Optical control of spin-dependent thermal transport in a quantum ring

We report on calculation of spin-dependent thermal transport through a quantum ring with the Rashba spin-orbit interaction. The quantum ring is connected to two electron reservoirs with different temperatures. Tuning the Rashba coupling constant, degenerate energy states are formed leading to a suppression of the heat and thermoelectric currents. In addition, the quantum ring is coupled to a photon cavity with a single photon mode and linearly polarized photon field. In a resonance regime, when the photon energy is approximately equal to the energy spacing between two lowest degenerate states of the ring, the polarized photon field can significantly control the heat and thermoelectric currents in the system. The roles of the number of photon initially in the cavity, and electron–photon coupling strength on spin-dependent heat and thermoelectric currents are presented.     

抛物量子点中弱耦合磁极化子的性质

应用线性组合算符和幺正变换方法研究了抛物量子点中磁极化子的基态性质。得出基态能和基态束缚能随有效束缚强度增大而减小,随回旋频率增大而增大。当有效柬缚强度给定,基态能量随电子-体纵光学声子耦合强度增加而减小。当有效束缚强度l0>0.3时,电子-体纵光学声子耦合强度的变化对量子点中弱耦合磁极化子的基态能量的影响变得显著。当有效束缚强度l0<0.3时,电子-体纵光学声子耦合强度的变化对基态能量影响很小。由于有效束缚强度与量子点受限强度的平方根成反比,所以量子点受限越强,基态能量、基态束缚能越大,电子一体纵光学声子耦合强度和磁场的变化对量子点的影响相对越小;当量子点受限变弱时,电子-声子耦合强度变化对量子点的影响变大,磁场对量子点的影响也变大,所以在量子点中,极化子对量子点的影响不容忽略。     

Electroluminescence Caused by the Transport of Interacting Electrons through Parallel Quantum Dots in a Photon Cavity

We show that a Rabi‐splitting of the states of strongly interacting electrons in parallel quantum dots embedded in a short quantum wire placed in a photon cavity can be produced by either the para‐ or the dia‐magnetic electron‐photon interactions when the geometry of the system is properly accounted for and the photon field is tuned close to a resonance with the electron system. We use these two resonances to explore the electroluminescence caused by the transport of electrons through the one‐ and two‐electron ground states of the system and their corresponding conventional and vacuum electroluminescense as the central system is opened up by coupling it to external leads acting as electron reservoirs. Our analysis indicates that high‐order electron‐photon processes are necessary to adequately construct the cavity‐photon dressed electron states needed to describe both types of electroluminescence.     

磁场对非对称量子点中极化子性质的影响

采用线性组合算符和幺正变换方法研究磁场对非对称量子点中弱耦合磁极化子性质的影响.导出了非对称量子点中弱耦合磁极化子的振动频率、基态能量和基态结合能随量子点的横向和纵向有效受限长度、磁场和电子-声子耦合强度的变化关系.数值计算结果表明:非对称量子点中弱耦合磁极化子的基态能量和基态结合能随量子点的横向和纵向有效受限长度的增加而迅速增大.随回旋频率的增加而增大,随电子-声子耦合强度的增加而减小.     

抛物量子点中强耦合束缚磁极化子的性质

采用Pekar类型的变分方法研究了抛物量子点中强耦合束缚磁极化子的基态和激发态的性质.计算了束缚磁极化子的基态和激发态的能量、光学声子平均数以及束缚磁极化子的共振频率.讨论了这些量对回旋频率和有效束缚强度以及库仑束缚势的依赖关系.数值计算结果表明:量子点中强耦合束缚磁极化子的基态能量和共振频率以及光学声子平均数均随量子点的有效束缚强度的增加而减小,基态能量随库仑束缚势的增加而减小,随回旋频率的增加而增大.     

抛物量子点中强耦合束缚磁极化子的声子平均数

采用线性组合算符和幺正变换方法导出了强耦合束缚磁极化子的振动频率和声子平均数。讨论了量子点的有效受限长度、磁场、库仑场和电子-LO声子耦合强度对抛物量子点中强耦合束缚磁极化子振动频率和声子平均数的影响。数值计算结果表明:强耦合束缚磁极化子的振动频率和声子平均数均随量子点的有效受限长度、回旋共振频率的增加而减小,随库仑束缚势的增加而增加,声子平均数随电子-LO声子耦合强度增加而减小。     

抛物量子点中强耦合磁极化子的性质

采用Pekar类型的变分方法研究了抛物量子点中强耦合磁极化子的基态和激发态的性质。计算了基态和激发态磁极化子的束缚能以及磁极化子的共振频率。讨论了这些量对回旋频率和有效限制强度的依赖关系,以及磁极化子光学声子平均数的性质,结果表明:由于Zeeman劈裂,抛物量子点中磁极化子的回旋共振频率劈裂为两支。基态和激发态磁极化子的束缚能以及磁极化子的共振频率都随回旋频率的增加而增大,随量子点的有效束缚强度的增大而减小。     

