342 research outputs found
Remote capacitive sensing in two-dimension quantum-dot arrays
We investigate gate-defined quantum dots in silicon on insulator nanowire
field-effect transistors fabricated using a foundry-compatible fully-depleted
silicon-on-insulator (FD-SOI) process. A series of split gates wrapped over the
silicon nanowire naturally produces a bilinear array of quantum
dots along a single nanowire. We begin by studying the capacitive coupling of
quantum dots within such a 22 array, and then show how such couplings
can be extended across two parallel silicon nanowires coupled together by
shared, electrically isolated, 'floating' electrodes. With one quantum dot
operating as a single-electron-box sensor, the floating gate serves to enhance
the charge sensitivity range, enabling it to detect charge state transitions in
a separate silicon nanowire. By comparing measurements from multiple devices we
illustrate the impact of the floating gate by quantifying both the charge
sensitivity decay as a function of dot-sensor separation and configuration
within the dual-nanowire structure.Comment: 9 pages, 3 figures, 35 cites and supplementar
Pauli spin blockade in CMOS double quantum dot devices
Silicon quantum dots are attractive candidates for the development of
scalable, spin-based qubits. Pauli spin blockade in double quantum dots
provides an efficient, temperature independent mechanism for qubit readout.
Here we report on transport experiments in double gate nanowire transistors
issued from a CMOS process on 300 mm silicon-on-insulator wafers. At low
temperature the devices behave as two few-electron quantum dots in series. We
observe signatures of Pauli spin blockade with a singlet-triplet splitting
ranging from 0.3 to 1.3 meV. Magneto-transport measurements show that
transitions which conserve spin are shown to be magnetic-field independent up
to B = 6 T.Comment: 5 pages , 4 figure
Programming the assembly of carboxylic acid-functionalised hybrid polyoxometalates
We report here the straightforward synthesis and characterisation of a series Anderson-type hybrid
polyoxometalates in high yield, functionalised with carboxylic acid following the reaction of anhydride
precursors with the starting hybrid cluster ([n-N(C4H9)4]3[MnMo6O18((OCH2)3CNH2)2]). Seven new
structures have been obtained, five of which have acid-terminated ligands. Six of these structures have
been isolated with a yield higher than 80% with high purity. This reaction is limited by the bulkiness of the
anhydride used; this effect can be employed to selectively synthesise one isomer out of three other
possibilities. The acid groups and aromatic platforms attached to the clusters can act as building tools to
bridge several length scales and engineer molecular packing within the crystal structure. The presence of
acids should also change the hydrophilicity of the clusters, and therefore the way they interact with
hydrophilic surfaces. We also show a potential relationship between the acid group interaction in the
packing diagram and the cluster’s tendency to interact with a hydrophilic surface. In addition to reporting
a derived synthetic path to new acid-terminated Mn-Anderson-type hybrids, we describe here a new way
to program self-assembly motifs of these compounds in the crystal structure and at interfaces
A CMOS silicon spin qubit
Silicon, the main constituent of microprocessor chips, is emerging as a
promising material for the realization of future quantum processors. Leveraging
its well-established complementary metal-oxide-semiconductor (CMOS) technology
would be a clear asset to the development of scalable quantum computing
architectures and to their co-integration with classical control hardware. Here
we report a silicon quantum bit (qubit) device made with an industry-standard
fabrication process. The device consists of a two-gate, p-type transistor with
an undoped channel. At low temperature, the first gate defines a quantum dot
(QD) encoding a hole spin qubit, the second one a QD used for the qubit
readout. All electrical, two-axis control of the spin qubit is achieved by
applying a phase-tunable microwave modulation to the first gate. Our result
opens a viable path to qubit up-scaling through a readily exploitable CMOS
platform.Comment: 12 pages, 4 figure
Remote Capacitive Sensing in Two-Dimensional Quantum-Dot Arrays
We investigate gate-induced quantum dots in silicon nanowire field-effect transistors fabricated using a foundry-compatible fully depleted silicon-on-insulator (FD-SOI) process. A series of split gates wrapped over the silicon nanowire naturally produces a 2 × n bilinear array of quantum dots along a single nanowire. We begin by studying the capacitive coupling of quantum dots within such a 2 × 2 array and then show how such couplings can be extended across two parallel silicon nanowires coupled together by shared, electrically isolated, “floating” electrodes. With one quantum dot operating as a single-electron-box sensor, the floating gate serves to enhance the charge sensitivity range, enabling it to detect charge state transitions in a separate silicon nanowire. By comparing measurements from multiple devices, we illustrate the impact of the floating gate by quantifying both the charge sensitivity decay as a function of dot-sensor separation and configuration within the dual-nanowire structure
