Physicists confirm 'negative time' is a real measurable quantum effect

[GlassKnight35]

A genuinely mind bending quantum experiment out of the University of Toronto has confirmed that negative time, the idea that a photon can appear to spend less than zero time interacting with atoms, is a real measurable physical effect rather than just a misleading artifact of how light pulses are shaped

The setup involves firing photons through a cloud of rubidium atoms that are resonant with the photons energy, meaning the photon can temporarily transfer its energy into the atoms as an excitation before being released again, because of a form of Heisenbergs uncertainty principle, a photon with well defined energy must have an uncertain timing, so you cant know exactly when it enters the cloud, only on average, and when researchers calculated the average time a successfully transmitted photon should arrive on the far side, they found it consistently arrives earlier than that calculation predicts, so early that the photon appears to have spent a negative amount of time dwelling in the cloud

This effect has actually been known since a 1993 experiment involving one of this papers own authors, Aephraim Steinberg, but physicists had mostly written it off as an artifact, the standard explanation was that only the very front edge of a long duration light pulse makes it through untouched while the rest gets scattered away, which would make an early arrival look like negative time without anything genuinely strange actually happening

What makes this new work different is that instead of just inferring dwell time from when the photon arrives, the researchers directly queried the atoms themselves, they fired a separate weak laser beam through the cloud and measured tiny phase shifts to probe whether the atoms were actually excited at any given moment, doing this with a precise measurement would have destroyed the effect entirely through the quantum Zeno effect, so they deliberately used a very imprecise but carefully calibrated weak measurement instead, averaging millions of individual runs to get an accurate reading

The result is what makes this genuinely significant, the weakly measured dwell time from directly querying the atoms came out exactly equal to the negative time implied by the photons arrival statistics, and critically, this weak measurement result cannot be explained away by the old only the front of the pulse gets through argument the way the arrival time result could, meaning two completely different measurement methods independently confirmed the same negative value, which nobody had actually expected to match this precisely before the experiment

The researchers are careful to stress this doesnt break standard physics or open the door to time travel, the whole result is fully consistent with established quantum mechanics, but it does confirm that this particularly strange feature of quantum theory has a directly measurable physical effect on the atoms a photon passes through, rather than being dismissible as just a quirk of how the light pulse happens to be shaped

Strange quantum experiment shows "negative time" is more than an illusionwww.sciencedaily.com