ABSTRACT
Scar eigenstates in a many-body system refers to a small subset of non-thermal finite energy density eigenstates embedded into an otherwise thermal spectrum. This novel non-thermal behaviour has been seen in recent experiments simulating a one-dimensional PXP model with a kinetically-constrained local Hilbert space realised by a chain of Rydberg atoms. We probe these small sets of special eigenstates starting from particular initial states by computing the spread complexity associated to time evolution of the PXP hamiltonian. Since the scar subspace in this model is embedded only loosely, the scar states form a weakly broken representation of the Lie algebra. We demonstrate why a careful usage of the forward scattering approximation (FSA), instead of any other method, is required to extract the most appropriate set of Lanczos coefficients in this case as the consequence of this approximate symmetry. Only such a method leads to a well defined notion of a closed Krylov subspace and consequently, that of spread complexity. We show this using three separate initial states, namely|Z2⟩,|Z3⟩and the vacuum state, due to the disparate classes of scar states hosted by these sectors. We also discuss systematic methods of remedying the imperfections in the FSA setup stemming from these approximate symmetries.
ABSTRACT
BACKGROUND AND AIM: Currently, ultrasound-guided (US-guided) internal jugular vein (IJV) cannulation is the recommended technique. However, it has a learning curve and might be unsafe in inexperienced hands. The present study aimed to compare the performance and complications with two levels of experience in performing US-guided right IJV cannulation. METHODS: With informed consent, 108 procedures were performed after random allocation into two groups based on operator experience. An operator with experience in performing 30 or more ultrasound-guided IJV cannulation was considered an expert. The rate of successful cannulation, the time needed, number of attempts, and complication rate were measured. Quantitative continuous variables were compared using the unpaired student's t-test, and the chi-square test or Fisher's-exact test was used for the comparison of qualitative variables; P-value < 0.05 was considered significant. RESULTS: The successful cannulation rates were 100% versus 94.44% in the expert and non-expert groups, respectively; (P=0.0803). The mean time for successful cannulation and the percentage of patients who required ≥ two attempts were significantly lower in the expert group (33.28 seconds and 12.96% versus 95.42 seconds and 61.12%). Although the incidence of carotid artery puncture and hematoma (7.4% and 5.56%) was higher in the non-expert group, it was not statistically different; (P=1.00). CONCLUSION: US-guided right IJV cannulation has a learning curve, and procedures as many as 30 US-guided IJV cannulation need to be observed and performed under the guidance to achieve it.
