Detection of moving charge in free space is presented in the framework of single electron CMOS devices. It opens the perspective for construction of new type detectors for beam diagnostic in accelerators or for the detection of solar wind. General phenomenological model of noise acting on position based qubit implemented in semiconductor quantum dots is given in the framework of simplistic tight-binding model. Furthermore the effect of accelerator beam on the system of 2 electrostatically coupled qubits is formulated by tight-binding equations. The position based qubits of various topologies are described as quantum detectors of moving electric charge.
Keywords: tight-binding model, position-based qubit, non-invasive quantum measurement, quantum decoherence of qubit system, accelerator beam diagnostics, electrostatic noise, phase rotating gate, roton position-based qubit
Recent advances in bottom-up growth are giving rise to a range of new two-dimensional nanostructures. Hall effect measurements play an important role in their electrical characterization. However, size constraints can lead to device geometries that deviate significantly from the ideal of elongated Hall bars with currentless contacts. Many devices using these new materials have a low aspect ratio and feature metal Hall probes that overlap with the semiconductor channel. This can lead to a significant distortion of the current flow. We present experimental data from InAs 2D nanofin devices with …
Transport studies of Andreev bound states (ABSs) are complicated by the interplay of charging effects and superconductivity. Here, we compare transport approaches to ABS spectroscopy in a semiconductor-superconductor island to a charge-sensing approach based on an integrated radio-frequency single-electron transistor. Consistency of the methods demonstrates that fast, non-invasive charge sensing allows accurate quantitative measurement of ABSs while eluding some complexities of transport.
Coupled quantum dots are potential candidates for qubit systems in quantum computing. We use a non-invasive voltage probe to study the evolution of a coupled dot system from a situation where the dots are coupled to the leads to a situation where they are isolated from the leads. Our measurements allow us to identify the movement of electrons between the dots and we can also identify the presence of a charge trap in our system by detecting the movement of electrons between the dots and the charge trap. The data also reveals evidence of electrons moving between the dots via excited states of ei…
We have studied interactions between two capacitively coupled GaAs/AlGaAs few-electron double quantum dots. Each double quantum dot defines a tunable two-level system, or qubit, in which a single excess electron occupies either the ground state of one dot or the other. Applying microwave radiation we resonantly drive transitions between states and non-invasively measure occupancy changes using proximal quantum point contact charge detectors. The level structure of the interacting two-qubit system is probed by driving it at a fixed microwave frequency whilst varying the energy detuning of both …
Typical measurements of nanowire devices rely on end-to-end measurements to reveal mesoscopic phenomena such as quantized conductance or Coulomb blockade. However, creating nanoscale tunnel junctions allows one to directly measure other properties such as the density of states or electronic energy distribution functions. In this paper, we demonstrate how to realize uniform tunnel junctions on InSb nanowires, where the low invasiveness preserves ballistic transport in the nanowires. The utility of the tunnel junctions is demonstrated via measurements using a superconducting tunneling probe, whi…
State readout is a key requirement for a quantum computer. For semiconductor-based qubit devices it is usually accomplished using a separate mesoscopic electrometer. Here we demonstrate a simple detection scheme in which a radio-frequency resonant circuit coupled to a semiconductor double quantum dot is used to probe its charge and spin states. These results demonstrate a new non-invasive technique for measuring charge and spin states in quantum dot systems without requiring a separate mesoscopic detector.
We study quantum coherence in a semiconductor charge qubit formed from a GaAs double quantum dot containing a single electron. Voltage pulses are applied to depletion gates to drive qubit rotations and non-invasive state readout is achieved using a quantum point contact charge detector. We measure a maximum coherence time of ~7 ns at the charge degeneracy point, where the qubit level splitting is first-order-insensitive to gate voltage fluctuations. We compare measurements of the coherence time as a function of detuning with predictions from a 1/f noise model.
The Schrodinger equation for a particle moving in a square well potential with BenDaniel - Duke boundary conditions is solved. Using algebraic approximations for trigonometric functions, the transcendental equations of the bound states energy are transformed into tractable, algebraic equations. For the ground state and the first excited state, they are cubic equations; we obtain simple formulas for their physically interesting roots. The case of higher excited states is also analyzed. Our results have direct applications in the physics of type I and type II semiconductor heterostructures.
