Description
Quantum mechanics allows particles to reside in classically forbidden regions without violating energy conservation, owing to the well-known fact that these regions are characterized by domains of negative kinetic energy. This raises a natural question: how is negative kinetic energy reflected in the particle's velocity (speed), and more broadly, how can the particle's motion be characterized? Here, we study evanescent quantum states within a reflective potential step, augmented by coupled waveguides to reconstruct particle speed. We implement this idea in an optical dye-filled microcavity, which allows us to create a 2D quantum-confined gas of massive photons, guide and control its motion, and observe its wave function. We measure an energy-speed relationship for classically forbidden motion. We find that, counterintuitively to classical expectations, the speed of photons in evanescent states increases the lower their energy is. This surprising result offers new insights into the long-debated problem of tunneling time. Moreover, our findings challenge the validity of Bohmian mechanics, which assumes that only the phase gradients of the wave function drive particle motion, predicting the absence of motion in classically forbidden regions.| Period | 21 Jan 2025 |
|---|---|
| Event title | NWO Physics 2025 |
| Event type | Conference |
| Location | Veldhoven, NetherlandsShow on map |
| Degree of Recognition | National |