Rapid assessment of injection practices in Cambodia, 2002
BACKGROUND: Injection overuse and unsafe injection practices facilitate transmission of bloodborne pathogens such as hepatitis B virus (HBV), hepatitis C virus (HCV), and human immunodeficiency virus (HIV). Anecdotal reports of unsafe and unnecessary therapeutic injections and the high prevalence of HBV (8.0%), HCV (6.5%), and HIV (2.6%) infection in Cambodia have raised concern over injection safety. To estimate the magnitude and patterns of such practices, a rapid assessment of injection practices was conducted. METHODS: We surveyed a random sample of the general population in Takeo Province and convenience samples of prescribers and injection providers in Takeo Province and Phnom Penh city regarding injection-related knowledge, attitudes, and practices. Injection providers were observed administering injections. Data were collected using standardized methods adapted from the World Health Organization safe injection assessment guidelines. RESULTS: Among the general population sample (n = 500), the overall injection rate was 5.9 injections per person-year, with 40% of participants reporting receipt of ≥ 1 injection during the previous 6 months. Therapeutic injections, intravenous infusions, and immunizations accounted for 74%, 16% and 10% of injections, respectively. The majority (>85%) of injections were received in the private sector. All participants who recalled their last injection reported the injection was administered with a newly opened disposable syringe and needle. Prescribers (n = 60) reported that 47% of the total prescriptions they wrote included a therapeutic injection or infusion. Among injection providers (n = 60), 58% recapped the syringe after use and 13% did not dispose of the used needle and syringe appropriately. Over half (53%) of the providers reported a needlestick injury during the previous 12 months. Ninety percent of prescribers and injection providers were aware HBV, HCV, and HIV were transmitted through unsafe injection practices. Knowledge of HIV transmission through "dirty" syringes among the general population was also high (95%). CONCLUSION: Our data suggest that Cambodia has one of the world's highest rates of overall injection usage, despite general awareness of associated infection risks. Although there was little evidence of reuse of needles and syringes, support is needed for interventions to address injection overuse, healthcare worker safety and appropriate waste disposal
Spin readout of a CMOS quantum dot by gate reflectometry and spin-dependent tunnelling
Silicon spin qubits are promising candidates for realising large scale quantum processors, benefitting from a magnetically quiet host material and the prospects of leveraging the mature silicon device fabrication industry. We report the measurement of an electron spin in a singly-occupied gate-defined quantum dot, fabricated using CMOS compatible processes at the 300 mm wafer scale. For readout, we employ spin-dependent tunneling combined with a low-footprint single-lead quantum dot charge sensor, measured using radiofrequency gate reflectometry. We demonstrate spin readout in two devices using this technique, obtaining valley splittings in the range 0.5-0.7 meV using excited state spectroscopy, and measure a maximum electron spin relaxation time () of s at 1 Tesla. These long lifetimes indicate the silicon nanowire geometry and fabrication processes employed here show a great deal of promise for qubit devices, while the spin-readout method demonstrated here is well-suited to a variety of scalable architectures
A quantum dot-based frequency multiplier
Silicon offers the enticing opportunity to integrate hybrid quantum-classical
computing systems on a single platform. For qubit control and readout,
high-frequency signals are required. Therefore, devices that can facilitate its
generation are needed. Here, we present a quantum dot-based radiofrequency
multiplier operated at cryogenic temperatures. The device is based on the
non-linear capacitance-voltage characteristics of quantum dot systems arising
from their low-dimensional density of states. We implement the multiplier in a
multi-gate silicon nanowire transistor using two complementary device
configurations: a single quantum dot coupled to a charge reservoir and a
coupled double quantum dot. We study the harmonic voltage conversion as a
function of energy detuning, multiplication factor and harmonic phase noise and
find near ideal performance up to a multiplication factor of 10. Our results
demonstrate a method for high-frequency conversion that could be readily
integrated into silicon-based quantum computing systems and be applied to other
semiconductors.Comment: 17 pages, 16 figure
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