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NIST physicist Sae Woo Credit: NIST |
Scientists at the
National Institute of Standards and Technology (NIST) have developed*
the world’s most efficient single photon detector, which is able to
count individual particles of light traveling through fiber optic cables
with roughly 99 percent efficiency. The team’s efforts could bring
improvements to secure electronic communication, advanced quantum
computation and the measurement of optical power.
Using essentially the same technology that
permitted them to achieve 88 percent detection efficiency five years
ago,** the team has enhanced its ability to detect photons largely by
improving the alignment of the detector and the optical fibers that
guide photons into it. The basic principle of the detector is to use a
superconductor as an ultra-sensitive thermometer. Each
individual photon hitting the detector raises the temperature—and
increases electrical resistance—by a minute amount, which the instrument
registers as the presence of a photon.
According to team member Sae Woo Nam, the
advantage of this type of single photon detector is that the new
detector design not only measures lower levels of light than have ever
been possible, but does so with great accuracy.
“When these detectors indicate they’ve spotted a
photon, they’re trustworthy. They don’t give false positives,” says
Nam, a physicist with NIST’s Optoelectronics division. “Other types of
detectors have really high gain so they can measure a single photon, but
their noise levels are such that occasionally a noise glitch is
mistakenly identified as a photon. This causes an error in the
measurement. Reducing these errors is really important for those who are
doing calculations or communications.”
The ability to count individual photons is
valuable to designers of certain types of quantum computers as well as
scientists engaged in quantum optical experiments, which concern exotic
states of light that cannot be described by classical physics. But one
of the most promising potential applications of a high-efficiency photon
detector is a way to secure long-distance data transmission against
unwanted interception. A detector that could recognize that a photon
forming part of a transmission was missing would be a substantial
defense against information theft.
The team has optimized the detection for 810
nanometers—an infrared wavelength—and it still has high efficiency at
other wavelengths that are interesting for fiber optic communications,
as well as the quantum optics community. Ironically, the detector is so
efficient that it outstrips current technology’s ability to determine
its precise efficiency.
“We can’t be sure from direct measurement that
we’ve achieved 99 percent efficiency because the metrology is not in
place to determine how close we are—there’s no well-established
technique,” Nam says. “What is great about our latest progress is that
we measure nearly the same detection efficiency for every device we
build, package and test. It’s the reproducibility that gives us
confidence.”
The team is currently working to develop
evaluation techniques that can measure up to the detector’s abilities,
and Nam says the team’s creation could also help evaluate other
light-gathering devices.
“NIST offers a standardized service for
measuring the efficiency of photodetectors and optical power meters,” he
says. “We’re trying to develop a calibration technique that extends to
ultra-low levels of light. It should be valuable for anyone looking at
single photons.”
* A.E. Lita, B. Calkins, L.A. Pellouchoud, A.J.
Miller and S. Nam. Superconducting transition-edge sensors optimized
for high-efficiency photon-number resolving detectors. Presented at the
SPIE Symposium on SPIE Defense, Security, and Sensing, Orlando World
Center Marriott Resort and Convention Center, Crystal J1 Ballroom, 3
p.m. April 7, 2010.
** See “NIST
Photon Detectors Have Record Efficiency” in NIST Tech Beat,
June 2, 2005, at www.nist.gov/public_affairs/techbeat/tb2005_0602.htm#photon.
Media Contact: Chad Boutin, boutin@nist.gov, (301) 975-4261
