Measuring the Luttinger liquid parameter with shot noise

We explore the low-frequency noise of interacting electrons in a one-dimensional structure (quantum wire or interaction-coupled edge states) with counterpropagating modes, assuming a single channel in each direction. The system is driven out of equilibrium by a quantum point contact (QPC) with an applied voltage, which induces a double-step energy distribution of incoming electrons on one side of the device. A second QPC serves to explore the statistics of outgoing electrons. We show that measurement of a low-frequency noise in such a setup allows one to extract the Luttinger liquid constant K which is the key parameter characterizing an interacting 1D system. We evaluate the dependence of the zero-frequency noise on K and on parameters of both QPCs (transparencies and voltages).     

Multi-user quantum private comparison with scattered preparation and one-way convergent transmission of quantum states

Quantum private comparison (QPC) aims to accomplish the equality comparison of the secrets from different users without disclosing their genuine contents by using the principles of quantum mechanics. In this paper, we summarize eight modes of quantum state preparation and transmission existing in current QPC protocols first. Then, by using the mode of scattered preparation and one-way convergent transmission, we construct a new multi-user quantum private comparison (MQPC) protocol with two-particle maximally entangled states, which can accomplish arbitrary pair’s comparison of equality among K users within one execution. Analysis turns out that its output correctness and its security against both the outside attack and the participant attack are guaranteed. The proposed MQPC protocol can be implemented with current technologies. It can be concluded that the mode of scattered preparation and one-way convergent transmission of quantum states is beneficial to designing the MQPC protocol which can accomplish arbitrary pair’s comparison of equality among K users within one execution.     

Shot noise of a mesoscopic two-particle collider

We investigate the shot noise generated by particle emission from a mesoscopic capacitor into an edge state coupled to another edge state at a quantum point contact (QPC). For a capacitor subject to a periodic voltage the resulting shot noise is proportional to the number of particles (both electrons and holes) emitted during a period. The shot noise is proportional to the driving frequency, however it is independent of the applied voltage. If two capacitors are coupled to a QPC at different sides then the resulting shot noise is maximally the sum of noises produced by each of the capacitors. However, the noise is suppressed if particles of the same kind are emitted simultaneously.     

Counterflow of electrons in two isolated quantum point contacts

We study the interaction between two adjacent but electrically isolated quantum point contacts (QPCs). At high enough source-drain bias on one QPC, the drive QPC, we detect a finite electric current in the second, unbiased, detector QPC. The current generated at the detector QPC always flows in the opposite direction than the current of the drive QPC. The generated current is maximal, if the detector QPC is tuned to a transition region between its quantized conductance plateaus and the drive QPC is almost pinched-off. We interpret this counterflow phenomenon in terms of an asymmetric phonon-induced excitation of electrons in the leads of the detector QPC.     

Integer and fractional quantum Hall effect in a strip of stripes

We study anisotropic stripe models of interacting electrons in the presence of magnetic fields in the quantum Hall regime with integer and fractional filling factors. The model consists of an infinite strip of finite width that contains periodically arranged stripes (forming supercells) to which the electrons are confined and between which they can hop with associated magnetic phases. The interacting electron system within the one-dimensional stripes are described by Luttinger liquids and shown to give rise to charge and spin density waves that lead to periodic structures within the stripe with a reciprocal wavevector 8k _F in a mean field approximation. This wavevector gives rise to Umklapp scattering and resonant scattering that results in gaps and chiral edge states at all known integer and fractional filling factors ν. The integer and odd denominator filling factors arise for a uniform distribution of stripes, whereas the even denominator filling factors arise for a non-uniform stripe distribution. We focus on the ground state of the system, and identify the quantum Hall regime via the quantized Hall conductance. For this we calculate the Hall conductance via the Streda formula and show that it is given by σ _H = νe ²/h for all filling factors. In addition, we show that the composite fermion picture follows directly from the condition of the resonant Umklapp scattering.     

Using a quantum dot as a high-frequency shot noise detector

We present the experimental realization of a quantum dot (QD) operating as a high-frequency noise detector. Current fluctuations produced in a nearby quantum point contact (QPC) ionize the QD and induce transport through excited states. The resulting transient current through the QD represents our detector signal. We investigate its dependence on the QPC transmission and voltage bias. We observe and explain a quantum threshold feature and a saturation in the detector signal. This experimental and theoretical study is relevant in understanding the backaction of a QPC used as a charge detector.     

Effect of Quantum Point Contact Measurement on Electron Spin State in Quantum Dots

We study the time evolution of two electron spin states in a double quantum-dot system, which includes a nearby quantum point contact （QPC） as a measurement device. We find that the QPC measurement induced decoherence is in the microsecond timescale. We also find that the enhanced QPC measurement will trap the system in its initial spin states, which is consistent with the quantum Zeno effect.     

