524 research outputs found
Monolayer graphene bolometer as a sensitive far-IR detector
In this paper we give a detailed analysis of the expected sensitivity and
operating conditions in the power detection mode of a hot-electron bolometer
(HEB) made from a few {\mu}m of monolayer graphene (MLG) flake which can be
embedded into either a planar antenna or waveguide circuit via NbN (or NbTiN)
superconducting contacts with critical temperature ~ 14 K. Recent data on the
strength of the electron-phonon coupling are used in the present analysis and
the contribution of the readout noise to the Noise Equivalent Power (NEP) is
explicitly computed. The readout scheme utilizes Johnson Noise Thermometry
(JNT) allowing for Frequency-Domain Multiplexing (FDM) using narrowband filter
coupling of the HEBs. In general, the filter bandwidth and the summing
amplifier noise have a significant effect on the overall system sensitivity.
The analysis shows that the readout contribution can be reduced to that of the
bolometer phonon noise if the detector device is operated at 0.05 K and the JNT
signal is read at about 10 GHz where the Johnson noise emitted in equilibrium
is substantially reduced. Beside the high sensitivity (NEP < 10
W/Hz, this bolometer does not have any hard saturation limit and thus
can be used for far-IR sky imaging with arbitrary contrast. By changing the
operating temperature of the bolometer the sensitivity can be fine tuned to
accommodate the background photon flux in a particular application. By using a
broadband low-noise kinetic inductance parametric amplifier, ~100s of graphene
HEBs can be read simultaneously without saturation of the system output.Comment: 9 pages. 6 figure, SPIE Astronomical Telescopes + Instrumentation,
Montr\'eal, Quebec, Canada, 22-27 June, 201
The critical current in a NbTi tape measured in different directions of magnetic field and the current reduction due to the self field
With reference to the application of NbTi tape in a superconducting thermal switch, the critical current of a 20-¿m-thick NbTi tape was measured in several directions of the magnetic field. The critical current was found to behave strongly anisotropically, due to the deformation of the NbTi. The tape is extrasensitive to the component of the magnetic field perpendicular to the surface. Without an external field this component of the self-field reduces the critical current far below its intrinsic value. A one-dimensional model can describe the reduction of critical current due to the self-field in a thin tap
The low-frequency response in the surface superconducting state of ZrB single crystal}
The large nonlinear response of a single crystal ZrB to an ac field
(frequency 40 - 2500 Hz) for has been observed. Direct
measurements of the ac wave form and the exact numerical solution of the
Ginzburg-Landau equations, as well as phenomenological relaxation equation,
permit the study of the surface superconducting states dynamics. It is shown,
that the low frequency response is defined by transitions between the
metastable superconducting states under the action of an ac field. The
relaxation rate which determines such transitions dynamics, is found.Comment: 7 pages, 11 figure
Energy resolution of terahertz single-photon-sensitive bolometric detectors
We report measurements of the energy resolution of ultra-sensitive
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 terahertz, near the predicted value due to intrinsic thermal fluctuation
noise.Comment: 11 pages (double-spaced), 5 figures; minor revision
Multi-particle decoherence free subspaces in extended systems
We develop a method to determine spatial configurations to realize decoherence-free subspaces for spatially extended multi-particle systems. We have assumed normal reservoir behavior including translational invariance of the reservoir and preparation in stationary states or mixture thereof and weak Markovian system-reservoir coupling that requires energy transfer. One important outcome of our method is a proof that there does not exist a multi-particle decoherence-free subspace in such systems except in the limit that the spatial extent of the system becomes infinitesimal
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