2,114 research outputs found
Towards visualisation of central-cell-effects in scanning-tunnelling-microscope images of subsurface dopant qubits in silicon
Atomic-scale understanding of phosphorous donor wave functions underpins the
design and optimisation of silicon based quantum devices. The accuracy of
large-scale theoretical methods to compute donor wave functions is dependent on
descriptions of central-cell-corrections, which are empirically fitted to match
experimental binding energies, or other quantities associated with the global
properties of the wave function. Direct approaches to understanding such
effects in donor wave functions are of great interest. Here, we apply a
comprehensive atomistic theoretical framework to compute scanning tunnelling
microscopy (STM) images of subsurface donor wave functions with two
central-cell-correction formalisms previously employed in the literature. The
comparison between central-cell models based on real-space image features and
the Fourier transform profiles indicate that the central-cell effects are
visible in the simulated STM images up to ten monolayers below the silicon
surface. Our study motivates a future experimental investigation of the
central-cell effects via STM imaging technique with potential of fine tuning
theoretical models, which could play a vital role in the design of donor-based
quantum systems in scalable quantum computer architectures.Comment: Nanoscale 201
ISM gas studies towards the TeV PWN HESS J1825-137 and northern region
HESS J1825-137 is a pulsar wind nebula (PWN) whose TeV emission extends
across ~1 deg. Its large asymmetric shape indicates that its progenitor
supernova interacted with a molecular cloud located in the north of the PWN as
detected by previous CO Galactic survey (e.g Lemiere, Terrier &
Djannati-Ata\"i 2006). Here we provide a detailed picture of the ISM towards
the region north of HESS J1825-137, with the analysis of the dense molecular
gas from our 7mm and 12mm Mopra survey and the more diffuse molecular gas from
the Nanten CO(1-0) and GRS CO(1-0) surveys. Our focus is the possible
association between HESS J1825-137 and the unidentified TeV source to the
north, HESS J1826-130. We report several dense molecular regions whose
kinematic distance matched the dispersion measured distance of the pulsar.
Among them, the dense molecular gas located at (RA,
Dec)=(18.421h,-13.282) shows enhanced turbulence and we suggest that
the velocity structure in this region may be explained by a cloud-cloud
collision scenario. Furthermore, the presence of a H rim may be the
first evidence of the progenitor SNR of the pulsar PSR J1826-1334 as the
distance between the H rim and the TeV source matched with the
predicted SNR radius R~120 pc. From our ISM study, we identify a
few plausible origins of the HESS J1826-130 emission, including the progenitor
SNR of PSR J1826-1334 and the PWN G018.5-0.4 powered by PSR J1826-1256. A
deeper TeV study however, is required to fully identify the origin of this
mysterious TeV source.Comment: 19 figures, 27 pages, accepted by MNRA
Optical alignment and polarization conversion of neutral exciton spin in individual InAs/GaAs quantum dots
We investigate exciton spin memory in individual InAs/GaAs self-assembled
quantum dots via optical alignment and conversion of exciton polarization in a
magnetic field. Quasiresonant phonon-assisted excitation is successfully
employed to define the initial spin polarization of neutral excitons. The
conservation of the linear polarization generated along the bright exciton
eigenaxes of up to 90% and the conversion from circular- to linear polarization
of up to 47% both demonstrate a very long spin relaxation time with respect to
the radiative lifetime. Results are quantitatively compared with a model of
pseudo-spin 1/2 including heavy-to-light hole mixing.Comment: 5 pages, 3 figure
Curve classes on irreducible holomorphic symplectic varieties
We prove that the integral Hodge conjecture holds for 1-cycles on irreducible
holomorphic symplectic varieties of K3 type and of Generalized Kummer type. As
an application, we give a new proof of the integral Hodge conjecture for cubic
fourfolds.Comment: 15 page
Optical properties of potential-inserted quantum wells in the near infrared and Terahertz ranges
We propose an engineering of the optical properties of GaAs/AlGaAs quantum
wells using AlAs and InAs monolayer insertions. A quantitative study of the
effects of the monolayer position and the well thickness on the interband and
intersubband transitions, based on the extended-basis sp3d5s* tight-binding
model, is presented. The effect of insertion on the interband transitions is
compared with existing experimental data. As for intersubband transitions, we
show that in a GaAs/AlGaAs quantum well including two AlAs and one InAs
insertions, a three level {e1 , e2 , e3 } system where the transition energy
e3-e2 is lower and the transition energy e2-e1 larger than the longitudinal
optical phonon energy (36 meV) can be engineered together with a e3-e2
transition energy widely tunable through the TeraHertz range
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