2,157 research outputs found
Nonadiabatic Electron Pumping: Maximal Current with Minimal Noise
The noise properties of pump currents through an open double quantum dot
setup with non-adiabatic ac driving are investigated. Driving frequencies close
to the internal resonances of the double dot-system mark the optimal working
points at which the pump current assumes a maximum while its noise power
possesses a remarkably low minimum. A rotating-wave approximation provides
analytical expressions for the current and its noise power and allows to
optimize the noise characteristics. The analytical results are compared to
numerical results from a Floquet transport theory.Comment: 4 pages, 3 figures, replaced Fig. 1, added new inset in Fig. 2,
extended paragraph on symmetry consideration
Punishing and Abstaining for Public Goods
The evolution of cooperation within sizeable groups of non-related humans offers many challenges for our understanding. Current research has highlighted two factors boosting cooperation in public goods interactions, namely costly punishment of defectors, and the option to defer from the joint enterprise. A recent modeling approach has suggested that the autarctic option acts as a catalyzer for the ultimate fixation of altruistic punishment. We present an alternative, more micro-economically based model which yields a bistable outcome instead. Evolutionary dynamics can either lead to a Nash equilibrium of punishing and non-punishing cooperators, or to an oscillating state without punishers
A Survey on Indirect Reciprocity
This survey deals with indirect reciprocity, i.e., with the possibility that altruistic acts are returned, not by the recipient, but by a third party. After briefly sketching how this problem is dealt with in classical game theory, we describe recent work on the assessment on interactions, and the evolutionary stability of strategies for indirect reciprocation. All stable strategies ( the 'leading eight') distinguish between justified and non-justified defections, and therefore are based on non-costly punishment. Next we consider the replicator dynamics of populations consisting of defectors, discriminators and undiscriminating altruists. We stress that errors can destabilise cooperation for strategies not distinguishing justified from unjustified defections, but that a fixed number of rounds, or the assumption of an individual's social network growing with age, can lead to cooperation based on a stable mixture of undiscriminating altruists and of discriminators who do not distinguish between justified and unjustified defection. We describe previous work using agent-based simulations for 'binary-score' and 'full score' models. Finally, we survey the recent results on experiments with the indirect reciprocation game
Nonadiabatic electron heat pump
We investigate a mechanism for extracting heat from metallic conductors based
on the energy-selective transmission of electrons through a spatially
asymmetric resonant structure subject to ac driving. This quantum refrigerator
can operate at zero net electronic current as it replaces hot by cold electrons
through two energetically symmetric inelastic channels. We present numerical
results for a specific heterostructure and discuss general trends. We also
explore the conditions under which the cooling rate may approach the ultimate
limit given by the quantum of cooling power.Comment: 4 pages, 3 figures; published version, typos correcte
To what extent are temperature levels changing due to greenhouse gas emissions?
Weather and temperatures vary in ways that are difficult to explain and predict precisely. In this
article we review data on temperature variations in the past as well possible reasons for these
variations. Subsequently, we review key properties of global climate models and statistical analyses
conducted by others on the ability of the global climate models to track historical temperatures.
These tests show that standard climate models are rejected by time series data on global
temperatures. Finally, we update and extend previous statistical analysis of temperature data
(Dagsvik et al., 2020). Using theoretical arguments and statistical tests we find, as in Dagsvik et al.
(2020), that the effect of man-made CO2 emissions does not appear to be strong enough to cause
systematic changes in the temperature fluctuations during the last 200 years
Molecular wires acting as quantum heat ratchets
We explore heat transfer in molecular junctions between two leads in the
absence of a finite net thermal bias. The application of an unbiased,
time-periodic temperature modulation of the leads entails a dynamical breaking
of reflection symmetry, such that a directed heat current may emerge (ratchet
effect). In particular, we consider two cases of adiabatically slow driving,
namely (i) periodic temperature modulation of only one lead and (ii)
temperature modulation of both leads with an ac driving that contains a second
harmonic, thus generating harmonic mixing. Both scenarios yield sizeable
directed heat currents which should be detectable with present techniques.
Adding a static thermal bias, allows one to compute the heat current-thermal
load characteristics which includes the ratchet effect of negative thermal bias
with positive-valued heat flow against the thermal bias, up to the thermal
stop-load. The ratchet heat flow in turn generates also an electric current. An
applied electric stop-voltage, yielding effective zero electric current flow,
then mimics a solely heat-ratchet-induced thermopower (``ratchet Seebeck
effect''), although no net thermal bias is acting. Moreover, we find that the
relative phase between the two harmonics in scenario (ii) enables steering the
net heat current into a direction of choice.Comment: 9 pages, 8 figure
Time-Resolved Measurement of a Charge Qubit
We propose a scheme for monitoring coherent quantum dynamics with good
time-resolution and low backaction, which relies on the response of the
considered quantum system to high-frequency ac driving. An approximate
analytical solution of the corresponding quantum master equation reveals that
the phase of an outgoing signal, which can directly be measured in an
experiment with lock-in technique, is proportional to the expectation value of
a particular system observable. This result is corroborated by the numerical
solution of the master equation for a charge qubit realized with a Cooper-pair
box, where we focus on monitoring coherent oscillations.Comment: 4 pages, 3 figure
Conditional strategies and the evolution of cooperation in spatial public goods games
The fact that individuals will most likely behave differently in different
situations begets the introduction of conditional strategies. Inspired by this,
we study the evolution of cooperation in the spatial public goods game, where
besides unconditional cooperators and defectors, also different types of
conditional cooperators compete for space. Conditional cooperators will
contribute to the public good only if other players within the group are likely
to cooperate as well, but will withhold their contribution otherwise. Depending
on the number of other cooperators that are required to elicit cooperation of a
conditional cooperator, the latter can be classified in as many types as there
are players within each group. We find that the most cautious cooperators, such
that require all other players within a group to be conditional cooperators,
are the undisputed victors of the evolutionary process, even at very low
synergy factors. We show that the remarkable promotion of cooperation is due
primarily to the spontaneous emergence of quarantining of defectors, which
become surrounded by conditional cooperators and are forced into isolated
convex "bubbles" from where they are unable to exploit the public good. This
phenomenon can be observed only in structured populations, thus adding to the
relevance of pattern formation for the successful evolution of cooperation.Comment: 7 two-column pages, 7 figures; accepted for publication in Physical
Review
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