. 155, 012001 (1 to 49)).
Abstract: Here we review the principles of operation, history, present status, and future prospects for the primary candidate detectors for Cosmic Microwave Background (CMB) polarization studies. The three detector types we will discuss are semiconductor-based bolometers, superconducting transition edge sensor (TES) bolometer, and Microwave Kinetic Inductance Detectors (MKIDs). All of these detector types can provide the sensitivity to permit background-limited measurements of the CMB, but the ultimate selection of detectors will be largely determined by the ease of production and reliability of large arrays of such detectors. This paper describes the present state of development of these detectors, efforts to integrate them into large arrays, and the detector system developments necessary to enable a space CMB polarization mission.
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Pekker, D., Shah, N., Sahu, M., Bezryadin, A., & Goldbart, P. M. (2009). Stochastic dynamics of phase-slip trains and superconductive-resistive switching in current-biased nanowires. Phys. Rev. B, 80, 214525 (1 to 17).
Abstract: Superconducting nanowires fabricated via carbon-nanotube templating can be used to realize and study quasi-one-dimensional superconductors. However, measurement of the linear resistance of these nanowires have been inconclusive in determining the low-temperature behavior of phase-slip fluctuations, both quantal and thermal. Thus, we are motivated to study the nonlinear current-voltage characteristics in current-biased nanowires and the stochastic dynamics of superconductive-resistive switching, as a way of probing phase-slip events. In particular, we address the question: can a single phase-slip event occurring somewhere along the wire—during which the order-parameter fluctuates to zero—induce switching, via the local heating it causes? We explore this and related issues by constructing a stochastic model for the time evolution of the temperature in a nanowire whose ends are maintained at a fixed temperature. We derive the corresponding master equation as a tool for evaluating and analyzing the mean switching time at a given value of current (smaller than the depairing critical current). The model indicates that although, in general, several phase-slip events are necessary to induce switching via a thermal runaway, there is indeed a regime of temperatures and currents in which a single event is sufficient. We carry out a detailed comparison of the results of the model with experimental measurements of the distribution of switching currents, and provide an explanation for the rather counterintuitive broadening of the distribution width that is observed upon lowering the temperature. Moreover, we identify a regime in which the experiments are probing individual phase-slip events, and thus offer a way of unearthing and exploring the physics of nanoscale quantum tunneling of the one-dimensional collective quantum field associated with the superconducting order parameter.
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