C. M. Wilson

Yale University, New Haven, CT, United States

Are you C. M. Wilson?

Claim your profile

Publications (26)44.67 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We describe recent work at Yale on Superconducting Tunnel Junction (STJ) direct detectors that have been developed for submillimeter astronomy. To monitor the response of the detector with large readout bandwidth and excellent sensitivity, we use a novel readout based on radio frequency (RF) reflectometry, like the readout invented for the RF-SET. For calibration of the detector, we have developed an in-situ, on-chip, hot-cold photon source. This is a voltage biased gold microbridge. Noise emitted by the microbridge couples via a coplanar stripline to the detector. This provides a calibrated blackbody photon source with near unity coupling, fast chopping, and calculable output. We present recent detection results in the range 100-160 GHz. These demonstrate the expected good responsivity, high sensitivity, and fast response. This approach is easily used with a frequency-multiplexed readout, allowing economy of cold electronics. Ultimate sensitivity is in the range 1 times 10<sup>-19</sup> W/(Hz)<sup>1/2</sup>.
    IEEE Transactions on Applied Superconductivity 07/2007; · 1.20 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have constructed a new type of amplifier whose primary purpose is the readout of superconducting quantum bits. It is based on the transition of an RF-driven Josephson junction between two distinct oscillation states near a dynamical bifurcation point. The main advantages of this new amplifier are speed, high-sensitivity, low back-action, and the absence of on-chip dissipation. Using pulsed microwave techniques, we demonstrate bifurcation amplification in nanofabricated Al junctions and verify that the performance predicted by theory is attained.
    08/2005;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have designed a diffusion-engineered, single-photon spectrometer in the optical-UV range using a superconducting tunnel junction. The optical photon is absorbed in a Ta film and creates excess quasiparticles. These trap into an Al tunnel junction. Internal charge multiplication is achieved with backtunneling, which occurs when the residence time of the quasiparticles near the junction is longer than the tunneling time. The collected charge is a multiple of the initially created charge. We implement backtunneling by geometrically constricting the outflow of quasiparticles, with a narrow lead. The outdiffusion time is set by the geometry of the narrow lead. Our geometry optimizes the energy resolution and count rate, while reducing the heating and noise seen with much longer confinement time. Long confinement times produce excess heating and noise, as we observed previously with quasiparticle confinement achieved via bandgap engineering.
    IEEE Transactions on Applied Superconductivity 07/2005; · 1.20 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We performed a novel phase-sensitive microwave reflection experiment which directly probes the dynamics of the Josephson plasma resonance in both the linear and the nonlinear regime. When the junction was driven below the plasma frequency into the nonlinear regime, we observed for the first time the transition between two different dynamical states predicted for nonlinear systems. In our experiment, this transition appears as an abrupt change in the reflected signal phase at a critical excitation power. This controlled dynamical switching can form the basis of a sensitive amplifier, in particular, for the readout of superconducting qubits.
    Physical Review Letters 02/2005; 94(2):027005. · 7.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have constructed a new type of amplifier whose primary purpose is the readout of superconducting quantum bits. It is based on the transition of a rf-driven Josephson junction between two distinct oscillation states near a dynamical bifurcation point. The main advantages of this new amplifier are speed, high sensitivity, low backaction, and the absence of on-chip dissipation. Pulsed microwave reflection measurements on nanofabricated Al junctions show that actual devices attain the performance predicted by theory.