On the phase-space analysis of photon mediated quantum state transfer in nanophotonic waveguidance

A cavity quantum electrodynamics (QED) based approach for transferring quantum state between quantum nodes has been proposed, wherein a rubidium (⁸⁷Rb) atom trapped inside a two-mode optical cavity forms the quantum node and photons serve as the information carrier between two such nodes. Information is encoded into polarized photon states generated through the application of a system of lasers. The focus is made on the phase-space analysis of the approach, wherein two subspaces of the hyperfine energy levels with magnetic sub-levels of rubidium (⁸⁷Rb) atom represent the logic states ‘0’ and ‘1’. The system of lasers initiates a cavity assisted Raman process which, in turn, generates a right- or left-circularly polarized photon depending on the logic state of the transmit node. Once the photon is received (at the receive node), the logic state of the transmit node is restored into the receive node through a cavity QED process.     

Kondo effect for electron transport through an artificial quantum dot

We have calculated the transport properties of electron through an artificial quantum dot by using the numerical renormalization group technique in this paper. We obtain the conductance for the system of a quantum dot which is embedded in a one-dimensional chain in zero and finite temperature cases. The external magnetic field gives rise to a negative magnetoconductance in the zero temperature case. It increases as the external magnetic field increases. We obtain the relation between the coupling coefficient and conductance. If the interaction is big enough to prevent conduction electrons from tunnelling through the dot, the dispersion effect is dominant in this case. In the Kondo temperature regime, we obtain the conductivity of a quantum dot system with Kondo correlation.     

Optical switching of electron transport in a waveguide-QED system

Electron switching in waveguides coupled to a photon cavity is found to be strongly influenced by the photon energy and polarization. Therefore, the charge dynamics in the system is investigated in two different regimes, for off-resonant and resonant photon fields. In the off-resonant photon field, the photon energy is smaller than the energy spacing between the first two lowest subbands of the waveguide system, the charge splits between the waveguides implementing a $\sqrt{\mathrm{NOT}}$-quantum logic gate action. In the resonant photon field, the charge is totally switched from one waveguide to the other due to the appearance of photon replica states of the first subband in the second subband region instigating a quantum-NOT transition. In addition, the importance of the photon polarization to control the charge motion in the waveguide system is demonstrated. The idea of charge switching in electronic circuits may serve to built quantum bits.     

非对称量子点中强耦合磁极化子激发态的性质

采用线性组合算符和幺正变换方法,研究非对称量子点中强耦合磁极化子的激发态性质。导出强耦合磁极化子的第一内部激发态能量、激发能量和从第一内部激发态到基态的跃迁谱线频率随量子点的横向和纵向有效受限长度、磁场的回旋频率和电子-声子耦合强度的变化关系。数值计算结果表明：第一内部激发态能量、激发能量和跃迁谱线频率随磁场的回旋频率和电子-声子耦合强度的增加而增大.随量子点的横向和纵向有效受限长度的减小而迅速增大,表现出奇特的量子尺寸效应。     

磁场对非对称量子点中束缚磁极化子性质的影响

采用线性组合算符和幺正变换方法研究磁场对非对称量子点中弱耦合束缚磁极化子性质的影响。导出量子点中弱耦合束缚磁极化子振动频率和基态能量随量子点的横向和纵向有效受限长度、库仑束缚势、磁场的回旋共振频率和电子-声子耦合强度的变化关系。数值计算结果表明:非对称量子点中弱耦合束缚磁极化子的振动频率和基态能量随量子点的横向和纵向有效受限长度的减小而迅速增大。振动频率随库仑束缚势和磁场的回旋共振频率的增加而增大。基态能量随库仑束缚势和电子-声子耦合强度的增加而减小。     

Quantum Information Transfer from a Double Quantum Dot System to a Cavity Field＊

In this paper, we propose a scheme to realize quantum information transfer from a double quantum dot （DQD） system to a quantized cavity field. The DQD and the cavity field are treated as a two-state charge qubit and a continuous-variable system, respectively. It is shown that quantum information encoded in the two-state DQD system can be transferred to quantum states of the cavity field with a continuous-variable basis through appropriate projective measurements with respect to the DQD.     

