14 research outputs found
High operating temperature in V-based superconducting quantum interference proximity transistors
Here we report the fabrication and characterization of fully superconducting
quantum interference proximity transistors (SQUIPTs) based on the
implementation of vanadium (V) in the superconducting loop. At low temperature,
the devices show high flux-to-voltage (up to 0.52) and
flux-to-current (above 12) transfer functions, with the
best estimated flux sensitivity 2.6
reached under fixed voltage bias, where is the flux quantum. The
interferometers operate up to 2 , with an
improvement of 70 of the maximal operating temperature with respect to
early SQUIPTs design. The main features of the V-based SQUIPT are described
within a simplified theoretical model. Our results open the way to the
realization of SQUIPTs that take advantage of the use of higher-gap
superconductors for ultra-sensitive nanoscale applications that operate at
temperatures well above 1 K.Comment: Published version with Supplementary Informatio
Preliminary demonstration of a persistent Josephson phase-slip memory cell with topological protection
Superconducting computing promises enhanced computational power in both classical and quantum approaches. Yet, scalable and fast superconducting memories are not implemented. Here, we propose a fully superconducting memory cell based on the hysteretic phase-slip transition existing in long aluminum nanowire Josephson junctions. Embraced by a superconducting ring, the memory cell codifies the logic state in the direction of the circulating persistent current, as commonly defined in flux-based superconducting memories. But, unlike the latter, the hysteresis here is a consequence of the phase-slip occurring in the long weak link and associated to the topological transition of its superconducting gap. This disentangles our memory scheme from the large-inductance constraint, thus enabling its miniaturization. Moreover, the strong activation energy for phase-slip nucleation provides a robust topological protection against stochastic phase-slips and magnetic-flux noise. These properties make the Josephson phase-slip memory a promising solution for advanced superconducting classical logic architectures or flux qubits
Thermal superconducting quantum interference proximity transistor
Superconductors are known to be excellent thermal insulators at low
temperature owing to the presence of the energy gap in their density of states
(DOS). In this context, the superconducting \textit{proximity effect} allows to
tune the local DOS of a metallic wire by controlling the phase bias ()
imposed across it. As a result, the wire thermal conductance can be tuned over
several orders of magnitude by phase manipulation. Despite strong implications
in nanoscale heat management, experimental proofs of phase-driven control of
thermal transport in superconducting proximitized nanostructures are still very
limited. Here, we report the experimental demonstration of efficient heat
current control by phase tuning the superconducting proximity effect. This is
achieved by exploiting the magnetic flux-driven manipulation of the DOS of a
quasi one-dimensional aluminum nanowire forming a weal-link embedded in a
superconducting ring. Our thermal superconducting quantum interference
transistor (T-SQUIPT) shows temperature modulations up to mK yielding
a temperature-to-flux transfer function as large as mK/. Yet,
phase-slip transitions occurring in the nanowire Josephson junction induce a
hysteretic dependence of its local DOS on the direction of the applied magnetic
field. Thus, we also prove the operation of the T-SQUIPT as a phase-tunable
\textit{thermal memory}, where the information is encoded in the temperature of
the metallic mesoscopic island. Besides their relevance in quantum physics, our
results are pivotal for the design of innovative coherent caloritronics devices
such as heat valves and temperature amplifiers suitable for thermal logic
architectures.Comment: 8 pages, 4 figure
Hypersensitive tunable Josephson escape sensor for gigahertz astronomy
Sensitive photon detection in the gigahertz band constitutes the cornerstone
to study different phenomena in astronomy, such as radio burst sources, galaxy
formation, cosmic microwave background, axions, comets, gigahertz-peaked
spectrum radio sources and supermassive black holes. Nowadays, state of the art
detectors for astrophysics are mainly based on transition edge sensors and
kinetic inductance detectors. Overall, most sensible nanobolometers so far are
superconducting detectors showing a noise equivalent power (NEP) as low as
2x10-20 W/Hz1/2. Yet, fast thermometry at the nanoscale was demonstrated as
well with Josephson junctions through switching current measurements. In
general, detection performance are set by the fabrication process and limited
