934 research outputs found
Polarization-preserving confocal microscope for optical experiments in a dilution refrigerator with high magnetic field
We present the design and operation of a fiber-based cryogenic confocal
microscope. It is designed as a compact cold-finger that fits inside the bore
of a superconducting magnet, and which is a modular unit that can be easily
swapped between use in a dilution refrigerator and other cryostats. We aimed at
application in quantum optical experiments with electron spins in
semiconductors and the design has been optimized for driving with, and
detection of optical fields with well-defined polarizations. This was
implemented with optical access via a polarization maintaining fiber together
with Voigt geometry at the cold finger, which circumvents Faraday rotations in
the optical components in high magnetic fields. Our unit is versatile for use
in experiments that measure photoluminescence, reflection, or transmission, as
we demonstrate with a quantum optical experiment with an ensemble of
donor-bound electrons in a thin GaAs film.Comment: 9 pages, 7 figure
Compact cryogenic Kerr microscope for time-resolved studies of electron spin transport in microstructures
A compact cryogenic Kerr microscope for operation in the small volume of
high-field magnets is described. It is suited for measurements both in Voigt
and Faraday configuration. Coupled with a pulsed laser source, the microscope
is used to measure the time-resolved Kerr rotation response of semiconductor
microstructures with ~1 micron spatial resolution. The microscope was designed
to study spin transport, a critical issue in the field of spintronics. It is
thus possible to generate spin polarization at a given location on a
microstructure and probe it at a different location. The operation of the
microscope is demonstrated by time-resolved measurements of micrometer distance
diffusion of spin polarized electrons in a GaAs/AlGaAs heterojunction quantum
well at 4.2 K and 7 Tesla
Electromagnetically Induced Transparency with an Ensemble of Donor-Bound Electron Spins in a Semiconductor
We present measurements of electromagnetically induced transparency with an
ensemble of donor- bound electrons in low-doped n-GaAs. We used optical
transitions from the Zeeman-split electron spin states to a bound trion state
in samples with optical densities of 0.3 and 1.0. The electron spin dephasing
time T* \approx 2 ns was limited by hyperfine coupling to fluctuating nuclear
spins. We also observe signatures of dynamical nuclear polarization, but find
these effects to be much weaker than in experiments that use electron spin
resonance and related experiments with quantum dots.Comment: 4 pages, 4 figures; Improved analysis of data in Fig. 3, corrected
factors of 2 and p
Suppressed spin dephasing for 2D and bulk electrons in GaAs wires due to engineered cancellation of spin-orbit interaction terms
We report a study of suppressed spin dephasing for quasi-one-dimensional
electron ensembles in wires etched into a GaAs/AlGaAs heterojunction system.
Time-resolved Kerr-rotation measurements show a suppression that is most
pronounced for wires along the [110] crystal direction. This is the fingerprint
of a suppression that is enhanced due to a strong anisotropy in spin-orbit
fields that can occur when the Rashba and Dresselhaus contributions are
engineered to cancel each other. A surprising observation is that this
mechanisms for suppressing spin dephasing is not only effective for electrons
in the heterojunction quantum well, but also for electrons in a deeper bulk
layer.Comment: 5 pages, 3 figure
Entanglement between charge qubits induced by a common dissipative environment
We study entanglement generation between two charge qubits due to the strong
coupling with a common bosonic environment (Ohmic bath). The coupling to the
boson bath is a source of both quantum noise (leading to decoherence) and an
indirect interaction between qubits. As a result, two effects compete as a
function of the coupling strength with the bath: entanglement generation and
charge localization induced by the bath. These two competing effects lead to a
non-monotonic behavior of the concurrence as a function of the coupling
strength with the bath. As an application, we present results for charge qubits
based on double quantum dots.Comment: 9 pages, 7 figure
An Easy-to-Use Prognostic Model for Survival Estimation for Patients with Symptomatic Long Bone Metastases
BACKGROUND: A survival estimation for patients with symptomatic long bone metastases (LBM) is crucial to prevent overtreatment and undertreatment. This study analyzed prognostic factors for overall survival and developed a simple, easy-to-use prognostic model. METHODS: A multicenter retrospective study of 1,520 patients treated for symptomatic LBM between 2000 and 2013 at the radiation therapy and/or orthopaedic departments was performed. Primary tumors were categorized into 3 clinical profiles (favorable, moderate, or unfavorable) according to an existing classification system. Associations between prognostic variables and overall survival were investigated using the Kaplan-Meier method and multivariate Cox regression models. The discriminatory ability of the developed model was assessed with the Harrell C-statistic. The observed and expected survival for each survival category were compared on the basis of an external cohort. RESULTS: Median overall survival was 7.4 months (95% confidence interval [CI], 6.7 to 8.1 months). On the basis of the independent prognostic factors, namely the clinical profile, Karnofsky Performance Score, and presence of visceral and/or brain metastases, 12 prognostic categories were created. The Harrell C-statistic was 0.70. A flowchart was developed to easily stratify patients. Using cutoff points for clinical decision-making, the 12 categories were narrowed down to 4 categories with clinical consequences. Median survival was 21.9 months (95% CI, 18.7 to 25.1 months), 10.5 months (95% CI, 7.9 to 13.1 months), 4.6 months (95% CI, 3.9 to 5.3 months), and 2.2 months (95% CI, 1.8 to 2.6 months) for the 4 categories. CONCLUSIONS: This study presents a model to easily stratify patients with symptomatic LBM according to their expected survival. The simplicity and clarity of the model facilitate and encourage its use in the routine care of patients with LBM, to provide the most appropriate treatment for each individual patient. LEVEL OF EVIDENCE: Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence
Optical probing of spin dynamics of two-dimensional and bulk electrons in a GaAs/AlGaAs heterojunction system
We present time-resolved Kerr rotation measurements of electron spin dynamics
in a GaAs/AlGaAs heterojunction system that contains a high-mobility
two-dimensional electron gas (2DEG). Due to the complex layer structure of this
material the Kerr rotation signals contain information from electron spins in
three different layers: the 2DEG layer, a GaAs epilayer in the heterostructure,
and the underlying GaAs substrate. The 2DEG electrons can be observed at low
pump intensities, using that they have a less negative g-factor than electrons
in bulk GaAs regions. At high pump intensities, the Kerr signals from the GaAs
epilayer and the substrate can be distinguished when using a barrier between
the two layers that blocks intermixing of the two electron populations. This
allows for stronger pumping of the epilayer, which results in a shift of the
effective g-factor. Thus, three populations can be distinguished using
differences in g-factor. We support this interpretation by studying how the
spin dynamics of each population has its unique dependence on temperature, and
how they correlate with time-resolved reflectance signals.Comment: 14 pages, 7 figure
Cross-Cultural Adaptation, Translation, and Validation of the Toronto Extremity Salvage Score for Extremity Bone and Soft Tissue Tumor Patients in Netherlands
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