Dynamics and detection of the Newton-Wigner time delays at interfaces using a swivelling method

Evanescent waves are ubiquitous at interfaces with optical, seismic or acoustic waves, and also with electron, neutron or atom beams. Newton was the first to suspect that both small time delays and spatial shifts exist during total internal reflection. However, these effects are so tiny that the spatial shifts were only observed in 1947 in optics, whereas the time delay values predicted by the Wigner model in the 10−14 s range in optics had to await femtosecond lasers to be detected with difficulty. The spatial shifts have been isolated in many areas but the time delays, though fundamental, generally remain out of reach, particularly with particles. In textbooks usually both quantities are supposed to be simply linked. Here we report, using swivelling detectors, that the spatial and temporal measurements are intimately intermingled, especially in the so-called cyclical regime. Indeed, while the spatial shift does not depend on the type of detection, the measured time delay can be positive, negative or zero, but controllable. We also discuss how such intricate measurements of spatial and temporal effects allow crucial time penalties to be eliminated in guided soliton propagation, and should be used to unambiguously identify the Newton-Wigner time delays for particles.