Ion trap in the lab of Dr. Roee Ozeri |
Weizmann
Institute scientists set a new record for measuring magnetic vibrations
using the spin of a single atom: 100 times more accurate than the
previous record
The
lab, though it may seem quiet and insulated, can be as full of
background noise as a crowded train station when we’re trying to catch
the announcements. Our brains can filter out the noise and focus on the
message up to a certain point, but turning up the volume on the
loudspeakers – improving the signal-to-noise ratio – helps as well.
Separating
out the signal from the noise – increasing one while reducing the other
– is so basic that much of scientific research could not take place
without it. One common method, developed by the physicist Robert Dicke
at Princeton University, is based on a principle similar to the one that
enables radio broadcasts to pass through the noisy atmosphere. In
short, one modulates electric waves (which correspond to the sound
waves) one wishes to send over long distances, adding them on top of a
high-frequency wave. To listen to the broadcast, one must have a
receiver that is tuned to the frequency of the carrier wave (that
numbered band on the FM dial), which then splits the two waves apart and
amplifies the second “rider” wave – the music or talk we want to hear.
The
method used by the physics labs is called “locked-in amplification.”
Here, too, a low-frequency, measured signal “rides” a high-frequency
wave. A locked-in amplifier singles out the specific wave from the rest
of the noise, “locking” onto the required signal and enabling scientists
to make all sorts of accurate measurements.
To
obtain good spatial resolution, one should measure with the smallest
possible detector; one can’t get much smaller than a single atom. The
world of single atoms, however, is governed by the laws of quantum
physics, and any sort of observation in the quantum world is a complex
undertaking. The Heisenberg uncertainty principle, one of the
cornerstones of quantum theory, sets limits on our ability to measure
with any kind of precision. But that very theory contains some clues as
to how these limits can be approached.
Dr. Roee Ozeri
and research students Shlomi Kotler, Nitzan Akerman, Yinnon Glickman
and Anna Keselman in the Weizmann Institute’s Physics of Complex Systems
Department applied the rules of quantum mechanics to a single
atomic-ion detector, building a quantum version of a locked-in
amplifier. Using the ions’ spin as a sensor, they were able to measure
magnetic vibrations with a spatial resolution of a just few nanometers
(a few billionths of a meter). The sensitivity of this measurement was
extremely high: around 100 times better than any previous such
measurement. This technique, says Ozeri, could be used in physics labs
around the world to improve the sensitivity of all sorts of quantum
sensors.
Dr.
Roee Ozeri’s research is supported by the Yeda-Sela Center for Basic
Research; the Wolfson Family Charitable Trust; David Dickstein, France;
and Martin Kushner Schnur, Mexico.
