This paper examines the performance analysis of quantum Otto machines (QOM) driven by a single qubit system embedded within a spin star environment. We investigate various thermodynamic correlations during the operation of these machines, including work performed, heat absorbed, and heat emissions. For the sake of simplicity, our exploration centers around two scenarios: one where the central qubit interacts with a single spin and another where it interacts with four qubits. Our findings reveal that QOM employing this system exhibit unique thermodynamic properties. Notably, we observe that the QOM can achieve enhanced levels of work performed as the number of spins in the environment increases. Furthermore, both the work performed and the efficiency of the QOM are influenced by the variation in detuning and coupling strength parameters across the four stages of its operation. Additionally, we demonstrate that careful selection of these parameters enables the optimization of QOM performance. In certain instances, the performance of the Otto cycle can be stabilized to emulate the behaviour of a heat engine by manipulating the coupling values while simultaneously controlling the frequency of the central qubit.
This paper examines the performance analysis of quantum Otto machines (QOM) driven by a single qubit system embedded within a spin star environment. We investigate various thermodynamic correlations during the operation of these machines, including work performed, heat absorbed, and heat emissions. For the sake of simplicity, our exploration centers around two scenarios: one where the central qubit interacts with a single spin and another where it interacts with four qubits. Our findings reveal that QOM employing this system exhibit unique thermodynamic properties. Notably, we observe that the QOM can achieve enhanced levels of work performed as the number of spins in the environment increases. Furthermore, both the work performed and the efficiency of the QOM are influenced by the variation in detuning and coupling strength parameters across the four stages of its operation. Additionally, we demonstrate that careful selection of these parameters enables the optimization of QOM performance. In certain instances, the performance of the Otto cycle can be stabilized to emulate the behaviour of a heat engine by manipulating the coupling values while simultaneously controlling the frequency of the central qubit.
We study quantum Otto thermal machines with a two-spin working system coupled by anisotropic interaction. Depending on the choice of different parameters, the quantum Otto cycle can function as different thermal machines, including a heat engine, refrigerator, accelerator, and heater. We aim to investigate how the anisotropy plays a fundamental role in the performance of the quantum Otto engine (QOE) operating in different timescales. We find that while the engine's efficiency increases with the increase in anisotropy for the quasistatic operation, quantum internal friction and incomplete thermalization degrade the performance in a finite-time cycle. Further, we study the quantum heat engine (QHE) with one of the spins (local spin) as the working system. We show that the efficiency of such an engine can surpass the standard quantum Otto limit, along with maximum power, thanks to the anisotropy. This can be attributed to quantum interference effects. We demonstrate that the enhanced performance of a local-spin QHE originates from the same interference effects, as in a measurement-based QOE for their finite-time operation.
We study a quantum Otto heat engine whose working substance is an anisotropic two-qubit Heisenberg XYZ model. Independent local magnetic fields are used to control each spin individually. The influence of the longitudinal coupling, anisotropy, transverse coupling, and local fields on the net work output and efficiency is systematically examined. Reducing the longitudinal coupling is found to markedly improve both the maximum work and the peak efficiency. The engine performance reaches an optimum at a particular value of the anisotropy parameter. A local work analysis clarifies how work is produced during the cycle. Because of the asymmetric local fields and the intrinsic spin-spin interaction, the two qubits play markedly different thermodynamic roles; the interaction term itself contributes crucially to the total work. We further analyze the variation of quantum entanglement, quantified by concurrence, along the cycle. The results indicate that a pronounced change in entanglement between the hot and cold isomagnetic strokes is closely correlated with the efficiency enhancement. This work offers new insight into the operating principles and control of quantum Otto heat engines.
Abstract This study investigates a theoretical model of a Quantum Otto Cycle (QOC) that utilizes a working fluid spin‐chain‐star model. The system consists of a central atom interacting with multiple Heisenberg spin chains. Employing unitary transformations, the spin‐chain‐star system is transformed into a spin‐star model. The work done and heat transferred for three distinct working fluid configurations: the , , and cases are discussed. The efficiency of the heat engine is examined, and a comparative study between the efficiencies of the three configurations is presented. The study assumes two interaction scenarios for the central atom: either with a single chain (resulting in a two‐qubit system after transformation) or with three Heisenberg chains. The results demonstrate that increasing the ratio between the central atom's frequency in the hot bath and the cold bath leads to an enhancement in positive work performed for the and cases. In the case, the magnitude of this enhancement exhibits a dependence on the system's temperature. The QOC employing the configuration working fluid exhibits superior efficiency compared to the other two configurations. Moreover, increasing the central atom's relative frequency improves efficiency for all three cases.
Abstract This paper presents an analysis of quantum Otto heat engines operating in non-equilibrium. It explores the fundamental thermodynamic principles that govern these engines, focusing on efficiency, work output, and the impact of environmental factors such as thermal gradients, external fields, noise, and decoherence. The study investigates the effects of non-equilibrium conditions on engine performance, highlighting challenges and opportunities in practical realizations. Through numerical simulations, the article examines the power, efficiency, and performance coefficients, revealing trade-offs between these metrics and the influence of temperature differences and internal coupling strength. The results demonstrate that non-equilibrium effects can significantly reduce efficiency compared to ideal scenarios, emphasizing the importance of considering both quantum effects and real-world limitations in the design and optimization of quantum heat engines. This work contributes to the growing body of knowledge in quantum thermodynamics, offering insights for quantum computing, sustainable energy technologies, and thermodynamic cycles at the quantum scale.
This paper presents an analysis of quantum Otto heat engines operating out of equilibrium. It explores the fundamental thermodynamic principles governing these engines, focusing on efficiency, work output, and the impact of environmental factors, including thermal gradients, external fields, noise, and decoherence. The study investigates the effects of non-equilibrium conditions on engine performance, highlighting challenges and opportunities in practical realizations. Through numerical simulations, the article examines the power, efficiency, and performance coefficients, revealing trade-offs between these metrics and the influence of temperature differences and internal coupling strength. The results demonstrate that non-equilibrium effects can significantly reduce efficiency compared to idealized scenarios, underscoring the importance of accounting for both quantum effects and real-world constraints in the design and optimization of quantum heat engines. This work contributes to the growing body of knowledge in quantum thermodynamics, offering insights for quantum computing, sustainable energy technologies, and thermodynamic cycles at the quantum scale.
Abstract This paper proposes a theoretical model for a heat engine operating on the Otto cycle, employing a two-qubit Heisenberg chain as its working substance. This system is subjected to an external, time-dependent homogeneous magnetic field and a symmetric cross-spin interaction. The interaction is configured to occur along two distinct orientations, contingent upon the direction of Zeeman energy and symmetric interaction: either exclusively along the X -direction or exclusively along the Z -direction. Furthermore, the thermal reservoirs integral to the Otto engine are considered to engage with the working substance via two discrete modes: a localized interaction or a collective interaction. The two qubits exhibit weak coupling to a non-equilibrium thermal environment during the isochoric heating and cooling strokes, thereby validating the application of a Markovian model as a suitable approximation for describing the time evolution of the working substance. This study investigates the influence of various system parameters on the thermodynamic quantities and the resultant power output. A principal finding is that refrigeration functionality is the predominant operational characteristic when the system engages in collective interaction with the reservoirs. Conversely, localized interactions facilitate dual operational modes, with the sign of the Zeeman energy determining the function as either a refrigerator or a heat engine. Significantly, positive power output is achieved in the engine regime, and we find that the choice of interaction axis acts as a powerful amplification mechanism for the thermodynamic output, while the system-environment coupling scheme proves to be the most decisive factor in determining the machine’s fundamental purpose.