Single-shot Charge Research Articles

Research on blasting vibration prediction based on BFO-LSSVM and its engineering application

In order to realize the accurate prediction of blasting vibration, the LS-SVM optimization model based on BFO algorithm is constructed with the help of bacterial foraging algorithm (BFO) and least squares support vector machine (LS-SVM) theory. 30 groups of blasting data are used as training samples to test the prediction accuracy of the model, and the main factors affecting the propagation of blasting vibration are selected as the input factors, such as single shot charge, blasting center distance, elevation difference, blockage, hole depth and other factors as the input factors, and blasting vibration as the output factor of the prediction model. The results show that the prediction accuracy of BFO-LSSVM model is higher than that of LS-SVM model under the same sample size. Taking the measured vibration data of excavation blasting of Wuqiangxi power station as an example, the average error of BFO-LSSVM model is 5.57%, which verifies the feasibility and practicability of the prediction model.

Probing Charge Dynamics in Diamond with an Individual Color Center.

Control over the charge states of color centers in solids is necessary to fully utilize them in quantum technologies. However, the microscopic charge dynamics of deep defects in wide-band-gap semiconductors are complex, and much remains unknown. We utilize a single-shot charge-state readout of an individual nitrogen-vacancy (NV) center to probe the charge dynamics of the surrounding defects in diamond. We show that the NV center charge state can be converted through the capture of holes produced by optical illumination of defects many micrometers away. With this method, we study the optical charge conversion of silicon-vacancy (SiV) centers and provide evidence that the dark state of the SiV center under optical illumination is SiV2-. These measurements illustrate that charge carrier generation, transport, and capture are important considerations in the design and implementation of quantum devices with color centers and provide a novel way to probe and control charge dynamics in diamond.

A High-Sensitivity Charge Sensor for Silicon Qubits above 1 K.

Recent studies of silicon spin qubits at temperatures above 1 K are encouraging demonstrations that the cooling requirements for solid-state quantum computing can be considerably relaxed. However, qubit readout mechanisms that rely on charge sensing with a single-island single-electron transistor (SISET) quickly lose sensitivity due to thermal broadening of the electron distribution in the reservoirs. Here we exploit the tunneling between two quantized states in a double-island single-electron transistor (SET) to demonstrate a charge sensor with an improvement in the signal-to-noise ratio by an order of magnitude compared to a standard SISET, and a single-shot charge readout fidelity above 99% up to 8 K at a bandwidth greater than 100 kHz. These improvements are consistent with our theoretical modeling of the temperature-dependent current transport for both types of SETs. With minor additional hardware overhead, these sensors can be integrated into existing qubit architectures for a high-fidelity charge readout at few-kelvin temperatures.

Fast Charge Sensing of Si/SiGe Quantum Dots via a High-Frequency Accumulation Gate.

Quantum dot arrays are a versatile platform for the implementation of spin qubits, as high-bandwidth sensor dots can be integrated with single-, double-, and triple-dot qubits yielding fast and high-fidelity qubit readout. However, for undoped silicon devices, reflectometry off sensor ohmics suffers from the finite resistivity of the two-dimensional electron gas (2DEG), and alternative readout methods are limited to measuring qubit capacitance, rather than qubit charge. By coupling a surface-mount resonant circuit to the plunger gate of a high-impedance sensor, we realized a fast charge sensing technique that is compatible with resistive 2DEGs. We demonstrate this by acquiring at high speed charge stability diagrams of double- and triple-dot arrays in Si/SiGe heterostructures as well as pulsed-gate single-shot charge and spin readout with integration times as low as 2.4 μs.

Spin-Blockade Spectroscopy of Si / Si - Ge Quantum Dots

We implement a technique for measuring the singlet-triplet energy splitting responsible for spin-to-charge conversion in semiconductor quantum dots. This method, which requires fast, single-shot charge measurement, reliably extracts an energy in the limits of both large and small splittings. We perform this technique on an undoped, accumulation-mode Si/SiGe triple-quantum dot and find that the measured splitting varies smoothly as a function of confinement gate biases. Not only does this demonstration prove the value of having an $in~situ$ excited-state measurement technique as part of a standard tune-up procedure, it also suggests that in typical Si/SiGe quantum dot devices, spin-blockade can be limited by lateral orbital excitation energy rather than valley splitting.

