Formation of robust bound states of interacting microwave photons.

Systems of correlated particles appear in many fields of modern science and represent some of the most intractable computational problems in nature. The computational challenge in these systems arises when interactions become comparable to other energy scales, which makes the state of each particle depend on all other particles1. The lack of general solutions for the three-body problem and acceptable theory for strongly correlated electrons shows that our understanding of correlated systems fades when the particle number or the interaction strength increases. One of the hallmarks of interacting systems is the formation of multiparticle bound states2-9. Here we develop a high-fidelity parameterizable fSim gate and implement the periodic quantum circuit of the spin-½ XXZ model in a ring of 24 superconducting qubits. We study the propagation of these excitations and observe their bound nature for up to five photons. We devise a phase-sensitive method for constructing the few-body spectrum of the bound states and extract their pseudo-charge by introducing a synthetic flux. By introducing interactions between the ring and additional qubits, we observe an unexpected resilience of the bound states to integrability breaking. This finding goes against the idea that bound states in non-integrable systems are unstable when their energies overlap with the continuum spectrum. Our work provides experimental evidence for bound states of interacting photons and discovers their stability beyond the integrability limit.

Dynamics of magnetization at infinite temperature in a Heisenberg spin chain.

Understanding universal aspects of quantum dynamics is an unresolved problem in statistical mechanics. In particular, the spin dynamics of the one-dimensional Heisenberg model were conjectured as to belong to the Kardar-Parisi-Zhang (KPZ) universality class based on the scaling of the infinite-temperature spin-spin correlation function. In a chain of 46 superconducting qubits, we studied the probability distribution of the magnetization transferred across the chain's center, [Formula: see text]. The first two moments of [Formula: see text] show superdiffusive behavior, a hallmark of KPZ universality. However, the third and fourth moments ruled out the KPZ conjecture and allow for evaluating other theories. Our results highlight the importance of studying higher moments in determining dynamic universality classes and provide insights into universal behavior in quantum systems.

Stable quantum-correlated many-body states through engineered dissipation.

Engineered dissipative reservoirs have the potential to steer many-body quantum systems toward correlated steady states useful for quantum simulation of high-temperature superconductivity or quantum magnetism. Using up to 49 superconducting qubits, we prepared low-energy states of the transverse-field Ising model through coupling to dissipative auxiliary qubits. In one dimension, we observed long-range quantum correlations and a ground-state fidelity of 0.86 for 18 qubits at the critical point. In two dimensions, we found mutual information that extends beyond nearest neighbors. Lastly, by coupling the system to auxiliaries emulating reservoirs with different chemical potentials, we explored transport in the quantum Heisenberg model. Our results establish engineered dissipation as a scalable alternative to unitary evolution for preparing entangled many-body states on noisy quantum processors.

Estimating population lung cancer risk from radon using a resource efficient stratified population weighted sample survey protocol - Lessons and results from Ireland.

A 2018 estimate indicates that there were 226,057 radon-attributable lung cancer deaths in 66 countries that had representative radon surveys. This is a shocking figure, and as it comes from only 66 countries it underestimates the worldwide death toll. Any research that enables countries to conduct representative radon surveys and to understand better the risk to citizens from radon is surely welcome. We hope this paper provides a useful methodology for estimating population risk. The estimation of population weighted average indoor radon levels requires statistically valid sampling methodologies that use a representative sample of occupied homes throughout the country. A literature review indicates that in many population weighted surveys, the sampling methodology may not have been designed to do this. This paper describes a simple, resource efficient methodology which produces statistically valid and reliable estimates based on a small scale sample that is representative of the population distribution. The resource efficient design of this study enables it to be repeated at frequent intervals providing for a longitudinal analysis of the population risk from indoor radon. This survey was conducted in Ireland using 653 measurements and a representative sampling strategy to provide a baseline population weighted radon exposure for future comparisons. This study estimates the average population weighted indoor radon concentration in Ireland to be 97.83 Bq m-3 (95% Confidence Interval 90.69 Bq m-3 to 105.53 Bq m-3), and that there are an estimated 350 lung cancer cases and 255 deaths per year due to radon exposure. The mortality rate of 5.3 per 100,000 due to indoor radon, demonstrates that radon remains one of the highest preventable causes of death in Ireland.

Transcriptional induction of cholinesterase expression and protection against chemical warfare nerve agents.

We investigated whether transcriptional inducers could enhance the expression of acetylcholinesterase (AChE) in cell lines to achieve protection against organophosphate (OP) poisoning. Trichostatin A (TSA), an inhibitor of histone deacetylase that de-condenses chromatin and increases the binding of transcription factors and mRNA synthesis, induced three- to four-fold extracellular and 8-10-fold intracellular AChE expression at the optimal dose of 165-333 nM in Neuro 2A cells. Pre-treatment with TSA protected against OP exposure. Thus, transcriptional inducers, such as TSA, up-regulate AChE, which then can scavenge the OP and protect the cells from OP-induced toxicity, and are potential novel ways to treat chemical warfare nerve agent (CWNA) exposure.

Normal and staphylomatous sclera of high myopia. An electron microscopic study.

The posterior sclera of three normal eyes and five staphylomatous, myopic eyes was examined by electron microscopy. The following notable differences were found in myopic sclera: a predominantly lamellar, collagen fiber bundle arrangement; a reduction in the diameter of the fibrils; a greater dispersion for the range of fibril diameters; an increase in unusual star-shaped fibrils on cross section; and a greater prevalence of fibril groups with uniform but extremely fine diameters. These findings essentially agree with those in other studies of the myopic sclera. The ultramicroscopic changes encountered inpathologic myopia are judged to be compatible with an abnormal proteoglycan composition of the interfibrillary substance in the ectatic sclera.

