1,334 research outputs found
Direct measurement of the hole-nuclear spin interaction in single quantum dots
We use photoluminescence spectroscopy of ''bright'' and ''dark'' exciton
states in single InP/GaInP quantum dots to measure hyperfine interaction of the
valence band hole with nuclear spins polarized along the sample growth axis.
The ratio of the hyperfine constants for the hole (C) and electron (A) is found
to be C/A~-0.11. In InP dots the contribution of spin 1/2 phosphorus nuclei to
the hole-nuclear interaction is weak, which enables us to determine
experimentally the value of C for spin 9/2 indium nuclei as C_In~-5 micro-eV.
This high value of C is in good agreement with recent theoretical predictions
and suggests that the hole-nuclear spin interaction has to be taken into
account when considering spin qubits based on holes.Comment: to be submitted to Phys Rev Let
Unilateral cleft lip repair: Technical maneuvers to achieve vermilion and mucosal height
Patients with unilateral cleft lip often require secondary procedures due to asymmetric fullness or deficiencies along the mucosal free margin of the upper lip. Here, we describe our technique for mucosal advancement and repair to attain symmetry.
Methods: Maneuvers to obtain vermilion and mucosal height include (1) use of a tailored vermilion flap; (2) supraperiosteal release of the lesser segment; (3) backcut poker incision to mobilize the mucosal flap on the lesser segment; (4) transverse release of mucosa across the greater segment; (5) accurate reduction along vermilion-mucosal junction; and (6) bilateral medial mucosal advancement. To examine postoperative outcomes, photographic data were available for 14 patients with unilateral complete cleft lip. The Cleft Lip Component Symmetry Index was then calculated as a ratio of upper lip height on cleft to noncleft sides, where an index of 1 indicates symmetry.
Results: Sixteen consecutive patients underwent unilateral cleft lip repair with this technique over a 3-year period, none of whom have required secondary operations. The symmetry index for 14 of 16 patients was 1.02 ± 0.11 (95% confidence interval [0.96, 1.08],
Conclusions: Postoperative asymmetry after unilateral cleft lip repair, particularly along the free margin, continues to be a common problem, necessitating secondary procedures. The technique of mucosal repair merits more careful attention than it has previously received, and here we describe in detail a method that has allowed for improved symmetry
Overhauser effect in individual InP/GaInP dots
Sizable nuclear spin polarization is pumped in individual InP/GaInP dots in a
wide range of external magnetic fields B_ext=0-5T by circularly polarized
optical excitation. We observe nuclear polarization of up to ~40% at Bext=1.5T
and corresponding to an Overhauser field of ~1.2T. We find a strong feedback of
the nuclear spin on the spin pumping efficiency. This feedback, produced by the
Overhauser field, leads to nuclear spin bi-stability at low magnetic fields of
Bext=0.5-1.5T. We find that the exciton Zeeman energy increases markedly, when
the Overhauser field cancels the external field. This counter-intuitive result
is shown to arise from the opposite contribution of the electron and hole
Zeeman splittings to the total exciton Zeeman energy
Pumping of nuclear spins by the optical solid effect in a quantum dot
We demonstrate that efficient optical pumping of nuclear spins in
semiconductor quantum dots (QDs) can be achieved by resonant pumping of
optically "forbidden" transitions. This process corresponds to one-to-one
conversion of a photon absorbed by the dot into a polarized nuclear spin, which
also has potential for initialization of hole spin in QDs. Pumping via the
"forbidden" transition is a manifestation of the "optical solid effect", an
optical analogue of the effect previously observed in electron spin resonance
experiments in the solid state. We find that by employing this effect, nuclear
polarization of 65% can be achieved, the highest reported so far in optical
orientation studies in QDs. The efficiency of the spin pumping exceeds that
employing the allowed transition, which saturates due to the low probability of
electron-nuclear spin flip-flop.Comment: 5 pages, 3 figures, submitted to Phys. Rev. Let
Overhauser effect in individual InP/GaInP dots
Sizable nuclear spin polarization is pumped in individual InP/GaInP dots in a
