Do single photons tunnel faster than light?

TL;DR

This paper clarifies that apparent superluminal tunneling times for photons are actually cavity lifetimes, resolving the Hartman paradox and confirming that tunneling does not exceed the speed of light.

Contribution

The paper provides a reinterpretation of tunneling delay measurements, demonstrating they are due to cavity lifetimes rather than true transit times, thus resolving the superluminal tunneling paradox.

Findings

Measured delays correspond to cavity lifetimes, not transit times.

Superluminal group velocities are artifacts of measurement, not actual faster-than-light travel.

Tunneling does not violate the speed of light limit.

Abstract

Experiments done in the early 1990's produced a surprising result: that single photons pass through a photonic tunnel barrier with a group velocity faster than the vacuum speed of light. Subsequent experiments with classical pulses have also revealed apparent superluminal group velocities as well as tunneling times that saturate with barrier length, a phenomenon known as the Hartman effect. In this paper we show that the measured delays are in fact cavity lifetimes as opposed to transit times. This interpretation resolves the Hartman paradox and shows that tunneling is not superluminal as widely believed.