70 research outputs found
Toward physical realizations of thermodynamic resource theories
Conventional statistical mechanics describes large systems and averages over
many particles or over many trials. But work, heat, and entropy impact the
small scales that experimentalists can increasingly control, e.g., in
single-molecule experiments. The statistical mechanics of small scales has been
quantified with two toolkits developed in quantum information theory: resource
theories and one-shot information theory. The field has boomed recently, but
the theorems amassed have hardly impacted experiments. Can thermodynamic
resource theories be realized experimentally? Via what steps can we shift the
theory toward physical realizations? Should we care? I present eleven
opportunities in physically realizing thermodynamic resource theories.Comment: Publication information added. Cosmetic change
Rectification of electronic heat current by a hybrid thermal diode
We report the realization of an ultra-efficient low-temperature hybrid heat
current rectifier, thermal counterpart of the well-known electric diode. Our
design is based on a tunnel junction between two different elements: a normal
metal and a superconducting island. Electronic heat current asymmetry in the
structure arises from large mismatch between the thermal properties of these
two. We demonstrate experimentally temperature differences exceeding mK
between the forward and reverse thermal bias configurations. Our device offers
a remarkably large heat rectification ratio up to and allows its
prompt implementation in true solid-state thermal nanocircuits and
general-purpose electronic applications requiring energy harvesting or thermal
management and isolation at the nanoscale.Comment: 8 pages, 6 color figure
Towards quantum thermodynamics in electronic circuits
Electronic circuits operating at sub-kelvin temperatures are attractive candidates for studying classical and quantum thermodynamics: their temperature can be controlled and measured locally with exquisite precision, and they allow experiments with large statistical samples. The availability and rapid development of devices such as quantum dots, single-electron boxes and superconducting qubits only enhance their appeal. But although these systems provide fertile ground for studying heat transport, entropy production and work in the context of quantum mechanics, the field remains in its infancy experimentally. Here, we review some recent experiments on quantum heat transport, fluctuation relations and implementations of Maxwell’s demon, revealing the rich physics yet to be fully probed in these systems.Peer reviewe
Detection of Geometric Phases in Superconducting Nanocircuits
When a quantum mechanical system undergoes an adiabatic cyclic evolution it
acquires a geometrical phase factor in addition to the dynamical one. This
effect has been demonstrated in a variety of microscopic systems. Advances in
nanotechnologies should enable the laws of quantum dynamics to be tested at the
macroscopic level, by providing controllable artificial two-level systems (for
example, in quantum dots and superconducting devices). Here we propose an
experimental method to detect geometric phases in a superconducting device. The
setup is a Josephson junction nanocircuit consisting of a superconducting
electron box. We discuss how interferometry based on geometrical phases may be
realized, and show how the effect may applied to the design of gates for
quantum computation.Comment: 12 page
Towards a quantum representation of the ampere using single electron pumps
Electron pumps generate a macroscopic electric current by controlled
manipulation of single electrons. Despite intensive research towards a quantum
current standard over the last 25 years, making a fast and accurate quantised
electron pump has proved extremely difficult. Here we demonstrate that the
accuracy of a semiconductor quantum dot pump can be dramatically improved by
using specially designed gate drive waveforms. Our pump can generate a current
of up to 150 pA, corresponding to almost a billion electrons per second, with
an experimentally demonstrated current accuracy better than 1.2 parts per
million (ppm) and strong evidence, based on fitting data to a model, that the
true accuracy is approaching 0.01 ppm. This type of pump is a promising
candidate for further development as a realisation of the SI base unit ampere,
following a re-definition of the ampere in terms of a fixed value of the
elementary charge.Comment: 8 pages, 7 figure
A Josephson Quantum Electron Pump
A macroscopic fluid pump works according to the law of Newtonian mechanics
and transfers a large number of molecules per cycle (of the order of 10^23). By
contrast, a nano-scale charge pump can be thought as the ultimate
miniaturization of a pump, with its operation being subject to quantum
mechanics and with only few electrons or even fractions of electrons transfered
per cycle. It generates a direct current in the absence of an applied voltage
exploiting the time-dependence of some properties of a nano-scale conductor.
The idea of pumping in nanostructures was discussed theoretically a few decades
ago [1-4]. So far, nano-scale pumps have been realised only in system
exhibiting strong Coulombic effects [5-12], whereas evidence for pumping in the
absence of Coulomb-blockade has been elusive. A pioneering experiment by
Switkes et al. [13] evidenced the difficulty of modulating in time the
properties of an open mesoscopic conductor at cryogenic temperatures without
generating undesired bias voltages due to stray capacitances [14,15]. One
possible solution to this problem is to use the ac Josephson effect to induce
periodically time-dependent Andreev-reflection amplitudes in a hybrid
normal-superconducting system [16]. Here we report the experimental detection
of charge flow in an unbiased InAs nanowire (NW) embedded in a superconducting
quantum interference device (SQUID). In this system, pumping may occur via the
cyclic modulation of the phase of the order parameter of different
superconducting electrodes. The symmetry of the current with respect to the
enclosed magnetic flux [17,18] and bias SQUID current is a discriminating
signature of pumping. Currents exceeding 20 pA are measured at 250 mK, and
exhibit symmetries compatible with a pumping mechanism in this setup which
realizes a Josephson quantum electron pump (JQEP).Comment: 7+ pages, 6 color figure
Gigahertz quantized charge pumping in graphene quantum dots
Single electron pumps are set to revolutionize electrical metrology by
enabling the ampere to be re-defined in terms of the elementary charge of an
electron. Pumps based on lithographically-fixed tunnel barriers in mesoscopic
metallic systems and normal/superconducting hybrid turnstiles can reach very
small error rates, but only at MHz pumping speeds corresponding to small
currents of the order 1 pA. Tunable barrier pumps in semiconductor structures
have been operated at GHz frequencies, but the theoretical treatment of the
error rate is more complex and only approximate predictions are available.
Here, we present a monolithic, fixed barrier single electron pump made entirely
from graphene. We demonstrate pump operation at frequencies up to 1.4 GHz, and
predict the error rate to be as low as 0.01 parts per million at 90 MHz.
Combined with the record-high accuracy of the quantum Hall effect and proximity
induced Josephson junctions, accurate quantized current generation brings an
all-graphene closure of the quantum metrological triangle within reach.
Envisaged applications for graphene charge pumps outside quantum metrology
include single photon generation via electron-hole recombination in
electrostatically doped bilayer graphene reservoirs, and for readout of
spin-based graphene qubits in quantum information processing.Comment: 13 pages, 11 figures, includes supplementary informatio
Production of zero energy radioactive beams through extraction across superfluid helium surface
A radioactive Ra-223 source was immersed in superfluid helium at 1.2-1.7 K. Electric fields transported recoiled Rn-219 ions in the form of snowballs to the surface and further extracted them across the surface. The ions were focussed onto an aluminium foil and alpha particle spectra were taken with a surface barrier spectrometer. This enabled us to determine the efficiency for each process unambiguously. The pulsed second sound wave proved effective in enhancing the extraction of positive ions from the surface. Thus we offer a novel method for study of impurities in superfluid helium and propose this method for production of zero energy nuclear beams for use at radioactive ion beam facilities. (C) 2003 Elsevier Science B.V. All rights reserved
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