New resonant backscattering mode in a small-size quantum interferometer

Giant conductance oscillations quasi-periodic in the gate voltage are observed in the open state of a small-size quantum interferometer (of effective radius r ≈ 100 nm) based on the high-mobility 2D electron gas of an AlGaAs/GaAs heterojunction. These oscillations presumably result from the multiparticle effects that occur in the interferometer arms and give rise to a strong backscattering and to conductance peaks, whose period corresponds to a one-electron change in the number of electrons in the arms.     

Enhanced resonant backscattering of excitons in disordered quantum wells

A clear signature of enhanced backscattering of excitons is observed in the directional resonant Rayleigh scattering of light from localized two-dimensional excitons in disordered quantum wells. Its spectral dependence and time dynamics are measured and theoretically predicted in a quantitative way. The intensity enhancement has a large momentum span extending beyond the external light emission cone. This is a consequence of the small localization length of the exciton as a massive particle probed close to the band bottom. The localization length can be controlled by the photon kinetic energy. This constitutes a qualitative difference to backscattering phenomena in other branches of physics.     

Nonlinear quantum mode of terahertz electromagnetic wave amplification in resonant tunneling heterostructures

An analysis of high-frequency properties of the resonant tunneling diode (RTD) in a strong microwave electromagnetic field showed that the high-frequency current response increasing with the microwave power significantly more rapidly saturates out in the case of classical amplification mode, than in the case of “quantum” amplification mode. This makes the “quantum” mode even more attractive in comparison with the classical mode from the viewpoint of the possibility of amplification and generation in the range of subterahertz and terahertz frequencies and offers new opportunities to advance towards these frequencies.     

谐振腔提高横向光电效应的量子效率

根据位置敏感探测器的原理,设计了p-i-n型的谐振腔结构,研究谐振腔提高横向光电效应的量子效率。以一维缺陷光子晶体作为顶部光学镜,底部为分布式Bragg反射镜(DBR),中间为激活介质谐振腔。利用传输矩阵法计算了一维缺陷光子晶体的透射特性。由于顶部和底部结构的高反作用,一维缺陷光子晶体的透射谐振导模将被有效地限制在激活介质中。通过对谐振腔模型的分析,得出了激活介质的量子效率,并进行了数值仿真。结果表明,一维缺陷光子晶体的谐振导模能有效提高谐振腔中激活介质的量子转换效率。     

谐振腔提高横向光电效应的量子效率

根据位置敏感探测器的原理,设计了p-i-n型的谐振腔结构,研究谐振腔提高横向光电效应的量子效率。以一维缺陷光子晶体作为顶部光学镜,底部为分布式Bragg反射镜(DBR),中间为激活介质谐振腔。利用传输矩阵法计算了一维缺陷光子晶体的透射特性。由于顶部和底部结构的高反作用,一维缺陷光子晶体的透射谐振导模将被有效地限制在激活介质中。通过对谐振腔模型的分析,得出了激活介质的量子效率,并进行了数值仿真。结果表明,一维缺陷光子晶体的谐振导模能有效提高谐振腔中激活介质的量子转换效率。     

Coulomb blockade in triangular lateral small-size quantum dots

An AlGaAs/GaAs lateral quantum dot of triangular shape with a characteristic size L<100 nm containing less than ten electrons was studied. Single-electron oscillations of the conductance G of this dot were measured at G<e²/h. When going from Ge²/h to G≈0.5e²/h, a decrease was found not only in the amplitude but also in the period of the oscillations. A calculation of the 3D-electrostatics demonstrated that this effect is due to a change in the dot size produced by control voltages.     

The quantum stellar interferometer

In this paper we propose a new interferometric scheme using photon entanglement. The two main limitations of stellar interferometry are (a) the small sensitivity and (b) the need for long delay-lines to compensate the path difference between the telescopes during observing runs. Entangled-photon pairs, generated by spontaneous parametric down-conversion, open the way to measuring quantum states correlation in the near infrared between two spatially separated telescopes and at very high sensitivities (down to a few stellar photons), thanks to a new interferometric layout which does not make use of complex long delay-lines. A femtosecond laser coupled to a nonlinear crystal is used as a local oscillator to perform the double homodyne measurements. This new quantum interferometer allows to measure astronomical objet sizes with very high angular resolution down to μas level.     

Vector mode analysis of a young interferometer

It is proved that, when the vector modal theory of coherence is applied to a pair of fixed points, exact results are obtained for the mode structure. In particular, it is shown that the field radiated by the pinholes of a Young interferometer can always be represented by the incoherent superposition of no more than four perfectly correlated and polarized modes. The role of such modes is illustrated through a simple example.     

The neutron interferometer as a macroscopic quantum device

Neutron interferometry is a unique tool for investigations in the field of particle-wave dualism because massive elementary particles behave like waves within the interferometer. The invention of perfect crystal neutron interferometers providing widely separated coherent beams stimulated a great variety of experiments with matter waves in the field of basic quantum mechanics. The phase of the spatial and spinor wave function become a measurable quantity and can be influenced individually. High degrees of coherence and high order interferences have been observed by this technique. The 4π-symmetry of a spinor wave function and the mutual modulation of nuclear and magnetic phase shifts have been measured in the past. Recent experiments dealt with polarized neutron beams, which are handled to realize the spin-superposition of two oppositionally polarized subbeams resulting in a final polarization perpendicular to both initial beam polarizations. The different actions on the coherent beams of static (DC) and dynamic (HF) flippers have been visualized.     