    Physical Review Letters 12/2004; 93(20):207002. · 7.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present the first measurements of the third moment of the voltage fluctuations in a conductor. This technique can provide new and complementary information on the electronic transport in conducting systems. The measurement was performed on non-superconducting tunnel junctions as a function of voltage bias, for various temperatures and bandwidths up to 1GHz. The data demonstrate the significant effect of the electromagnetic environment of the sample. Comment: 13 pages, for the SPIE International Symposium on Fluctuations and Noise, Maspalomas, Gran Canaria, Spain (May 2004)
    Proc SPIE 03/2004;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We have developed a novel amplifier based on the switching between two dynamical states of a capacitively-shunted, driven Josephson junction. This non-linear oscillator is biased near a Hopf bifurcation with an amplitude modulated monochromatic microwave drive signal. The two dynamical states differ in their oscillation phase and can be readily distinguished in a microwave reflection experiment. In the vicinity of the bifurcation, the switching probability is sensitive to small relative variations in critical current. In this amplifier, there is strictly no on-chip dissipation, resulting in minimal back-action. We discuss the dynamics of this system and present classical calculations of the sensitivity and back-action. The optimization of this bifurcation amplifier for practical systems such as superconducting qubits and photon detectors is also treated.
    03/2004;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present first measurements of a new, high-sensitivity amplifier for the readout of superconducting quantum bits. It is based on the dynamical switching of a Josephson junction driven by RF pulses from a low-amplitude to a high-amplitude oscillation state. A convenient signature of this transition is a change in phase of the reflected drive signal. At T=300mK, we discriminate 1% variations in critical current of a 1 microamp junction in 80ns with 60% fidelity. Comparable sensitivity with a DC current-biased junction is achieved only at 60mK. Detailed measurements of the dynamical transition rates as a function of temperature and RF drive amplitude are in good quantitative agreement with theory. Since no on-chip resistors are required and the junction does not switch into the voltage state, no quasiparticles are generated and the back-action of the amplifier is minimal, making it therefore well-suited for qubits. This high-fidelity readout should permit stringent tests of quantum mechanics such as the violation of Bell's inequalities.
    02/2004; -1:37007.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We performed a novel phase sensitive microwave reflection experiment which directly probes the dynamics of the Josephson plasma resonance in both the linear and non-linear regime. When the junction was driven below the plasma frequency into the non-linear regime, we observed for the first time the transition between two different dynamical states predicted for non-linear systems. In our experiment, this transition appears as an abrupt change in the reflected signal phase at a critical excitation power.
    01/2004;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present predictions for a diffusion-engineered, single-photon spectrometer in the UV–visible range using a superconducting tunnel junction. Quasiparticles are created by photoexcitation, with charge Q0. After tunneling through the junction, the quasiparticles can either backtunnel or diffuse away. With confinement by a higher gap or by narrow leads the quasiparticles in the counterelectrode dwell next to the junction and backtunnel, increasing the collected charge to Q=pQ0, p>1. For very narrow leads the dwell time is inversely proportional to the lead width, up to the recombination time of Al, 1ms at 0.2K. The new aspect of our work is the use of narrow leads to control the charge gain p, while minimizing self-heating. This charge gain will improve the energy resolution compared to the case p=1, where the electronic noise is dominant, and compared to much larger charge gain, p≈50, where large self-heating resulted with extra noise.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2004; · 1.14 Impact Factor
  • Source
    C. M. Wilson, D. E. Prober
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a general theory of quasiparticle number fluctuations in superconductors. The theory uses the master equation formalism. First, we develop the theory for a single occupation variable. Although this simple system is insufficient to describe fluctuations in a physical superconductor, it is illustrative, allowing this discussion to serve as a self-contained introduction. We go on to develop a multivariate theory that allows for an arbitrary number of levels with transitions of arbitrary size between levels. We specialize the multivariate theory for two particular cases. First, we consider intrinsic quasiparticle fluctuations. In a previous Letter, these results were used to describe time-resolved measurements of thermodynamic fluctuations in a superconducting Al box [C.M. Wilson, L. Frunzio and D.E. Prober, Phys. Rev. Lett. 87, 067004 (2001)]. Finally, we extend these results to include fluctuations due to extrinsic loss processes. Comment: 35 pages (double spaced), 3 figures
    Physical Review B 10/2003; · 3.66 Impact Factor
  • Source
    C.M. Wilson, L. Frunzio, D.E. Prober
    [Show abstract] [Hide abstract]
    ABSTRACT: We present measurements of superconducting tunnel junction (STJ) spectrometers optimized for extreme ultraviolet (EUV) energies, between 20-200 eV. The high count rates demands of astronomical applications, such as solar flare studies, uniquely suit STJs as compared to other cryogenic spectrometers. We have simulated EUV measurements with the technique of multiphoton absorption using a pulsed UV laser as a light source. We have demonstrated an energy resolution of 2.15 eV, close to the requirements of the applications. This resolution is limited by amplifier noise. We present predictions of improved resolution based on new amplifier designs.
