Physicists confirmed photons passing through cloud of atoms can spend negative amount of time there with atoms themselves providing the evidence. University of Toronto researchers led by Daniela Angulo published findings in Physical Review Letters demonstrating photons can appear to exit material before entering it.
The experiment used photons passing through cloud of rubidium atoms demonstrating light particles can exhibit negative dwell time. When photons passed through and excited atoms, probe beam detected tiny changes revealing exactly how long atoms remained excited. The answer came back negative confirming quantum quirk is real physical phenomenon not mathematical illusion.
Researchers used two laser beams with one carrying signal to study and other acting like heartbeat monitor for atoms. The team discovered when light pulses experienced negative group delay the atoms showed corresponding negative excitation times. The two measurements matched perfectly proving this represented real physical phenomenon rather than visual trick.
Aephraim Steinberg, physicist at University of Toronto, stated photons can make atoms seem to spend negative amount of time in excited state. The phenomenon settles long debate among physicists with some arguing negative group delay was mathematical sleight of hand while others suspected it represented something physically real.
“This doesn’t mean that we’re on the verge of building a time machine or anything like that,” study co-author Howard Wiseman, a theoretical quantum physicist at Griffith University in Australia said, talking to media. “It can all be understood with standard physics, but it’s yet one more weird property of quantum physics that people hadn’t suspected.”
Setup required extraordinary precision trapping rubidium-85 atoms in tiny cloud sending shaped signal pulses through it. Tests across different pulse durations and cloud densities confirmed predictions every time. Howard Wiseman, theoretical quantum physicist at Griffith University in Australia, collaborated on developing theoretical framework underlying experiment.
The team’s next target involves photons that don’t make it through cloud. Theory predicts scattered photons carry extra positive excitation time balancing negative time of transmitted ones keeping overall average for beam at zero or above. That prediction has never been tested according to researchers.
It is also important to note that experiments going back to 1993 have suggested that transmitted photons often reach a detector before the main part of their pulse even makes it into the cloud. This indicates a negative transit time.
