By exploiting
the weird quantum behavior of atoms, physicists at the
Commerce Department’s National Institute of
Standards and Technology (NIST) have demonstrated a new technique
that someday could be used to save weeks of measurements
needed to operate ultraprecise atomic clocks. The technique
also could be used to improve the precision of other measurement
processes such as spectroscopy.
The technique,
described in today’s issue of Science,
effectively turns atoms into better frequency sensors. Eventually,
the technique could help scientists measure the ticks of
an atomic clock faster and more accurately. Just as a grandfather
clock uses the regular swings of a pendulum to count off
each second of time, an atomic clock produces billions of
ticks per second by detecting the regular oscillations of
atoms. The trick to producing extremely accurate atomic clocks
is to measure this frequency very precisely for a specific
atom.
In the latest
experiment, the scientists used very brief pulses of ultraviolet
light in a NIST-developed technique
to put three beryllium ions (charged atoms) into a special
quantum state called entanglement. In simple terms, entanglement
involves correlating the fates of two or more atoms such
that their behavior—in concert—is very different
from the independent actions of unentangled atoms. One effect
is that, once a measurement is made on one atom, it becomes
possible to predict the result of a measurement on another.
When applied to atoms in an atomic clock, the effect is that
n entangled atoms will tick n times faster than the unentangled
atoms.
Currently, scientists at NIST and other laboratories make
many thousands of measurements of the ticks of unentangled
atoms and average these results to get highly accurate
atomic clocks (currently keeping time to better than one
second in 40 million years).
If entangled atoms could be used in a clock, the same or
better results could be achieved with far fewer separate
measurements. The current experiment demonstrates this
new approach to precision measurement with three ions;
however, the researchers are looking forward to entangling
even more ions to take greater advantage of the technique.
"Even if we could implement this new technique with
only 10 ions, in the clock business that's really important
because the clocks must be averaged for weeks and even months," says
NIST physicist Dave Wineland, leader of the research group. "The
time needed to do that would be reduced by a factor of 10."
In the experiment
reported in Science, scientists entangled the ions with
two laser beams, using a technique originally
developed for quantum computing applications. The ions are
hit with another series of laser pulses and their fluorescence
(emitted light, which represents the ions’ quantum
state) is measured for a specific period of time. The duration
of the steps, number of ions, and other experimental conditions
are controlled carefully to ensure all the ions are in the
same state when they are measured, so that either all or
none fluoresce, which simplifies the readout.
The research was supported in part by the Advanced Research
and Development Activity and the National Security Agency.
As a non-regulatory
agency of the U.S. Department of Commerce’s
Technology Administration, NIST develops and promotes measurement,
standards and technology to enhance productivity, facilitate
trade and improve the quality of life.
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Created:
06/04//04
Last
updated:
06/04/2004
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