Elimination of X-Ray Diffraction through Stimulated X-Ray Transmission.

X-ray diffractive imaging with laterally coherent x-ray free-electron laser (XFEL) pulses is increasingly utilized to obtain ultrafast snapshots of matter. Here we report the amazing disappearance of single-shot charge and magnetic diffraction patterns recorded with resonantly tuned, narrow bandwidth XFEL pulses. Our experimental results reveal the exquisite sensitivity of single-shot charge and magnetic diffraction patterns of a magnetic film to the onset of field-induced stimulated elastic x-ray forward scattering. The loss in diffraction contrast, measured over 3 orders of magnitude in intensity, is in remarkable quantitative agreement with a recent theory that is extended to include diffraction.

Photo-induced ionization dynamics of the nitrogen vacancy defect in diamond investigated by single-shot charge state detection

The nitrogen–vacancy centre (NV) has drawn much attention for over a decade, yet detailed knowledge of the photophysics needs to be established. Under typical conditions, the NV can have two stable charge states, negative (NV−) or neutral (NV0), with photo-induced interconversion of these two states. Here, we present detailed studies of the ionization dynamics of single NV centres in bulk diamond at room temperature during illumination and its dependence on the excitation wavelength and power. We apply a recent method which allows us to directly measure the charge state of a single NV centre, and observe its temporal evolution. We find that the steady-state NV− population is always ⩽75% for 450–610 nm excitation wavelength. In combination with saturation measurements, we show that the optimal excitation wavelength is around 510–540 nm. Furthermore, the relative absorption cross-section of NV− is determined for 540–610 nm, revealing a double-peak structure. Finally, the energy of the NV− ground state of 2.6 eV below the conduction band is measured. These results reveal new insights into the charge state dynamics of the NV centre.

Relaxation and readout visibility of a singlet-triplet qubit in an Overhauser field gradient

Using single-shot charge detection in a GaAs double quantum dot, we investigate spin relaxation time T_1 and readout visibility of a two-electron singlet-triplet qubit following single-electron dynamic nuclear polarization (DNP). For magnetic fields up to 2 T, the DNP cycle is in all cases found to increase Overhauser field gradients, which in turn decrease T_1 and consequently reduce readout visibility. This effect was previously attributed to a suppression of singlet-triplet dephasing under a similar DNP cycle. A model describing relaxation after singlet-triplet mixing agrees well with experiment. Effects of pulse bandwidth on visibility are also investigated.

Single shot charge detection using a radio-frequency quantum point contact

We report on charge sensing measurements of a GaAs semiconductor quantum dot device using a radio frequency quantum point contact (rf-QPC). The rf-QPC is fully characterized at 4K and millikelvin temperatures and found to have a bandwidth exceeding 20MHz. For single shot charge sensing, we achieve a charge sensitivity of ∼2×10−4e∕Hz referred to the neighboring dot’s charge. The rf-QPC compares favorably with rf single electron transistor electrometers and promises to be an extremely useful tool for characterizing and measuring semiconductor quantum systems on fast time scales.

Single-shot charge qubit read-out using a single electron transistor: back-action and fidelity

We analyze the fidelity of single shot read-out of a superconducting charge qubit (Cooper pair box) using a capacitively coupled radio-frequency single electron transistor (RF-SET). By comparing the time needed to separate the two qubit states with the time after which the initial state of the qubit is destroyed, due to back-action from the SET, we find that a signal to noise ratio substantially larger than unity is obtainable. To evaluate the back-action at the relevant frequencies, which are comparable to the tunneling rates in the SET, we use a fully quantum mechanical expression for the voltage fluctuations on the SET island.

Single shot charge analyzer for laser-produced plasma studies

The theory and design of a single shot charge analyzer is described which is capable of separating a multispecies ion beam from an instantaneous point source of plasma, such as laser-produced plasma, into several single species ion beams. A time-dependent deflection in planar geometry is employed which continuously steers each ion beam into a separate Faraday cup. Two important processes, space charge spreading of the ion beams and charge exchange with background gas in the chamber, that may alter the performance of the analyzer, are studied in detail. The charge state distribution of a laser-produced plasma obtained by this device is compared to that obtained by a 45° electrostatic analyzer using multiple laser shots.