Spatio-temporal coherence in vertically emitting GaAs-based electrically driven polariton lasers

Authors gratefully acknowledge the financial support by the state of Bavaria, the DFG within the projects Schn1376-3.1 as well as KL3124/2-1 and the Wurzburg-Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter - ct.qmat. S.H. is grateful for funding received within the EPSRC Hybrid Polaritonics programme grant (EP/M025330/1).We report on the implementation of a GaAs-based, vertically emitting electrically pumped polariton laser operated at cryogenic temperatures. The structure consists of a high quality factor AlGaAs/AlAs microcavity (Q=15 000) with two stacks of four GaAs quantum wells and features a Rabi splitting of 11 meV. Polariton lasing manifests by a clear threshold in the input–output characteristics of our device with a sharp drop in the emission linewidth and a continuous blueshift of 0.7 meV above threshold with increasing injection current. We measure spatial and temporal coherence of our device in the condensed phase by utilizing interference spectroscopy. Our results clearly demonstrate that electrically driven polariton lasers have promise as monolithic polaritonic sources of coherent light.PostprintPeer reviewe

Software environment for controlling and re-configuration of Xilinx Virtex FPGAs – TWEPP-07

The Time Projection Chamber is one of the detectors of the ALICE experiment, that is currently being commissioned at the Large Hadron Collider at CERN. The Detector Control System is used for control and monitoring of the system. For the TPC Front-End Electronics (FEE) the control node is a Readout Control Unit that communicates to higher layers via Ethernet, using the standard framework DIM. The Readout Control Unit is equipped with commercial SRAM based FPGAs that will experience errors due to the radiation environment they are operating in. This article will present the implemented hardware solution for error correction and will focus on the software environment for configuration and controlling of the system – TWEPP-07

Braneworld effective action and origin of inflation

We construct braneworld effective action in two brane Randall-Sundrum model and show that the radion mode plays the role of a scalar field localizing essentially nonlocal part of this action. Non-minimal curvature coupling of this field reflects the violation of AdS/CFT-correspondence for finite values of brane separation. Under small detuning of the brane tension from the Randall-Sundrum flat brane value, the radion mode can play the role of inflaton. Inflationary dynamics corresponds to branes moving apart in the field of repelling interbrane inflaton-radion potential and implies the existence acceleration stage caused by remnant cosmological constant at late (large brane separation) stages of evolution. We discuss the possibility of fixing initial conditions in this model within the concept of braneworld creation from the tunneling or no-boundary cosmological state, which formally replaces the conventional moduli stabilization mechanism.Comment: 18 pages, LaTeX, the effective action form factor is corrected for small separation between branes and new references are adde

Counter-directional polariton coupler

The Wurzburg group acknowledges the financial support by the state of Bavaria and the DFG within the project Schn1376-3.1. J.B. and S.K. acknowledge funding from DFG grant KL3124/2-1. The Madrid team acknowledges financial support by the Spanish MINECO Grants MAT2014-53119-C2-1-R and MAT2017-83722-R.We report on an on-chip routing device for propagating condensates of exciton-polaritons. This counter-directional coupler implements signal control by a photonic microdisk potential, which couples two lithographically defined waveguides and reverses the condensate's propagation direction. By varying the structural sizes, we utilize the conjunction of the different dimensionalities to additionally evidence the functionality of a polaritonic resonant tunnel diode. Furthermore, we show the ultra fast time dynamics of the device via ps-resolved streak camera measurements. This scalable, all-directional coupler element is a central building block for compact non-linear on-chip photonic architectures.PostprintPeer reviewe

Local circuits targeting parvalbumin-containing interneurons in layer IV of rat barrel cortex

