We compare two different scenarios at relativistic quantum heat engine by considering three-level energy, and two non-interacting fermion in one-dimensional potential well. The difference between the scenarios is abou...We compare two different scenarios at relativistic quantum heat engine by considering three-level energy, and two non-interacting fermion in one-dimensional potential well. The difference between the scenarios is about mechanism to get into excited state by two fermions. We apply iso-energetic cycle that consists of two iso-energetic and two iso-entropic processes, and then compute and compare the efficiency at both scenarios. We also compare it with non-relativistic case. The result is that one scenario has larger efficiency than the other that does not happen at non-relativistic case.展开更多
Based on a two-qubit isotropic Heisenberg XY model under a constant external magnetic field,we construct a four-level entangled quantum heat engine（QHE）.The expressions for the heat transferred,the work,and the effi...Based on a two-qubit isotropic Heisenberg XY model under a constant external magnetic field,we construct a four-level entangled quantum heat engine（QHE）.The expressions for the heat transferred,the work,and the efficiency are derived.Moreover,the influence of the entanglement on the thermodynamic quantities is investigated analytically and numerically.Several interesting features of the variations of the heat transferred,the work,and the efficiency with the concurrences of the thermal entanglement of two different thermal equilibrium states in zero and nonzero magnetic fields are obtained.展开更多
To clarify the ambiguity on negative Boltzmann temperature in literature, we study the Carnot and the Otto cycle with one of the heat reservoirs at the negative Boltzmann temperature based on a canonical ensemble desc...To clarify the ambiguity on negative Boltzmann temperature in literature, we study the Carnot and the Otto cycle with one of the heat reservoirs at the negative Boltzmann temperature based on a canonical ensemble description. The work extraction, entropy production and the efficiency of these cycles are explored. Conditions for constructing and properties of these thermodynamic cycles are elucidated. We find that the apparent "violation" of the second law of thermodynamics in these cycles are due to the fact that the traditional definition of thermodynamic efficiency is inappropriate in this situation. When properly understanding the efficiency and the adiabatic processes, in which the system crosses over "absolute ZERO" in a limit sense, the Carnot cycle with one of the heat reservoirs at a negative Boltzmann temperature can be understood straightforwardly, and it contradicts neither the second nor the third law of thermodynamics. Hence, negative Boltzmann temperature is a consistent concept in thermodynamics. We use a two-level system and an Ising spin system to illustrate our central results.展开更多
The second law of thermodynamics has been proven by many facts in classical world. Is there any new property of it in quantum world？ In this paper, we calculate the change of entropy in T.D. Kieu＇s model for quantum...The second law of thermodynamics has been proven by many facts in classical world. Is there any new property of it in quantum world？ In this paper, we calculate the change of entropy in T.D. Kieu＇s model for quantum heat engine （QHE） and prove the broad validity of the second law of thermodynamics. It is shown that the entropy of the quantum heat engine neither decreases in a whole cycle, nor decreases in either stage of the cycle. The second law of thermodynamics still holds in this QHE model. Moreover, although the modified quantum heat engine is capable of extracting more work, its efficiency does not improve at all. It is neither beyond the efficiency of T.D. Kieu＇s initial model,nor greater than the reversible Carnot efficiency.展开更多
A new model of a quantum heat engine （QHE） cycle is established, in which the working substance consists of an interacting electrons system. One of our purposes is to test the validity of the second law of thermodyn...A new model of a quantum heat engine （QHE） cycle is established, in which the working substance consists of an interacting electrons system. One of our purposes is to test the validity of the second law of thermodynamics by this model, which is more general than the spin-1/2 antiferromagnetic Heisenberg model since it would recover the spin model when the on-site Coulomb interaction U is strong enough. On the basis of quantum mechanics and the first law of thermodynamics, we show no violation of the second law of thermodynamics during the cycle. We further study the performance characteristics of the cycle by investigating in detail the optimal relations of efficiency and dimensionless power output. We find that the efficiency of our engine can be expressed as η = t22/t21 in the large-U limit, which is valid even for a four sites QHE.展开更多
