Spin-Mediated Mott Excitons

Motivated by recent experiments on Mott insulators, in both iridates and ultracold atoms, we theoretically study the effects of magnetic order on the Mott-Hubbard excitons. In particular, we focus on spin-mediated doublon-holon pairing in Hubbard materials. We use several complementary theoretical techniques: mean-field theory to describe the spin degrees of freedom, the self-consistent Born approximation to characterize individual charge excitations across the Hubbard gap, and the Bethe-Salpeter equation to identify bound states of doublons and holons. The binding energy of the Hubbard exciton is found to increase with increasing the N{\'e}el order parameter, while the exciton mass decreases. We observe that these trends rely significantly on the retardation of the effective interaction, and require consideration of multiple effects from changing the magnetic order. Our results are consistent with the key qualitative trends observed in recent experiments on iridates. Moreover, the findings could have direct implications on ultracold atom Mott insulators, where the Hubbard model is the exact description of the system and the microscopic degrees of freedom can be directly accessed.Comment: 11 pages, 11 figure

Synthetic, non-intoxicating 8,9-dihydrocannabidiol for the mitigation of seizures

There can be a fine line between therapeutic intervention and substance abuse, and this point is clearly exemplified in herbal cannabis and its products. Therapies involving cannabis have been the treatment of last resort for some cases of refractory epilepsy, and this has been among the strongest medical justifications for legalization of marijuana. In order to circumvent the narcotic effects of 9-tetrahydrocannabinol (THC), many studies have concentrated on its less intoxicating isomer cannabidiol (CBD). However, CBD, like all natural cannabinoids, is a controlled substance in most countries, and its conversion into THC can be easily performed using common chemicals. We describe here the anticonvulsant properties of 8,9-dihydrocannibidiol (H2CBD), a fully synthetic analogue of CBD that is prepared from inexpensive, non-cannabis derived precursors. H2CBD was found to have effectiveness comparable to CBD both for decreasing the number and reducing the severity of pentylenetetrazole-induced seizures in rats. Finally, H2CBD cannot be converted by any reasonable synthetic route into THC, and thus has the potential to act as a safe, noncontroversial drug for seizure mitigation

Topological Photonics

Topology is revolutionizing photonics, bringing with it new theoretical discoveries and a wealth of potential applications. This field was inspired by the discovery of topological insulators, in which interfacial electrons transport without dissipation even in the presence of impurities. Similarly, new optical mirrors of different wave-vector space topologies have been constructed to support new states of light propagating at their interfaces. These novel waveguides allow light to flow around large imperfections without back-reflection. The present review explains the underlying principles and highlights the major findings in photonic crystals, coupled resonators, metamaterials and quasicrystals.Comment: progress and review of an emerging field, 12 pages, 6 figures and 1 tabl

Generalized nonreciprocity in an optomechanical circuit via synthetic magnetism and reservoir engineering

Synthetic magnetism has been used to control charge neutral excitations for applications ranging from classical beam steering to quantum simulation. In optomechanics, radiation-pressure-induced parametric coupling between optical (photon) and mechanical (phonon) excitations may be used to break time-reversal symmetry, providing the prerequisite for synthetic magnetism. Here we design and fabricate a silicon optomechanical circuit with both optical and mechanical connectivity between two optomechanical cavities. Driving the two cavities with phase-correlated laser light results in a synthetic magnetic flux, which in combination with dissipative coupling to the mechanical bath, leads to nonreciprocal transport of photons with 35dB of isolation. Additionally, optical pumping with blue-detuned light manifests as a particle non-conserving interaction between photons and phonons, resulting in directional optical amplification of 12dB in the isolator through direction. These results indicate the feasibility of utilizing optomechanical circuits to create a more general class of nonreciprocal optical devices, and further, to enable novel topological phases for both light and sound on a microchip.Comment: 18 pages, 8 figures, 4 appendice

Experimental Measurement of the Berry Curvature from Anomalous Transport

Geometrical properties of energy bands underlie fascinating phenomena in a wide-range of systems, including solid-state materials, ultracold gases and photonics. Most famously, local geometrical characteristics like the Berry curvature can be related to global topological invariants such as those classifying quantum Hall states or topological insulators. Regardless of the band topology, however, any non-zero Berry curvature can have important consequences, such as in the semi-classical evolution of a wave packet. Here, we experimentally demonstrate for the first time that wave packet dynamics can be used to directly map out the Berry curvature. To this end, we use optical pulses in two coupled fibre loops to study the discrete time-evolution of a wave packet in a 1D geometrical "charge" pump, where the Berry curvature leads to an anomalous displacement of the wave packet under pumping. This is both the first direct observation of Berry curvature effects in an optical system, and, more generally, the proof-of-principle demonstration that semi-classical dynamics can serve as a high-resolution tool for mapping out geometrical properties

Partial splenectomy in children: Long-term reoperative outcomes

PURPOSE: Partial, or subtotal, splenectomy (PS) has become an accepted alternative to total splenectomy (TS) for management of hematologic disorders in children, but little is known about its long-term outcomes. Here, we present our institutional experience with partial splenectomy, to determine rate of subsequent TS or cholecystectomy and identify if any factors affected this need. METHODS: All patients who underwent partial splenectomy at a single tertiary children's hospital were retrospectively reviewed from 2002 through 2019 after IRB approval. Primary outcome of interest was rate of reoperation to completion splenectomy (CS) and rate of cholecystectomy. Secondary outcome were positive predictor(s) for these subsequent procedures. RESULTS: Twenty-four patients underwent PS, at median age 6.0 years, with preoperative spleen size of 12.7 cm by ultrasound. At median follow up time of 8.0 years, 29% of all patients and 24% of hereditary spherocytosis (HS) patients underwent completion splenectomy at median 34 months and 45 months, respectively. Amongst HS patients who did not have a cholecystectomy with or prior to PS, 39% underwent a delayed cholecystectomy following PS. There were no significant differences in age at index procedure, preoperative splenic volume, weight of splenic specimen removed, transfusion requirements, preoperative or postoperative hematologic parameters (including hemoglobin, hematocrit, total bilirubin, and reticulocyte count) amongst patients of all diagnoses and HS only who underwent PS alone compared to those who went on to CS. There were no cases of OPSS or deaths. CONCLUSION: Partial splenectomy is a safe alternative to total splenectomy in children with hematologic disease with theoretical decreased susceptibility to OPSS. However, families should be counseled of a 29% chance of reoperation to completion splenectomy, and, in HS patients, a 39% chance of delayed cholecystectomy if not performed prior to or with PS. Further studies are needed to understand predictors of these outcomes