Autonomous quantum thermodynamic machines

In dieser Arbeit werden bis in den Quantenlimes skalierbare thermodynamische Maschinen untersucht, die autonom arbeiten, d.h. ohne zeitabhängige (klassische) Kontrolle von außen funktionsfähig sind. Inwieweit stößt die Skalierung an fundamentale quantenmechanische Grenzen wie Dekohärenz? Das quantenmechanische Minimalmodell besteht aus einem einzelnen Spin (Zwei-Niveau-System), der an einen harmonischen Oszillator und an zwei thermische Bäder unterschiedlicher Temperatur koppelt. Durch eine entsprechend gestaltete Lindbladgleichung kann dieses System als thermodynamische Maschine wirken, die Carnot-Zyklen aufweist. Der Badkontakt wird dabei vom Oszillatorzustand mit Hilfe hier vorgestellter so genannter Time-slot-Operatoren autonom gesteuert: Time-slot-Operatoren ermöglichen es, eine beliebige Kontrollfunktion auf Quantenebene zu implementieren. Selbst nahe des Quantenlimes kann für das Minimalmodell der Wärmekraftmaschine eine Verstärkung der kohärenten Oszillatorbewegung nachgewiesen werden. In unserem Modell kommt Wärme im Spinsystem und Arbeit im Oszillator vor. Die Energie im Oszillator liegt als kohärente Energie und inkohärente Energie vor, während im klassischen Fall alle Arbeit kohärent gespeichert wäre. Im Gegensatz zu Quantengattern besitzt solch eine Maschine sowohl einen Quantenlimes wie auch einen klassischen Limes. Im Quantenlimes nähert sich das Modell asymptotisch einem stationären Transportproblem. Desweiteren diskutieren wir verschiedene erweiterte Modelle, die den Badkontakt expliziter behandeln, indem der Kontakt durch zwei weitere Spins hergestellt wird. Um einen Schalteffekt bezüglich der Bäder zu erreichen werden entweder die Resonanzeigenschaften der Badkontaktspins genutzt (die auch durch Time-slot-Operatoren gesteuert werden können) oder die Kopplung der Spins selbst gesteuert. Durch die explizite Modellierung können Dekohärenzeffekte minimiert werden. Leistungsfähige autonome Quantenkontrolle ist damit selbst in offenen Systemen und im Quantenlimes möglich.We investigate thermodynamic machines, that are scalable to the quantum limit while working autonomously, i.e. without time-dependent external (classical) control. To what extent does scaling come up against limiting quantum mechanical factors like decoherence? The quantum minimal model consists of a single spin (two-level system) coupled to a harmonic oscillator and two thermal baths at different temperatures. By means of an adequately designed Lindblad equation, it is shown that this device can function as a thermodynamic machine exhibiting Carnot-type cycles. The bath contact is controlled by the oscillator state with the help of so-called time-slot operators, here presented for the first time: Time-slot operators facilitate the implementation of an arbitrary control function in the quantum domain. This means in the case of a heat engine that the coherent motion of the oscillator is amplified, even near the quantum limit of the minimal model. In our model heat occurs in the spin system, work in the oscillator. The energy in the oscillator is of two kinds: Coherent energy and incoherent energy, while in the classical case all mechanical energy would be stored coherently. Contrary to quantum gates, our machine has a quantum limit and a classical limit. In the quantum limit, it asymptotically approaches a stationary transport scenario. Furthermore we discuss several extended models, that explore the bath contact more explicitly by adding two extra spins. To achieve a switching effect with respect to the baths, we use either the resonance properties of the bath contact spins (they may be controlled by time-slot operators, too) or control the coupling between the spins directly. By modeling the bath contact explicitly, decoherence effects can be minimized. Thus efficient autonomous quantum control is possible even in open quantum systems and in the quantum limit

Experimental investigations on carbon nanotube actuators defining the operation point and its standard deviation

