129 research outputs found
Single ion heat engine with maximum efficiency at maximum power
We propose an experimental scheme to realize a nano heat engine with a single
ion. An Otto cycle may be implemented by confining the ion in a linear Paul
trap with tapered geometry and coupling it to engineered laser reservoirs. The
quantum efficiency at maximum power is analytically determined in various
regimes. Moreover, Monte Carlo simulations of the engine are performed that
demonstrate its feasibility and its ability to operate at maximum efficiency of
30% under realistic conditions.Comment: 5 pages, 3 figure
Quantum Rotor Engines
This chapter presents autonomous quantum engines that generate work in the
form of directed motion for a rotor. We first formulate a prototypical
clock-driven model in a time-dependent framework and demonstrate how it can be
translated into an autonomous engine with the introduction of a planar rotor
degree of freedom. The rotor plays both the roles of internal engine clock and
of work repository. Using the example of a single-qubit piston engine, the
thermodynamic performance is then reviewed. We evaluate the extractable work in
terms of ergotropy, the kinetic energy associated to net directed rotation, as
well as the intrinsic work based on the exerted torque under autonomous
operation; and we compare them with the actual energy output to an external
dissipative load. The chapter closes with a quantum-classical comparison of the
engine's dynamics. For the single-qubit piston example, we propose two
alternative representations of the qubit in an entirely classical framework:
(i) a coin flip model and (ii) a classical magnet moment, showing subtle
differences between the quantum and classical descriptions.Comment: Chapter of the upcoming book "Thermodynamics in the Quantum Regime -
Recent Progress and Outlook
The second law and beyond in microscopic quantum setups
The Clausius inequality (CI) is one of the most versatile forms of the second
law. Although it was originally conceived for macroscopic steam engines, it is
also applicable to quantum single particle machines. Moreover, the CI is the
main connecting thread between classical microscopic thermodynamics and
nanoscopic quantum thermodynamics. In this chapter, we study three different
approaches for obtaining the CI. Each approach shows different aspects of the
CI. The goals of this chapter are: (i) To show the exact assumptions made in
various derivations of the CI. (ii) To elucidate the structure of the second
law and its origin. (iii) To discuss the possibilities each approach offers for
finding additional second-law like inequalities. (iv) To pose challenges
related to the second law in nanoscopic setups. In particular, we introduce and
briefly discuss the notions of exotic heat machines (X machines), and "lazy
demons".Comment: As a chapter of: F. Binder, L. A. Correa, C. Gogolin, J. Anders, and
G. Adesso (eds.), "Thermodynamics in the quantum regime - Recent Progress and
Outlook", (Springer International Publishing). v1 does not include references
to other book chapter
Brownian Carnot engine
The Carnot cycle imposes a fundamental upper limit to the efficiency of a
macroscopic motor operating between two thermal baths. However, this bound
needs to be reinterpreted at microscopic scales, where molecular bio-motors and
some artificial micro-engines operate. As described by stochastic
thermodynamics, energy transfers in microscopic systems are random and thermal
fluctuations induce transient decreases of entropy, allowing for possible
violations of the Carnot limit. Despite its potential relevance for the
development of a thermodynamics of small systems, an experimental study of
microscopic Carnot engines is still lacking. Here we report on an experimental
realization of a Carnot engine with a single optically trapped Brownian
particle as working substance. We present an exhaustive study of the energetics
of the engine and analyze the fluctuations of the finite-time efficiency,
showing that the Carnot bound can be surpassed for a small number of
non-equilibrium cycles. As its macroscopic counterpart, the energetics of our
Carnot device exhibits basic properties that one would expect to observe in any
microscopic energy transducer operating with baths at different temperatures.
Our results characterize the sources of irreversibility in the engine and the
statistical properties of the efficiency -an insight that could inspire novel
strategies in the design of efficient nano-motors.Comment: 7 pages, 7 figure
Secure Mobile Support of Independent Sales Agencies
Sales agents depend on mobile support systems for their daily work. Independent sales agencies, however, are not able to facilitate this kind of mobile support on their own due to their small size and lack of the necessary funds. Since their processes correlate with confidential information and include the initiation and alteration of legally binding transactions they have a high need for security. In this contribution we first propose an IT-artifact consisting of a service platform that supports multi-vendor sales processes based on previous work. We then analyze use cases of sales representatives of independent sales agencies using this system and derive their security requirements. We then propose a security extension to the IT-artifact and evaluate this extension by comparing it to existing solutions. Our results show that the proposed artifact extension provides a more convenient and secure solution than already existing approaches
Thermodynamic principles and implementations of quantum machines
The efficiency of cyclic heat engines is limited by the Carnot bound. This
bound follows from the second law of thermodynamics and is attained by engines
that operate between two thermal baths under the reversibility condition
whereby the total entropy does not increase. By contrast, the efficiency of
engines powered by quantum non-thermal baths has been claimed to surpass the
thermodynamic Carnot bound. The key to understanding the performance of such
engines is a proper division of the energy supplied by the bath to the system
into heat and work, depending on the associated change in the system entropy
and ergotropy. Due to their hybrid character, the efficiency bound for quantum
engines powered by a non-thermal bath does not solely follow from the laws of
thermodynamics. Hence, the thermodynamic Carnot bound is inapplicable to such
hybrid engines. Yet, they do not violate the principles of thermodynamics.
An alternative means of boosting machine performance is the concept of
heat-to-work conversion catalysis by quantum non-linear (squeezed) pumping of
the piston mode. This enhancement is due to the increased ability of the
squeezed piston to store ergotropy. Since the catalyzed machine is fueled by
thermal baths, it adheres to the Carnot bound.
We conclude by arguing that it is not quantumness per se that improves the
machine performance, but rather the properties of the baths, the working fluid
and the piston that boost the ergotropy and minimize the wasted heat in both
the input and the output.Comment: As a chapter of: F. Binder, L. A. Correa, C. Gogolin, J. Anders, and
G. Adesso (eds.), "Thermodynamics in the quantum regime - Recent Progress and
Outlook", (Springer International Publishing
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