21,778 research outputs found
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
Global passivity in microscopic thermodynamics
The main thread that links classical thermodynamics and the thermodynamics of
small quantum systems is the celebrated Clausius inequality form of the second
law. However, its application to small quantum systems suffers from two
cardinal problems: (i) The Clausius inequality does not hold when the system
and environment are initially correlated - a commonly encountered scenario in
microscopic setups. (ii) In some other cases, the Clausius inequality does not
provide any useful information (e.g. in dephasing scenarios). We address these
deficiencies by developing the notion of global passivity and employing it as a
tool for deriving thermodynamic inequalities on observables. For initially
uncorrelated thermal environments the global passivity framework recovers the
Clausius inequality. More generally, global passivity provides an extension of
the Clausius inequality that holds even in the presences of strong initial
system-environment correlations. Crucially, the present framework provides
additional thermodynamic bounds on expectation values. To illustrate the role
of the additional bounds we use them to detect unaccounted heat leaks and weak
feedback operations ("Maxwell's demons") that the Clausius inequality cannot
detect. In addition, it is shown that global passivity can put practical upper
and lower bounds on the buildup of system-environment correlation for dephasing
interactions. Our findings are highly relevant for experiments in various
systems such as ion traps, superconducting circuits, atoms in optical cavities
and more.Comment: Accepted to Phy. Rev.
Thermodynamics of quantum systems under dynamical control
In this review the debated rapport between thermodynamics and quantum
mechanics is addressed in the framework of the theory of
periodically-driven/controlled quantum-thermodynamic machines. The basic model
studied here is that of a two-level system (TLS), whose energy is periodically
modulated while the system is coupled to thermal baths. When the modulation
interval is short compared to the bath memory time, the system-bath
correlations are affected, thereby causing cooling or heating of the TLS,
depending on the interval. In steady state, a periodically-modulated TLS
coupled to two distinct baths constitutes the simplest quantum heat machine
(QHM) that may operate as either an engine or a refrigerator, depending on the
modulation rate. We find their efficiency and power-output bounds and the
conditions for attaining these bounds. An extension of this model to multilevel
systems shows that the QHM power output can be boosted by the multilevel
degeneracy.
These results are used to scrutinize basic thermodynamic principles: (i)
Externally-driven/modulated QHMs may attain the Carnot efficiency bound, but
when the driving is done by a quantum device ("piston"), the efficiency
strongly depends on its initial quantum state. Such dependence has been unknown
thus far. (ii) The refrigeration rate effected by QHMs does not vanish as the
temperature approaches absolute zero for certain quantized baths, e.g.,
magnons, thous challenging Nernst's unattainability principle. (iii)
System-bath correlations allow more work extraction under periodic control than
that expected from the Szilard-Landauer principle, provided the period is in
the non-Markovian domain. Thus, dynamically-controlled QHMs may benefit from
hitherto unexploited thermodynamic resources
Direct and Indirect Couplings in Coherent Feedback Control of Linear Quantum Systems
The purpose of this paper is to study and design direct and indirect
couplings for use in coherent feedback control of a class of linear quantum
stochastic systems. A general physical model for a nominal linear quantum
system coupled directly and indirectly to external systems is presented.
Fundamental properties of stability, dissipation, passivity, and gain for this
class of linear quantum models are presented and characterized using complex
Lyapunov equations and linear matrix inequalities (LMIs). Coherent
and LQG synthesis methods are extended to accommodate direct couplings using
multistep optimization. Examples are given to illustrate the results.Comment: 33 pages, 7 figures; accepted for publication in IEEE Transactions on
Automatic Control, October 201
Partial order on passive states and Hoffman majorization in quantum thermodynamics
Passive states, i.e., those states from which no work can be extracted via
unitary operations, play an important role in the foundations and applications
of quantum thermodynamics. They generalize the familiar Gibbs thermal states,
which are the sole passive states being stable under tensor product. Here, we
introduce a partial order on the set of passive states that captures the idea
of a passive state being virtually cooler than another one. This partial order,
which we build by defining the notion of relative passivity, offers a
fine-grained comparison between passive states based on virtual temperatures
(just like thermal states are compared based on their temperatures). We then
characterize the quantum operations that are closed on the set of virtually
cooler states with respect to some fixed input and output passive states.