    IEEE Transactions on Applied Superconductivity 07/2003; · 1.20 Impact Factor
  • Source
    L. Li, L. Frunzio, C.M. Wilson, D.E. Prober
    [Show abstract] [Hide abstract]
    ABSTRACT: We have developed single-photon 1-D imaging detectors based on superconducting tunnel junctions. The devices have a Ta film with an Al/AlO<sub>x</sub>/Al tunnel junction on each end and a Nb contact in the center. The best energy resolution of this kind of detector is 13 eV for 5.9 keV X-ray photons. Two devices with different lengths: 500 and 1000 μm are measured to study the nonequilibrium quasiparticle dynamics in the superconducting Ta film. The diffusion constant and lifetime of quasiparticles in the Ta films have been derived by fitting the measured current pulses to the model. The comparison of the simulation and measurement results proves that the quasiparticle loss is not primarily due to the Nb ground contact in the center of the Ta absorber, but is due to the uniform nonthermal loss in the Ta film. The Nb ground contact does contribute to the broadening of the energy width in the center of the Ta film.
    IEEE Transactions on Applied Superconductivity 07/2003; · 1.20 Impact Factor
  • Source
    L. Li, L. Frunzio, C. M. Wilson, D. E. Prober
    [Show abstract] [Hide abstract]
    ABSTRACT: Nonequilibrium quasiparticle dynamics in Ta are studied using a superconducting Ta film with an Al tunnel junction connected at each end. The quasiparticle system is driven out of the equilibrium by absorption of an x-ray photon. Millions of quasiparticles, created by each photon, diffuse in the Ta film. When the quasiparticles reach the Al junctions they lose energy by emitting phonons and are trapped in the Al film. By measuring the tunneling current, the number of excess quasiparticles can be calculated. In Ta, the diffusion constant of 8.2±0.2 cm2/s and quasiparticle lifetime of 83±5 μs at 0.21 K are derived from fitting the measured current pulses, and are compared with theoretical predictions.
    Journal of Applied Physics 01/2003; 93(2). · 2.21 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present results of development of imaging superconducting tunnel junction detectors in the optical/UV energy range. Our detectors have a Ta strip absorber with Al tunnel junctions located on the two ends of the strip. The tunnel junction area does not overlap the absorber. Using devices designed for large backtunneling gain, we have measured an energy resolution of 0.4 eV at 4.89 eV. The resolution in these devices is limited by thermodynamic fluctuations of the thermal quasiparticle number in the Al trapping layers. We predict that this previously unconsidered noise source should be important in any backtunneling device with “deep” traps. We are currently developing detectors designed to eliminate this noise and, consequently, backtunneling gain. These devices need small junctions, of order 1 square micron, for best noise performance. The resolution of these devices should approach the intrinsic limits of creation and trapping statistics, and exceed the resolution of devices with backtunneling. © 2002 American Institute of Physics.
    AIP Conference Proceedings. 02/2002; 605(1):15-18.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have developed single-photon, one-dimensional imaging detectors based on superconducting tunnel junctions. The devices have a Ta absorber with an Al/AlOx/Al tunnel junction readout on each end. The best energy resolution is 13 eV FWHM at 6 keV in an area of 20×100 mum2. For devices with a Nb ground contact to the center of the Ta absorber, the energy resolution is worse in the center of the Ta absorber. This nonuniformity is caused by the Nb ground contact. A device with a Ta ground contact to the base electrode of one of the junctions was tested. We obtain an energy resolution of 26 eV in the large region at the center of the absorber, where this energy resolution is determined by the junction response. The diffusion constant of Ta and the loss time of quasiparticles in Ta are also studied by measuring three devices with different size absorbers. .