The hyperfine coupling between the spin of a charge carrier and the nuclear spin bath is a predominant channel for the carrier spin relaxation in many organic semiconductors. We theoretically investigate the hyperfine-induced spin relaxation of a carrier performing a random walk on a d-dimensional regular lattice, in a transport regime typical for organic semiconductors. We show that in d=1 and d=2 the time dependence of the space-integrated spin polarization, P(t), is dominated by a superexponential decay, crossing over to a stretched exponential tail at long times. The faster decay is attrib…
Solid-state systems which mimic two-level atoms are being actively developed. Improving the quantum coherence of these systems, for instance spin qubits or single photon emitters using semiconductor quantum dots, involves dealing with noise. The sources of noise are inherent to the semiconductor and are complex. Charge noise results in a fluctuating electric field, spin noise in a fluctuating magnetic field at the location of the qubit, and both can lead to dephasing and decoherence of optical and spin states. We investigate noise in an ultra-pure semiconductor using a minimally-invasive, ultr…
We report on the time-resolved detection of the anomalous velocity, constituting charge carriers moving perpendicular to an electric driving field, in undoped GaAs quantum wells. For this we optically excite the quantum wells with circularly polarized femtosecond laser pulses, thereby creating a state which breaks time-inversion symmetry. We then employ a quasi single cycle terahertz pulse as electric driving field to induce the anomalous velocity. The electromagnetic radiation emitted from the anomalous velocity is studied with a sub-picosecond time resolution and reveals intriguing results. …
Berry phase in semiconductor quantum dots (QDs) can be induced by moving the dots adiabatically in a closed loop with the application of the distortion potential in the lateral direction. We show that the Berry phase is highly sensitive to the electric fields arising from the interplay between the Rashba and the Dresselhaus spin-orbit couplings. We report that the accumulated Berry phase can be induced from other available quantum state that are only differed by one quantum number of the same spin state. The sign change in the g-factor due to the penetration of the Bloch wavefunctions into the…
A model for charge transport in undoped, photo-excited semiconductor superlattices, which includes the dependence of the electron-hole recombination on the electric field and on the photo-excitation intensity through the field-dependent recombination coefficient, is proposed and analyzed. Under dc voltage bias and high photo-excitation intensities, there appear self-sustained oscillations of the current due to a repeated homogeneous nucleation of a number of charge dipole waves inside the superlattice. In contrast to the case of a constant recombination coefficient, nucleated dipole waves can …
The ability to convert spin accumulation to charge currents is essential for applications in spintronics. In semiconductors, spin-to-charge conversion is typically achieved using the inverse spin Hall effect or using a large magnetic field. Here we demonstrate a general method that exploits the non-linear interactions between spin and charge currents to perform all-electrical, rapid and non-invasive detection of spin accumulation without the need for a magnetic field. We demonstrate the operation of this technique with ballistic GaAs holes as a model system with strong spin-orbit coupling, in …
Direct Spatiotemporal Imaging of Charge Carrier Dynamics in Operative Semiconductor Devices
CNR IMM, Institute for Microelectronics and Microsystems（意大利国家研究委员会微电子与微系统研究所）；Institute of Physics, Charles University（查理大学物理研究所）；CNR NANOTEC, Institute of Nanotechnology（意大利国家研究委员会纳米技术研究所）
We report absorption and photoluminescence spectra of Si and SnO$_2$ polycrystalline nanofilms in the UV-Vis-NIR range, featuring discrete bands resulting from transverse quantum confinement. The film thickness ranged 3.9 nm to 12.2 nm, depending on the material. The results are interpreted within the particle-in-a-box model, with the box width equal to the layer mass thickness. The energy levels and transitions scale as the inverse square of the film thickness. The calculated values of the effective electron mass are independent on the film thickness and equal to 0.17m$_o$ (Si) and 0.21m$_o$ …
The efficient control of a large number of qubits is one of most challenging aspects for practical quantum computing. Current approaches in solid-state quantum technology are based on brute-force methods, where each and every qubit requires at least one unique control line, an approach that will become unsustainable when scaling to the required millions of qubits. Here, inspired by random access architectures in classical electronics, we introduce the shared control of semiconductor quantum dots to efficiently operate a two-dimensional crossbar array in planar germanium. We tune the entire arr…
Ultrafast Electron Microscopy of Nanoscale Charge Dynamics in Semiconductors
Technion - Israel Institute of Technology（以色列理工学院）；École Polytechnique Fédérale de Lausanne（洛桑联邦理工学院）；University of Geneva（日内瓦大学）；ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology（ICFO-光子科学研究所，巴塞罗那科学技术研究院）；University of Milano-Bicocca（米兰比可卡大学）；Massachusetts Institute of Technology（麻省理工学院）
In the surface acoustic wave quantum computer, the spin state of an electron trapped in a moving quantum dot comprises the physical qubit of the scheme. Via detailed analytic and numerical modeling of the qubit dynamics, we discuss the effect of excitations into higher-energy orbital states of the quantum dot that occur when the qubits pass through magnetic fields. We describe how single-qubit quantum operations, such as single-qubit rotations and single-qubit measurements, can be performed using only localized static magnetic fields. The models provide useful parameter regimes to be explored …
I've been building Powerpoint-based quantum computers with electron spins in silicon for 20 years. Unfortunately, real-life-based quantum dot quantum computers are harder to implement. Materials, fabrication, and control challenges still impede progress. The way to accelerate discovery is to make and measure more qubits. Here I discuss separating the qubit realization and testing circuitry from the materials science and on-chip fabrication that will ultimately be necessary. This approach should allow us, in the shorter term, to characterize wafers non-invasively for their qubit-relevant proper…
