Bulk-edge coupling in the non-Abelian nu=5/2 quantum hall interferometer

Recent schemes for probing non-Abelian statistics in the quantum Hall effect are based on geometries where current-carrying quasiparticles flow along edges that encircle bulk quasiparticles, which are localized. Here we consider one such scheme, the Fabry-Perot interferometer, and analyze how its interference patterns are affected by a coupling that allows tunneling of neutral Majorana fermions between the bulk and edge. While at weak coupling this tunneling degrades the interference signal, we find that at strong coupling, the bulk quasiparticle becomes essentially absorbed by the edge and the intereference signal is fully restored. Furthermore, we find that the strength of the coupling can be tuned by the source-drain voltage.     

e/3 Laughlin quasiparticle primary-filling nu=1/3 interferometer

We report experimental realization of a quasiparticle interferometer where the entire system is in 1/3 primary fractional quantum Hall state. The interferometer consists of chiral edge channels coupled by quantum-coherent tunneling in two constrictions, thus enclosing an Aharonov-Bohm area. We observe magnetic flux and charge periods h/e and e/3, equivalent to the creation of one quasielectron in the island. Quantum theory predicts a 3h/e flux period for charge e/3, integer statistics particles. Thus, the observed periods demonstrate the anyonic braiding statistics of Laughlin quasiparticles.     

Fano-type spin-flip mesoscopic transport through an Aharonov-Bohm interferometer

We have investigated the mesoscopic transport properties of a quantum dot embedded Aharonov-Bohm (AB) interferometer applied with a rotating magnetic field. The spin-flip effect is induced by the rotating magnetic field, and the tunneling current is sensitive to the spin-flip effect. The spin-flipped electrons tunneling from the direct channel and the resonant channel interfere with each other to form spin-polarized tunneling current components. The non-resonant tunneling (direct transmission) strength and the AB phase φ play important roles. When the non-resonant tunneling (background transmission) exists, the spin and charge currents form asymmetric peaks and valleys, which exhibit Fano-type line shapes by varying the source-drain bias voltage, or gate voltage. The AB oscillations of the spin and charge currents exhibit distinct dependence on the magnetic flux and direct tunneling strength.     

Continuous-time monitoring of Landau-Zener interference in a cooper-pair box

Landau-Zener (LZ) tunneling can occur with a certain probability when crossing energy levels of a quantum two-level system are swept across the minimum energy separation. Here we present experimental evidence of quantum interference effects in solid-state LZ tunneling. We used a Cooper-pair box qubit where the LZ tunneling occurs at the charge degeneracy. By employing a weak nondemolition monitoring, we observe interference between consecutive LZ-tunneling events; we find that the average level occupancies depend on the dynamical phase. The system's unusually strong linear response is explained by interband relaxation. Our interferometer can be used as a high-resolution Mach-Zehnder-type detector for phase and charge.     

Opto-mechatronic configurations to maximize dynamic range and optimize resolution of optical instruments

We developed a new mechanical configuration which combines various optical techniques to maximize dynamic range and to optimize resolution in optical instruments. We assessed various optical configurations by looking at such variables as electronic signal processing and mechanical construction. Previous configurations developed over the last 10 years are discussed. In our new configuration, we adopted and integrated devices such as a microscopic, an interferometer, an electronic speckle pattern interferometer, and a photon tunneling microscope. We examined the impact of our new configuration on future opto-mechatronic systems design. Our new configuration can be an effective and versatile optical metrology tool for enhancing the performance of MEMS and NEMS devices.     

X射线干涉仪实现扫描探针显微镜样板线间距纳米测量

X射线干涉仪以非常稳定的单晶硅晶格作为长度单位 ,可以实现亚纳米精度的微位移测量。提出了将 X射线干涉仪和扫描隧道显微镜结合起来 ,利用单晶硅的晶格尺度测量扫描探针显微镜样板节距的技术方案 ,并进行了实验研究     

通过嵌入铁磁电极之间 Aharonov-Bohm 干涉仪自旋极化输运性质的研究

使用非平衡态格林函数方法和运动方程近似,研究了嵌入铁磁电极之间Aharonov-Bohm 干涉仪的自旋极化输运性质.在左右铁磁电极平行和反平行两种磁组态下,结合Fano因子分析和讨论了Fano 和Kondo 共振对该系统电导的影响,以及电导随自旋极化强度和磁通的变化.结果表明,自旋极化强度和磁通能有效地调节和控制电导,但电导的线形主要由磁通决定;在适当的条件下能导致大的正磁阻和负磁阻的出现.因此,该系统是一个很好的自旋阀晶体管,在自旋电子学中有潜在的应用价值. 关键词： Fano和Kondo共振 自旋极化强度 Fano因子 隧道磁阻     

