1,002 research outputs found
Photonic heat transport from weak to strong coupling
Superconducting circuits provide a favorable platform for quantum
thermodynamic experiments. An important component for such experiments is a
heat valve, i.e. a device which allows one to control the heat power flowing
through the system. Here we theoretically study the heat valve based on a
superconducting quantum interference device (SQUID) coupled to two heat baths
via two resonators. The heat current in such system can be tuned by magnetic
flux. We investigate how does the heat current modulation depend on the
coupling strength g between the SQUID and the resonators. In the weak coupling
regime the heat current modulation grows as g2, but, surprisingly, at the
intermediate coupling it can be strongly suppressed. This effect is linked to
the resonant nature of the heat transport at weak coupling, where the heat
current dependence on the magnetic flux is a periodic set of narrow peaks. At
the intermediate coupling, the peaks become broader and overlap, thus reducing
the heat modulation. At very strong coupling the heat modulation grows again
and finally saturates at a constant value.Comment: 8 pages, 3 figure
Universal scaling of current fluctuations in disordered graphene
We analyze the full transport statistics of graphene with smooth disorder at
low dopings. First we consider the case of 1D disorder for which the
transmission probability distribution is given analytically in terms of the
graphene-specific mean free path. All current cumulants are shown to scale with
system parameters (doping, size, disorder strength and correlation length) in
an identical fashion for large enough systems. In the case of 2D disorder,
numerical evidence is given for the same kind of identical scaling of all
current cumulants, so that the ratio of any two such cumulants is universal.
Specific universal values are given for the Fano factor, which is smaller than
the pseudodiffusive value of ballistic graphene (F=1/3) both for 1D (F=0.243)
and 2D (F=0.295) disorder. On the other hand, conductivity in wide samples is
shown to grow without saturation as \sqrt{L} and Log L with system length L in
the 1D and 2D cases respectively.Comment: 9 pages, 7 figures. Published version, includes corrected figure for
Fano facto
Extreme reductions of entropy in an electronic double dot
We experimentally study negative fluctuations of stochastic entropy
production in an electronic double dot operating in nonequilibrium steady-state
conditions. We record millions of random electron tunneling events at different
bias points, thus collecting extensive statistics. We show that for all bias
voltages the experimental average values of the minima of stochastic entropy
production lie above , where is the Boltzmann constant, in
agreement with recent theoretical predictions for nonequilibrium steady states.
Furthermore, we also demonstrate that the experimental cumulative distribution
of the entropy production minima is bounded, at all times and for all bias
voltages, by a universal expression predicted by the theory. We also extend our
theory by deriving a general bound for the average value of the maximum heat
absorbed by a mesoscopic system from the environment and compare this result
with experimental data. Finally, we show by numerical simulations that these
results are not necessarily valid under non-stationary conditions.Comment: 16 pages, 12 figure
Determining the parameters of a random telegraph signal by digital low pass filtering
We propose a method to determine the switching rates of a random telegraph
signal. We apply digital low pass filtering with varying bandwidth to the raw
signal, evaluate the cumulants of the resulting distributions and compare them
with the analytical prediction. This technique is useful in case of a slow
detector with response time comparable to the time interval between the
switching events. We demonstrate the efficiency of this method by analyzing
random telegraph signals generated by individual charge tunneling events in
metallic single-electron transistors.Comment: 5 pages, 6 figure
Bolometric detection of coherent Josephson coupling in a highly dissipative environment
The Josephson junction is a building block of quantum circuits. Its behavior,
well understood when treated as an isolated entity, is strongly affected by
coupling to an electromagnetic environment. In 1983 Schmid predicted that a
Josephson junction shunted by a resistance exceeding the resistance quantum
k for
Cooper pairs would become insulating since the phase fluctuations would destroy
the coherent Josephson coupling. Although this prediction has been confirmed in
charge transport experiments, recent microwave measurements have questioned
this interpretation. Here, we insert a small junction in a Johnson-Nyquist type
setup, where it is driven by weak current noise arising from thermal
fluctuations. Our heat probe minimally perturbs the junction's equilibrium,
shedding light on features not visible in charge transport. We find that while
charge transport through the junction is dissipative as expected, thermal
transport is determined by the inductive-like Josephson response, unambiguously
demonstrating that a supercurrent survives even deep into the expected
insulating regime. The discrepancy between these two measurements highlights
the difference between the low frequency and the high frequency response of a
junction and calls for further theoretical and experimental inputs on the
dynamics of Josephson junctions in a highly dissipative environment.Comment: Typo corrected in the ending discussion, with added discussion on the
results of ref.[16] cited in the main tex
Plants with genetically encoded autoluminescence
Autoluminescent plants engineered to express a bacterial bioluminescence gene cluster in plastids have not been widely adopted because of low light output. We engineered tobacco plants with a fungal bioluminescence system that converts caffeic acid (present in all plants) into luciferin and report self-sustained luminescence that is visible to the naked eye. Our findings could underpin development of a suite of imaging tools for plants
Nuclear astrophysics with radioactive ions at FAIR
The nucleosynthesis of elements beyond iron is dominated by neutron captures in the s and r processes. However, 32 stable, proton-rich isotopes cannot be formed during those processes, because they are shielded from the s-process flow and r-process, β-decay chains. These nuclei are attributed to the p and rp process. For all those processes, current research in nuclear astrophysics addresses the need for more precise reaction data involving radioactive isotopes. Depending on the particular reaction, direct or inverse kinematics, forward or time-reversed direction are investigated to determine or at least to constrain the desired reaction cross sections. The Facility for Antiproton and Ion Research (FAIR) will offer unique, unprecedented opportunities to investigate many of the important reactions. The high yield of radioactive isotopes, even far away from the valley of stability, allows the investigation of isotopes involved in processes as exotic as the r or rp processes
Coulomb dissociation of N 20,21
Neutron-rich light nuclei and their reactions play an important role in the creation of chemical elements. Here, data from a Coulomb dissociation experiment on N20,21 are reported. Relativistic N20,21 ions impinged on a lead target and the Coulomb dissociation cross section was determined in a kinematically complete experiment. Using the detailed balance theorem, the N19(n,γ)N20 and N20(n,γ)N21 excitation functions and thermonuclear reaction rates have been determined. The N19(n,γ)N20 rate is up to a factor of 5 higher at
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