wide range of external magnetic fields B_ext=0-5T by circularly polarized
optical excitation. We observe nuclear polarization of up to ~40% at Bext=1.5T
and corresponding to an Overhauser field of ~1.2T. We find a strong feedback of
the nuclear spin on the spin pumping efficiency. This feedback, produced by the
Overhauser field, leads to nuclear spin bi-stability at low magnetic fields of
Bext=0.5-1.5T. We find that the exciton Zeeman energy increases markedly, when
the Overhauser field cancels the external field. This counter-intuitive result
is shown to arise from the opposite contribution of the electron and hole
Zeeman splittings to the total exciton Zeeman energy
Barbiturate and picrotoxin-sensitive chloride efflux in rat cerebral cortical synaptoneurosomes
AbstractThe effects of various barbiturates and picrotoxin in modifying the efflux of chloride (36Cl−) was studied in a novel subcellular preparation from rat cerebral cortex, the ‘synaptoneurosome’. Dilution of synaptoneurosomes pre-loaded with 36Cl− resulted in rapid efflux of 36Cl− that could be measured as early as 10 s following dilution. In the presence of barbiturates such as pentobarbital and hexobarbital there was a significant increase in 36Cl− efflux which was not observed with the pharmacologically-inactive barbiturate, barbital. The effect of barbiturates in enhancing 36Cl− efflux was also stereospecific [(−)-DMBB > (+)-DMBB] and reversed by picrotoxin. By contrast, picrotoxin alone significantly inhibited 36Cl− efflux. These data demonstrate pharmacologically relevant Cl− transport for the first time in a subcellular brain preparation
On-chip electrically controlled routing of photons from a single quantum dot
Electrical control of on-chip routing of photons emitted by a single InAs/GaAs self-assembled quantum dot (SAQD) is demonstrated in a photonic crystal cavity-waveguide system. The SAQD is located inside an H1 cavity, which is coupled to two photonic crystal waveguides. The SAQD emission wavelength is electrically tunable by the quantum-confined Stark effect. When the SAQD emission is brought into resonance with one of two H1 cavity modes, it is preferentially routed to the waveguide to which that mode is selectively coupled. This proof of concept provides the basis for scalable, low-power, high-speed operation of single-photon routers for use in integrated quantum photonic circuits
Fast optical preparation, control, and readout of a single quantum dot spin
We propose and demonstrate the sequential initialization, optical control, and readout of a single spin trapped in a semiconductor quantum dot. Hole spin preparation is achieved through ionization of a resonantly excited electron-hole pair. Optical control is observed as a coherent Rabi rotation between the hole and charged-exciton states, which is conditional on the initial hole spin state. The spin-selective creation of the charged exciton provides a photocurrent readout of the hole spin state. © 2008 The American Physical Society
The new physics of non-equilibrium condensates: insights from classical dynamics
We discuss the dynamics of classical Dicke-type models, aiming to clarify the
mechanisms by which coherent states could develop in potentially
non-equilibrium systems such as semiconductor microcavities. We present
simulations of an undamped model which show spontaneous coherent states with
persistent oscillations in the magnitude of the order parameter. These states
are generalisations of superradiant ringing to the case of inhomogeneous
broadening. They correspond to the persistent gap oscillations proposed in
fermionic atomic condensates, and arise from a variety of initial conditions.
We show that introducing randomness into the couplings can suppress the
oscillations, leading to a limiting dynamics with a time-independent order
parameter. This demonstrates that non-equilibrium generalisations of polariton
condensates can be created even without dissipation. We explain the dynamical
origins of the coherence in terms of instabilities of the normal state, and
consider how it can additionally develop through scattering and dissipation.Comment: 10 pages, 4 figures, submitted for a special issue of J. Phys.:
Condensed Matter on "Optical coherence and collective phenomena in
nanostructures". v2: added discussion of links to exact solution
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