We analyze the performance of a quantum Stirling heat engine(QSHE), using a two-level system and a harmonic oscillator as the working medium, that is in contact with a squeezed thermal reservoir and a cold reservoir. ...We analyze the performance of a quantum Stirling heat engine(QSHE), using a two-level system and a harmonic oscillator as the working medium, that is in contact with a squeezed thermal reservoir and a cold reservoir. First, we derive closed-form expressions for the produced work and efficiency, which strongly depend on the squeezing parameter rh. Then, we prove that the effect of squeezing heats the working medium to a higher effective temperature, which leads to better overall performance. In particular, the efficiency increases with the degree of squeezing, surpassing the standard Carnot limit when the ratio of the temperatures of the hot and cold reservoirs is small. Furthermore, we derive the analytical expressions for the efficiency at maximum work and the maximum produced work in the high and low temperature regimes,and we find that at extreme temperatures the squeezing parameter rhdoes not affect the performance of the QSHE. Finally,the performance of the QSHE depends on the nature of the working medium.展开更多
The efficiency at the maximum power(EMP)for finite-time Carnot engines established with the low-dissipation model,relies significantly on the assumption of the inverse proportion scaling of the irreversible entropy ge...The efficiency at the maximum power(EMP)for finite-time Carnot engines established with the low-dissipation model,relies significantly on the assumption of the inverse proportion scaling of the irreversible entropy generationΔS^(ir)on the operation timeτ,i.e.ΔS^(ir)∝1/τ.The optimal operation time of the finite-time isothermal process for EMP has to be within the valid regime of the inverse proportion scaling.Yet,such consistency was not tested due to the unknown coefficient of the 1/τ-scaling.In this paper,we reveal that the optimization of the finite-time two-level atomic Carnot engines with the low-dissipation model is consistent only in the regime ofη_(C)<<2(1-δ)/(1+δ),whereη_(C)is the Carnot efficiency,andδis the compression ratio in energy level difference of the heat engine cycle.In the large-η_(C)regime,the operation time for EMP obtained with the low-dissipation model is not within the valid regime of the 1/τ-scaling,and the exact EMP of the engine is found to surpass the well-known boundη_(C)=η_(C)/(2-η_(C)).展开更多
We consider a quantum endoreversible Otto engine cycle and its inverse operation-Otto refrigeration cycle,employing two-level systems as the working substance and operating in dual-squeezed reservoirs.We demonstrate t...We consider a quantum endoreversible Otto engine cycle and its inverse operation-Otto refrigeration cycle,employing two-level systems as the working substance and operating in dual-squeezed reservoirs.We demonstrate that the efficiency of heat engines at maximum work output and the coefficient of performance for refrigerators at the maximum c criterion will degenerate toη-=η_(C)/(2-η_(C))andε-=(√9+8ε_(C)-3)/2 when symmetric squeezing is satisfied,respectively.We also investigated the influences of squeezing degree on the performance optimization of quantum Otto heat engines at the maximum work output and refrigerators at the maximum X criterion.These analytical results show that the efficiency of heat engines at maximum work output and the coefficient of performance for refrigerators at the maximum X criterion can be improved,reduced or even inhibited in asymmetric squeezing.Furthermore,we also find that the efficiency of quantum Otto heat engines at maximum work output is lower than that obtained from the Otto heat engines based on a single harmonic oscillator system.However,the coefficient of performance of the corresponding refrigerator is higher.展开更多
Based on a two-qubit isotropic Heisenberg XXX model with a constant external magnetic field,we construct a four-level entangled quantum heat engine(QHE).The expressions for several thermodynamic quantities such as the...Based on a two-qubit isotropic Heisenberg XXX model with a constant external magnetic field,we construct a four-level entangled quantum heat engine(QHE).The expressions for several thermodynamic quantities such as the heat transferred,the work and efficiency are derived.Moreover,the influence of the entanglement on the thermodynamic quantities is investigated analytically and numerically.Several interesting features of the variation of the heat transferred,the work and the efficiency with the concurrences of the thermal entanglement of different thermal equilibrium states are obtained.展开更多
文摘We compare two different scenarios at relativistic quantum heat engine by considering three-level energy, and two non-interacting fermion in one-dimensional potential well. The difference between the scenarios is about mechanism to get into excited state by two fermions. We apply iso-energetic cycle that consists of two iso-energetic and two iso-entropic processes, and then compute and compare the efficiency at both scenarios. We also compare it with non-relativistic case. The result is that one scenario has larger efficiency than the other that does not happen at non-relativistic case.