Entangled Bell states of two electrons in coupled quantum dots—phonon decoherence

We demonstrate coupling and entangling of quantum states in a pair of vertically aligned self assembled quantum dots by studying the dynamics of two interacting electrons driven by external electric field. The present entanglement involves the spatial degree of freedom for the two electrons system. We show that system of two interacting electrons initially delocalized (localized each in one dot) oscillate slowly in response to electric field, since the strong Coulomb repulsion makes them behaving so. We use an explicit formula for the entanglement of formation of two qubit in terms of the concurrence of the density operator. In ideal situations, entangled quantum states would not decohere during processing and transmission of quantum information. However, real quantum systems will inevitably be influenced by surrounding environments. We discuss the degree of entanglement of this system in which we introduce the decoherence effect caused by the acoustic phonon. In this entangled states proposal, the decohering time depends on the external parameters.     

Scattering of a Light Particle by a System of Harmonic Oscillators

We discuss the asymptotic wave function of a quantum system in ?³ composed by heavy and light particles, in the case where the light particles are in scattering states and no interaction is assumed among particles of the same kind. We first review a recent result concerning the case of K heavy and N light particles, where the one-particle potential acting on each heavy particle decays at infinity. Then we consider the case of one light particle interacting with a system of harmonic oscillators and prove the same kind of result following, with some modification, the proof of the previous case. A possible application to the analysis of the scattering of a light particle from condensed matter is also outlined.     

Two-Party Quantum Private Comparison Using Single Photons

Quantum private comparison (QPC) aims to determine whether two parties’ private inputs are equal or not without leaking out their genuine contents. At present, there is seldom QPC protocol which uses single photons as quantum resource. In this paper, we are devoted to converting Zhang et al.’s three-party quantum summation (QS) protocol based on single photons (Int. J. Quantum Inf. 15(2), 1750010, 2017) into the corresponding two-party QPC protocol with single photons. The correctness and the security of the proposed QPC protocol with single photons can be guaranteed. The proposed QPC protocol is naturally free from Trojan horse attacks because of its single directional particle transmission mode.     

Instabilities in quantum point contact structures

We discuss the appearance of strong nonlinearities including S-type negative differential conductance in theI–Vcharacteristics of quantum point contact (QPC) structures. Time-dependent measurements demonstrate that the highly nonlinear d.c.I–Vfeatures are associated with a temporal average of random telegraph switching (RTS) between different current levels. The RTS is only observed when the voltage across the device is such that the chemical potential on one side of the QPC is aligned with the bottom of a one-dimensional subband in the QPC. As the chemical potential is moved further into the subband, the switching behavior disappears until the next subband minimum is reached.     

Spin interaction and magnetic field strength effects on the system of two interacting electrons in a 2D quartic confinement potential

In this study we review concepts of double quantum dot, quantum chaos with shifted 1/N expansion method associated with semiquantum nonlinear system. We present a numerical study of two interacting particle motions in a time dependent magnetic field in quartic geometry. It is evident that, the area where the interaction particle motions are stochastic decreases as the spin interaction strength decreases, as well as, the magnetic field strength decreases. Moreover, we describe their possible connections with other aspects of quantum information. Furthermore, we pay attention to a system of two interacting electrons in a two-dimensional quartic confinement potential and hypothesis leading to analytical energy expression. The dynamics of double quantum dot gallium arsenide are of great importance and are also emphasized.     

The quantum acoustomagnetoelectric field in a quantum well with a parabolic potential

The acoustomagnetoelectric (AME) field in a quantum well with a parabolic potential (QWPP) has been studied in the presence of an external magnetic field. The analytic expression for the AME field in the QWPP is obtained by using the quantum kinetic equation for the distribution function of electrons interacting with external phonons. The dependence of the AME field on the temperature T of the system, the wavenumber q of the acoustic wave and external magnetic field B for the specific AlAs/GaAs/AlAs is achieved by using a numerical method. The problem is considered for both cases: The weak magnetic field region and the quantized magnetic field region. The results are compared with those for normal bulk semiconductor and superlattices to show the differences, and we use the quantum theory to calculate the AME field in the QWPP.     

Cyclotron toroidal braids: A cure for portrayal composite fermions on a torus

We present an inspection of the statistics of particles including composite fermions on a torus starting from a braid group analysis. For this purpose we considered a system of electrons confined to the surface of a torus under the influence of a strong magnetic field and interacting through a general rotational invariant potential. An explanation of the appearance of the cyclotron braids as an effect of restriction imposed by magnetic field on braid trajectories which in analyzed case reduces the full braid group to one of its subgroups (i.e. cyclotron subgroups), is given. The modified Feynman path-integral method is also reproduced with some minor enhancements. We improve known results concerning on braid groups on a torus in two directions: we obtain new estimates in terms of cyclotron braid subgroups and cyclotron band generator, respectively; we demonstrate that only multi-loop generators are accessible in the fractional quantum regime well and we also formally explain the unique statistic of composite fermions by construct trial wave function for the system on a torus, based on this idea. The topological oddness of torus geometry can be driven by shifting of electrons between the two different group of generators allowed for an explanation in satisfactory accordance the both compact commensurability condition and some numerical calculations in toroidal geometry. Besides, our approach may shed some new light on few interesting aspects in better understanding the fractional quantum Hall effect.     

