5,684 research outputs found
Functional renormalization group approach to the singlet-triplet transition in quantum dots
We present a functional renormalization group approach to the zero bias
transport properties of a quantum dot with two different orbitals and in
presence of Hund's coupling. Tuning the energy separation of the orbital
states, the quantum dot can be driven through a singlet-triplet transition. Our
approach, based on the approach by Karrasch {\em et al} which we apply to
spin-dependent interactions, recovers the key characteristics of the quantum
dot transport properties with very little numerical effort. We present results
on the conductance in the vicinity of the transition and compare our results
both with previous numerical renormalization group results and with predictions
of the perturbative renormalization group.Comment: 15 pages, 9 figure
Spin-orbit coupled cold exciton condensates
We analyze theoretically the dynamics of degenerate condensate of cold
indirect excitons. We account for both linear spin dependent terms arising from
spin-orbit interaction of Rashba and Dresselhaus types and non-linear terms
transforming a pair of bright excitons into a pair of dark ones. We show that
both terms should lead to the qualitative changes in the dynamics of cold
exciton droplets in the real space and time.Comment: 14 pages, 7 figure
Density-matrix approach for an interacting polariton system
Using the Lindblad approach we develop a general formalism for theoretical
description of a spatially inhomogeneous bosonic system with dissipation
provided by the interaction of bosons with a phonon bath. We apply our results
to model the dynamics of an interacting one-dimensional polariton system in
real space and time, analyzing in detail the role of polariton-polariton and
polariton-phonon interactions.Comment: 7 pages + 3 figures. arXiv admin note: text overlap with
arXiv:1103.1336 by other author
Bistability phenomena in one-dimensional polariton wires
We investigate the phenomena of bistability and domain wall propagation in
polaritonic systems with dissipation provided by the interaction with
incoherent phonon bath. The results on the temperature dependence of the
polariton bistability behavior and polariton neuron switching are presented.Comment: 6 pages + 4 figures. Continuation of the work published in Phys. Rev.
B 83, 165316 (2011
Phonon-mediated Josephson oscillations in excitonic and polaritonic condensates
We analyze theoretically the role of the exciton-phonon interactions in
phenomena related to the Josephson effect between two spatially separated
exciton and exciton-polariton condensates. We consider the role of the
dephasing introduced by phonons in such phenomena as Josephson tunneling,
self-trapping and spontaneous polarization separation. In the regime of cw
pumping we find a remarkable bistability effect arising from exciton- exciton
interactions as well as regimes of self- sustained regular and chaotic
oscillations.Comment: 10 pages, Submitted to Phys. Rev.
Enkel resipientundersøkelse i Oslofjorden ved Alnas munning for å belyse eventuelle skader forårsaket av utslipp av akrylamid fra Romeriksporten
Det ble ikke påvist akrylamid i vann og sedimenter i Alnaelvas munning eller sjøområdet utenfor. I selve munningen var bunnen død. Også Oslofjorden utenfor var kraftig forurensningspåvirket, men med en viss bedring i faunatilstanden med økende avstand fra Alnas munning. Dette kan tyde på at de samlede forurensninger fra Alna spiller en meget betydelig rolle for den dårlige tilstanden. Uavhengig av akrylamidutslippene var det imidlertid forventet å finne en meget dårlig faunatilstand i dette fra før av sterkt forurensede området. Om akrylamidutslippene har bidratt til å ytterligere utarme den allerede svært forurensningspregede faunaen innerst i indre Oslofjorden, er ikke mulig å fastslå ved hjelp av den enkle undersøkelsen som her er foretatt. Den observerte tilstand var omtrent som forventet, tatt i betraktning den fra før av sterke forurensningen i området og tidligere beskrivelser av faunatilstanden. Det var ingen ting som spesifikt tydet på at akrylamidforurensning hadde bidratt til en ytterligere forverring
Unsupervised quantum machine learning for fraud detection
We develop quantum protocols for anomaly detection and apply them to the task
of credit card fraud detection (FD). First, we establish classical benchmarks
based on supervised and unsupervised machine learning methods, where average
precision is chosen as a robust metric for detecting anomalous data. We focus
on kernel-based approaches for ease of direct comparison, basing our
unsupervised modelling on one-class support vector machines (OC-SVM). Next, we
employ quantum kernels of different type for performing anomaly detection, and
observe that quantum FD can challenge equivalent classical protocols at
increasing number of features (equal to the number of qubits for data
embedding). Performing simulations with registers up to 20 qubits, we find that
quantum kernels with re-uploading demonstrate better average precision, with
the advantage increasing with system size. Specifically, at 20 qubits we reach
the quantum-classical separation of average precision being equal to 15%. We
discuss the prospects of fraud detection with near- and mid-term quantum
hardware, and describe possible future improvements.Comment: 7 pages, 4 figure
Clustering of vacancy defects in high-purity semi-insulating SiC
Positron lifetime spectroscopy was used to study native vacancy defects in
semi-insulating silicon carbide. The material is shown to contain (i) vacancy
clusters consisting of 4--5 missing atoms and (ii) Si vacancy related
negatively charged defects. The total open volume bound to the clusters
anticorrelates with the electrical resistivity both in as-grown and annealed
material. Our results suggest that Si vacancy related complexes compensate
electrically the as-grown material, but migrate to increase the size of the
clusters during annealing, leading to loss of resistivity.Comment: 8 pages, 5 figure
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