Long-term results of scleral reinforcement surgery.

Of 40 scleral reinforcement operations for progressive severe myopia, 23 patients were followed up for a minimum of five years. Ten of 23 patients showed an essentially stable postoperative course (43%) while 13 (57%) had increases in myopia of -1.0 diopter or more. Among the operated on eyes, 17 of 23 eventually had some increase in myopia. Of the 20 eyes that had preoperative axial measurements, 18 (90%) had increases in axial diameter of 0.3 mm or more. There were complications in six of the 40 eyes, including anterior uveitis, motility disorders, and retinal detachment. Progression of posterior staphyloma formation or the onset of myopic fundus degeneration was observed in ten eyes. Two problems with this surgery are the limited scleral area reinforced by narrow grafts and the possible late involvement of graft collagen in the disease process of host sclera.

Lacquer crack lesions in pathologic myopia.

In evaluating the anatomic and functional status of 22 eyes of 14 patients demonstrating lacquer cracks, these lesions occurred in the eyes of young adults with posterior staphylomas and markedly increased axial lengths. Decreased visual acuity and altered visual fields were the rule; choroidal hemorrhage and focal chorioretinal atrophy were less frequently associated. Fluorescein angiography revealed early and late pseudofluorescence and late staining of the lesions. These clinical data suggest that lacquer cracks represent healed, mechanical breaks in the pigment epithelium-Bruch's membrane-choriocapillaris complex. The presence of these lesions implies a guarded prognosis for the retention of central vision.

Peripheral chorioretinal lesions and axial length of the myopic eye.

A study of the retinal periphery of 1,437 predominantly myopic eyes revealed a statistically significant association of four types of peripheral chorioretinal degenerations with increased axial length of the eye. These were white without pressure, pigmentary degeneration, pavingstone degeneration, and lattice degeneration. There was a tendency for both white without pressure and lattice degeneration jointly to affect eyes of individuals 19 years of age and younger. Increasing age was a significant factor in the incidence of pigmentary and pavingstone degenerations, whereas aging significantly reduced the prevalence of white without pressure.

Scleral hyperplasia induced by heat.

We evaluated low-level heating as a stimulus to induce hyperplasia of normal rabbit sclera. Heat treatments were administered by placing an etched-element heater on bare sclera. Contact thermotherapy with a conductive device provided a favorable dose distribution for local scleral heating. A purely conductive heat source was selected to minimize intraocular heat penetration and to determine whether the scleral reaction was a primary thermal effect. Histologic examination of treated specimens showed thickening of normal rabbit sclera with preservation of the underlying normal ocular structures. Electron microscopic examination of treated sclera showed newly formed collagen fibrils adjacent to sclerocytes. These fibroblasts were activated, as manifested by well-developed rough-surfaced endoplasmic reticulum and hypertrophic Golgi complexes.

The posterior staphyloma of pathologic myopia.

A total of 250 myopic patients with posterior staphyloma affecting one or both eyes received a complete ocular examination including binocular indirect ophthalmoscopy, refraction, and axial length measurement. Ten types of staphyloma were noted; five primary and five compound. The primary staphyloma involved the posterior pole (Type I), macular area (Type II), peripapillary area (Type III), the fundus nasal to the disc (Type IV) and the area below the disc (Type V). Compound staphylomas consisted of combined primary staphylomas or distinctive and complex variations of a primary staphyloma, usually Type I. This type also was found to have the greatest prevalence of all ten types. Patients in this group had a 19% incidence of legal blindness with 34.5% of staphylomatous eyes having a vision of 20/200 or less. A remarkably wide range of refractions and axial lengths were found for each staphyloma type. These results indicate the importance of the staphyloma in the diagnosis and prognosis of pathologic myopia. It also offers an improved basis for genetic studies of this disease.

Role of carbon fibre implants in osteochondral defects of the knee.

Articular cartilage defects of the knee are a common condition diagnosed at arthroscopy. The management of these osteochondral lesions is controversial. We present our experience using carbon fibre implants to repair these defects in 18 patients. Eleven patients (61 per cent) had an osteochondral defect of the medial femoral condyle. Two patients had isolated patellar defects. The mean knee assessment and functional scores were 75 and 80 respectively using The Knee Society Clinical Rating System. Serial post-operative M.R.I. scanning revealed that there was no loss of implant position with an extensive local tissue response and good joint congruity. Overall, 11 patients (61 per cent) returned to their normal sporting activity, while 3 patients (18 per cent) had a poor result. One of these underwent a patellectomy. We conclude that carbon fibre implants may have a role to play in the management of osteochondral defects of the femoral condyles.

Cataract extraction in pathological myopia.

Fifty-three cataract extractions in eyes with pathological myopia effected visual improvement in 47 eyes (89%). The median visual acuity increased from a preoperative level of 20/300 to 20/40 postoperatively. The incidence in this series of vitreous loss (1.9%) and retinal detachment (1.9%), are within the expected range of such complications. Four cases developed aphakic glaucoma which has necessitated continued therapy. All four had both enzyme zonulolysis and topical steroids, postoperatively. Other problems unique to surgery in these eyes are the missed diagnosis of nuclear cataract, possible dislocation of the lens, perforation of the sclera during retrobulbar injection, and rupture of the globe with vigorous digital massage.

Physiologic vs pathologic myopia: genetics vs environment.

Physiologic myopia occurs as the result of a correlation failure of refraction components in the normal eye. Pathologic myopia is caused by excessive axial elongation that primarily involves the ora-equatorial area and the posterior pole. Peripheral fundus changes and posterior staphyloma formation are ophthalmoscopic evidences of this process. Heredity is the basic determinant of ocular refraction, but numerous agents produce both temporary and permanent myopias.