Fig. 1: Experimental setup for measuring the speed of particles.
From: Energy–speed relationship of quantum particles challenges Bohmian mechanics
a, Schematic of the experimental setup. The microcavity consists of two planar mirrors, one of which is nanostructured, with an optically active dye in between. The optical medium can be non-resonantly pumped to induce a lasing process, generating microcavity photons at the point of pumping. A small amount of the light circulating in the microcavity is transmitted through the mirrors and can be imaged onto a camera. b, Height map and cross-sections (see colour coding) of the nanostructured mirror. The height profile of the nanostructured mirror effectively induces a potential energy landscape that confines and guides the photons in the transverse plane of the resonator. Specifically, the light is guided in a waveguiding potential from x = −900 μm to the end of the structure at x = 500 μm. In the first section, from x = −900 μm to x = −600 μm, a linear ramp potential is superimposed on the waveguide potential. By changing the position of the non-resonant optical pumping along the ramp with a spatial light modulator (SLM), we can set the initial potential energy of photons. At x = 0, a step potential of height V0 = (0.538 ± 0.003) meV is superimposed on the waveguide that runs from x = 0 μm to x = 500 μm. Apart from the main waveguide described above (red cross-section), an auxiliary waveguide (green cross-section) is introduced at the start of the step potential at x = 0. This effectively creates a double-well potential in the direction orthogonal to the waveguide axis (grey cross-section), with a coupling between the respective ground states of the wells of J0 = 2π(6.34 ± 0.01) GHz. c, Camera images showing the photon populations in the coupled waveguides for three distinct energy regimes associated with three different dynamics: population oscillations in the classically allowed regime \((\varDelta > {\hbar }{J}_{0})\), long-range non-oscillatory propagation \((|\varDelta |\le {\hbar }{J}_{0})\) and evanescent decay \((\varDelta < -{\hbar }{J}_{0})\). Scale bar, 50 μm (b, height); 100 μm (b, length).
