Quantum test confirms photons can exhibit negative time
Physicists report that photons passing through a cloud of atoms can appear to exit before entering, i.e., negative transit time. In a Physical Review Letters study, the researchers monitored the atoms’ excited state during the photon’s passage with a second readout beam and used weak measurements, requiring about 1 million trials across seven parameter sets to obtain a clear signal. The result, which aligns with standard quantum mechanics, shows transmitted photons can have negative time while scattered photons carry positive time, keeping the beam’s average time nonnegative. The next step is to test time effects for photons that don’t pass through the cloud.
