At certain frequencies, a phenomenon recently identified as "collectively
induced transparency" (CIT) causes groups of atoms to abruptly stop
reflecting light.
By trapping ytterbium atoms inside an optical cavity—basically a small cage
for light—and firing a laser at them, CIT was discovered. As the frequency
of the light is changed, a transparency window forms in which the light
simply travels through the cavity unhindered, even though the laser's light
would initially bounce off the atoms up to a point.
"We never knew this transparency window existed," says Andrei Faraon (BS
'04), a professor of applied physics and electrical engineering at Caltech
and co-corresponding author of an article on the finding that appeared in
the journal Nature on April 26. "Our research has largely evolved into a
quest to understand why,"
Analysis of the transparency window suggests that interactions between
groupings of atoms and light in the cavity are what caused it. Destructive
interference is a phenomena where waves from two or more sources can cancel
one another out. The groupings of atoms continuously absorb and reemit
light, which often causes the laser's light to be reflected. At the CIT
frequency, however, a balance is established by the light that each atom in
a group reemits, which causes a decrease in reflection.
A graduate student at Caltech named Mi Lei is the co-lead author and
co-opinionated on the study. "An ensemble of atoms strongly coupled to the
same optical field can lead to unexpected results," she adds.
The optical resonator, which has features smaller than 1 micron in size and
is just 20 microns long, was created at the Kavli Nanoscience Institute at
Caltech.
A graduate student named Rikuto Fukumori is the paper's co-lead author.
"Through conventional quantum optics measurement techniques, we found that
our system had reached an unexplored regime, revealing new physics," he
adds.
In addition to the transparency phenomena, the researchers also noticed
that depending on the laser's strength, a group of atoms may absorb and emit
light from the laser either considerably quicker or much slower than a
single atom. Because there are so many interacting quantum particles, the
physics underpinning these processes, known as superradiance and
subradiance, is still not well understood.
"We were able to monitor and control quantum mechanical light-matter
interactions at the nanoscale," explains co-corresponding author Joonhee
Choi, a former postdoctoral fellow at Caltech who is currently an assistant
professor at Stanford University.
This discovery has the potential to one day help pave the road to more
effective quantum memory in which information is stored in an ensemble of
highly linked atoms, even though the study is essentially foundational and
increases our comprehension of the enigmatic realm of quantum effects.
Faraon has also experimented with controlling the interactions between
several vanadium atoms to provide quantum storage.
In addition to memory, these experimental systems offer crucial insight
into future links between quantum computers, according to co-author and
physics professor Manuel Endres, a Rosenberg Scholar.
Provided by
California Institute of Technology