Thermodynamic properties of a quantum Hall anti-dot interferometer

We study quantum Hall interferometers in which the interference loop encircles a quantum anti-dot. We base our study on thermodynamic considerations, which we believe reflect the essential aspects of interference transport phenomena. We find that similar to the more conventional Fabry–Perot quantum Hall interferometers, in which the interference loop forms a quantum dot, the anti-dot interferometer is affected by the electro-static Coulomb interaction between the edge modes defining the loop. We show that in the Aharonov–Bohm regime, in which effects of fractional statistics should be visible, is easier to access in interferometers based on anti-dots than in those based on dots. We discuss the relevance of our results to recent measurements on anti-dots interferometers.     

Lifetime of resonant state in a spherical quantum dot

This paper calculates the lifetime of resonant state and transmission probability of a single electron tunnelling in a spherical quantum dot (SQD) structure by using the transfer matrix technique. In the SQD, the electron is confined both transversally and longitudinally, the motion in the transverse and longitudinal directions is separated by using the adiabatic approximation theory. Meanwhile, the energy levels of the former are considered as the effective confining potential. The numerical calculations are carried out for the SQD consisting of GaAs/InAs material. The obtained results show that the bigger radius of the quantum dot not only leads significantly to the shifts of resonant peaks toward the low-energy region, but also causes the lengthening of the lifetime of resonant state. The lifetime of resonant state can be calculated from the uncertainty principle between the energy half width and lifetime.     

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.     

Aharanov-Bohm interference and fractional statistics in a quantum Hall interferometer

We compute the temperature, voltage, and magnetic field dependences of the conductance oscillations of a model interferometer designed to measure the fractional statistics of the quasiparticles in the fractional quantum Hall effect. The geometry is the same as that used in recent experiments. With appropriate assumptions concerning the relative areas of the inner and outer rings of the interferometer, we find the theoretical results, including the existence of super periodic Aharonov-Bohm oscillations, to be in remarkably good agreement with experiment. We then make additional experimental predictions with no adjustable parameters which, if verified, would confirm the proposed interpretation of the experiment as a measurement of fractional statistics.     

Single-electron charging of triangular quantum dots in a ring interferometer

Small-size semiconductor ring interferometers operating in the Coulomb blockade regime have been experimentally and theoretically studied. The conductance as a function of the gate voltage exhibits narrow quasiperiodic peaks, which are further split into doublets. Based on the experimental structural data, a three-dimensional electrostatic potential, the energy spectrum, and the single-electron transport in the interferometer were modeled. The electron system can be divided into two triangular quantum dots connected by single-mode microcontacts to each other and to the reservoirs. A model of quantum dot charging in this system is proposed that explains the appearance of doublets in the conductance-gate voltage characteristics.     

New collective mode in the fractional quantum Hall liquid

We apply the methods of continuum mechanics to the study of the collective modes of the fractional quantum Hall liquid. Our main result is that at long-wavelength, there are two distinct modes of oscillations, while previous theories predicted only one. The two modes are shown to arise from the internal dynamics of shear stresses created by the Coulomb interaction in the liquid. Our prediction is supported by recent light scattering experiments, which report the observation of two long-wavelength modes in a quantum Hall liquid.     

Physical realisation of Weierstrass scaling using a quantum interferometer

We show that self-similar magneto-conductance fluctuations observed in semiconductor Sinai billiards originate from quantum interference processes, which are associated with classical trajectories that enclose discrete areas. We identify the exact areal distributions and reproduce the self-similarity with remarkable accuracy.     

Current bistability in resonant tunneling through a semiconductor quantum dot

We discuss resonant tunneling through quantum dot energy levels considering the charging energy of the dot. The hamiltonian of the system is reduced to a form of the Anderson hamiltonian of resonant tunneling. The mean-field approximation is applied and current–voltage characteristics are evaluated. The self-consistent solution is investigated for the low tunneling rate case in the low-temperature condition. The current bistability and the related current hysteresis are pointed out. The Coulomb staircase is shown in the current–voltage characteristics. These features are all due to Coulomb repulsion within the dot.     

Measuring the transmission phase of a quantum dot in a closed interferometer

The electron transmission through a closed Aharonov-Bohm mesoscopic solid-state interferometer, with a quantum dot (QD) on one of the paths, is calculated exactly for a simple model. Although the conductance is an even function of the magnetic flux (due to Onsager's relations), in many cases one can use the measured conductance to extract both the amplitude and the phase of the "intrinsic" transmission amplitude t(D)=-i|t(D)|e(ialpha(D)) through the "bare" QD. We also propose to compare this indirect measurement with the (hitherto untested) direct relation sin((2)(alpha(D)) identical with |t(D)|(2)/max((|t(D)|(2)).