A5071523080- Quantum and electron transport phenomena
- Advanced Electrical Measurement Techniques
- Atomic and Subatomic Physics Research
- Semiconductor materials and devices
- Quantum Information and Cryptography
- Electronic and Structural Properties of Oxides
- Scientific Measurement and Uncertainty Evaluation
- Advancements in Semiconductor Devices and Circuit Design
- Semiconductor Quantum Structures and Devices
- Superconducting and THz Device Technology
- Surface and Thin Film Phenomena
- Electrochemical Analysis and Applications
- Non-Destructive Testing Techniques
- Analytical Chemistry and Sensors
- Mechanical and Optical Resonators
- Terahertz technology and applications
- Electrical and Bioimpedance Tomography
- Advanced Thermodynamics and Statistical Mechanics
- Advanced Sensor Technologies Research
- Molecular Junctions and Nanostructures
- Quantum Computing Algorithms and Architecture
- Analog and Mixed-Signal Circuit Design
- Sensor Technology and Measurement Systems
- Thermal Radiation and Cooling Technologies
- Magnetic Field Sensors Techniques
National Physical Laboratory
2013-2024
Middlesex University
2018
Royal Holloway University of London
2006
We demonstrate the transmission of single electron wavepackets from a clock-controlled source through an empty high-energy edge channel. The quantum dot is loaded with electrons which are then emitted high kinetic energy ($\sim$150 meV). find at magnetic field that these can be transported over several microns without inelastic electron-electron or electron-phonon scattering. Using time-resolved spectroscopic technique, we measure and wavepacket size picosecond time scales. also show how our...
High-speed and high-accuracy pumping of a single electron is crucial for realizing an accurate current source, which promising candidate quantum standard. Here, using measurement system traceable to primary standards, we evaluate the accuracy Si tunable-barrier single-electron pump driven by sinusoidal signal. The operates at frequencies up 6.5 GHz, producing more than 1 nA. At plateau with level about 160 pA found be better 0.92 ppm (parts per million), record value 1-GHz operation. 2...
We report the observation of nonadiabatic excitations single electrons in a quantum dot. Using tunable-barrier single-electron pump, we have developed way reading out excitation spectrum and level population dot by using pump current as probe. When potential well is deformed at subnanosecond time scales, are excited to higher levels. In presence perpendicular magnetic field, states follow Fock-Darwin spectrum. Our experiments provide simple model system study processes particles.
Using standard microfabrication techniques it is now possible to construct devices, which appear reliably manipulate electrons one at a time. These devices have potential use as building blocks in quantum computing or of electrical current derived only from frequency and the fundamental charge. To date error rate semiconductor 'tuneable-barrier' pump those show most promise for high operation, not been tested detail. We present accuracy measurements an etched GaAs dot pump, operated zero...
We study the effect of perpendicular magnetic fields on a single-electron system with strongly time-dependent electrostatic potential. Continuous improvements to current quantization in these electron pumps are revealed by high-resolution measurements. Simulations show that sensitivity tunnel rates barrier potential is enhanced, stabilizing particular charge states. Nonadiabatic excitations also suppressed due reduced Fock-Darwin states The combination effects leads significantly more...
We present a detailed report of microwave irradiation ultranarrow superconducting nanowires. In our nanofabricated circuits containing NbSi nanowire, dc blockade current flow was observed at low temperatures below critical voltage ${V}_{\mathrm{c}}$, strong indicator the existence quantum phase-slip (QPS) in nanowire. describe results applying microwaves to these samples, using range frequencies and both continuous-wave pulsed drive, order search for dual Shapiro steps which would constitute...
We performed a precision measurement of the current from single-parameter electron pump, where potential-profile for quantum dot was manipulated by multiple top-metal gates. In an optimally tuned condition, driven with sinusoidal-waveform microwave at f = 0.95 GHz, B 11 T, and T 0.3 K, relative deviation pump ef, δIp/ef ≡ (Ip − ef)/ef measured to be (−0.92 ± 1.37) ppm. Our experiment reproduces quantisation accuracy previous but in device fabricated using very different geometry, thereby...
Abstract A gigahertz single-electron (SE) pump with a semiconductor charge island is promising for future quantum current standard. However, high-accuracy in the nanoampere regime still difficult to achieve because performance of SE pumps tends degrade significantly at frequencies exceeding 1 GHz. Here, we demonstrate robust pumping via single-trap level silicon up 7.4 GHz, which exceeds nA. An accuracy test an uncertainty about one part per million (ppm) reveals that deviates from ideal...
