9,021 research outputs found
Thermodynamics of Quantum Feedback Cooling
This is the final version. Available on open access from MDPI via the DOI in this reocrdThe ability to initialize quantum registers in pure states lies at the core of many applications of quantum technologies, from sensing to quantum information processing and computation. In this paper, we tackle the problem of increasing the polarization bias of an ensemble of two-level register spins by means of joint coherent manipulations, involving a second ensemble of ancillary spins and energy dissipation into an external heat bath. We formulate this spin refrigeration protocol, akin to algorithmic cooling, in the general language of quantum feedback control, and identify the relevant thermodynamic variables involved. Our analysis is two-fold: on the one hand, we assess the optimality of the protocol by means of suitable figures of merit, accounting for both its work cost and effectiveness; on the other hand, we characterise the nature of correlations built up between the register and the ancilla. In particular, we observe that neither the amount of classical correlations nor the quantum entanglement seem to be key ingredients fuelling our spin refrigeration protocol. We report instead that a more general indicator of quantumness beyond entanglement, the so-called quantum discord, is closely related to the cooling performance.COST ActionUniversity of NottinghamSpanish MINECOGeneralitat de Catalunya Consejo Interdepartamental de Investigación e Innovación TecnológicaAcademy of FinlandFoundational Questions InstituteEuropean Research Counci
Quantum Thermodynamics
Quantum thermodynamics is an emerging research field aiming to extend
standard thermodynamics and non-equilibrium statistical physics to ensembles of
sizes well below the thermodynamic limit, in non-equilibrium situations, and
with the full inclusion of quantum effects. Fuelled by experimental advances
and the potential of future nanoscale applications this research effort is
pursued by scientists with different backgrounds, including statistical
physics, many-body theory, mesoscopic physics and quantum information theory,
who bring various tools and methods to the field. A multitude of theoretical
questions are being addressed ranging from issues of thermalisation of quantum
systems and various definitions of "work", to the efficiency and power of
quantum engines. This overview provides a perspective on a selection of these
current trends accessible to postgraduate students and researchers alike.Comment: 48 pages, improved and expanded several sections. Comments welcom
The role of quantum information in thermodynamics --- a topical review
This topical review article gives an overview of the interplay between
quantum information theory and thermodynamics of quantum systems. We focus on
several trending topics including the foundations of statistical mechanics,
resource theories, entanglement in thermodynamic settings, fluctuation theorems
and thermal machines. This is not a comprehensive review of the diverse field
of quantum thermodynamics; rather, it is a convenient entry point for the
thermo-curious information theorist. Furthermore this review should facilitate
the unification and understanding of different interdisciplinary approaches
emerging in research groups around the world.Comment: published version. 34 pages, 6 figure
Quantum Thermodynamics
Quantum thermodynamics addresses the emergence of thermodynamical laws from
quantum mechanics. The link is based on the intimate connection of quantum
thermodynamics with the theory of open quantum systems. Quantum mechanics
inserts dynamics into thermodynamics giving a sound foundation to
finite-time-thermodynamics. The emergence of the 0-law I-law II-law and III-law
of thermodynamics from quantum considerations is presented. The emphasis is on
consistence between the two theories which address the same subject from
different foundations. We claim that inconsistency is the result of faulty
analysis pointing to flaws in approximations
Time-Optimal Frictionless Atom Cooling in Harmonic Traps
Frictionless atom cooling in harmonic traps is formulated as a time-optimal
control problem and a synthesis of optimal controlled trajectories is obtained.
This work has already been used to determine the minimum time for transition
between two thermal states and to show the emergence of the third law of
classical thermodynamics from quantum thermodynamics. It can also find
application in the fast adiabatic-like expansion of Bose-Einstein condensates,
with possible applications in atom interferometry. This paper is based on our
recently published article in SIAM J. Control Optim.Comment: Submitted to 51st IEEE Conference on Decision and Control as a SIAM
regular paper, it is a shorter version of our recently published article in
SIAM J. Control Optim., vol. 49, pp. 2440-2462, 2011. It contains an elegant
proof of the main technical point using the symmetries of the system, and a
discussion of the implications of the results on finite time thermodynamic
processe
Thermodynamics and Chemistry of the Early Universe
The interplay between chemistry and thermodynamics determines the final
outcome of the process of gravitational collapse and sets the conditions for
the formation of the first cosmological objects, including primordial
supermassive black holes. In this chapter, we will review the main chemical
reactions and the most important heating/cooling processes taking place in a
gas of primordial composition, including the effects of local and cosmological
radiation backgrounds.Comment: Preprint of the Chapter "Thermodynamics and Chemistry of the Early
Universe", to be published in the review volume "Formation of the First Black
Holes", Latif M. and Schleicher D.R.G., eds., World Scientific Publishing
Company, 2018, pp. [see
http://www.worldscientific.com/worldscibooks/10.1142/10652
Narrow Line Cooling and Momentum-Space Crystals
Narrow line laser cooling is advancing the frontier for experiments ranging
from studies of fundamental atomic physics to high precision optical frequency
standards. In this paper, we present an extensive description of the systems
and techniques necessary to realize 689 nm 1S0 - 3P1 narrow line cooling of
atomic 88Sr. Narrow line cooling and trapping dynamics are also studied in
detail. By controlling the relative size of the power broadened transition
linewidth and the single-photon recoil frequency shift, we show that it is
possible to continuously bridge the gap between semiclassical and quantum
mechanical cooling. Novel semiclassical cooling process, some of which are
intimately linked to gravity, are also explored. Moreover, for laser
frequencies tuned above the atomic resonance, we demonstrate momentum-space
crystals containing up to 26 well defined lattice points. Gravitationally
assisted cooling is also achieved with blue-detuned light. Theoretically, we
find the blue detuned dynamics are universal to Doppler limited systems. This
paper offers the most comprehensive study of narrow line laser cooling to date.Comment: 14 pages, 19 figure
Thermodynamics of adiabatic feedback control
We study adaptive control of classical ergodic Hamiltonian systems, where the
controlling parameter varies slowly in time and is influenced by system's state
(feedback). An effective adiabatic description is obtained for slow variables
of the system. A general limit on the feedback induced negative entropy
production is uncovered. It relates the quickest negentropy production to
fluctuations of the control Hamiltonian. The method deals efficiently with the
entropy-information trade off.Comment: 6 pages, 1 figur
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