点间耦合强度对三耦合量子点系统微分电导的影响

本文利用非平衡格林函数运动方程方法,研究了与两个电极耦合在一起的三耦合量子点系统的微分电导及量子干涉的AB振荡问题.通过理论计算发现,由于量子点上的局域态密度的不同从而导致系统电导或隧穿性质的不同,而且量子点间耦合强度、量子点能级等都会对输运性质产生影响. 关键词： 量子点 非平衡格林函数 运动方程 局域态密度     

Thermodynamic behaviour of Rashba quantum dot in the presence of magnetic field

The thermodynamic properties of an In Sb quantum dot have been investigated in the presence of Rashba spin–orbit interaction and a static magnetic field. The energy spectrum and wave-functions for the system are obtained by solving the Schrodinger wave-equation analytically. These energy levels are employed to calculate the specific heat, entropy,magnetization and susceptibility of the quantum dot system using canonical formalism. It is observed that the system is susceptible to maximum heat absorption at a particular value of magnetic field which depends on the Rashba coupling parameter as well as the temperature. The variation of specific heat shows a Schottky-like anomaly in the low temperature limit and rapidly converges to the value of 2kB with the further increase in temperature. The entropy of the quantum dot is found to be inversely proportional to the magnetic field but has a direct variation with temperature. The substantial effect of Rashba spin–orbit interaction on the magnetic properties of quantum dot is observed at low values of magnetic field and temperature.     

Cavity‐photon contribution to the effective interaction of electrons in parallel quantum dots

A single cavity photon mode is expected to modify the Coulomb interaction of an electron system in the cavity. Here we investigate this phenomena in a parallel double quantum dot system. We explore properties of the closed system and the system after it has been opened up for electron transport. We show how results for both cases support the idea that the effective electron‐electron interaction becomes more repulsive in the presence of a cavity photon field. This can be understood in terms of the cavity photons dressing the polarization terms in the effective mutual electron interaction leading to nontrivial delocalization or polarization of the charge in the double parallel dot potential. In addition, we find that the effective repulsion of the electrons can be reduced by quadrupolar collective oscillations excited by an external classical dipole electric field.     

Cavity‐Photon‐Induced High‐Order Transitions between Ground States of Quantum Dots

It is shown that quantum electromagnetic transitions to high orders are essential to describe the time‐dependent path of a nanoscale electron system in a Coulomb blockade regime when coupled to external leads and placed in a 3D rectangular photon cavity. The electronic system consists of two quantum dots embedded asymmetrically in a short quantum wire. The two lowest in energy spin degenerate electron states are mostly localized in each dot with only a tiny probability in the other dot. In the presence of the leads, a slow high‐order transition between the ground states of the two quantum dots is identified. The Fourier power spectrum for photon–photon correlations in the steady state shows a Fano type of resonance for the frequency of the slow transition. Full account is taken of the geometry of the multilevel electronic system, and the electron–electron Coulomb interactions together with the para‐ and diamagnetic electron–photon interactions are treated with step‐wise exact numerical diagonalization and truncation of appropriate many‐body Fock spaces. The matrix elements for all interactions are computed analytically or numerically exactly.     

抛物量子点中强耦合束缚极化子的光学声子平均数

采用线性组合算符和幺正变换方法研究了在库仑场束缚下抛物量子点中强耦合束缚极化子的振动频率和光学声子平均数,并对其进行了数值计算。结果表明:强耦合束缚极化子的振动频率和光学声子平均数随量子点的有效受限长度的增加而减小,随电子-LO声子耦合强度的增强而增加,束缚极化子的振动频率随库仑势的增加而减小。     

Smearing of the two-dimensional Kohn anomaly in a nonquantizing magnetic field: implications for interaction effects

Thermodynamic and transport characteristics of a clean two-dimensional interacting electron gas are shown to be sensitive to the weak perpendicular magnetic field even at temperatures much higher than the cyclotron energy, when the quantum oscillations are completely washed out. We demonstrate this sensitivity for two interaction-related characteristics: electron lifetime and the tunnel density of states. The origin of the sensitivity is traced to the field-induced smearing of the Kohn anomaly; this smearing is the result of curving of the semiclassical electron trajectories in magnetic field.     

柱形量子点中弱耦合磁极化子的性质

应用线性组合算符方法和幺正变换方法,研究在抛物势作用下的柱形量子点中磁极化子的性质。对ZnS量子点的数值计算表明,量子点中磁极化子的基态能量随特征频率、回旋共振频率的增大而增加,这是由于特征频率增加时振动能量、回旋共振频率增加时外磁场中的附加能量增加所致。当特征频率(或回旋共振频率)增加到某一值时,磁极化子能量由负变为正。基态能量随柱高的减小而增加,且柱高越小,增加越快;当柱高减小到某一值时,磁极化子能量也由负变为正。总之,柱形量子点中的磁极化子,其基态能量与量子点的尺度、外磁场、特征频率等有关。