Mode analysis of surface plasmon metal-dielectric-metal nanowire array waveguide at sub-wavelength scale

The investigation of quantum and classical correlations has mostly concentrated on two-qubit states because the minimization in the classical correlation is quite complicated for high-dimensional states. Thermal quantum and classical correlations are studied for a two-qutrit system with various coupling constants, external magnetic fields, and temperatures as well, where the quantum correlation is described in terms of the quantum discord that has been extensively used in recent literature. The entanglement negativity is calculated for comparison. It is shown that the discord is nonzero whereas the negativity is zero in some ranges of system parameters and temperature. Moreover, the discord is more robust than the entanglement against temperature and magnetic field. However, at lower temperatures all three correlations behave similarly. Those are useful for understanding quantum correlations in high-dimensional mixed states and quantum information processing.     

Magneto-optics of zero-dimensional electron systems

Photoluminescence spectroscopy has been used to probe the occupied electron states below the Fermi energy of zero-dimensional electron systems (0DESs) in both zero and finite magnetic fields. The arrays of modulation-doped quantum dots investigated were fabricated by both reactive-ion etching and strain-confining GaAs heterojunctions with a -layer of Be present in the GaAs, in order to improve luminescence efficiency. For the etched quantum dots we show that the low magnetic field dispersion T) of the acceptor recombination line is directly related to the magnetic field dependence of the total ground-state energy of interacting electrons in the quantum dots. For the strain-confined 0DESs we have mapped the magneto-dispersion of the quantum confined electron states to reveal 15 electrons per dot.     

Quantum-size states of the deformed nanosphere

The effect of shape deformation of a spherical nano-object on quantum states of a particle in it has been analyzed theoretically. For this purpose, a functional method of surface shape perturbation theory has been proposed. The method allows us to determine the effect of a wide range of deviations of a limited three-dimensional volume (nano-object) from the initial shape on the quantum characteristics of a charge localized inside the nano-object. An analysis has demonstrated that the probability density for a particle in quantum-size states is more sensitive to surface shape perturbations than the energy spectrum and the density of quantum states. Even small shape perturbations lead to a smearing of the probability density for the location of a particle inside a nano-object and lift the degeneracy in the magnetic quantum number. A mixing of pure states corresponding to a sphere has been observed. The degree of mixing and the splitting of the energy levels increase with increasing quantum numbers l and m.     

Absorption and emission of terahertz radiation in doped GaAs/AlGaAs quantum wells

Spontaneous emission of terahertz radiation from structures with GaAs/AlGaAs quantum wells in a longitudinal magnetic field has been studied. It is shown that some bands in the emission spectrum can be related to radiative electron transitions between resonant and localized impurity states, as well as to the transitions with participation of subband states. The temperature dependence of the equilibrium intraband absorption of terahertz radiation and its modulation in a longitudinal electric field in GaAs/AlGaAs quantum wells has been investigated.     

Mesoscopic one-way channels for quantum state transfer via the quantum Hall effect

We show that the one-way channel formalism of quantum optics has a physical realization in electronic systems. In particular, we show that magnetic edge states form unidirectional quantum channels capable of coherently transporting electronic quantum information. Using the equivalence between one-way photonic channels and magnetic edge states, we adapt a proposal for quantum state transfer to mesoscopic systems using edge states as a quantum channel, and show that it is feasible with reasonable experimental parameters. We discuss how this protocol may be used to transfer information encoded in number, charge, or spin states of quantum dots, so it may prove useful for transferring quantum information between parts of a solid-state quantum computer.     

磁场下量子点的电子态

原子和核结构的少体理论方法改进后用以研究磁场下包含三个电子的二维量子点的电子性质。我们首先解析地证明了对应于三电子系统基态的幻数角动量的存在起源于量子力学对称性的要求。基于少体理论方法的计算确认了上述理论分析的正确性,计算同时显示出磁场强度和约束势对三电子系统基态的影响。 关键词：     

Negative magnetoresistance in the regime of hopping conduction through <Emphasis Type="Italic">p</Emphasis> states at quantum dots

The magnetoresistance in the system of quantum dots with hopping conduction and filling factor 2 < ν < 3 in the limit of small quantum dots has been considered. In this case, hopping conduction is determined by p states. It has been shown that the system exhibits negative magnetoresistance associated with a change in the wavefunctions of p states in a magnetic field. This mechanism of magnetoresistance is linear in magnetic field in a certain range of fields and can compete with the known interference mechanism of magnetoresistance. The magnitude of this magnetoresistance is independent of the temperature at fairly low temperatures and increases with a decrease in the size of a quantum dot.     

Two interacting electrons in a Gaussian confining potential quantum dot

Two interacting electrons in a Gaussian confining potential quantum dot are considered under the influence of a perpendicular homogeneous magnetic field. The energy levels of the low-lying states are calculated as a function of magnetic field. Calculations are made by using the method of few-body physics within the effective-mass approximation. A ground state behavior (singlet→triplet state transitions) as a function of the strength of a magnetic field has been found in the weak confinement case as a two-electron quantum dot with parabolic confining potential.     

Pulsed and monochromatic excitation of semiconductor quantum wells under the conditions of quantum confinement

The reflectance and absorbance of light by quantum wells whose width is comparable to the light wavelength have been calculated. The difference in the refractive indices of the materials of the quantum well and the barriers has been taken into account. Pulsed irradiation with an arbitrary shape of the exciting pulse has been considered, and the existence of two closely spaced discrete excitation levels has been assumed. This pair of levels can correspond to two magnetopolaron states in a quantizing magnetic field directed perpendicular to the plane of the quantum well. The ratio between the magnitudes of nonradiative and radiative dampings of electronic excitations is arbitrary. The final results have been obtained without invoking the approximation in which the Coulomb interaction of electrons and holes is negligible.     

