229 research outputs found
Towards phase-coherent caloritronics in superconducting circuits
The emerging field of phase-coherent caloritronics (from the Latin word
"calor", i.e., heat) is based on the possibility to control heat currents using
the phase difference of the superconducting order parameter. The goal is to
design and implement thermal devices able to master energy transfer with a
degree of accuracy approaching the one reached for charge transport by
contemporary electronic components. This can be obtained by exploiting the
macroscopic quantum coherence intrinsic to superconducting condensates, which
manifests itself through the Josephson and the proximity effect. Here, we
review recent experimental results obtained in the realization of heat
interferometers and thermal rectifiers, and discuss a few proposals for exotic
non-linear phase-coherent caloritronic devices, such as thermal transistors,
solid-state memories, phase-coherent heat splitters, microwave refrigerators,
thermal engines and heat valves. Besides being very attractive from the
fundamental physics point of view, these systems are expected to have a vast
impact on many cryogenic microcircuits requiring energy management, and
possibly lay the first stone for the foundation of electronic thermal logic.Comment: 11 pages, 6 colour figure
Efficient and tunable Aharonov-Bohm quantum heat engine
We propose a quantum heat engine based on an Aharonov-Bohm interferometer in
a two-terminal geometry, and investigate its thermoelectric performances in the
linear response regime. Sizeable thermopower (up to /K) as
well as values largely exceeding unity can be achieved by simply adjusting
parameters of the setup and temperature bias across the interferometer leading
to thermal efficiency at maximum power approaching of the Carnot limit.
This is close to the optimal efficiency at maximum power achievable for a
two-terminal heat engine. Changing the magnetic flux, the asymmetry of the
structure, a side-gate bias voltage through a capacitively-coupled electrode
and the transmission of the T-junctions connecting the AB ring to the contacts
allows to finely tune the operation of the quantum heat engine. The exploration
of the parameters' space demonstrates that the high performances of the
Aharonov-Bohm two-terminal device as a quantum heat engine are stable over a
wide range of temperatures and length imbalances, promising towards
experimental realization.Comment: 5 pages, 4 figures, published versio
On-Chip Cooling by Heating with Superconducting Tunnel Junctions
Heat management and refrigeration are key concepts for nanoscale devices
operating at cryogenic temperatures. The design of an on-chip mesoscopic
refrigerator that works thanks to the input heat is presented, thus realizing a
solid state implementation of the concept of cooling by heating. The system
consists of a circuit featuring a thermoelectric element based on a
ferromagnetic insulator-superconductor tunnel junction (N-FI-S) and a series of
two normal metal-superconductor tunnel junctions (SINIS). The N-FI-S element
converts the incoming heat in a thermovoltage, which is applied to the SINIS,
thereby yielding cooling. The cooler's performance is investigated as a
function of the input heat current for different bath temperatures. We show
that this system can efficiently employ the performance of SINIS refrigeration,
with a substantial cooling of the normal metal island. Its scalability and
simplicity in the design makes it a promising building block for
low-temperature on-chip energy management applications.Comment: 7 pages, 6 figure
Parasitic effects in SQUID-based radiation comb generators
We study several parasitic effects on the implementation of a Josephson
radiation comb generator (JRCG) based on a dc superconducting quantum
interference device (SQUID) driven by an external magnetic field. This system
can be used as a radiation generator similarly to what is done in optics and
metrology, and allows one to generate up to several hundreds of harmonics of
the driving frequency. First we take into account how assuming a finite loop
geometrical inductance and junction capacitance in each SQUID may alter the
operation of this device. Then, we estimate the effect of imperfections in the
fabrication of an array of SQUIDs, which is an unavoidable source of errors in
practical situations. We show that the role of the junction capacitance is in
general negligible, whereas the geometrical inductance has a beneficial effect
on the performance of the device. The errors on the areas and junction
resistance asymmetries may deteriorate the performance, but their effect can be
limited up to a large extent with a suitable choice of fabrication parameters.Comment: 9 pages, 9 figure
A Microwave Josephson Refrigerator
We present a microwave quantum refrigeration principle based on the Josephson
effect. When a superconducting quantum interference device (SQUID) is pierced
by a time-dependent magnetic flux, it induces changes in the macroscopic
quantum phase and an effective finite bias voltage appears across the SQUID.
This voltage can be used to actively cool well below the lattice temperature
one of the superconducting electrodes forming the interferometer. The
achievable cooling performance combined with the simplicity and scalability
intrinsic to the structure pave the way to a number of applications in quantum
technology.Comment: 6 pages, 3 figure
Balanced double-loop mesoscopic interferometer based on Josephson proximity nanojunctions
We report on the fabrication and characterization of a two-terminal
mesoscopic interferometer based on three V/Cu/V Josephson junctions having
nanoscale cross-section. The junctions have been arranged in a double-ring
geometry realized by metallic thin film deposition through a suspended mask
defined by electron beam lithography. Although a significant amount of
asymmetry between the critical current of each junction is observed we show
that the interferometer is able to suppress the supercurrent to a level lower
than 6 parts per thousand, being here limited by measurement resolution. The
present nano-device is suitable for low-temperature magnetometric and
gradiometric measurements over the micrometric scale.Comment: 5 pages, 4 figure
Phase-Tunable Temperature Amplifier
Coherent caloritronics, the thermal counterpart of coherent electronics, has
drawn growing attention since the discovery of heat interference in 2012.
Thermal interferometers, diodes, transistors and nano-valves have been
theoretically proposed and experimentally demonstrated by exploiting the
quantum phase difference between two superconductors coupled through a
Josephson junction. So far, the quantum-phase modulator has been realized in
the form of a superconducting quantum interference device (SQUID) or a
superconducting quantum interference proximity transistor (SQUIPT). Thence, an
external magnetic field is necessary in order to manipulate the heat transport.
Here, we theoretically propose the first on-chip fully thermal caloritronic
device: the phase-tunable temperature amplifier. Taking advantage of a recent
thermoelectric effect discovered in spin-split superconductors coupled to a
spin-polarized system, by a temperature gradient we generate the magnetic flux
controlling the transport through a temperature biased SQUIPT. By employing
commonly used materials and a geometry compatible with state-of-the-art
nano-fabrication techniques, we simulate the behavior of the temperature
amplifier and define a number of figures of merit in full analogy with voltage
amplifiers. Notably, our architecture ensures infinite input thermal impedance,
maximum gain of about 11 and efficiency reaching the 95%. This device concept
could represent a breakthrough in coherent caloritronic devices, and paves the
way for applications in radiation sensing, thermal logics and quantum
information.Comment: 7 pages, 3 figure
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