    Low Temperature Detectors. 02/2002;
  • Source
    C M Wilson, L Frunzio, D E Prober
    [Show abstract] [Hide abstract]
    ABSTRACT: We report on time-resolved measurements of thermodynamic fluctuations in the number of particles in a nondegenerate Fermi gas. The gas is comprised of thermal quasiparticles, confined in a superconducting Al box by large-gap Ta leads. The average number of quasiparticles is about 10(5). This number fluctuates due to quasiparticle generation and recombination. The number is measured from the tunneling current through a barrier that bisects the box. The recombination time is independently measured by single-photon excitation and agrees with the frequency dependence of the fluctuations.
    Physical Review Letters 09/2001; 87(6):067004. · 7.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report on the development of an “all-in-one” detector that provides spectroscopy, imaging, photon timing, and high quantum efficiency with single photon sensitivity: the optical/UV single-photon imaging spectrometer using superconducting tunnel junctions. Our devices utilize a lateral trapping geometry. Photons are absorbed in a Ta thin film, creating excess quasiparticles. Quasiparticles diffuse and are trapped by Al/AlO<sub>x</sub>/Al tunnel junctions located on the sides of the absorber. Imaging devices have tunnel junctions on two opposite sides of the absorber. Position information is obtained from the fraction of the total charge collected by each junction. We have measured the single photon response of our devices. For photon energies between 2 eV and 5 eV we measure an energy resolution between 0.47 eV and 0.40 eV respectively on a selected region of the absorber. We see evidence that thermodynamic fluctuations of the number of thermal quasiparticles in the junction electrodes leads to current noise that far exceeds the expected shot noise of the dc bias current. We believe that this may limit the resolution of our present generation of detectors at the operating temperature of 0.22 K
    IEEE Transactions on Applied Superconductivity 04/2001; · 1.20 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present preliminary test results of optical/UV single-photon imaging spectrometers using superconducting tunnel junctions. Our devices utilize a lateral trapping geometry. Photons are absorbed in a Ta thin film, creating excess quasiparticles. Quasiparticles diffuse and are trapped by Al/AlOx/Al tunnel junctions located on the sides of the absorber. The Ta/Al interface does not overlap the junction area. Imaging devices have tunnel junctions on two opposite sides of the absorber. Position information is obtained from the fraction of the total charge collected by each junction. We have fabricated high-quality junctions with a ratio of subgap resistance to normal state resistance greater than 100 000 at 0.22 K. We have measured the single-photon response of our devices. For photon energies between 2 and 5 eV, we measure an energy resolution between 1 and 1.6 eV. We can estimate the number of pixels the device can resolve from the energy resolution. We find that these early devices have as many as 4 pixels per strip.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 08/2000; · 1.14 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We are developing single-photon 2-D imaging X-ray spectrometers for applications in X-ray astrophysics. The devices employing a Ta strip X-ray absorber with Al traps and a tunnel junction at each end have been tested. They achieve an energy resolution of 26 eV out of 5.9 keV over a limited length (Segall, IEEE Trans., in press) with a 1-D spatial resolution of about 2 μm over the full 160 μm length. By analytical and numerical simulations of the quasiparticle diffusion process, we study related devices with a square Ta absorber having four traps and attached junctions to provide 2-D imaging. The traps give charge division to the corners or to the edges of the square absorber. We find that these devices can give good 2-D spatial resolution. We discuss the operating principle and the factors which affect the spatial resolution.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 04/2000; 444(s 1–2):228–231. · 1.14 Impact Factor