An interlaboratory comparison of small-current generation and measurement capability is presented with the ultrastable low-noise current amplifier (ULCA) acting as travelling standard. Various measurements at direct currents between 0.16 nA 13 were performed to verify degree agreement three national metrology institutes involved in study. Consistency well within one part per million (ppm) was found. Due harsh environmental conditions during shipment, ULCA's transfer accuracy had been limited...
A silicon electron pump operating at the temperature of liquid helium has demonstrated repeatable operation with sub-ppm accuracy. The current, approximately 168 pA, is measured by three laboratories, and measurements agree expected current ef within uncertainties which range from 0.2 ppm to 1.3 ppm. All are carried out in zero applied magnetic field, drive signal a sine wave. combination simple conditions high accuracy demonstrates possibility that an can operate as standard National...
A well-characterised sample of silicon tunable-barrier electron pump has been operated at a frequency 2 GHz using custom drive waveform, generating current 320 pA. Precision measurements the were made as function control parameters, blind protocol, over 7-week campaign. The combined standard uncertainty for each 10 hour measurement was 0.1 parts per million. exhibits plateau along exit gate voltage flat to approximately million, but offset from ef by 0.2 This may be sign errors in...
We present an experimental study of a large quantum dot (QD) capacitively coupled to aluminum single electron transistor (SET) and irradiated with terahertz radiation from blackbody source. The SET is used as noninvasive electrometer sensitive single-charge fluctuation on the QD. Qualitatively different regimes QD confinement have been identified response. demonstrate that state nearly isolated can potentially be for counting individual photons.
Single-electron pumps based on quantum dots (QDs) with tunable barriers are promising candidates for the emerging standard of electrical current, but accuracy at elevated reservoir temperatures can be challenging. In this study, a planar silicon QD achieves accurate, high-speed single-electron pumping in thermal regime, where temperature could rise to few kelvin. This device operates without demanding conditions previous experiments, indicating that it deliver cost-effective and easily...
We demonstrate the robust operation of a gallium arsenide tunable-barrier single-electron pump operating with 1 part-per-million accuracy at temperature 1.3 K and pumping frequency 500 MHz. The current quantisation is investigated as function multiple control parameters, plateaus are seen three gate voltages RF drive power. electron capture found to be in decay-cascade, rather than thermally-broadened regime. observation an elevated which does not require expensive refrigeration important...
We review recent precision measurements on semiconductor tunable-barrier electron pumps operating in a ratchet mode. Seven studies five different designs of have reported the pump current with relative total uncertainties around $10^{-6}$ or less. Combined theoretical models capture by pumps, these experimental data exhibits encouraging evidence that operate according to universal mechanism, independent details device design. Evidence for robustness against changes control parameters is at...
This paper describes two systems recently developed at the National Physical Laboratory (NPL), Teddington, U.K., for generation and measurement of dc currents in range 100 fA to 1 nA. Both are based on capacitor charging technique. One system generates known currents, constitutes a new reference NPL. The other was designed meet traceability requirements Ionizing Radiation sections NPL combines commercially available instrumentation standards produce reliable stand-alone measuring small
We measure the frequency dependence of a sample commercial air- and gas-dielectric capacitors between 1 kHz ≈0.01 Hz. find that capacitance sealed-gas can change by more than 100 μF/F over this range. This has important implications for use gas in reference sub-nA current generators.
A new four terminal-pair bridge has been developed and used for traceable measurement of capacitance resistance at frequencies up to 1 MHz. The apparent a gas-filled 100-pF standard agrees with calculated values better than 200 /spl mu/F/F This is an order magnitude improvement on existing capabilities NPL. frequency dependence the dissipation factor standards discussed, ceramic NPO-dielectric also measured. measurements calculable coaxial 100-/spl Omega/ 1-k/spl are presented.
We measure the rectified dc currents resulting when a 3-terminal semiconductor device with gate-dependent conductance is driven an ac gate voltage. The exhibit surprisingly complex behaviour as source-drain bias voltage, voltage and amplitude of are varied. obtain good agreement between our data model based on simple assumptions about stray impedances sample chip, over wide frequency range. This method applicable to many types experiment which involve gating non-linear device, where...
A project funded by the European Commission which started in 1998 has been completed. The aim of this was to establish a measurement system that allows calibration standard capacitors terms R/sub K-90/. whole comprises quantum Hall samples, an automated modular bridge system, and devices calibrate characterize set-up. uncertainty for 10-pF capacitor is about one part 10/sup 7/.
The dynamic capture of electrons in a semiconductor quantum dot (QD) by raising potential barrier is crucial stage metrological quantized charge pumping. In this work, we use point contact (QPC) sensor to study errors the electron process QD formed GaAs heterostructure. Using two-step measurement protocol compensate for 1/f noise QPC current, and repeating more than 106 times, are able resolve with probabilities order 10−6. For studied sample, one-electron affected ∼30 out every million...