Non-linear exciton spin-splitting in single InAs/GaAs self-assembled quantum structures in ultrahigh magnetic fields

We report on the magnetic field dispersion of the exciton spin-splitting and diamagnetic shift in single InAs/GaAs quantum dots (QDs) and dot molecules (QDMs) up to $B$ = 28 T. Only for systems with strong geometric confinement, the dispersions can be well described by simple field dependencies, while for dots with weaker confinement considerable deviations are observed: most importantly, in the high field limit the spin-splitting shows a non-linear dependence on $B$, clearly indicating light hole admixtures to the valence band ground state

Interpreting myocardial perfusion scintigraphy using single-photon emission computed tomography. Part 1

This article discusses the protocol for myocardial perfusion scintigraphy performed with single-photon emission computed tomography (SPECT). Indications for SPECT are listed with consideration given to the results of the increasingly more common angio-CT examinations of the coronary arteries (multislice computed tomography). The paper also presents basic information about interpreting the results, including the scores of left ventricle myocardial perfusion using the 17-segment polar map, and explains the concept of total perfusion deficit

THz ultra-strong light-matter coupling up to 200K with continuously-graded parabolic quantum wells

Continuously graded parabolic quantum wells with excellent optical performances are used to overcome the low-frequency and thermal limitations of square quantum wells at terahertz frequencies. The formation of microcavity intersubband polaritons at frequencies as low as 1.8 THz is demonstrated, with a sustained ultra-strong coupling regime up to a temperature of 200K. It is additionally shown that the ultra-strong coupling regime is preserved when the active region is embedded in sub-wavelength resonators, with an estimated relative strength $\eta = \Omega_R / \omega_0 = 0.12$. This represents an important milestone for future studies of quantum vacuum radiation because such resonators can be optically modulated at ultrafast rates, possibly leading to the generation of non-classical light via the dynamic Casimir effect. Finally, with an effective volume of $2.10^{-6} \lambda_0^3$, it is estimated that fewer than 3000 electrons per resonator are ultra-strongly coupled to the quantized electromagnetic mode, proving it is also a promising approach to explore few-electron polaritonic systems operating at relatively high temperatures.Comment: 7 pages, 4 figure

Stable electroluminescence in ambipolar dopant-free lateral p-n junctions

Dopant-free lateral p-n junctions in the GaAs/AlGaAs material system have attracted interest due to their potential use in quantum optoelectronics (e.g., optical quantum computers or quantum repeaters) and ease of integration with other components, such as single electron pumps and spin qubits. A major obstacle to integration has been unwanted charge accumulation at the p-n junction gap that suppresses light emission, either due to enhanced non-radiative recombination or inhibition of p-n current. Typically, samples must frequently be warmed to room temperature to dissipate this built-up charge and restore light emission in a subsequent cooldown. Here, we introduce a practical gate voltage protocol that clears this parasitic charge accumulation, in-situ at low temperature, enabling the indefinite cryogenic operation of devices. This reset protocol enabled the optical characterization of stable, bright, dopant-free lateral p-n junctions with electroluminescence linewidths among the narrowest (< 1 meV; < 0.5 nm) reported in this type of device. It also enabled the unambiguous identification of the ground state of neutral free excitons (heavy and light holes), as well as charged excitons (trions). The free exciton emission energies for both photoluminescence and electroluminescence are found to be nearly identical (within 0.2 meV or 0.1 nm). The binding and dissociation energies for free and charged excitons are reported. A free exciton lifetime of 237 ps was measured by time-resolved electroluminescence, compared to 419 ps with time-resolved photoluminescence.Comment: Main text: 5 pages and 5 figures. Supplementary: 18 pages and 11 figure

Generating coherence and entanglement with a finite-size atomic ensemble in a ring cavity

We propose a model to study the coherence and entanglement resulting from the interaction of a finite-size atomic ensemble with degenerate counter-propagating field modes of a high-Q ring cavity. Our approach applies to an arbitrary number of atoms N and includes the spatial variation of the field throughout the ensemble. We report several new interesting aspects of coherence and entangled behavior that emerge when the size of the atomic ensemble is not taken to the thermodynamic limit of N>>1. Under such conditions, it is found that the counter-propagating cavity modes, although in the thermodynamic limit are mutually incoherent and exhibit no one-photon interference, the modes can, however, be made mutually coherent and exhibit interference after interacting with a finite-size atomic ensemble. It is also found that the spatial redistribution of the atoms over a finite size results in nonorthogonality of the collective bosonic modes. This nonorthogonality leads to the super-bunching effect that the correlations of photons of the individual cavity modes and of different modes are stronger than those of a thermal field. However, we find that the correlations are not strong enough to violate the Cauchy-Schwarz inequality and to produce squeezing and entanglement between the modes. Therefore, we investigate the spectral distributions of the logarithmic negativity and the variances of the output fields. These functions determine squeezing and entanglement properties of the output cavity fields and can be measured by a homodyne technique. We find that the entanglement is redistributed over several components of the spectrum and the finite-size effect is to concentrate the entanglement at the zero-frequency component of the spectrum.Comment: Published versio

Uwagi o resztach BLUS

W pracy rozważa się problemy dotyczące wyboru bazy przekształcania, prowadzącego do otrzymania estymatora wektora reszt m.n.k . o skalarnej macierzy wariancji kowariancji, w przypadku występowania obserwacji nietypowych. Zaproponowano wykorzystanie zerowych reszt otrzymanych w wyniku estymacji minimalizującej sumę odchyleń bezwzględnych do określania bazy tej transformacji. Umożliwia to uniknięcie wyboru obserwacji, nietypowych dla bazy, co znacznie poprawia jakość estymacji.Zadanie pt. „Digitalizacja i udostępnienie w Cyfrowym Repozytorium Uniwersytetu Łódzkiego kolekcji czasopism naukowych wydawanych przez Uniwersytet Łódzki” nr 885/P-DUN/2014 dofinansowane zostało ze środków MNiSW w ramach działalności upowszechniającej naukę

O efektywność ważonych estymatorów najmniejszych kwadratów w przypadku ogólnego modelu liniowego

Głównym calem pracy jest zaprezentowanie jednego z możliwych sposobów mierzenia efektywności w małych próbach i zanalizowanie niektórych własności ważonych estymatorów najmniejszych kwadratów 1 przedstawionej wyznacznikowej miary efektywności. W szczególności przedstawiono: a) analizę własności estymatorów ważonych w przypadku ogólnego modelu liniowego, b) dowód, że miaro efektywności znajduje się w przedziale c ) wyznaczanie dolnego kresu wyznacznikowej miary efektywności.Zadanie pt. „Digitalizacja i udostępnienie w Cyfrowym Repozytorium Uniwersytetu Łódzkiego kolekcji czasopism naukowych wydawanych przez Uniwersytet Łódzki” nr 885/P-DUN/2014 dofinansowane zostało ze środków MNiSW w ramach działalności upowszechniającej naukę

Resonance raman spectroscopy of Ga1-xAlxAs mediated via compositional variation

NRC publication: Ye