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.     

Multi-Party Quantum Private Comparison Protocol with an Almost-Dishonest Third Party using GHZ States

This article proposes an innovative quantum private comparison (QPC) protocol for n users using GHZ states, where an almost-dishonest third party (TP) is introduced to assist the participants for comparing their secrets. It is argued that as compared to the existing QPC protocols our proposed scheme has some considerable advantages. First, in the existing QPC protocols, the TP can only to determine whether all participants’ secrets are equal or not. Instead of that, in our proposed scheme a TP can even compare the secrets between any subsects of users. Second, since our proposed scheme is based on GHZ state; hence it can ensure higher efficiency as compared to other existing multi-party QPC protocols on d-dimension photons.     

Fractional statistics,Hanbury-Brown and Twiss correlations and the quantum Hall effect

The direct detection of the statistics of the quasiparticles in the quantum Hall effect has so far eluded experimental discovery. Here a quantum transport geometry is analyzed, which could provide a link to the fractional statistics via the measurement of low frequency noise correlations. The proposal constitutes an analog of the Hanbury-Brown and Twiss experiment, this time for three chiral edges – one injector edge and two collectors. Luttinger liquid theory reveals that the real time correlator decays much slower than in the case of fermions, and exhibits oscillations with a frequency scale corresponding to the applied bias multiplied by the quasiparticle charge. The zero frequency noise correlations are negative at filling factor 1/3 as for bare electrons (anti-bunching). However they are strongly reduced in amplitude, which constitutes a first evidence of unusual correlations. The noise correlations become positive (suggesting bunching) for ν⩽1/5, however with a much reduced amplitude, when one computes the noise assuming that only the most relevant operators contribute. To cite this article: R. Guyon et al., C. R. Physique 3 (2002) 697–707.     

Ionization of deep quantum wells: Optical trampoline effect

A new mechanism of transitions of an electronic system from the ground state to states with excitation energies exceeding many times the energy of a light photon initiating the transitions has been considered. This mechanism is based on the so-called optical “trampoline” effect: one of the interacting electrons receives energy from another electron and, simultaneously absorbing a photon ?ω, overcomes the energy gap significantly exceeding ?ω. Ionization of deep quantum wells by low-frequency light of moderate intensity due to the optical trampoline effect was calculated.     

Anomalous fluctuations of 2D-electron recombination radiation intensity in the quantum Hall regime

Anomalous intensity fluctuations are observed in the spectrum of radiative ecombination of quasi-two-dimensional (2D) electrons with photoexcited holes in a single quantum well. The fluctuations are observed exclusively under the conditions of the quantum Hall effect (QHE). It is shown that, if the QHE conditions are not fulfilled, the radiation intensity fluctuates strictly following the Poisson distribution 〈δN ²〉/〈N〉= 1), whereas in the QHE regime the fluctuation amplitude increases by several orders of magnitude (〈δ N ²〉/〈N〉～10²). It is demonstrated that the maxima of the emission noise amplitude coincide with the maxima of inverse magnetoresistance of 2D electrons in the QHE regime and correspond to establishing an anomalously high uniformity of the system.     

Spin-polarized transport in adiabatic quantum point contact with strong Rashba spin-orbit interaction

We first report 0.5(2e²/h) conductance quantization in adiabatic quantum point contacts (QPCs) fabricated at high In-content InGaAs/InAlAs single heterojunctions under no magnetic field. This quantization seems difficult to understand, since the spin one-dimensional (1D) subbands in the QPCs are generally degenerated when B=0. However, this observation is reproducible in various QPC samples with different dimensions but not likely so definite as the conductance quantization in usual QPCs. It is noted that this particular heterojunction 2DEG is found to have high electron mobility of <5×10⁵ cm²/Vs as well as very large Rashba spin-orbit (SO) coupling constant of <35×10⁻¹² eVm. So that, the QPCs realized here can be regarded as a kind of Tomonaga-Luttinger wire with an enhanced Rashba interaction. In such a case, a mode coupling between the Rashba splitting 1D subbands gives rise to a spin-polarized transport in each ±k direction. This theory could be the one plausible candidate to explain the 0.5(2e²/h) conductance quantization observed here in the adiabatic QPC. This finding would be developed to novel spin-filters or spin-directional coupler devices based on nonmagnetic semiconductors.