无穷级数求和的一种量子力学解法

在一维无限深方势阱的解析解的基础上,利用波函数的归一化常数及能量平均值的两种不同算法的等价性,导出了∑n=1^∞ 1/n^2、∑n=1^∞ 1/n^4等24个无穷级数的求和公式。     

Shot noise in a quantum dot with the coulomb interaction

We study the noise in a quantum dot which is coupled to metallic leads by using the non-equation of motion technique at the Kondo temperature T_K. We compute the out of equilibrium density of states, the current and the shot noise. We find that the shot noise exhibits a nonmonotonic dependence on the voltage when variation of ε_d values of the QD energy in the absence of the external magnetic field occurs. We also find that the amplitude of current exhibits a saturation behavior when driving field is increased.     

Amplification of noise in the quantum theory of parametric processes

A quantum mechanical treatment is given of the acousto-optical parametric amplification processes in dielectric crystals when the signal acoustical and idler light waves are amplified in the presence of intensive optical pumping. The approximate Heisenberg equations of motion are found and solved for the creation and annihilation operators of signal and idler modes with due regard for the interaction of these modes with other light and vibratory modes of the crystal (“the thermostat”). It is shown that the thermostat influence results in noise and attenuation effects. These persistent noises are also amplified. If the pumping is not far above the threshold the persistent noises are more important than the initial ones.     

Experimental test of the high-frequency quantum shot noise theory in a quantum point contact

We report on direct measurements of the electronic shot noise of a quantum point contact at frequencies nu in the range 4-8 GHz. The very small energy scale used ensures energy independent transmissions of the few transmitted electronic modes and their accurate knowledge. Both the thermal energy and the quantum point contact drain-source voltage V_{ds} are comparable to the photon energy hnu leading to observation of the shot noise suppression when V_{ds}相似文献   

An operational construction of the sum of two non-commuting observables in quantum theory and related constructions

Letters in Mathematical Physics - The existence of a real linear space structure on the set of observables of a quantum system—i.e., the requirement that the linear combination of two...     

Dynamics of quantum discord in a two-qubit system under classical noise

We study the quantum discord dynamics of two noninteracting qubits that are, respectively, subject to classical noise. The results show that the dynamics of quantum discord are dependent on both the coupling between the qubits and classical noise, and the average switching rate of the classical noise. In the weak-coupling Markovian region, quantum discord exhibits exponent decay without revival, and can be well protected by increasing the average classical noise switching rate. While in the strong-coupling non-Markovian region, quantum discord reveals slowly decayed oscillations with quick revival by decreasing the average switching rate of the classical noise. Thus, our results provide a new method of protecting quantum discord in a two-qubit system by controlling the coupling between the qubits and classical noise, and the average switching rate of the classical noise.     

Cumulative quantum work-deficit versus entanglement in the dynamics of an infinite spin chain

We find that the dynamical phase transition (DPT) in nearest-neighbor bipartite entanglement of time-evolved states of the anisotropic infinite quantum XY spin chain, in a transverse time-dependent magnetic field, can be quantitatively characterized by the dynamics of an information-theoretic quantum correlation measure, namely, quantum work-deficit (QWD). We show that only those nonequilibrium states exhibit entanglement resurrection after death, on changing the field parameter during the DPT, for which the cumulative bipartite QWD is above a threshold. The results point to an interesting inter-relation between two quantum correlation measures that are conceptualized from different perspectives.     

Reprint of : A computational approach to quantum noise in time-dependent nanoelectronic devices

We derive simple expressions that relate the noise and correlation properties of a general time-dependent quantum conductor to the wave functions of the system. The formalism provides a practical route for numerical calculations of quantum noise in an externally driven system. We illustrate the approach with numerical calculations of the noise properties associated to a voltage pulse applied on a one-dimensional conductor. The methodology is however fully general and can be used for a large class of mesoscopic conductors.     

Effect of external noise on the dynamical localization of two coupling electrons in quantum dot array

The effect of external noise, which is characterized byan Ornstein--Uhlenbeck process, on the dynamical localization oftwo coupling electrons in a quantum dot array under the action ofan ac electric field is studied. A numerical solution of the stochasticequations is obtained by averaging over stochastictrajectories. The results show that the external noise may destroy thedynamical localization, but the anti-noise capacity of the systemis stronger when the two electrons are localized at the ends ofthe quantum dot array.     

Quantum relativistic theory of an electron in terms of local observables

Dirac equation is reformulated in terms of real local observables, which are mean values of the wave function . The quadrivector current is shown to be a function of the potential vector and of other local observables. The equations describe the evolution of a four dimensional system T, X, Y, Z, and of two scalars, in the coordinate system ct, x, y, z. The current is proportional to the T vector. The Z vector is associated with the spin of the electron. Energy and gauge transformations correspond to rotations in the plane (X, Y). In the presence of a static field, the (real) solutions of the equations appear as eigenfunctions associated with energy eigenvalues. Received 7 September 1998     

The shot noise of the quantum dot weakly coupled to Luttinger liquid

We study the nonequilibrium transport through a single-level quantum dot weakly coupled to Luttinger liquid leads. A general shot noise expression is derived by using nonequilibrium Green function technique. We find that the differential shot noise and differential conductance demonstrate resonant-like behavior as a function of the bias voltage and the quantum dot's energy level for a weak or moderately strong interaction. In the limit of strong electron-electron interaction, the resonant behavior disappears and shows bias-voltage-dependent power law scalings. And the Fano factor also scales as a power law in high bias voltage region. In addition, the Fano factor is enhanced with the electron-electron interaction increased. It implies that the Fano factor can be controlled by tuning the electron-electron interaction in the leads.     

