Ultra-low threshold polariton lasing at room temperature in a GaN membrane microcavity with a zero-dimensional trap.

Polariton lasers are coherent light sources based on the condensation of exciton-polaritons in semiconductor microcavities, which occurs either in the kinetic or thermodynamic (Bose-Einstein) regime. Besides their fundamental interest, polariton lasers have the potential of extremely low operating thresholds. Here, we demonstrate ultra-low threshold polariton lasing at room temperature, using an all-dielectric, GaN membrane-based microcavity, with a spontaneously-formed zero-dimensional trap. The microcavity is fabricated using an innovative method, which involves photo-electrochemical etching of an InGaN sacrificial layer and allows for the incorporation of optimally-grown GaN active quantum wells inside a cavity with atomically-smooth surfaces. The resulting structure presents near-theoretical Q-factors and pronounced strong-coupling effects, with a record-high Rabi splitting of 64 meV at room-temperature. Polariton lasing is observed at threshold carrier densities 2.5 orders of magnitude lower than the exciton saturation density. Above threshold, angle-resolved emission spectra reveal an ordered pattern in k-space, attributed to polariton condensation at discrete levels of a single confinement site. This confinement mechanism along with the high material and optical quality of the microcavity, accounts for the enhanced performance of our polariton laser, and pave the way for further developments in the area of robust room temperature polaritonic devices.

Optical superfluid phase transitions and trapping of polariton condensates.

Semiconductor microcavities are used to support freely flowing polariton quantum liquids allowing the direct observation and optical manipulation of macroscopic quantum states. Incoherent optical excitation at a point produces radially expanding condensate clouds within the planar geometry. By using arbitrary configurations of multiple pump spots, we discover a geometrically controlled phase transition, switching from the coherent phase-locking of multiple condensates to the formation of a single trapped condensate. The condensation threshold becomes strongly dependent on the programmed superfluid geometry and sensitive to cooperative interactions between condensates. We directly image persistently circulating superfluid and show how flows of light-matter quasiparticles are dominated by the quantum pressure in such configurable laser-written potential landscapes.

Geometrically locked vortex lattices in semiconductor quantum fluids.

Macroscopic quantum states can be easily created and manipulated within semiconductor microcavity chips using exciton-photon quasiparticles called polaritons. Besides being a new platform for technology, polaritons have proven to be ideal systems to study out-of-equilibrium condensates. Here we harness the photonic component of such a semiconductor quantum fluid to measure its coherent wavefunction on macroscopic scales. Polaritons originating from separated and independent incoherently pumped spots are shown to phase-lock only in high-quality microcavities, producing up to 100 vortices and antivortices that extend over tens of microns across the sample and remain locked for many minutes. The resultant regular vortex lattices are highly sensitive to the optically imposed geometry, with modulational instabilities present only in square and not triangular lattices. Such systems describe the optical equivalents to one- and two-dimensional spin systems with (anti)-ferromagnetic interactions controlled by their symmetry, which can be reconfigured on the fly, paving the way to widespread applications in the control of quantum fluidic circuits.

Bragg polaritons: strong coupling and amplification in an unfolded microcavity.

Periodic incorporation of quantum wells inside a one-dimensional Bragg structure is shown to enhance coherent coupling of excitons to the electromagnetic Bloch waves. We demonstrate strong coupling of quantum well excitons to photonic crystal Bragg modes at the edge of the photonic band gap, which gives rise to mixed Bragg polariton eigenstates. The resulting Bragg polariton branches are in good agreement with the theory and allow demonstration of Bragg polariton parametric amplification.

Spontaneous polarization buildup in a room-temperature polariton laser.

We observe the buildup of strong (approximately 50%) spontaneous vector polarization in emission from a GaN-based polariton laser excited by short optical pulses at room temperature. The Stokes vector of emitted light changes its orientation randomly from one excitation pulse to another, so that the time-integrated polarization remains zero. This behavior is completely different from any previous laser. We interpret this observation in terms of the spontaneous symmetry breaking in a Bose-Einstein condensate of exciton polaritons.

Room-temperature polariton lasing in semiconductor microcavities.

