Using a two-photon interferometer, we have measured the time delay for a photon to tunnel across a barrier consisting of a 1.1-μm-thick 1D photonic band-gap material. The peak of the photon wave packet appears on the far side of the barrier 1.47±0.21 fs earlier than it would if it were to travel at the vacuum speed of light c. Although the apparent tunneling velocity (1.7±0.2)c is superluminal, this is not a genuine signal velocity, and Einstein causality is not violated. The measured tunneling time is consistent with the group delay ("phase time"), but not with the semiclassical time.
ASJC Scopus subject areas
- Physics and Astronomy(all)