Photon-assisted Shot noise of the double quantum dot interferometer in weak Kondo regime

The shot noise of a parallel double quantum dot (DQD) system under the perturbation of microwave fields is investigated in the weak Kondo regime. Peak-valley structures exhibit in the differential conductance and shot noise, and side resonant peaks emerge around the Kondo peak due to the absorption and emission of photons. The shot noise is sensitively dependent on the adjusting approach through changing the gate voltages. Large resonant Fano factor accompanying photon-induced side peaks appear by simultaneously varying the two gate voltages. The photon suppression and enhancement of shot noise have been evaluated corresponding to the coherent and incoherent current correlation. The destructive interference causes the suppression of shot noise by changing the Aharonov–Bohm phase.     

The shot noise of a strongly correlated quantum dot coupled to the Luttinger liquid leads

We study the shot noise of a strongly correlated quantum dot weakly coupled to Luttinger liquid leads in the Kondo regime by means of the extended equation of motion method. A general zero-frequency shot noise formula with good convergence is derived. The shot noise exhibits a non-monotonic dependence on voltage for weak intralead interaction. There is a peak around the Kondo temperature at low voltage when the interaction is very weak, and its height decreases rapidly with the intralead interaction increasing. When the interaction is moderately strong the peak disappears and the shot noise scales as a power law in bias voltage, indicating that the intralead electron interaction suppresses the shot noise. It is possible that the measurements of the shot noise spectrum can extract the information of the intralead interaction.     

The effect of noise on the dirac phase of electron in the presence of screw dislocation

The effect of noise on the Dirac phase of electron in the presence of screw dislocation is studied. An uncorrelated noise, which coincides with the nature of thermal fluctuations, is adopted. Results indicate that the Dirac phase is robust against the existing noise in the system.     

平衡接收直接检测DPSK接收机噪声统计特性分析

以带光前置放大器且采用MZI相干和直接检测方式的DPSK接收机为分析模型,从考虑线性附加噪声和非线性相位噪声入手,对噪声统计特性进行了数学分析,并推导出了概率密度函数和BER公式。结果表明:数值计算结果与已发表论文的试验结果较为吻合;非线性相位噪声会对系统性能造成严重影响;高斯近似法不能很好的分析此模型。     

Estimation of the disorder degree of the classical static noise using three entangled qubits as quantum probes

The paper investigates the estimation of the disorder degree of the classical static noise using three entangled qubits as quantum probes together with the tools of local quantum estimation theory. Three probing schemes namely common environment (CE), independent environments (IEs) and mixed environments (MEs) are investigated and the optimal initial state preparation of the probes taken as a partially depolarized GHZ state. The results show that: (i) the IEs probing scheme allows one to achieve better estimation precision compared to both MEs and CE schemes respectively; (ii) the higher is the initial amount of entanglement of the probes, the larger is the estimation precision, independently of the scheme considered; (iii) both small and large values of the disorder parameter are uniformly estimable at the optimal interaction time; (iv) entangled qubits probes quickly encode information about the disorder parameter than single-qubit probe; (v) there is an improvement in the estimation of the disorder parameter when entangled probes interacting either in IEs or MEs are used instead of a single probe, demonstrating that a single probe is not sufficient to optimally estimate the disorder parameter of the static noise. On the other hand, we have also investigated the relationship between the residual amount of entanglement present in the probes at the optimal interaction time and the estimation precision of the disorder parameter. We show that the higher the residual amount of entanglement at the optimal interaction time, the smaller the estimation precision.     

Application of the group pulse processes in the theory of Barkhausen noise

In the paper the 2nd-order periodic group pulse process is considered a statistical model of the Barkhausen voltage. Using this model an analytical formula for the power spectrum is derived and further specified to fit the measured spectrograms of Barkhausen noise. The results are interpreted with respect to the generating physical mechanism and examples of several numerical values are given.     

Time evolution of the intensity correlation function in a single-mode laser driven by both the coloured pump noise with signal modulation and the quantum noise with cross-correlation between the real and imaginary parts

Using the linear approximation, we have studied the time evolution of intensity correlation function C（t） in a single-mode laser driven by both the colored pump noise with signal modulation and the quantum noise with cross-correlation between its real and imaginary parts. In the case of the pump noise self-correlation time, we find that the time evolution of C（t） varies with modulation signal frequency Ω, amplitude B, and net gain ɑ0. (i) As the Ω increases, the time evolution of C（t） experiences a process changing from the monotonous descension to the descension with a flat appearing initially, and finally to the a form of damping oscillation; (ii) As the B increases, it experiences from monotonous descension to the appearance of a maximum; (iii) As the net gain ɑ0 increases, it experiences a process repeatedly changing from the monotonous descension to monotonous ascension, and to the appearance of a maximum, finally to monotonous descension again. However, in the case of, the time evolution of C（t） only exhibits a form of damping oscillation .