We observe a room-temperature low-threshold transition to a coherent polariton state in bulk GaN microcavities in the strong-coupling regime. Nonresonant pulsed optical pumping produces rapid thermalization and yields a clear emission threshold of 1 mW, corresponding to an absorbed energy density of 29 microJ cm-2, 1 order of magnitude smaller than the best optically pumped (In,Ga)N quantum-well surface-emitting lasers (VCSELs). Angular and spectrally resolved luminescence show that the polariton emission is beamed in the normal direction with an angular width of +/-5 degrees and spatial size around 5 microm.

[Anesthesiologic management in cardiomyoplasty]. / Anästhesiologisches Management bei Kardiomyoplastie.

Dynamic cardiomyoplasty is a therapeutic possibility in irreversible cardiac insufficiency. With this operation, the latissimus dorsi muscle is mobilised and drawn into the thorax where it is placed around the heart. Lateral and supine positioning as well as thoracotomy and direct manipulation of the heart are associated with particular risks during surgery. Eight patients with the diagnosis of cardiomyopathy underwent cardiomyoplasty. The patients were classified as NYHA III-IV. Continuous dobutamine infusions were routinely started after induction of anaesthesia. All patients were intubated with single-lumen tubes. After sternotomy, lidocaine was administered. Monitoring included Swan-Ganz catheterisation and invasive blood pressure measurement. With early use of inotropic and vasodilatator agents the cardiac index and peripheral vascular resistance were adequately maintained. Double-lumen intubation seems to be unnecessary during cardiomyoplasty and only increases patient risk. Prophylactic lidocaine infusions are effective in preventing ventricular tachycardia and fibrillation. We conclude that adequate intraoperative management can improve the haemodynamic status of these patients so that cardiomyoplasty may be performed without significant morbidity.

Safety and effectiveness of an oral premedication regimen before cardiac surgery.

Thirty-five adult cardiac surgical patients received 20 mg dipotassium clorazepate orally the evening before surgery and 2 mg flunitrazepam 60 min before induction of anaesthesia. If anaesthesia was to be induced after 08.30 hours patients received an additional 20 mg dipotassium clorazepate at 06.15 hours. The following measurements were made: peripheral arterial oxygen saturation (Spo2) breathing room air; anxiety by visual analogue scale; degree of sedation; and haemodynamic variables. Mean (Spo2) was 95.9% (SD 1.8%) on the day before surgery and 95.4% (SD 1.5%) on arrival at the operating room. When the operation started after 08.30 hours, mean (Spo2) at 09.00 hours was 96.0% (SD 1.4%). There were no detected episodes of hypoxaemia after premedication. Mean anxiety score decreased significantly from 3.9 (SD 2.6) on the day before surgery to 3.3 (SD 2.1) on arrival at the operating room (patients' score; P < 0.002) and from 4.6 (SD 2.4) to 3.3 (SD 2.0) (anaesthesiologists' score; P < 0.001). Nearly all patients were considered well sedated, which was reflected by normal haemodynamic variables on arrival at the operating room. The combination of clorazepate and flunitrazepam is effective oral premedication for adult cardiac surgery, causing no obvious desaturation even when supplemental oxygen is not given.

Anaerobic bacteremia following tooth extraction and removal of osteosynthesis plates.

The occurrence of bacteremia was investigated in 39 patients undergoing tooth extraction (Group 1), surgical removal of impacted third molars (Group 2), or removal of osteosynthesis plates (Group 3). None of the 39 patients had bacteremia before anesthesia or after nasal intubation for general anesthesia. In two of 23 patients bacteria could be isolated after local anesthesia. Microorganisms were isolated in 14 of 19 patients (74%) with tooth extraction. In nine, a mixture of facultative anaerobic ("aerobic") and strict anaerobic bacteria were identified; in five, anaerobes were isolated exclusively. Two to 130 bacteria were cultured per 10 ml venous blood. Endocarditis causing alpha-hemolytic streptococci were found in seven cases (50%). At least one of the predominating anaerobes (Bacteroides, Fusobacteria, or Peptostreptococci) were found in all positive cases. Bacteremia was found in 40% of the Group 2 patients. There was no bacteremia in the Group 3 patients. The pathogenic relevance of anaerobic bacteremia is discussed and as a consequence it is suggested that the risk of developing organ abscesses as well as the problem of endocarditis following dental bacteremia has to be taken into consideration. On the basis of sensitivity testing, erythromycin does not appear to be the drug of choice in penicillin-allergic patients.