不同序列拉曼光脉冲对原子重力仪灵敏度的影响

研究了不同序列拉曼光脉冲对原子重力仪灵敏度的影响.结果表明,通过调节脉冲间隔可以改善原子干涉重力仪的灵敏度.在标准配置下,只考虑重力及一阶重力梯度时,三脉冲序列（π/2-π-π/2）的原子干涉重力仪具有较大的灵敏度,四脉冲序列（π/2-π-π-π/2）的原子干涉重力仪对重力不敏感,可用来测量重力梯度,五脉冲作用会降低原子干涉重力仪的灵敏度. 关键词： 原子重力仪 拉曼激光脉冲序列 灵敏度     

Resonant Photon-Assisted Tunneling Through a Coupled Double-Quantum-Dot System

An analytical formula of the tunneling current through a coupled double-quantumdot system in the presence of a time-dependent electric field is obtained by using the Keldysh nonequilibrium Green's function technique. The dependence of the time-averaged current on the frequency of the electric field, as well as the dependence of the multiphoton assisted tunneling on the strength of the electric field are studied. The features of I-V_dc characteristic are also investigated. Besides, we present a simplified formula which can be used to determine the heights of the resonant peaks conveniently.     

Effective field theory and tunneling currents in the fractional quantum Hall effect

We review the construction of a low-energy effective field theory and its state space for “abelian” quantum Hall fluids. The scaling limit of the incompressible fluid is described by a Chern–Simons theory in 2+1 dimensions on a manifold with boundary. In such a field theory, gauge invariance implies the presence of anomalous chiral modes localized on the edge of the sample. We assume a simple boundary structure, i.e., the absence of a reconstructed edge. For the bulk, we consider a multiply connected planar geometry. We study tunneling processes between two boundary components of the fluid and calculate the tunneling current to lowest order in perturbation theory as a function of dc bias voltage. Particular attention is paid to the special cases when the edge modes propagate at the same speed, and when they exhibit two significantly distinct propagation speeds. We distinguish between two “geometries” of interference contours corresponding to the (electronic) Fabry–Perot and Mach–Zehnder interferometers, respectively. We find that the interference term in the current is absent when exactly one hole in the fluid corresponding to one of the two edge components involved in the tunneling processes lies inside the interference contour (i.e., in the case of a Mach–Zehnder interferometer). We analyze the dependence of the tunneling current on the state of the quantum Hall fluid and on the external magnetic flux through the sample.     

高灵敏度的量子迈克耳孙干涉仪

迈克耳孙干涉仪不仅可以用来研究物理学的基本问题,而且能够用于精密测量,比如引力波信号的测量.因此,构建高灵敏度的迈克耳孙干涉仪是实现微弱信号测量的关键.目前,人们利用压缩态可以降低迈克耳孙干涉仪的噪声;通过光学四波混频过程能够放大马赫·曾德尔干涉仪中的相位信号,从而提高干涉仪的信噪比和灵敏度.本文研究了一种用于高灵敏度相位测量的量子迈克耳孙干涉仪.在迈克耳孙干涉仪中,利用非简并光学参量放大器取代干涉仪中的线性光学分束器;并且将压缩态注入干涉仪的真空通道,可以得到高信噪比和高灵敏度的干涉仪.由于存在不可避免的光学损耗,分析了迈克耳孙干涉仪内部和外部的损耗对相位测量灵敏度的影响.通过理论计算研究了干涉仪的相位测量灵敏度随系统参数的变化关系,得到了高灵敏度的相位测量量子迈克耳孙干涉仪的实现条件,为用于精密测量的干涉仪的设计提供了直接参考.     

Theory of resonant tunneling through the insulator conduction band of a thin film metal-insulator-metal (MIM) heterojunction

An “atomic” model of an insulating barrier between two free-electron model metals is used to investigate resonant tunneling across the insulator in the presence of a medium to large, externally applied electric field (bias). The exact numerically calculated tunneling current exhibits a pronounced oscillatory bias dependence superposed on the dominant roughly exponential tunneling characteristic. The interpretation of these results in terms of an internal field emission or Fowler-Nordheim type tunneling subject to “periodic deviations” (or interferences) seems plausible and was suggested by Maserjian. To test this conjecture, a trapezoidal barrier model of our “atomic” model analyzed numerically. As expected, the trapezoidal barrier model could only qualitatively reproduce the oscillatory bias dependence of the barrier transmissivity and of the current. Furthermore this limited agreement depends on allowing the effective mass in the barrier to become a strictly adjustable parameter. This failure of the conventional model of the junction can be interpreted as follows: (i) For moderate external (bias) fields the trapezoidal barrier fails to account for the correct position dependence of the Blochwave vector in the insulator's conduction band, hence the correct interference conditions cannot be reproduced. (ii) For large external fields the band model itself begins to fail. An explanation of oscillatory bias dependence at the tunneling current in terms of splitting of the insulator's conduction band into a set of discrete Stark levels is suggested. It is demonstrated that a fit of the oscillatory tunneling characteristics in the “Fowler-Nordheim regime” is not a reliable technique to determine the effective mass in the thin insulating film of tunneling junctions over the energy interval containing the forbidden gap and the adjoining conduction-band.     

