74 research outputs found
Picosecond coherent electron motion in a silicon single-electron source
Understanding ultrafast coherent electron dynamics is necessary for
application of a single-electron source to metrological standards, quantum
information processing, including electron quantum optics, and quantum sensing.
While the dynamics of an electron emitted from the source has been extensively
studied, there is as yet no study of the dynamics inside the source. This is
because the speed of the internal dynamics is typically higher than 100 GHz,
beyond state-of-the-art experimental bandwidth. Here, we theoretically and
experimentally demonstrate that the internal dynamics in a silicon
singleelectron source comprising a dynamic quantum dot can be detected,
utilising a resonant level with which the dynamics is read out as
gate-dependent current oscillations. Our experimental observation and
simulation with realistic parameters show that an electron wave packet
spatially oscillates quantum-coherently at 200 GHz inside the source.
Our results will lead to a protocol for detecting such fast dynamics in a
cavity and offer a means of engineering electron wave packets. This could allow
high-accuracy current sources, high-resolution and high-speed
electromagnetic-field sensing, and high-fidelity initialisation of flying
qubits
Design and fabrication of densely integrated silicon quantum dots using a VLSI compatible hydrogen silsesquioxane electron beam lithography process
Hydrogen silsesquioxane (HSQ) is a high resolution negative-tone electron beam resist allowing for direct transfer of nanostructures into silicon-on-insulator. Using this resist for electron beam lithography, we fabricate high density lithographically defined Silicon double quantum dot (QD) transistors. We show that our approach is compatible with very large scale integration, allowing for parallel fabrication of up to 144 scalable devices. HSQ process optimisation allowed for realisation of reproducible QD dimensions of 50 nm and tunnel junction down to 25 nm. We observed that 80% of the fabricated devices had dimensional variations of less than 5 nm. These are the smallest high density double QD transistors achieved to date. Single electron simulations combined with preliminary electrical characterisations justify the reliability of our device and process
A ferrofluid micropump for lab-on-a-chip applications
A disposable micropump is presented that uses the piston actuation principle and relies on the magnetic properties of a ferrofluid, a colloidal suspension of nanosize ferromagnetic particles. The cost effective micropump consists of 7 bonded layers of polymethylmetacrylate (PMMA) that are either micromachined or structured by powder blasting. Two silicone check-valves are also integrated in the microchip. External dimensions of our prototype are 36 mm x 22 mm x 5 mm. The magnetic liquid plug is externally actuated by a motorized permanent magnet. Water has been successfully pumped at a flow rate of 30 µL/min without backpressure; pumping is demonstrated up to a backpressure of 25 mbar
Giga-Hertz quantized charge pumping in bottom gate defined InAs nanowire quantum dots
Semiconducting nanowires (NWs) are a versatile, highly tunable material
platform at the heart of many new developments in nanoscale and quantum
physics. Here, we demonstrate charge pumping, i.e., the controlled transport of
individual electrons through an InAs NW quantum dot (QD) device at frequencies
up to GHz. The QD is induced electrostatically in the NW by a series of
local bottom gates in a state of the art device geometry. A periodic modulation
of a single gate is enough to obtain a dc current proportional to the frequency
of the modulation. The dc bias, the modulation amplitude and the gate voltages
on the local gates can be used to control the number of charges conveyed per
cycle. Charge pumping in InAs NWs is relevant not only in metrology as a
current standard, but also opens up the opportunity to investigate a variety of
exotic states of matter, e.g. Majorana modes, by single electron spectroscopy
and correlation experiments.Comment: 21 page
Pumping of mammalian cells with a nozzle-diffuser micropump
We discuss the successful transport of jurkat cells and 5D10 hybridoma cells using a reciprocating micropump with nozzle-diffuser elements. The effect of the pumping action on cell viability and proliferation, as well as on the damaging of cellular membranes is quantified using four types of well-established biological tests: a trypan blue solution, the tetrazolium salt WST-1 reagent, the LDH cytotoxicity assay and the calcium imaging ATP test. The high viability levels obtained after pumping, even for the most sensitive cells (5D10), indicate that a micropump with nozzle-diffuser elements can be very appropriate for handling living cells in cell-on-a-chip applications
Dispersively detected Pauli Spin-Blockade in a Silicon Nanowire Field-Effect Transistor
We report the dispersive readout of the spin state of a double quantum dot
formed at the corner states of a silicon nanowire field-effect transistor. Two
face-to-face top-gate electrodes allow us to independently tune the charge
occupation of the quantum dot system down to the few-electron limit. We measure
the charge stability of the double quantum dot in DC transport as well as
dispersively via in-situ gate-based radio frequency reflectometry, where one
top-gate electrode is connected to a resonator. The latter removes the need for
external charge sensors in quantum computing architectures and provides a
compact way to readout the dispersive shift caused by changes in the quantum
capacitance during interdot charge transitions. Here, we observe Pauli
spin-blockade in the high-frequency response of the circuit at finite magnetic
fields between singlet and triplet states. The blockade is lifted at higher
magnetic fields when intra-dot triplet states become the ground state
configuration. A lineshape analysis of the dispersive phase shift reveals
furthermore an intradot valley-orbit splitting of 145 eV.
Our results open up the possibility to operate compact CMOS technology as a
singlet-triplet qubit and make split-gate silicon nanowire architectures an
ideal candidate for the study of spin dynamics
Gigahertz quantized charge pumping in graphene quantum dots
Single electron pumps are set to revolutionize electrical metrology by
enabling the ampere to be re-defined in terms of the elementary charge of an
electron. Pumps based on lithographically-fixed tunnel barriers in mesoscopic
metallic systems and normal/superconducting hybrid turnstiles can reach very
small error rates, but only at MHz pumping speeds corresponding to small
currents of the order 1 pA. Tunable barrier pumps in semiconductor structures
have been operated at GHz frequencies, but the theoretical treatment of the
error rate is more complex and only approximate predictions are available.
Here, we present a monolithic, fixed barrier single electron pump made entirely
from graphene. We demonstrate pump operation at frequencies up to 1.4 GHz, and
predict the error rate to be as low as 0.01 parts per million at 90 MHz.
Combined with the record-high accuracy of the quantum Hall effect and proximity
induced Josephson junctions, accurate quantized current generation brings an
all-graphene closure of the quantum metrological triangle within reach.
Envisaged applications for graphene charge pumps outside quantum metrology
include single photon generation via electron-hole recombination in
electrostatically doped bilayer graphene reservoirs, and for readout of
spin-based graphene qubits in quantum information processing.Comment: 13 pages, 11 figures, includes supplementary informatio
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