Researcher:
Çakmak, Selçuk

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Selçuk

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Çakmak

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Çakmak, Selçuk

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2016 - 20174

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Now showing 1 - 4 of 4
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    Irreversible work and internal friction in a quantum otto cycle of a single arbitrary spin
    (Springer, 2017) Gencten, Azmi; Department of Physics; Department of Physics; Department of Physics; Çakmak, Selçuk; Altıntaş, Ferdi; Müstecaplıoğlu, Özgür Esat; Other; Researcher; Faculty Member; Department of Physics; College of Sciences; College of Sciences; College of Sciences; 301753; 126883; 1674
    We propose an arbitrary driven spin as the working fluid of a quantum Otto cycle in the presence of internal friction. The role of total allocated time to the adiabatic branches of the cycle, generated by different control field profiles, on the extractable work and the thermal efficiency are analyzed in detail. The internal friction is characterized by the excess entropy production and quantitatively determined by studying the closeness of an actual unitary process to an infinitely long one via quantum relative entropy. It is found that the non-ideal, finite-time adiabatic transformations negatively effect the work output and the thermal efficiency of the quantum heat engine. The non-monotone dependence of the work output, thermal efficiency, entropy production and the internal friction on the total adiabatic time are elucidated. It is also found that almost frictionless adiabatic transformations with small entropy production can be obtained in a short adiabatic time. Complete frictionless solutions for finite adiabatic times, possible implementation of our engine in NMR setups and the estimation of the power output have also been analyzed.
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    Special coupled quantum Otto and Carnot cycles
    (Springer Heidelberg, 2017) Türkpençe, Deniz; Altıntaş, Ferdi; Department of Physics; Çakmak, Selçuk; Other; Department of Physics; College of Sciences; 301753
    Two special coupled spins, one is an arbitrary spin-s and the other is a fixed spin-1/2, are proposed as the working substance of the quantum Otto and Carnot cycles. The quantum adiabatic stages of the cycles are considered the simultaneous changes of the frequencies of the spins and the interaction strength in which all the energy gaps of the working substance are changed by the same ratios in the two quantum adiabatic stages. The role of quantum interactions and the spin-s on the performance of the quantum cycles is investigated in detail. It is found that the thermal efficiencies of the cycles are independent of the spin-s and the interaction strength and are also equivalent to their classical counterparts. The work output of the cycles is found to be significantly enhanced by the quantum interactions. Compared to the uncoupled case, the coupled working substance with a smaller spin-s is found to produce more useful work in the weak coupling regime, while the harvested work with a smaller spin-s is less in the strong coupling regime. The concept of local thermodynamics and the role of inner friction are also addressed for the proposed quantum Otto and Carnot cycles.
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    Irreversibility in a unitary finite-rate protocol: the concept of internal friction
    (Institute of Physics (IOP) Publishing, 2016) Department of Physics; Department of Physics; Department of Physics; Çakmak, Selçuk; Altıntaş, Ferdi; Müstecaplıoğlu, Özgür Esat; Other; Researcher; Faculty Member; Department of Physics; College of Sciences; College of Sciences; College of Sciences; 301753; 126883; 1674
    The concept of internal friction, a fully quantum mechanical phenomena, is investigated in a simple, experimentally accessible quantum system in which a spin-1/2 is driven by a transverse magnetic field in a quantum adiabatic process. The irreversible production of the waste energy due to the quantum friction is quantitatively analyzed in a forward-backward unitary transform of the system Hamiltonian by using the quantum relative entropy between the actual density matrix obtained in a parametric transformation and the one in a reversible adiabatic process. Analyzing the role of total transformation time and the different pulse control schemes on the internal friction reveal the non-monotone character of the internal friction as a function of the total protocol time and the possibility for almost frictionless solutions in finite-time transformations.
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    Lipkin-Meshkov-Glick model in a quantum Otto cycle
    (Springer Heidelberg, 2016) Department of Physics; Department of Physics; Department of Physics; Çakmak, Selçuk; Altıntaş, Ferdi; Müstecaplıoğlu, Özgür Esat; Other; Researcher; Faculty Member; Department of Physics; College of Sciences; College of Sciences; College of Sciences; 301753; 126883; 1674
    The Lipkin-Meshkov-Glick model of two anisotropically interacting spins in a magnetic field is proposed as a working substance of a quantum Otto engine to explore and exploit the anisotropy effects for the optimization of engine operation. Three different cases for the adiabatic branches of the cycle have been considered. In the first two cases, either the magnetic field or coupling strength are changed while, in the third case, both the magnetic field and the coupling strength are changed by the same ratio. The system parameters for which the engine can operate similar to or dramatically different from the engines of non-interacting spins or of coupled spins with Ising model or isotropic XY model interactions are determined. In particular, the role of anisotropy to enhance cooperative work, and to optimize maximum work with high efficiency, as well as to operate the engine near the Carnot bound are revealed.