by used materials. Here, we conceive and demonstrate an innovative tunable
Josephson escape sensor (JES) based on the precise current control of the
temperature dependence of a fully superconducting one-dimensional nanowire
Josephson junction. The JES might be at the core of future hypersensitive in
situ-tunable bolometers or single-photon detectors working in the gigahertz
regime. Operated as a bolometer the JES points to a thermal fluctuation noise
(TFN) NEP_TFN 1x10-25 W/Hz1/2, which as a calorimeter bounds the frequency
resolution above 2 GHz, and resolving power below 40 at 50 GHz, as deduced from
the experimental data. Beyond the obvious applications in advanced ground-based
and space telescopes for gigahertz astronomy, the JES might represent a
breakthrough in several fields of quantum technologies ranging from subTHz
communications and quantum computing to cryptography and quantum key
distribution.Comment: 14 pages, 8 figure
InAs nanowire superconducting tunnel junctions: spectroscopy, thermometry and nanorefrigeration
We demonstrate an original method -- based on controlled oxidation -- to
create high-quality tunnel junctions between superconducting Al reservoirs and
InAs semiconductor nanowires. We show clean tunnel characteristics with a
current suppression by over orders of magnitude for a junction bias well
below the Al gap . The experimental data
are in close agreement with the BCS theoretical expectations of a
superconducting tunnel junction. The studied devices combine small-scale tunnel
contacts working as thermometers as well as larger electrodes that provide a
proof-of-principle active {\em cooling} of the electron distribution in the
nanowire. A peak refrigeration of about is achieved
at a bath temperature in our prototype
devices. This method opens important perspectives for the investigation of
thermoelectric effects in semiconductor nanostructures and for nanoscale
refrigeration.Comment: 6 pages, 4 color figure
Development of highly sensitive nanoscale transition edge sensors for gigahertz astronomy and dark matter search
Terahertz and sub-terahertz band detection has a key role both in fundamental
interactions physics and technological applications, such as medical imaging,
industrial quality control and homeland security. In particular, transition
edge sensors (TESs) and kinetic inductance detectors (KIDs) are the most
employed bolometers and calorimeters in the THz and sub-THz band for
astrophysics and astroparticles research. Here, we present the electronic,
thermal and spectral characterization of an aluminum/copper bilayer sensing
structure that, thanks to its thermal properties and a simple miniaturized
design, could be considered a perfect candidate to realize an extremely
sensitive class of nanoscale TES (nano-TES) for the giga-therahertz band.
Indeed, thanks to the reduced dimensionality of the active region and the
efficient Andreev mirror (AM) heat confinement, our devices are predicted to
reach state-of-the-art TES performance. In particular, as a bolometer the
nano-TES is expected to have a noise equivalent power (NEP) of
W/ and a relaxation time of ns
for the sub-THz band, typical of cosmic microwave background studies. When
operated as single-photon sensor, the devices are expected to show a remarkable
frequency resolution of 100 GHz, pointing towards the necessary energy
sensitivity requested in laboratory axion search experiments. Finally,
different multiplexing schemes are proposed and sized for imaging applications.Comment: 12 page, 7 figure
Proprietà elettroniche collettive del grafene supportato: influenza del substrato
Dottorato di Ricerca in Fisica e Tecnologie Quantistiche Ciclo XXVII, a.a. 2014Università della Calabri
Gate-control of the current-flux relation of a Josephson quantum interferometer based on proximitized metallic nanojuntions
We demonstrate an Al superconducting quantum interference device in which the
Josephson junctions are implemented through gate-controlled proximitized Cu
mesoscopic weak-links. The latter behave analogously to genuine superconducting
metals in terms of the response to electrostatic gating, and provide a good
performance in terms of current-modulation visibility. We show that, through
the application of a static gate voltage, we are able to modify the
interferometer current-flux relation in a fashion which seems compatible with
the introduction of -channels within the gated weak-link. Our results
suggest that the microscopic mechanism at the origin of the suppression of the
switching current in the interferometer is apparently phase coherent, resulting
in an overall damping of the superconducting phase rigidity. We finally tackle
the performance of the interferometer in terms of responsivity to magnetic flux
variations in the dissipative regime, and discuss the practical relevance of
gated proximity-based all-metallic SQUIDs for magnetometry at the nanoscale.Comment: 8 pages, 5 figure