54 research outputs found
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
Glauber coherence of single electron sources
Recently demonstrated solid state single electron sources generate different
quantum states depending on their operation condition. For adiabatic and
non-adiabatic sources we determine the Glauber correlation function in terms of
the Floquet scattering matrix of the source. The correlation function provides
full information on the shape of the state, on its time-dependent amplitude and
phase, which makes the coherence properties of single electron states essential
for the production of quantum multi-particle states.Comment: 4+ pages, 4 figure
Distributions of electron waiting times in quantum-coherent conductors
The distribution of electron waiting times is useful to characterize quantum
transport in mesoscopic structures. Here we consider a generic quantum-coherent
conductor consisting of a mesoscopic scatterer in a two-terminal setup. We
extend earlier results for single-channel conductors to setups with several
(possibly spin-degenerate) conduction channels and we discuss the effect of a
finite electronic temperature. We present detailed investigations of the
electron waiting times in a quantum point contact as well as in two mesoscopic
interferometers with energy-dependent transmissions: a Fabry-P\'erot
interferometer and a Mach-Zehnder interferometer. We show that the waiting time
distributions allow us to determine characteristic features of the scatterers,
for instance the number of resonant levels in the Fabry-P\'erot interferometer
that contribute to the electronic transport.Comment: 13 pages, 11 figure
Coherence of Single Electron Sources from Mach-Zehnder Interferometry
A new type of electron sources has emerged which permits to inject particles
in a controllable manner, one at a time, into an electronic circuit. Such
single electron sources make it possible to fully exploit the particles'
quantum nature. We determine the single-particle coherence length from the
decay of the Aharonov-Bohm oscillations as a function of the imbalance of a
Mach-Zehnder interferometer connected to a single electron source. The
single-particle coherence length is of particular importance as it is an
intrinsic property of the source in contrast to the dephasing length.Comment: 4 pages, 4 figure
Autonomous quantum thermal machine for generating steady-state entanglement
We discuss a simple quantum thermal machine for the generation of
steady-state entanglement between two interacting qubits. The machine is
autonomous in the sense that it uses only incoherent interactions with thermal
baths, but no source of coherence or external control. By weakly coupling the
qubits to thermal baths at different temperatures, inducing a heat current
through the system, steady-state entanglement is generated far from thermal
equilibrium. Finally, we discuss two possible implementations, using
superconducting flux qubits or a semiconductor double quantum dot. Experimental
prospects for steady-state entanglement are promising in both systems.Comment: 14 pages, 4 figure
Adiabatic versus nonadiabatic emission
We investigate adiabatic and nonadiabatic emission of single particles into an
edge state using an analytically solvable dynamical scattering matrix model of
an on-demand source. We compare adiabatic and nonadiabatic emissions by
considering two geometries: a collider geometry where two emitters are coupled
to two different edge states and a series geometry where two emitters are
coupled to the same edge state. Most effects observed for adiabatic emitters
also occur for nonadiabatic emitters. In particular this applies to effects
arising due to the overlap of wave packets colliding at a quantum point
contact. Specifically we compare the Pauli peak (the fermionic analog of the
bosonic Hong-Ou-Mandel dip) for the adiabatic and nonadiabatic collider and
find them to be similar. In contrast we find a striking difference between the
two operating conditions in the series geometry in which particles are emitted
into the same edge state. Whereas the squared average charge current can be
nullified for both operating conditions, the heat current can be made to
vanish only with adiabatic emitters
Unifying paradigms of quantum refrigeration: fundamental limits of cooling and associated work costs
In classical thermodynamics the work cost of control can typically be
neglected. On the contrary, in quantum thermodynamics the cost of control
constitutes a fundamental contribution to the total work cost. Here, focusing
on quantum refrigeration, we investigate how the level of control determines
the fundamental limits to cooling and how much work is expended in the
corresponding process. \jona{We compare two extremal levels of control. First
coherent operations, where the entropy of the resource is left unchanged, and
second incoherent operations, where only energy at maximum entropy (i.e. heat)
is extracted from the resource. For minimal machines, we find that the lowest
achievable temperature and associated work cost depend strongly on the type of
control, in both single-cycle and asymptotic regimes. We also extend our
analysis to general machines.} Our work provides a unified picture of the
different approaches to quantum refrigeration developed in the literature,
including algorithmic cooling, autonomous quantum refrigerators, and the
resource theory of quantum thermodynamics.Comment: 17 + 28 pages, 10 figure
Critical heat current for operating an entanglement engine
Autonomous entanglement engines have recently been proposed to generate
steady-state bipartite and multipartite entanglement exploiting only incoherent
interactions with thermal baths at different temperatures. In this work, we
investigate the interplay between heat current and entanglement in a two-qubit
entanglement engine, deriving a critical heat current for successful operation
of the engine, i.e. a cut-off above which entanglement is present. The heat
current can thus be seen as a witness to the presence of entanglement. In the
regime of weak-inter qubit coupling, we also investigate the effect of two
experimentally relevant parameters for the qubits, the energy detuning and
tunnelling, on the entanglement production. Finally, we show that the regime of
strong inter-qubit coupling provides no clear advantage over the weak regime,
in the context of out-of-equilibrium entanglement engines.Comment: 18 pages, 6 figures, discussion on strong inter-qubit coupling adde
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