Thermal entangled quantum heat engine

Based on a two-qubit Heisenberg XY model, we construct a four-level entangled quantum heat engine (QHE). It is an interesting quantum Otto cycle where the exchange constant is fixed and only the magnetic field is varied during the adiabatic steps. The expressions for several thermodynamic quantities such as the heat transferred, the work and the efficiency are derived. Moreover, the influence of the entanglement on the thermodynamic quantities is investigated 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. Finally, we discussed the maximum efficiency of the QHE.     

Entangled quantum heat engine based on two-qubit Heisenberg XY model

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.     

Thermal Entangled Quantum Refrigerator Working with Three-Qubit Heisenberg XX Model

An entangled quantum refrigerator working with a three-qubit one-dimensional isotropic Heisenberg XX model in a constant external magnetic field is constructed in this paper. Based on the quantum first law of thermodynamics, the expressions for several basic thermodynamic quantities such as the heat transferred, the net work and the coefficient of performance are derived. Moreover, the influence of the thermal entanglement on the basic thermodynamic
quantities is investigated. Several interesting features of the variation of the basic thermodynamic quantities with the thermal entanglement in zero and nonzero magnetic field are obtained.     

A thermal entangled quantum refrigerator based on a two-qubit Heisenberg model with Dzyaloshinskii-Moriya interaction in an external magnetic field

Based on an isotropic two spin-1/2 qubits Heisenberg model with the Dzyaloshinskii-Moriya interaction in an external magnetic field, we have constructed an entangled quantum refrigerator. Expressions for the basic thermodynamic quantities, i.e., the heat exchanged, the net work input, and the coefficient of performance, are derived. Some intriguing features and their qualitative explanations in zero and non zero magnetic fields are given. The influence of the thermal entanglement on the refrigerator is investigated. The results obtained here have general significance and will be helpful to understand the performance of an entangled quantum refrigerator.     

Entangled quantum heat engines based on two two-spin systems with Dzyaloshinski-Moriya anisotropic antisymmetric interaction

We construct an entangled quantum heat engine (EQHE) based on two two-spin systems with Dzyaloshinski-Moriya (DM) anisotropic antisymmetric interaction. By applying the explanations of heat transferred and work performed at the quantum level in Kieu’s work [Phys. Rev. Lett. 93, 140403 (2004)], the basic thermodynamic quantities, i.e., heat transferred, net work done in a cycle and efficiency of EQHE are investigated in terms of DM interaction and concurrence. The validity of the second law of thermodynamics is confirmed in the entangled system. It is found that there is a same efficiency for both antiferromagnetic and ferromagnetic cases, and the efficiency can be controlled in two manners: (1) only by spin-spin interaction J and DM interaction D; (2) only by the temperature T and concurrence C. In order to obtain a positive net work, we need not entangle all qubits in two two-spin systems and we only require the entanglement between qubits in a two-spin system not be zero. As the ratio of entanglement between qubits in two two-spin systems increases, the efficiency will approach infinitely the classical Carnot one. An interesting phenomenon is an abrupt transition of the efficiency when the entanglements between qubits in two two-spin systems are equal.     

带有Dzyaloshinski-Mariya相互作用的两比特纠缠量子Otto热机和量子Stirling热机

研究了以带有Dzyaloshinski-Mariya(DM)相互作用的两比特自旋体系为工质的量子纠缠Otto热机和量子Stirling热机.两种不同热机在各自的循环过程中,通过保持其他参量不变,只有DM相互作用发生改变,从而分析热机循环中DM相互作用与热传递、做功以及效率等热力学量之间的关系.研究结果表明:DM相互作用对两种热机的基本量子热力学量都具有重要的影响,但量子Stirling热机由于回热器的使用,其循环效率会大于量子Otto纠缠热机的效率,甚至会超过Carnot效率;得到了量子Otto纠缠热机和量子Stirling热机做正功的条件.因此,在这两个纠缠体系中,热力学第二定律都依然成立.     

