|
Adiabatic Quantum Motor
An adiabatic quantum motor is a mechanical device, typically nanometric, driven by a flux of quantum particles and able to perform cyclic motions. The adjective “adiabatic” in this context refers to the limit when the dynamics of the mechanical degrees of freedom is slow compared with the dwell time of the particles passing through the device. In this regime, it is commonly assumed that the mechanical degrees of freedom behave classically. This class of devices works essentially as quantum pumps operated in reverse. While in a quantum pump, the periodic movement of some parameters pumps quantum particles from one reservoir to another, in a quantum motor a DC current of particles induces the cyclic motion of the device. One key feature of these motors is that quantum interferences can be used to increase their efficiency by enhancing the reflection coefficient In physics and electrical engineering the reflection coefficient is a parameter that describes how much of a wave is r ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quantum Stirring, Ratchets, And Pumping
A pump is an alternating current-driven device that generates a direct current (DC). In the simplest configuration a pump has two leads connected to two reservoirs. In such open geometry, the pump takes particles from one reservoir and emits them into the other. Accordingly, a current is produced even if the reservoirs have the same temperature and chemical potential. Stirring is the operation of inducing a circulating current with a non-vanishing DC component in a closed system. The simplest geometry is obtained by integrating a pump in a closed circuit. More generally one can consider any type of stirring mechanism such as moving a spoon in a cup of coffee. Main observations Pumping and stirring effects in quantum physics have counterparts in purely classical stochastic and dissipative processes. The studies of quantum pumpingM. Buttiker, H. Thomas and A Pretre, Z. Phys. B Condens. Mat. 94, 133 (1994). P. W. Brouwer, Phys. Rev. B 58, R10135 (1998).B. L. Altshuler, L. I. Gla ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
DC Current
Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or even through a vacuum as in electron or ion beams. The electric current flows in a constant direction, distinguishing it from alternating current (AC). A term formerly used for this type of current was galvanic current. The abbreviations ''AC'' and ''DC'' are often used to mean simply ''alternating'' and ''direct'', as when they modify ''current'' or ''voltage''. Direct current may be converted from an alternating current supply by use of a rectifier, which contains electronic elements (usually) or electromechanical elements (historically) that allow current to flow only in one direction. Direct current may be converted into alternating current via an inverter. Direct current has many uses, from the charging of batteries to large power supp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reflection Coefficient
In physics and electrical engineering the reflection coefficient is a parameter that describes how much of a wave is reflected by an impedance discontinuity in the transmission medium. It is equal to the ratio of the amplitude of the reflected wave to the incident wave, with each expressed as phasors. For example, it is used in optics to calculate the amount of light that is reflected from a surface with a different index of refraction, such as a glass surface, or in an electrical transmission line to calculate how much of the electromagnetic wave is reflected by an impedance discontinuity. The reflection coefficient is closely related to the ''transmission coefficient''. The reflectance of a system is also sometimes called a "reflection coefficient". Different specialties have different applications for the term. Transmission lines In telecommunications and transmission line theory, the reflection coefficient is the ratio of the complex amplitude of the reflected wave to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