Viewing the activity, i.e., non-passivity, of a state as a resource, our main
result is then a necessary and sufficient condition on the transformation of a
class of pure active states under these relative passivity-preserving
operations. This condition gives a quantum thermodynamical meaning to the
majorization relation on the set of non-increasing vectors due to Hoffman. The
maximum extractable work under relative passivity-preserving operations is then
shown to be equal to the ergotropy of these pure active states. Finally, we are
able to fully characterize passivity-preserving operations in the simpler case
of qubit systems, and hence to derive a state interconversion condition under
passivity-preserving qubit operations. The prospect of this work is a general
resource-theoretical framework for the extractable work via quantum operations
going beyond thermal operations.Comment: 21 pages, 3 figure
Webscience, 'social machines' and principles for redesigning theories of agency: a prolegomenon
This paper argues that the advent of the WWW and the principles now developing for the move ‘social machines’ has posed serious challenges to traditional social theory. In particular, it is argued that the concept of social machines and the forms of distributed agency they imply amplify ‘deep flaws’ in the underlying principles of current agency theories that make empirical work using such frameworks ‘undecidable’. The occasioning of social machines and the WWW here are examined for the ways in which the traditional models of agency, involving reflexivity/skill dynamics, can be dismantled and new principles for re-designed agency theory posed. One key problem and three re-design principles are identified
Extractable Work from Correlations
Work and quantum correlations are two fundamental resources in thermodynamics
and quantum information theory. In this work we study how to use correlations
among quantum systems to optimally store work. We analyse this question for
isolated quantum ensembles, where the work can be naturally divided into two
contributions: a local contribution from each system, and a global contribution
originating from correlations among systems. We focus on the latter and
consider quantum systems which are locally thermal, thus from which any
extractable work can only come from correlations. We compute the maximum
extractable work for general entangled states, separable states, and states
with fixed entropy. Our results show that while entanglement gives an advantage
for small quantum ensembles, this gain vanishes for a large number of systems.Comment: 5+6 pages; 1 figure. Some minor changes, close to published versio
TONI BLANK: A CASE STUDY OF THE LANGUAGE OF A SCHIZOPHRENE
Schizophrenia is one of the chronic mental disorders. Patients of schizophrenia cannot
communicate with others properly. Also, they cannot produce good utterances syntactically and
semantically. This is caused by their language dysfunction. In this research, I am interested in
analyzing language dysfunction in schizophrenia. I choose Toni Blank‟s utterances in “Toni
Blank Show Session One” as the object of my research. I focus on how schizophrenic‟s language
dysfunctions are classified and how these dysfunctions are being analyzed using linguistic
framework. To analyze the data, I used Thought, Language, and Communication (TLC) scale
and cohesion coherence frameworks. The purpose of this study is to give linguistic analysis
about phenomena of language dysfunctions uttered by Toni Blank in “Toni Blank Show Session
One”. The data used in this research are utterances which contain language dysfunctions from
three episodes in “Toni Blank Show Session One”, entitled “Valentine Day”, “Teroris”, and
“Sehat Ala Mas Toni”. I used purposive sampling to collect the data. In analyzing the data, I used
Padan and Agih methods by Sudaryanto (1993). To interpret the data, I used cohesion and
coherence framework. In 26 utterances which contain schizophrenic‟s language dysfunctions in
“Toni Blank Show Session One”, I find that the language dysfunctions which are uttered by Toni
are poverty of content, tangentiality, loss of goal, circumstantiality, illogicality, incoherence
(word salad), neologism, clanging, echolalia, and self-reference. Poverty of speech, pressure of
speech, distractibility, derailment, stilted speech, perseveration, and blocking are not found in the
data.
Keywords: schizophrenia, language dysfunction, Toni Blan
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