Fundamental limitations for quantum and nano thermodynamics

The relationship between thermodynamics and statistical physics is valid in the thermodynamic limit - when the number of particles becomes very large. Here, we study thermodynamics in the opposite regime - at both the nano scale, and when quantum effects become important. Applying results from quantum information theory we construct a theory of thermodynamics in these limits. We derive general criteria for thermodynamical state transformations, and as special cases, find two free energies: one that quantifies the deterministically extractable work from a small system in contact with a heat bath, and the other that quantifies the reverse process. We find that there are fundamental limitations on work extraction from nonequilibrium states, owing to finite size effects and quantum coherences. This implies that thermodynamical transitions are generically irreversible at this scale. As one application of these methods, we analyse the efficiency of small heat engines and find that they are irreversible during the adiabatic stages of the cycle.Comment: Final, published versio

Quantum thermodynamic processes: A control theory for machine cycles

The minimal set of thermodynamic control parameters consists of a statistical (thermal) and a mechanical one. These suffice to introduce all the pertinent thermodynamic variables; thermodynamic processes can then be defined as paths on this 2-dimensional control plane. Putting aside coherence we show that for a large class of quantum objects with discrete spectra and for the cycles considered the Carnot efficiency applies as a universal upper bound. In the dynamic (finite time) regime renormalized thermodynamic variables allow to include non-equilibrium phenomena in a systematic way. The machine function ceases to exist in the large speed limit; the way, in which this limit is reached, depends on the type of cycle considered.Comment: 14 pages, 12 figures, Replaced by version accepted for publication in European Physical Journal

Quantum-enhanced absorption refrigerators

Thermodynamics is a branch of science blessed by an unparalleled combination of generality of scope and formal simplicity. Based on few natural assumptions together with the four laws, it sets the boundaries between possible and impossible in macroscopic aggregates of matter. This triggered groundbreaking achievements in physics, chemistry and engineering over the last two centuries. Close analogues of those fundamental laws are now being established at the level of individual quantum systems, thus placing limits on the operation of quantum-mechanical devices. Here we study quantum absorption refrigerators, which are driven by heat rather than external work. We establish thermodynamic performance bounds for these machines and investigate their quantum origin. We also show how those bounds may be pushed beyond what is classically achievable, by suitably tailoring the environmental fluctuations via quantum reservoir engineering techniques. Such superefficient quantum-enhanced cooling realises a promising step towards the technological exploitation of autonomous quantum refrigerators

Energetic instability of passive states in thermodynamics

Passivity is a fundamental concept in thermodynamics that demands a quantum system’s energy cannot be lowered by any reversible, unitary process acting on the system. In the limit of many such systems, passivity leads in turn to the concept of complete passivity, thermal states and the emergence of a thermodynamic temperature. Here we only consider a single system and show that every passive state except the thermal state is unstable under a weaker form of reversibility. Indeed, we show that given a single copy of any athermal quantum state, an optimal amount of energy can be extracted from it when we utilise a machine that operates in a reversible cycle. This means that for individual systems, the only form of passivity that is stable under general reversible processes is complete passivity, and thus provides a physically motivated identification of thermal states when we are not operating in the thermodynamic limit

A pilot study to assess the usability of software for simulated office work

This pilot investigation tested the usability of custom designed computerized software to test typing, proofreading and reaction time skills. The software will be used to determine the effects of lighting quality on office work performance in future studies. Six temporary office workers did 36, 10 minute sessions of the three tasks for one 7.5 hour day. Both Proofreading Task and Typing Task used conditions of 3 screen colours x 2 font types x 2 font sizes. Conveyor Belt, the reaction time test, used 5 symbol speeds x 3 symbol colours x 2 target frequencies x 2 times of day. Typing Task and Proofreading Task were familiar to the subjects, making the tasks too easy and the results less clearly related to font size and screen colour. Smaller font size and gray background made the most difficult typing conditions; small font and blue background were the most difficult for proofreading. Conveyor Belt was more sensitive to changes in other variables at high symbol speeds. Low target probability with blue symbols at the fastest speeds gave thepoorest performance.Dans le cadre de cette investigation pilote, on a test\ue9 la convivialit\ue9 d?un logiciel con\ue7u sur mesures pour tester les habilit\ue9s en termes de dactylographie, de lecture d?\ue9preuves et de temps de r\ue9action. Le logiciel sera utilis\ue9, \ue0 l?occasion d?\ue9tudes futures, pour d\ue9terminer les incidences de la qualit\ue9 de l?\ue9clairage sur le rendement au travail d?employ\ue9s de bureau. Six (6) employ\ue9s de bureau temporaires ont suivi 36 s\ue9ances de 10 minutes chacune pour les trois (3) t\ue2ches susmentionn\ue9es, pendant une journ\ue9e de 7,5 heures. Les conditions des t\ue2ches de lecture d?\ue9preuves et de dactylographie \ue9taient les suivantes: 3 couleurs d?\ue9cran x 2 polices de caract\ue8res x 2 grosseurs de police. L?essai de temps de r\ue9action dit avec courroie de d\ue9filement utilisait des vitesses de d\ue9filement \ue0 5 symboles x 3 couleurs de symbole x 2 fr\ue9quences cibles x 2 heures du jour diff\ue9rentes. Les sujets \ue9taient familiaris\ue9s avec les t\ue2ches de dactylographie et de lecture d?\ue9preuves; celles-ci se r\ue9v\ue9l\ue8rent donc trop faciles, et les r\ue9sultats \ue9taient corr\ue9l\ue9s de fa\ue7on moins \ue9vidente \ue0 la grosseur de police et \ue0 la couleur de l?\ue9cran. Les conditions de dactylographie \ue9taient les plus difficiles avec les polices plus petites et l?arri\ue8re-plan d?\ue9cran gris, et les conditions de lecture d?\ue9preuves, avec les petites polices et l?arri\ue8re-plan bleu. Le test avec courroie de d\ue9filement \ue9tait plus sensible aux changements d?autres variables aux vitesses de d\ue9filement rapide des symboles. La performance la plus m\ue9diocre a \ue9t\ue9 enregistr\ue9e avec les probabilit\ue9s cibles faibles, avec les symboles bleus et les vitesses les plus \ue9lev\ue9es.Peer reviewed: NoNRC publication: Ye

Typing task: software to measure the speed and accuracy with which presented text is typed

Peer reviewed: NoNRC publication: Ye

Scheduler & Experiment Setup: Software to Automate the Sequencing, Running and Data Collection of Computerized Tasks

Peer reviewed: NoNRC publication: Ye

Conveyor Belt Task: Software to Test User Reaction Time Using Targets on a Simulated Conveyor Belt

Peer reviewed: NoNRC publication: Ye

Proofreading Task: Software to Measure the Speed and Accuracy of Proofreading from a Computer VDT Screen

Peer reviewed: NoNRC publication: Ye