LL11945

Reducing quantum noise in atomic clocks with light

Researchers have demonstrated a new method to improve the sensitivity
of atomic clocks, by using a light field to shuttle information
between distant atoms so that their quantum errors cancel out.
Ensembles of atoms in vacuum are exquisitely sensitive detectors for
measuring time, magnetic fields, gravity and other fundamental
physical effects. Normally, each atom acts as an independent
detector, with some unavoidable measurement noise due to quantum
uncertainty. Adding up the signal from these independent atoms also
adds up their noise. However, if the atoms can communicate, they can
be coaxed into an entangled quantum state where fluctuations of
different atoms are correlated in such a way that the total quantum
noise is reduced, while the full signal is maintained. This is
achieved by placing the atoms in an optical resonator, configured so
that the intensity of the light circulating within it depends on the
internal state of all atoms in the ensemble. Distant atoms, which
never interact directly with one another, nevertheless acquire quantum
correlations as they experience a light field that depends on the
state of all their peers. The new method results in the greatest
entanglement-enabled improvement in signal-to-noise-ratio to date.