1,169 research outputs found
Microwave-induced nonequilibrium temperature in a suspended carbon nanotube
Antenna-coupled suspended single carbon nanotubes exposed to 108 GHz
microwave radiation are shown to be selectively heated with respect to their
metal contacts. This leads to an increase in the conductance as well as to the
development of a power-dependent DC voltage. The increased conductance stems
from the temperature dependence of tunneling into a one-dimensional electron
system. The DC voltage is interpreted as a thermovoltage, due to the increased
temperature of the electron liquid compared to the equilibrium temperature in
the leads
Uniform non-stoichiometric titanium nitride thin films for improved kinetic inductance detector array
We describe the fabrication of homogeneous sub-stoichiometric titanium
nitride films for microwave kinetic inductance detector (mKID) arrays. Using a
6 inch sputtering target and a homogeneous nitrogen inlet, the variation of the
critical temperature over a 2 inch wafer was reduced to <25 %. Measurements of
a 132-pixel mKID array from these films reveal a sensitivity of 16 kHz/pW in
the 100 GHz band, comparable to the best aluminium mKIDs. We measured a noise
equivalent power of NEP = 3.6e-15 W/Hz^(1/2). Finally, we describe possible
routes to further improve the performance of these TiN mKID arrays.Comment: 7 pages, 4 figures, submitted to Journal of low temperature physics,
Proceedings of LTD-1
Probing thermalization and dynamics of high-energy quasiparticles in a superconducting nanowire by scanning critical current microscopy
Besides its fundamental interest, understanding the dynamics of pair breaking
in superconducting nanostructures is a central issue to optimize the
performances of superconducting devices such as qubits or photon detectors.
However, despite substantial research efforts, these dynamics are still not
well understood as this requires experiments in which quasiparticles are
injected in a controlled fashion. Until now, such experiments have employed
solid-state tunnel junctions with a fixed tunnel barrier. Here we use instead a
cryogenic scanning tunnelling microscope to tune independently the energy and
the rate of quasiparticle injection through, respectively, the bias voltage and
the tunnelling current. For high energy quasiparticles, we observe the
reduction of the critical current of a nanowire and show it is mainly
controlled by the injected power and, marginally, by the injection rate. Our
results prove a thermal mechanism for the reduction of the critical current and
unveil the rapid dynamics of the generated hot spot.Comment: 25 pages, 14 figure
One- and two-photon spectroscopy of a flux qubit coupled to a microscopic defect
We observed the dynamics of a superconducting flux qubit coupled to an
extrinsic quantum system (EQS). The presence of the EQS is revealed by an
anticrossing in the spectroscopy of the qubit. The excitation of a two-photon
transition to the third excited state of the qubit-EQS system allows us to
extract detailed information about the energy level structure and the coupling
of the EQS. We deduce that the EQS is a two-level system, with a transverse
coupling to the qubit. The transition frequency and the coupling of the EQS
changed during experiments, which supports the idea that the EQS is a two-level
system of microscopic origin.Comment: accepted in Physical Review
Efficient and robust fiber coupling of superconducting single photon detectors
We applied a recently developed fiber coupling technique to superconducting
single photon detectors (SSPDs). As the detector area of SSPDs has to be kept
as small as possible, coupling to an optical fiber has been either inefficient
or unreliable. Etching through the silicon substrate allows fabrication of a
circularly shaped chip which self aligns to the core of a ferrule terminated
fiber in a fiber sleeve. In situ alignment at cryogenic temperatures is
unnecessary and no thermal stress during cooldown, causing misalignment, is
induced. We measured the quantum efficiency of these devices with an attenuated
tunable broadband source. The combination of a lithographically defined chip
and high precision standard telecommunication components yields near unity
coupling efficiency and a system detection efficiency of 34% at a wavelength of
1200 nm. This quantum efficiency measurement is confirmed by an absolute
efficiency measurement using correlated photon pairs (with = 1064 nm)
produced by spontaneous parametric down-conversion. The efficiency obtained via
this method agrees well with the efficiency measured with the attenuated
tunable broadband source
Anomalous response of superconducting titanium nitride resonators to terahertz radiation
We present an experimental study of KIDs fabricated of atomic layer deposited
TiN films, and characterized at radiation frequencies of ~GHz. The
responsivity to radiation is measured and found to increase with increasing
radiation powers, opposite to what is expected from theory and observed for
hybrid niobium titanium nitride / aluminium (NbTiN/Al) and all-aluminium
(all-Al) KIDs. The noise is found to be independent of the level of the
radiation power. The noise equivalent power (NEP) improves with higher
radiation powers, also opposite to what is observed and well understood for
hybrid NbTiN/Al and all-Al KIDs. We suggest that an inhomogeneous state of
these disordered superconductors should be used to explain these observations
Critical-Current Reduction in Thin Superconducting Wires Due to Current Crowding
We demonstrate experimentally that the critical current in superconducting
NbTiN wires is dependent on their geometrical shape, due to current-crowding
effects. Geometric patterns such as 90 degree corners and sudden expansions of
wire width are shown to result in the reduction of critical currents. The
results are relevant for single-photon detectors as well as parametric
amplifiers
Low loss, high contrast optical waveguides based on CMOS compatible LPCVD processing
A new class of integrated optical waveguide structures is presented, based on low cost CMOS compatible LPCVD processing. This technology allows for medium and high index contrast waveguides with very low channel attenuation. The geometry is basically formed by a rectangular cross-section silicon nitride filled with and encapsulated by silicon dioxide . The birefringence and minimal bend radius of the waveguide is completely controlled by the geometry of the waveguide layer structures. Experiments on typical geometries will be presented, showing excellent characteristics (channel attenuation â€0.06 dB/cm, IL â€0.6 dB, PDL â€0.2 dB, Bg «1 x , bend radius â€500 ÎŒm)
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