Conductance in an Aharonov-Bohm Interferometer with Parallel-Coupled Double Dots

We present a theoretical study of the conductance in an Aharonov-Bohm interferometer containing two coupled quantum dots. The interdot tunneling divides the interferometer into two coupled subrings, where opposite magnetic fluxes are threaded separately while the net flux is kept zero. Using the Green function technique we derive the expression of the linear conductance. It is found that the Aharonov-Bohm effect still exists, and when the level of each dot is aligned, the exchange of the Fano and Breit-Wigner resonances in the conductance can be achieved by tuning the magnetic flux. When the two levels are mismatched the exchange may not happen. Further, for some specific asymmetric systems where the coupling strengths between the two dots and the leads are not equal, the flux can change the Fano resonance into an antiresonance, which is absent in symmetric systems.     

Nonmonotonic inelastic tunneling spectra due to surface spin excitations in ferromagnetic junctions

The paper addresses inelastic spin-flip tunneling accompanied by surface spin excitations (magnons) in ferromagnetic junctions. The inelastic tunneling current is proportional to the magnon density of states which is energy-independent for the surface waves and, for this reason, cannot account for the bias-voltage dependence of the observed inelastic tunneling spectra. This paper shows that the bias-voltage dependence of the tunneling spectra can arise from the tunneling matrix elements of the electron-magnon interaction. These matrix elements are derived from the Coulomb exchange interaction using the itinerant-electron model of magnon-assisted tunneling. The results for the inelastic tunneling spectra, based on the nonequilibrium Green’s function calculations, are presented for both parallel and antiparallel magnetizations in the ferromagnetic leads.     

Aharonov–Bohm Interferometry Based on Helical Edge States (Brief Review)

JETP Letters - We review recent studies of the spin-dependent tunneling transport via an Aharonov–Bohm interferometer (ABI) formed by helical edge states. We focus on the experimentally...     

Coulomb potential influence in the attoclock experimental scheme

Coulomb potential may induce a significant angular offset to the two-dimensional photoelectron momentum distributions for atoms subject to strong elliptically polarized laser fields.In the attoclock experiment,this offset usually cannot be easily disentangled from the contribution of tunneling delay and poses a main obstacle to the precise measurement of tunneling delay.Based on semiclassical calculations,here,we propose a method to extract the equivalent temporal offset induced solely by Coulomb potential(TOCP)in an attoclock experiment.Our calculations indicate that,at constant laser intensity,the TOCP shows distinctive wavelength dependence laws for different model atoms,and the ratio of the target atom’s TOCP to that of H becomes insensitive to wavelength and linearly proportional to(2Ip)?3/2,where Ip is the ionization potential of the target atom.This wavelength and Ip dependence of TOCP can be further applied to extract the Coulomb potential influence.Our work paves the way for an accurate measurement of the tunneling delay in the tunneling ionization of atoms subject to intense elliptically polarized laser fields.     

Band offsets, Fermi levels and impurity bands in doped contact layers

A mathematical formalism for use in the study of the temperature dependence of Tsu-Esaki tunneling currents is developed. The discussion includes recently discovered corrections to the Tsu-Esaki tunneling current calculation. These corrections involve emitter and collector electron density effects. The tunneling current is fully amenable to numerical calculation, but some calculations can be facilitated by analytic techniques. An operator technique of Blankenbecler is illustrated and used to generate low temperature series expansions for the tunneling current and emitter-collector electron densities.     

Analytic techniques and corrections to the Tsu-Esaki tunneling current

A mathematical formalism for use in the study of the temperature dependence of Tsu-Esaki tunneling currents is developed. The discussion includes recently discovered corrections to the Tsu-Esaki tunneling current calculation. These corrections involve emitter and collector electron density effects. The tunneling current is fully amenable to numerical calculation, but some calculations can be facilitated by analytic techniques. An operator technique of Blankenbecler is illustrated and used to generate low temperature series expansions for the tunneling current and emitter-collector electron densities.