Identification of intrinsic gapped behavior in spin-1/2 ladder with staggered dimerization

The zero- and low-temperature behaviors of spin-1/2 two-leg ladder with staggered dimerization are investigated by the Green’s function theory. At zero temperature, the ground state phase diagram is explored, wherein the leg-dimer and rung-singlet phases are revealed, which reflect two different intrinsic gapped behaviors. The former is attributed to the bond alternation along the legs, while the latter is due to the strong rung coupling. It is found that the quantum phase transition from one to another is of the first order, which can be clearly signaled by the rung entanglement entropy. At finite temperatures, the temperature dependence of thermodynamic quantities such as the magnetic susceptibility, specific heat, thermal Drude weight and rung entanglement entropy are calculated to characterize the corresponding quantum phases. It is shown that the magnetic behaviors clearly manifest a typical antiferromagnetism at low temperature, which is in accordance with the experimental results. It is also found that the intrinsic gapped low-lying excitations are responsible for the observed thermodynamic behaviors.     

Quantum Heat Engine Based on Working Substance of Two Particles Heisenberg XXX Model with the Dzyaloshinskii-Moriya Interaction

A quantum heat engine (QHE) with a working substance of two-particle \( \left(\frac{1}{2},1\right) \) Heisenberg XXX model with Dzyaloshinskii–Moriya (DM) interaction in the external magnetic field B is studied, and the influences of the DM interaction on the efficiency, work are examined under different coupling strengths. The results show that the QHE can operate and produce positive work and the efficiency on the two magnetic field conditions B₁ < B₂ and B₁ > B₂. Moreover, the efficiency can achieve the large value and several interesting effects of the DM interaction on the local work are obtained.

     

Three-dimensional quantum Hall effect in Weyl and double-Weyl semimetals

The well-known quantum Hall effect (QHE) was usually studied in 2D systems. In this work, we investigate the integer QHE in 3D Weyl and double-Weyl semimetals. Based on the lattice models of Weyl and double-Weyl semimetals subjected to a uniform magnetic field, we derive the generalized 3D spinfull Hofstadter Hamiltonians and Harper equations for the two systems, and obtain their corresponding energy spectra. Furthermore, we show that for proper hopping parameters and rational magnetic fluxes, both systems exhibit the 3D QHE when the Fermi level lies in some band gaps. The 3D QHE is topologically characterized by three Chern numbers with one or two nonzero Chern values which are respectively defined for three crystal planes. The possible experimental realization and detection of the 3D QHE are also discussed.     

Maxwell's demon assisted thermodynamic cycle in superconducting quantum circuits

We study a new quantum heat engine (QHE), which is assisted by a Maxwell's demon. The QHE requires three steps: thermalization, quantum measurement, and quantum feedback controlled by the Maxwell demon. We derive the positive-work condition and operation efficiency of this composite QHE. Using controllable superconducting quantum circuits as an example, we show how to construct our QHE. The essential role of the demon is explicitly demonstrated in this macroscopic QHE.     

The Second Law of Thermodynamics in a Quantum Heat Engine Model

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.     

Thermal Entanglement and Correlated Coherence in Two Coupled Double Quantum Dots Systems

In this work, the thermal quantum correlations in two coupled double semiconductor charge qubits are investigated. This is carried out by deriving analytical expressions for both the thermal concurrence and the correlated coherence. The effects of the tunneling parameters, the Coulomb interaction, and the temperature on the thermal entanglement and on the correlated coherence are studied in detail. It is found that the Coulomb potential plays an important role in the thermal entanglement and in the correlated coherence of the system. The results also indicate that the Coulomb potential can be used for significant enhancement of the thermal entanglement and quantum coherence. One interesting aspect is that the correlated coherence capture all the thermal entanglement at low temperatures, that is, the local coherences are totally transferred to the thermal entanglement. Finally, the role played by thermal entanglement and the correlated coherence responsible for quantum correlations are focused on. It is shown that in all cases, the correlated coherence is more robust than the thermal entanglement so that quantum algorithms based only on correlated coherence may be more robust than those based on entanglement.     

Quantum phase transitions in matrix product states of one-dimensional spin-1 chains

We present a new model of quantum phase transitions in matrix product systems of one-dimensional spin-1 chains and study the phases coexistence phenomenon. We find that in the thermodynamic limit the proposed system has three different quantum phases and by adjusting the control parameters we are able to realize any phase, any two phases equal coexistence and the three phases equal coexistence. At every critical point the physical quantities including the entanglement are not discontinuous and the matrix product system has long-range correlation and N-spin maximal entanglement. We believe that our work is helpful for having a comprehensive understanding of quantum phase transitions in matrix product states of one-dimensional spin chains and of certain directive significance to the preparation and control of one-dimensional spin lattice models with stable coherence and N-spin maximal entanglement.     