基金Project supported by the National Natural Science Foundation of China (Grant No. 11065008)
文摘Based on a two-qubit isotropic Heisenberg XY model under a constant external magnetic field,we construct a four-level entangled quantum heat engine（QHE）.The expressions for the heat transferred,the work,and the efficiency are derived.Moreover,the influence of the entanglement on the thermodynamic quantities is investigated analytically and numerically.Several interesting features of the variations of the heat transferred,the work,and the efficiency with the concurrences of the thermal entanglement of two different thermal equilibrium states in zero and nonzero magnetic fields are obtained.
基金Support from the National Science Foundation of China under Grants Nos.11375012,11534002The Recruitment Program of Global Youth Experts of China
文摘To clarify the ambiguity on negative Boltzmann temperature in literature, we study the Carnot and the Otto cycle with one of the heat reservoirs at the negative Boltzmann temperature based on a canonical ensemble description. The work extraction, entropy production and the efficiency of these cycles are explored. Conditions for constructing and properties of these thermodynamic cycles are elucidated. We find that the apparent "violation" of the second law of thermodynamics in these cycles are due to the fact that the traditional definition of thermodynamic efficiency is inappropriate in this situation. When properly understanding the efficiency and the adiabatic processes, in which the system crosses over "absolute ZERO" in a limit sense, the Carnot cycle with one of the heat reservoirs at a negative Boltzmann temperature can be understood straightforwardly, and it contradicts neither the second nor the third law of thermodynamics. Hence, negative Boltzmann temperature is a consistent concept in thermodynamics. We use a two-level system and an Ising spin system to illustrate our central results.
基金The project supported by National Natural Science Foundation of China under Grant No. 10404039
文摘The second law of thermodynamics has been proven by many facts in classical world. Is there any new property of it in quantum world？ In this paper, we calculate the change of entropy in T.D. Kieu＇s model for quantum heat engine （QHE） and prove the broad validity of the second law of thermodynamics. It is shown that the entropy of the quantum heat engine neither decreases in a whole cycle, nor decreases in either stage of the cycle. The second law of thermodynamics still holds in this QHE model. Moreover, although the modified quantum heat engine is capable of extracting more work, its efficiency does not improve at all. It is neither beyond the efficiency of T.D. Kieu＇s initial model,nor greater than the reversible Carnot efficiency.
基金supported by the National Natural Science Foundation of China (Grant Nos.50971011,11174022 and 10974011)the Beijing Natural Science Foundation (Grant No.1102025)+1 种基金the State Key Laboratory of Software Development Environment (Grant No.SKLSDE-2011ZX-19)the Research Fund for the Doctoral Program of Higher Education of China(Grant No.20091102110038)
文摘A new model of a quantum heat engine （QHE） cycle is established, in which the working substance consists of an interacting electrons system. One of our purposes is to test the validity of the second law of thermodynamics by this model, which is more general than the spin-1/2 antiferromagnetic Heisenberg model since it would recover the spin model when the on-site Coulomb interaction U is strong enough. On the basis of quantum mechanics and the first law of thermodynamics, we show no violation of the second law of thermodynamics during the cycle. We further study the performance characteristics of the cycle by investigating in detail the optimal relations of efficiency and dimensionless power output. We find that the efficiency of our engine can be expressed as η = t22/t21 in the large-U limit, which is valid even for a four sites QHE.
