68 research outputs found
Magnetic moment of an electron gas on the surface of constant negative curvature
The magnetic moment of an electron gas on the surface of constant negative
curvature is investigated. It is shown that the surface curvature leads to the
appearance of the region of the monotonic dependence at low magnetic
fields. At high magnetic fields, the dependence of the magnetic moment on a
magnetic field is the oscillating one. The effect of the surface curvature is
to increase the region of the monotonic dependence of the magnetic moment and
to break the periodicity of oscillations of the magnetic moment as a function
of an inverse magnetic field.Comment: 4 pages, 1 figur
Observation of extremely slow hole spin relaxation in self-assembled quantum dots
We report the measurement of extremely slow hole spin relaxation dynamics in
small ensembles of self-assembled InGaAs quantum dots. Individual spin
orientated holes are optically created in the lowest orbital state of each dot
and read out after a defined storage time using spin memory devices. The
resulting luminescence signal exhibits a pronounced polarization memory effect
that vanishes for long storage times. The hole spin relaxation dynamics are
measured as a function of external magnetic field and lattice temperature. We
show that hole spin relaxation can occur over remarkably long timescales in
strongly confined quantum dots (up to ~270 us), as predicted by recent theory.
Our findings are supported by calculations that reproduce both the observed
magnetic field and temperature dependencies. The results suggest that hole spin
relaxation in strongly confined quantum dots is due to spin orbit mediated
phonon scattering between Zeeman levels, in marked contrast to higher
dimensional nanostructures where it is limited by valence band mixing.Comment: Published by Physical Review
Coupling curvature to a uniform magnetic field; an analytic and numerical study
The Schrodinger equation for an electron near an azimuthally symmetric curved
surface in the presence of an arbitrary uniform magnetic field
is developed. A thin layer quantization procedure is implemented to
bring the electron onto , leading to the well known geometric potential
and a second potential that couples , the component of
normal to to mean surface curvature, as well as a term
dependent on the normal derivative of
evaluated on . Numerical results in the form of ground state
energies as a function of the applied field in several orientations are
presented for a toroidal model.Comment: 12 pages, 3 figure
Real Time Electron Tunneling and Pulse Spectroscopy in Carbon Nanotube Quantum Dots
We investigate a Quantum Dot (QD) in a Carbon Nanotube (CNT) in the regime
where the QD is nearly isolated from the leads. An aluminum single electron
transistor (SET) serves as a charge detector for the QD. We precisely measure
and tune the tunnel rates into the QD in the range between 1 kHz and 1 Hz,
using both pulse spectroscopy and real - time charge detection and measure the
excitation spectrum of the isolated QD.Comment: 12 pages, 5 figure
Spin decoherence of a heavy hole coupled to nuclear spins in a quantum dot
We theoretically study the interaction of a heavy hole with nuclear spins in
a quasi-two-dimensional III-V semiconductor quantum dot and the resulting
dephasing of heavy-hole spin states. It has frequently been stated in the
literature that heavy holes have a negligible interaction with nuclear spins.
We show that this is not the case. In contrast, the interaction can be rather
strong and will be the dominant source of decoherence in some cases. We also
show that for unstrained quantum dots the form of the interaction is
Ising-like, resulting in unique and interesting decoherence properties, which
might provide a crucial advantage to using dot-confined hole spins for quantum
information processing, as compared to electron spins
Gallstone ileus in a middle-aged male with an atypical history: a case report
Currently, gallstone ileus is an unusual complication of cholelithiasis (0.3–3.0 %) and a rare cause of mechanical bowel obstruction (0.1–4.0 %). The rarity of the condition makes it impossible to plan the large prospective randomized clinical trials, so the analysis of case reports is significant for decision making in the management of gallstone ileus. We report a case of gallstone ileus in a middle-aged male who had a history of surgery for duodenal ulcer perforation in past. A combination of peptic ulcer disease and cholelithiasis is based on a reduced gastrointestinal hormones secretion. Clinical specialists need to consider information about the greater frequency and asymptomatic clinical course of gallstone disease against a background of duodenal ulcer. Duodenal ulcer scar and bulbar deformity may promote to the cholecystoduodenal fistula formation. In the presence of an acute bowel obstruction symptoms and the absence of gallbladder instrumental examination results, it is possible to recommend the prior gastroduodenoscopy for the pre-operative pneumobilia detection. The optimal surgical approaches for acute gallstone ileus are still controversial
Tunable few-electron double quantum dots and Klein tunnelling in ultra-clean carbon nanotubes
Quantum dots defined in carbon nanotubes are a platform for both basic
scientific studies and research into new device applications. In particular,
they have unique properties that make them attractive for studying the coherent
properties of single electron spins. To perform such experiments it is
necessary to confine a single electron in a quantum dot with highly tunable
barriers, but disorder has until now prevented tunable nanotube-based
quantum-dot devices from reaching the single-electron regime. Here, we use
local gate voltages applied to an ultra-clean suspended nanotube to confine a
single electron in both a single quantum dot and, for the first time, in a
tunable double quantum dot. This tunability is limited by a novel type of
tunnelling that is analogous to that in the Klein paradox of relativistic
quantum mechanics.Comment: 21 pages including supplementary informatio
Double quantum dot with integrated charge sensor based on Ge/Si heterostructure nanowires
Coupled electron spins in semiconductor double quantum dots hold promise as
the basis for solid-state qubits. To date, most experiments have used III-V
materials, in which coherence is limited by hyperfine interactions. Ge/Si
heterostructure nanowires seem ideally suited to overcome this limitation: the
predominance of spin-zero nuclei suppresses the hyperfine interaction and
chemical synthesis creates a clean and defect-free system with highly
controllable properties. Here we present a top gate-defined double quantum dot
based on Ge/Si heterostructure nanowires with fully tunable coupling between
the dots and to the leads. We also demonstrate a novel approach to charge
sensing in a one-dimensional nanostructure by capacitively coupling the double
dot to a single dot on an adjacent nanowire. The double quantum dot and
integrated charge sensor serve as an essential building block required to form
a solid-state spin qubit free of nuclear spin.Comment: Related work at http://marcuslab.harvard.edu and
http://cmliris.harvard.ed
Electrical control over single hole spins in nanowire quantum dots
Single electron spins in semiconductor quantum dots (QDs) are a versatile
platform for quantum information processing, however controlling decoherence
remains a considerable challenge. Recently, hole spins have emerged as a
promising alternative. Holes in III-V semiconductors have unique properties,
such as strong spin-orbit interaction and weak coupling to nuclear spins, and
therefore have potential for enhanced spin control and longer coherence times.
Weaker hyperfine interaction has already been reported in self-assembled
quantum dots using quantum optics techniques. However, challenging fabrication
has so far kept the promise of hole-spin-based electronic devices out of reach
in conventional III-V heterostructures. Here, we report gate-tuneable hole
quantum dots formed in InSb nanowires. Using these devices we demonstrate Pauli
spin blockade and electrical control of single hole spins. The devices are
fully tuneable between hole and electron QDs, enabling direct comparison
between the hyperfine interaction strengths, g-factors and spin blockade
anisotropies in the two regimes
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