磁场中量子点四电子系统的基态性质

利用少体物理的方法，研究了磁场中二维量子点四电子系统基态能量与角动量间的变化关系，以及磁场强度和约束势的大小对四电子系统基态的影响.数值计算表明，量子力学对称性是幻数角动量出现的重要因素. 关键词：     

Quantum states of magnetically induced anions

In a magnetic field, an atom (or molecule) can attach an extra electron to form an unconventional anionic state which has no counterparts in field-free space. Assuming the atom to be infinitely heavy, these magnetically induced anionic states are known to constitute an infinite manifold of bound states. In reality, the species can move and its motion across the magnetic field couples to the motion of the attached electron. We treat this coupling, for the first time, quantum mechanically, and show that it makes the number of bound anionic states finite. Explicit numerical quantum results are presented and discussed.     

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。     

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。     

Spin-orbit coupling and anisotropy of spin splitting in quantum dots

In lateral quantum dots, the combined effect of both Dresselhaus and Bychkov-Rashba spin-orbit coupling is equivalent to an effective magnetic field +/- B(SO) which has the opposite sign for s(z)= +/- 1/2 spin electrons. When the external magnetic field is perpendicular to the planar structure, the field B(SO) generates an additional splitting for electron states as compared to the spin splitting in the in-plane field orientation. The anisotropy of spin splitting has been measured and then analyzed in terms of spin-orbit coupling in several AlGaAs/GaAs quantum dots by means of resonant tunneling spectroscopy. From the measured values and sign of the anisotropy we are able to determine the dominating spin-orbit coupling mechanism.     

Magnetic quantum ring in two-dimensional topological insulators

The quantum properties of topological insulator magnetic quantum rings formed by inhomogeneous magnetic fields are investigated using a series expansion method for the modified Dirac equation. Cycloid-like and snake-like magnetic edge states are respectively found in the bulk gap for the normal and inverted magnetic field profiles. The energy spectra, current densities and classical trajectories of the magnetic edge states are discussed in detail. The bulk band inversion is found to manifest itself through the angular momentum transition in the ground state for the cycloid-like states and the resonance tunneling effect for the snake-like states.     

Thermodynamic properties of a superconducting quantum cylinder and their fluctuations

A numerical and analytical investigation of thermodynamic properties of a magnetized superconducting quantum cylinder has been carried out. The dependence of the difference in the magnetizations of the superconducting and normal phases on the parameters of the nanotube, temperature, and magnetic field has been analyzed. The jump in the heat capacity of the superconducting and normal states at the critical temperature has been calculated. The fluctuation contribution to the thermodynamic properties of the nanotube at a temperature above the transition point has been studied.     

Implementation of Full Spin-State Interferometer

Matter-wave interferometers with spin quantum states are attractive in quantum manipulation and precision measurements. Here, five spatial interference patterns corresponding to the full spin states are observed in each run of the experiment, by the combination of the Majorana transition according to the exponential modulation of the magnetic field pulse decline curve and radio frequency coupling among multiple magnetic sub-states.Compared to the realization of two Majorana transitions, the interference fringe for the magnetic field insensitive state also has a higher contrast. After spatially overlapping the full magnetic sub-state interference patterns dozens of times in consecutive experimental measurements, clear fringes are still observed, indicating the great stability of the relative phases of different components. This indicates the potential to achieve an interferometer with multiple spin clocks.     

Environment-induced sudden transition in quantum discord dynamics

Nonclassical correlations play a crucial role in the development of quantum information science. The recent discovery that nonclassical correlations can be present even in separable (nonentangled) states has broadened this scenario. This generalized quantum correlation has been increasing in relevance in several fields, among them quantum communication, quantum computation, quantum phase transitions, and biological systems. We demonstrate here the occurrence of the sudden-change phenomenon and immunity against some sources of noise for the quantum discord and its classical counterpart, in a room temperature nuclear magnetic resonance setup. The experiment is performed in a decohering environment causing loss of phase relations among the energy eigenstates and exchange of energy between system and environment, resulting in relaxation to the Gibbs ensemble.     

Entanglement and Zeeman interaction in diluted magnetic semiconductor quantum dot

We present theoretically the Zeeman coupling and exchange-induced swap action in spin-based quantum dot quantum computer models in the presence of magnetic field. We study the valence and conduction band states in a double quantum dots made in diluted magnetic semiconductor. The latter have been proven to be very useful in building an all-semiconductor platform for spintronics. Due to a strong p–d exchange interaction in diluted magnetic semiconductor (Cd_0.57Mn_0.43Te), the relative contribution of this component is strongly affected by an external magnetic field, a feature that is absent in nonmagnetic double quantum dots. We determine the energy spectrum as a function of magnetic field within the Hund–Mulliken molecular-orbit approach and by including the Coulomb interaction. Since we show that the ground state of the two carriers confined in a vertically coupled quantum dots provide a possible realization for a gate of a quantum computer, the crossing between the lowest states, caused by the giant spin splitting, can be observed as a pronounced jump in the magnetization of small magnetic field amplitude. Finally, we determine the swap time as a function of magnetic field and the inter dot distance. We estimate quantitatively swap errors caused by the field, establishing that error correction would, in principle, be possible in the presence of nonuniform magnetic field in realistic structures.