Molecular dynamics study of the stability of a carbon nanotube atop a catalytic nanoparticle

The effect of spontaneously generated coherence (SGC) on the quantum heat engine (QHE) consisting of a laser system is studied in terms of its dynamical evolution and the generation of coherences. The QHE is coupled to the two thermal photon reservoirs, a squeezed thermal bath as well as to a cavity mode. The coherence associated with the transition interacting with squeezed reservoir and the average thermal photon number of the hot (as well as cold) reservoir shows a non monotonous behavior between them. The dynamics along with generated coherences of the system and the laser power emitted depend sensitively on the hot, cold and squeezed reservoir parameters.     

Some New Solutions of Jacobi Elliptic Functions to mBBM Equation

The modified mapping method is further improved by the expanded expression of u（ξ） that contains the terms of the first-order derivative of function f（ξ）. Some new exact solutions to the mBBM equation are determined by means of the method. We can obtain many new solutions in terms of the Jacobi elliptic functions of the equation.     

四能级量子制冷循环

本文提出以两个qubit量子纠缠系统为工质的四能级制冷循环模型, 基于量子热力学第一定律和热纠缠概念, 分析了在循环中系统与外界交换的热量、输入功、制冷系数等热力学参数与量子纠缠之间的关系, 结果表明: 制冷系数等高线图是环状曲线, 随纠缠比r增加而非单调变化; 当相互作用常数J比较小时, 量子制冷机运行区间在c₁>c₂, 当增加J值时, 制冷机运行区间在c₁>c₂和 c₁<c₂两个区域; 最大制冷系数ε_max随J值增大而增加.     

强磁场中弱相互作用费米气体的热力学性质

基于赝势法和局域密度近似研究了强磁场中弱相互作用费米气体的热力学性质,得出化学势、总能和热容量的解析式,同时分析了磁场及相互作用对系统热力学性质的影响.研究表明,无论是高温情况还是低温情况下,磁场都能调节相互作用的影响.低温下,与无磁场的系统相比,磁场降低系统的化学势、总能和热容量;与无相互作用系统相比,排斥作用增加化学势而降低总能及热容量.高温下,磁场和排斥作用均可降低系统的总能而增加热容量,强磁场可以改变相互作用对总能及热容量的影响. 关键词： 强磁场 弱相互作用 费米气体 热力学性质     

内禀退相干下海森伯XY模型中的热纠缠性质及其相干调控

通过求解系统的Milburn方程,研究了内禀退相干下两比特海森伯XY模型中的热纠缠性质. 讨论了非均匀磁场、系统初始纠缠度、 两比特的相对相位对系统热纠缠的调控作用.结果表明:在系统一定的初始条件下, 磁场的引入能够大大提高两比特间的热纠缠 程度;在固有退相干存在的情况下,系统热纠缠强烈依赖于两个自旋比特的初始态, 通过控制两自旋比特的相对相位和振幅,可以 获得系统的稳定热纠缠.结果还表明:在没有外界磁场时,发现Bell正交态是系统的"暗态", 它的热纠缠度在演化过程中不受系 统内禀退相干的影响.     

Thermodynamical properties of graphene in noncommutative phase–space

We investigated the thermodynamic properties of graphene in a noncommutative phase–space in the presence of a constant magnetic field. In particular, we determined the behaviour of the main thermodynamical functions: the Helmholtz free energy, the mean energy, the entropy and the specific heat. The high temperature limit is worked out and the thermodynamic quantities, such as mean energy and specific heat, exhibit the same features as the commutative case. Possible connections with the results already established in the literature are discussed briefly.     

Specific Heat and Magnetic Susceptibility of Graphene: A RenormalizationGroup Study

In the present paper, we study effect of the long-range Coulomb interaction on the thermodynamic properties of graphene by renormalization group methods. Our calculations show that both the specific heat and the magnetic susceptibility of the material behave differently from the Landau Fermi liquid. More precisely, we find that these quantities are logarithmically suppressed with respect to its noninteracting counterpart when temperature is low.