Spin-Flipping Half Vortex in a Macroscopic Polariton Spinor Ring Condensate

We report the observation of vorticity in a macroscopic Bose-Einstein condensate of polaritons in a ring geometry. Because it is a spinor condensate, the elementary excitations are "half vortices" in which there is a phase rotation of $\pi$ in connection with a polarization vector rotation of $\pi$ around a closed path. This is clearly seen in the experimental observations of the polarization rotation around the ring. In the ring geometry, a new type of half vortex is allowed in which the handedness of the spin flips from one side of the ring to the other, in addition to the rotation of the linear polarization component; such a state is not allowed in a simply-connected geometry. Theoretical calculation of the energy of this state shows that when many-body interactions are taken into account, it is lower in energy than a simple half vortex. The direction of circulation of the flow around the ring fluctuates randomly between clockwise and counterclockwise from one shot to the next; this corresponds to spontaneous breaking of time-reversal symmetry in the system. These new, macroscopic polariton ring condensates allow for the possibility of direct control of the vorticity of the condensate.Comment: 21 pages, 10 figures, including supplemental information; Proceedings of the National Academy of Sciences (USA) (2015

Bose-Einstein condensation and quantized flow of microcavity polaritons with long lifetime

Over the last two decades, the system of exciton-polaritons (polaritons) in a semiconductor microcavity has become an important platform for studying the physics of quantum fluids in a solid-state system. Polaritons are formed by the strong coupling between photons and a sharp electronic resonance (e.g. an exciton resonance) in a cavity. They are interacting bosonic particles with a small effective mass due to their half-light and half-matter nature. Spontaneous coherence phenomena, such as the superfluid transition and Bose-Einstein condensation (BEC), have been observed in polariton systems at temperatures in the range from several Kelvin to room temperature. This dissertation focuses on new methods of trapping polaritons and the BEC and superfluidity of polaritons in these new traps. The first part of this dissertation describes experiments on trapping polaritons with an optically generated potential barrier. When the polariton density increases, there is a transition from ballistic motion to coherent motion of polaritons over hundreds of micrometers. At even higher particle density, there is a very sharp transition from the coherent motion state to the ground state of the trap. The second part of this dissertation explores the superfluid properties of polaritons in a ring-shaped trap. This ring trap is formed by combining a stress-induced harmonic trap with an optically created barrier at the trap center. This trapping method enables fine control of the trap profile as well as the properties of the polaritons in the trap. The formation of a polariton ring condensate is observed in this trap. The phase and polarization measurement of the ring condensate reveals that it is in a half-quantized circulation state which features a phase shift of π and a polarization vector rotation of π of the polaritons around a closed path in the ring. The direction of the circulation of the flow around the ring fluctuates randomly between clockwise and counter-clockwise from one shot to the next. In contrast, the rotation of the polarization of polaritons is very stable. This property is experimentally studied, and it is found that the stable spatial polarization pattern may relate to the optical spin Hall effect

Bose-Einstein Condensation of Long-Lifetime Polaritons in Thermal Equilibrium

Exciton-polaritons in semiconductor microcavities have been used to demonstrate quantum effects such as Bose-Einstein condensation, superfluity, and quantized vortices. However, in these experiments, the polaritons have not reached thermal equilibrium when they undergo the transition to a coherent state. This has prevented the verification of one of the canonical predictions for condensation, namely the phase diagram. In this work, we have created a polariton gas in a semiconductor microcavity in which the quasiparticles have a lifetime much longer than their thermalization time. This allows them to reach thermal equilibrium in a laser-generated confining trap. Their energy distributions are well fit by equilibrium Bose-Einstein distributions over a broad range of densities and temperatures from very low densities all the way up to the threshold for Bose-Einstein condensation. The good fits of the Bose-Einstein distribution over a broad range of density and temperature imply that the particles obey the predicted power law for the phase boundary of Bose-Einstein condensation

Experimental investigation on expansion characteristics and strength of carbonating reactive magnesia solidified clay

The carbonated reactive magnesia (CRM) method is superior in energy conservation, carbon capture, and rapid solidification in soil improvement. It has been revealed that CRM method could cause apparent volumetric expansion during carbonation, which may cause apparent compaction impact on the surrounding soils when used for soft foundation improvement. However, this expansion hasn't been discussed systematically. In this study, the evolutions of expansion stress (σEx) and volumetric expansion (ΔV) during carbonation process were successfully monitored. Two factors, including reactive MgO content (Cm) and net confining pressure (Pnc), were investigated. The internal relations between σEx, ΔV, and unconfined compressive strength (UCS) together with the influences of Cm and Pnc on them were discussed. Besides, the intrinsic mechanisms were discussed based on density variations, pore structures, and microstructures. According to the findings, σEx and ΔV invariably exhibited a three-stage behavior consisting of stability-rapid increase-stability. By increasing Cm or Pnc, the σEx, UCS, and density were all significantly increased, while the volume increment was obviously reduced. For the completely confined specimen, the σEx and UCS were found to approach 3 MPa and 9 MPa, respectively. The increase in Cm promoted the crystallization of hydrated magnesium carbonates (HMCs), leading to lower porosity in solidified soils. Increasing Pnc also improved the crystallization of HMCs and modified pore structures, causing further increases in σEx and UCS

Codon optimization, constitutive expression and antimicrobial characterization of hen egg white lysozyme (HEWL) in Pichia pastoris

Fusarium oxysporum (F. oxysporum) and Verticillium dahlia (V. dahlia) causes severe cotton disease in China and other cotton-producing countries. Hen egg white lysozyme (HEWL) has antimicrobial properties. In this study, a codon-optimized HEWL gene was synthesized and cloned into the yeast expression vector, pPIC9K, under the control of the Pichia pastoris (P. pastoris) glyceraldehyde-3-phosphate dehydrogenase promoter (pGAP). Results showed that codon-optimized HEWL (oHEWL) was constitutively expressed. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) indicated that the molecular weight of recombinant HEWL (roHEWL) was 14 kDa which corresponds to the standard HEWL. The expression of the roHEWL reached to 54 mg/L. Activity of the roHEWL was 1680 U/mL. The optimum pH for roHEWL was from 6.0 to 7.0, and the optimum temperature was 55°C. In vitro antimicrobial activity assay revealed that roHEWL can lyse cell walls of the gram positive bacteria, Micrococcus lysodeikticus (M. lysodeikticus). In vivo studies showed that it inhibits plant fungi, F. oxysporum and V. dahlia. roHEWL anti-fungal properties might be useful for future genetically engineered cotton plant resistance against pathogenic fungal disease.Keywords: Hen egg white lysozyme (HEWL), antimicrobial activity, glyceraldehyde-3-phosphate dehydrogenase (GAP) promoter, codon optimization, constitutive expressio