2,956 research outputs found
Nongalvanic thermometry for ultracold two-dimensional electron domains
Measuring the temperature of a two-dimensional electron gas at temperatures
of a few mK is a challenging issue, which standard thermometry schemes may fail
to tackle. We propose and analyze a nongalvanic thermometer, based on a quantum
point contact and quantum dot, which delivers virtually no power to the
electron system to be measured.Comment: 5 pages, 3 figure
The Kondo Effect in the Unitary Limit
We observe a strong Kondo effect in a semiconductor quantum dot when a small
magnetic field is applied. The Coulomb blockade for electron tunneling is
overcome completely by the Kondo effect and the conductance reaches the
unitary-limit value. We compare the experimental Kondo temperature with the
theoretical predictions for the spin-1/2 Anderson impurity model. Excellent
agreement is found throughout the Kondo regime. Phase coherence is preserved
when a Kondo quantum dot is included in one of the arms of an Aharonov-Bohm
ring structure and the phase behavior differs from previous results on a
non-Kondo dot.Comment: 10 page
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
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
Single-electron tunneling in InP nanowires
We report on the fabrication and electrical characterization of field-effect
devices based on wire-shaped InP crystals grown from Au catalyst particles by a
vapor-liquid-solid process. Our InP wires are n-type doped with diameters in
the 40-55 nm range and lengths of several microns. After being deposited on an
oxidized Si substrate, wires are contacted individually via e-beam fabricated
Ti/Al electrodes. We obtain contact resistances as low as ~10 kOhm, with minor
temperature dependence. The distance between the electrodes varies between 0.2
and 2 micron. The electron density in the wires is changed with a back gate.
Low-temperature transport measurements show Coulomb-blockade behavior with
single-electron charging energies of ~1 meV. We also demonstrate energy
quantization resulting from the confinement in the wire.Comment: 4 pages, 3 figure
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