Carbon nanotube (CNT) actuators have been extensively investigated from the perspective of materials, their composition, and system construction as well as from three main performance features, which are displacement, force and velocity. However, up till now none of the CNT actuators have reached the stage of implementation into products. It is due to the fact that even though from the point of view of performance each property can reach satisfactory values, their combination is much more difficult, as they are not proportional. This relation of properties motivated the work to test and investigate currently available CNT-polymer actuators to define their operation point. Under this term one should understand a performance of actuator where displacement, force and velocity do not affect each other. In other words, any change in one of the properties will adversely affect at least one of the remaining ones. The measurements are performed in out-of-plane mode on 2 cm diameter samples in low frequency range (0.01 - 1 Hz) under application of low voltage (2 V). Measurement curves of three main actuator properties are plotted together against the frequency resulting in operation point as the intersection point of those curves. Additionally the deviations in actuator performance are assessed to reflect the actuators' reproducibility and their production process stability by means of standard deviation. Knowledge about the relation between actuator properties and the value of operation point will facilitate evaluation of the existing CNT actuator against its potential applications

Development and investigations on multiple carbon nanotube actuator systems for magnified performance and minimization of performance losses

Carbon nanotubes (CNT), as active materials have shown a great potential for industrial applications especially in medical technology due to their high strain, low driving voltage, light weight and flexibility. The driving principle of CNT actuator operation is electrochemical double layer charging, which necessities the presence of electrolyte. This represents a major set back with respect to possible applications. This has been overcome by the development of so called "dry" actuators. These are based on CNT -polymer composites, where the electrolyte is encapsulated within the polymer matrix. Such composites have been build up and used as three layer actuators, where two outer layers containing CNTs are considered as active layers and are separated by the middle layer, separator, which serves as electrical isolator as weH as an ion reservoir. CNT-polymer actuators, although appropriate from the performance point of view, have not yet reached the medical market due to the unknown interactions between CNTs and living organisms. However, the achievements obtained in the development of CNT actuators highlight the potential for applications in other market sectors. CNT actuators could be used as positioning systems, valves and pumps, switches and brakes. In order to have the possibility to offer CNT actuators to a broader spectrum of industries, further developments must be carried out. Within this work multiple actuator systems were developed with a target of multiplication of actuator performance by combining several of them together. Such developments demonstrated the possibility of symbiotic cooperation between integrated CNT actuators and mechanical systems to work as one. Multiple actuator systems were tested in respect to their displacement and force generation as the primary characteristic features of any actuator. Those systems were experimentally measured in an out-of-plane mode of operation at low frequency ranges « 1 Hz) and under Iow driving voltages (2 Volt). The first results indicated that there is no direct proportionality between the multiple actuator system performance and the number of actuators involved. For this reason experimental investigations were undertaken in order to define the performance of actuator systems and minimize the losses, which may occur due to the unsuitable amount of actuators used in a stack. Furthermore, in order to minimize the losses in the performance of actuator system extensive development work was carried out on the optimum design and implementation of electrodes within the system. In parallel various materials where tested in a search for best electrode, as it was observed that they can greatly influence the operating characteristics. The investigations carried out within this research are targeted in finding the optimum design for multiple actuator systems with improved displacement and exertion of force

Integration of CNT-based actuators for bio-medical applications: Example printed circuit board CNT actuator pipette

In order to strengthen the position of CNT actuator technology and fasten the transfer of scientific results into application development and market introduction scientific institutes AIST Kansai and Fraunhofer IPA cooperated in the field of electroactive polymers. Automated dosing of small amounts of liquids normally involves quite large pipettes and motors for pipette actuation. Miniaturized pipettes can enable new areas, in which micro dosing is demanded and could be particularly beneficial in the field of medical or (bio-) chemical applications. The approach was the direct integration of a bending CNT actuator into a PCB design, which enables a frictionless induction of movement onto a liquid. The driving electronics control the actuator with a low voltage and can be placed on the same PCB. The result is a smooth, tailorable dispensation of liquid from the pipette with the ability to integrate the pipette into a fully automated system