Probing quantum many-body correlations by universal ramping dynamics.

Ramping a physical parameter is one of the most common experimental protocols in studying a quantum system, and ramping dynamics has been widely used in preparing a quantum state and probing physical properties. Here, we present a novel method of probing quantum many-body correlation by ramping dynamics. We ramp a Hamiltonian parameter to the same target value from different initial values and with different velocities, and we show that the first-order correction on the finite ramping velocity is universal and path-independent, revealing a novel quantum many-body correlation function of the equilibrium phases at the target values. We term this method as the non-adiabatic linear response since this is the leading order correction beyond the adiabatic limit. We demonstrate this method experimentally by studying the Bose-Hubbard model with ultracold atoms in three-dimensional optical lattices. Unlike the conventional linear response that reveals whether the quasi-particle dispersion of a quantum phase is gapped or gapless, this probe is more sensitive to whether the quasi-particle lifetime is long enough such that the quantum phase possesses a well-defined quasi-particle description. In the Bose-Hubbard model, this non-adiabatic linear response is significant in the quantum critical regime where well-defined quasi-particles are absent. And in contrast, this response is vanishingly small in both superfluid and Mott insulators which possess well-defined quasi-particles. Because our proposal uses the most common experimental protocol, we envision that our method can find broad applications in probing various quantum systems.

Global topological dominance in the left hemisphere.

A series of experiments with right-handers demonstrated that the left hemisphere (LH) is reliably and consistently superior to the right hemisphere (RH) for global topological perception. These experiments generalized the topological account of lateralization to different kinds of topological properties (including holes, inside/outside relation, and "presence vs. absence") in comparison with a broad spectrum of geometric properties, including orientation, distance, size, mirror-symmetry, parallelism, collinearity, etc. The stimuli and paradigms used were also designed to prevent subjects from using various nontopological properties in performing the tasks of topological discrimination. Furthermore, task factors commonly considered in the study of hemispheric asymmetry, such as response latency vs. accuracy, vertical vs. horizontal presentation, detection vs. recognition, and simultaneous vs. sequential judgment, were manipulated to not be confounding factors. Moreover, left-handed subjects were tested and showed the right lateralization of topological perception, in the opposite direction of lateralization compared with right-handers. In addition, the functional magnetic resonance imaging measure revealed that only a region in the left temporal gyrus was consistently more activated across subjects in the task of topological discrimination, consistent with the behavioral results. In summary, the global topological dominance in the LH is well supported by the converging evidence from the variety of paradigms and techniques, and it suggests a unified solution to the current major controversies on visual lateralization.

[Study of functional magnetic resonance imaging in strabismic and anisometropic amblyopic patients].

OBJECTIVE: To elucidate the difference in the pathogenesis between strabismic amblyopia and anisometropic amblyopia. METHODS: Using an EPI gradient echo sequence in 1.5 T MRI and visual electrophysiological system, the pattern visual evoked potentials and calcarine activation by monocular viewing of check-board pattern with reversal were examined in 18 strabismic amblyopes and 15 anisometropic amblyopes. The calcarine activation in terms of binocular voxels index and dependence on the spatial frequency of the stimuli were compared. The correlation between PVEP P(100) latency and activation intensity was also analyzed. RESULTS: The binocular voxels index was lower in the strabismic amblyope than that in the anisometropic amblyope. The calcarine activation from amblyopic eyes in strabismic amblyopes was more suppressed at higher spatial frequencies (1, 2 c/d); while that from amblyopic eyes in anisometropic amblyopes was more suppressed at all spatial frequencies (0.25, 0.5, 1 and 2 c/d). Inverse correlations existed between PVEP P(100) latency and activation intensity in two types amblyopia (P < 0.05). CONCLUSIONS: The binocular interaction is not equal in these two different types of amblyopia. Meanwhile, the amblyopia-related deficits in the low and high-spatial-frequency pathway of visual system are not similar between these two different types of amblyopia.

Contributions of the visual ventral pathway to long-range apparent motion.

Objects displaced intermittently across the visual field will nonetheless give an illusion of continuous motion [called apparent motion (AM)] under many common conditions. It is believed that form perception is of minor importance in determining AM, and that AM is mediated by motion-sensitive areas in the "where" pathway of the cortex. However, form and motion typically interact in specific ways when natural objects move through the environment. We used functional magnetic resonance imaging to measure cortical activation to long-range AM, compared to short-range AM and flicker, while we varied stability of structural differences between forms. Long-range AM activated the anterior-temporal lobe in the visual ventral pathway, and the response varied according to the form stability. The results suggest that long-range AM is associated with neural systems for form perception.