文摘We analyze the performance of a quantum Stirling heat engine(QSHE), using a two-level system and a harmonic oscillator as the working medium, that is in contact with a squeezed thermal reservoir and a cold reservoir. First, we derive closed-form expressions for the produced work and efficiency, which strongly depend on the squeezing parameter rh. Then, we prove that the effect of squeezing heats the working medium to a higher effective temperature, which leads to better overall performance. In particular, the efficiency increases with the degree of squeezing, surpassing the standard Carnot limit when the ratio of the temperatures of the hot and cold reservoirs is small. Furthermore, we derive the analytical expressions for the efficiency at maximum work and the maximum produced work in the high and low temperature regimes,and we find that at extreme temperatures the squeezing parameter rhdoes not affect the performance of the QSHE. Finally,the performance of the QSHE depends on the nature of the working medium.
基金supported by the National Natural Science Foundation of China(NSFC)(Grants No.11534002,No.11875049,No.U1730449,No.U1530401,No.U1930403)the National Basic Research Program of China(Grant No.2016YFA0301201)the China Postdoctoral Science Foundation(Grant No.BX2021030)。
文摘The efficiency at the maximum power(EMP)for finite-time Carnot engines established with the low-dissipation model,relies significantly on the assumption of the inverse proportion scaling of the irreversible entropy generationΔS^(ir)on the operation timeτ,i.e.ΔS^(ir)∝1/τ.The optimal operation time of the finite-time isothermal process for EMP has to be within the valid regime of the inverse proportion scaling.Yet,such consistency was not tested due to the unknown coefficient of the 1/τ-scaling.In this paper,we reveal that the optimization of the finite-time two-level atomic Carnot engines with the low-dissipation model is consistent only in the regime ofη_(C)<<2(1-δ)/(1+δ),whereη_(C)is the Carnot efficiency,andδis the compression ratio in energy level difference of the heat engine cycle.In the large-η_(C)regime,the operation time for EMP obtained with the low-dissipation model is not within the valid regime of the 1/τ-scaling,and the exact EMP of the engine is found to surpass the well-known boundη_(C)=η_(C)/(2-η_(C)).
文摘We consider a quantum endoreversible Otto engine cycle and its inverse operation-Otto refrigeration cycle,employing two-level systems as the working substance and operating in dual-squeezed reservoirs.We demonstrate that the efficiency of heat engines at maximum work output and the coefficient of performance for refrigerators at the maximum c criterion will degenerate toη-=η_(C)/(2-η_(C))andε-=(√9+8ε_(C)-3)/2 when symmetric squeezing is satisfied,respectively.We also investigated the influences of squeezing degree on the performance optimization of quantum Otto heat engines at the maximum work output and refrigerators at the maximum X criterion.These analytical results show that the efficiency of heat engines at maximum work output and the coefficient of performance for refrigerators at the maximum X criterion can be improved,reduced or even inhibited in asymmetric squeezing.Furthermore,we also find that the efficiency of quantum Otto heat engines at maximum work output is lower than that obtained from the Otto heat engines based on a single harmonic oscillator system.However,the coefficient of performance of the corresponding refrigerator is higher.
基金supported by the National Natural Science Foundation of China (Grant No. 11065008)
文摘Based on a two-qubit isotropic Heisenberg XXX model with a constant external magnetic field,we construct a four-level entangled quantum heat engine(QHE).The expressions for several thermodynamic quantities such as the heat transferred,the work and efficiency are derived.Moreover,the influence of the entanglement on the thermodynamic quantities is investigated analytically and numerically.Several interesting features of the variation of the heat transferred,the work and the efficiency with the concurrences of the thermal entanglement of different thermal equilibrium states are obtained.