Interactions between inhibitory interneurons and excitatory spiny neurons and also other inhibitory cells represent fundamental network properties which cause the so-called thalamo-cortical response transformation and account for the well-known receptive field differences of cortical layer IV versus thalamic neurons. We investigated the currently largely unknown morphological basis of these interactions utilizing acute slice preparations of barrel cortex in P19-21 rats. Layer IV spiny (spiny stellate, star pyramidal and pyramidal) neurons or inhibitory (basket and bitufted) interneurons were electrophysiologically characterized and intracellularly biocytin-labeled. In the same slice, we stained parvalbumin-immunoreactive (PV-ir) interneurons as putative target cells after which the tissue was subjected to confocal image acquisition. Parallel experiments confirmed the existence of synaptic contacts in these types of connection by correlated light and electron microscopy. The axons of the filled neurons differentially targeted barrel PV-ir interneurons: (1) The relative number of all contacted PV-ir cells within the axonal sphere was 5–17% for spiny (n = 10), 32 and 58% for basket (n = 2) and 12 and 13% for bitufted (n = 2) cells. (2) The preferential subcellular site which was contacted on PV-ir target cells was somatic for four and dendritic for five spiny cells; for basket cells, there was a somatic and for bitufted cells a dendritic preference in each examined case. (3) The highest number of contacts on a single PV-ir cell was 9 (4 somatic and 5 dendritic) for spiny neurons, 15 (10 somatic and 5 dendritic) for basket cells and 4 (1 somatic and 3 dendritic) for bitufted cells. These patterns suggest a cell type-dependent communication within layer IV microcircuits in which PV-ir interneurons provide not only feed-forward but also feedback inhibition thus triggering the thalamo-cortical response transformation

Mechanisms underlying a thalamocortical transformation during active tactile sensation

During active somatosensation, neural signals expected from movement of the sensors are suppressed in the cortex, whereas information related to touch is enhanced. This tactile suppression underlies low-noise encoding of relevant tactile features and the brain’s ability to make fine tactile discriminations. Layer (L) 4 excitatory neurons in the barrel cortex, the major target of the somatosensory thalamus (VPM), respond to touch, but have low spike rates and low sensitivity to the movement of whiskers. Most neurons in VPM respond to touch and also show an increase in spike rate with whisker movement. Therefore, signals related to self-movement are suppressed in L4. Fast-spiking (FS) interneurons in L4 show similar dynamics to VPM neurons. Stimulation of halorhodopsin in FS interneurons causes a reduction in FS neuron activity and an increase in L4 excitatory neuron activity. This decrease of activity of L4 FS neurons contradicts the "paradoxical effect" predicted in networks stabilized by inhibition and in strongly-coupled networks. To explain these observations, we constructed a model of the L4 circuit, with connectivity constrained by in vitro measurements. The model explores the various synaptic conductance strengths for which L4 FS neurons actively suppress baseline and movement-related activity in layer 4 excitatory neurons. Feedforward inhibition, in concert with recurrent intracortical circuitry, produces tactile suppression. Synaptic delays in feedforward inhibition allow transmission of temporally brief volleys of activity associated with touch. Our model provides a mechanistic explanation of a behavior-related computation implemented by the thalamocortical circuit

Using Parahydrogen Induced Polarization to Study Steps in the Hydroformylation Reaction.

A range of iridium complexes, Ir(η3-C3H5)(CO)(PR2R’)2 (1a-1e) [where 1a, PR2R’ = PPh3, 1b P(p-tol)3, 1c PMePh2, 1d PMe2Ph and 1e PMe3] were synthesized and their reactivity as stoichiometric hydroformylation precursors studied. Para-hydrogen assisted NMR spectroscopy detected the following intermediates: Ir(H)2(η3-C3H5)(CO)(PR2R’) (2a-e), Ir(H)2(η1-C3H5)(CO)(PR2R’)2 (4d-e), Ir(H)2(η1-C3H5)(CO)2(PR2R’) (10a-e), Ir(H)2(CO-C3H5)(CO)2(PR2R’) (11a-c), Ir(H)2(CO-C3H7)(CO)2(PR2R’) (12a-c) and Ir(H)2(CO-C3H5)(CO)(PR2R’)2 (13d-e). Some of these species exist as two geometric isomers according to their multinuclear NMR characteristics. The NMR studies suggest a role for the following 16 electron species in these reactions: Ir(η3-C3H5)(CO)(PR2R’), Ir(η1-C3H5)(CO)(PR2R’)2, Ir(η1-C3H5)(CO)2(PR2R’), Ir(CO-C3H5)(CO)2(PR2R’), Ir(CO-C3H7)(CO)2(PR2R’) and Ir(CO-C3H5)(CO)(PR2R’)2. Their role is linked to several 18 electron species in order to confirm the route by which hydroformylation and hydrogenation proceeds