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Topic Name: The latest in encryption technology—have been sent over a record-setting 200-kilometer fiber-optic link
Category: Photonics
Research persons: H. Takesue, S.W. Nam, Q. Zhang, R.H. Hadfield, T. Honjo, K. Tamaki and Y. Yamamoto
Location: NIST, 100 Bureau Drive, Stop 1070, Gaithersburg, MD 20899-1070, United States
Details
Particles of light
serving as “quantum keys”—the latest in encryption technology—have been
sent over a record-setting 200-kilometer fiber-optic link by researchers from
the National Institute of Standards and Technology (NIST), NTT Corp. in Japan,
and Stanford University. The experiment, using mostly standard components and
transmitting at telecommunications frequencies, offers an approach for making
practical inter-city terrestrial quantum communications networks as well as
long-range wireless systems using communication satellites.The demonstration,
described in Nature Photonics,* was conducted in a Stanford lab with
optical fiber wrapped around a spool. In addition to setting a distance record
for quantum key distribution (QKD), it also is the first gigabit-rate
experiment—transmitting at 10 billion light pulses per second—to produce
secure keys. The rate of processed key production—the keys corrected
for errors and enhanced for privacy—was much lower due to the long distance
involved, and the key was not used to encrypt a digital message as it would be
in a complete QKD system. QKD systems transmit a stream of single photons with
their electric fields in different orientations to represent 1s and 0s, which
are used to make quantum keys to encrypt and decrypt messages. Properly
executed, quantum encryption is “unbreakable” because eavesdropping changes
the state of the photons.
A key aspect of the
experiment is the use of ultra fast super conducting single-photon detectors
developed in Russia, with packaging and cooling technology custom-made at NIST
labs in Boulder, Colo. Counting single photons (the smallest particles of light)
rapidly and reliably has been a major challenge limiting the development of
practical QKD systems. The Russian detectors have very low false count rates
because of their low-noise cryogenic operation, as well as superior timing
resolution due to the physics of superconductors, in which electrons can switch
from excited to relaxed states in just trillionths of a second. Each detector
consists of a super conducting niobium nitride nanowire operating just below the
“critical current” at which it conducts electricity without resistance. When
a single photon hits the wire, a hot spot is formed, and the current density
increases until it exceeds the critical current. At this point, a non-superconducting
barrier forms across the wire, and a voltage pulse is created. The starting edge
of the voltage pulse pinpoints the photon’s arrival time.
Sae Woo Nam, a NIST
physicist who packaged the detectors, said NIST offers unique expertise in
connecting the single-photon detector chips to optical fiber and in designing
refrigeration systems to operate at -270 degrees C (-454 degrees F) without
liquid cryogens. “You need to know how to efficiently get light to the
detector and how to amplify the signals,” he says.
The detectors
were designed and fabricated at the Moscow State Pedagogical University. The
project was supported by the Japan Science and Technology Agency, National
Institute of Information and Communications Technology of Japan, MURI Center for
Photonic Quantum Information Systems, Disruptive Technology Office, Defense
Advanced Research Projects Agency, and NIST.
About Researchers:
Hiroki Takesue
Ph. D., Senior Research Scientist
Quantum Optical State Control Research Group
NTT Basic Research Laboratories, NTT Corporation
3-1 Morinosato-Wakamiya, Atsugi, Kanagawa, 243-0198 Japan
E-mail: htakesue
Qing Zhang
Professor
Department of Mathematics
University of Georgia
Athens, GA 30602, USA
Tel. (706) 542-2616
Fax. (706) 542-2573
qingz@math.uga.edu
Toshimori Honjo, Ph.D.
Research scientist,
Quantum Optical State Control Research Group
Optical Science Laboratory
NTT Basic Research Laboratories
3-1, Morinosato-Wakamiya, Atsugi-shi,
Kanagawa Pref., 243-0198 Japan
Phone: +81 46 240 3416
Fax: +81 46 240 4726
E-mail: honjo
Yoshihisa Yamamoto
Address
Edward L. Ginzton Laboratory Stanford University
Stanford, CA 94305-4088
Telephone: 650-725-3327
FAX: 650-723-5320
E-mail: yyamamoto@stanford.edu
K. Tamaki
phone@: 81-3-5841-7018
fax
address : Department of Geosystem Engineering Graduate Schools of Engineering, The University of Tokyo
7-3-1, Hongo, Bunkyo-ku,
Tokyo, 113-8656 Japan
Funded:
The detectors were designed and
fabricated at the Moscow
State Pedagogical University. The project was supported by the Japan
Science and Technology Agency, National
Institute of Information and Communications Technology of Japan, MURI
Center for Photonic Quantum Information Systems, Disruptive Technology
Office, Defense
Advanced Research Projects Agency, and NIST
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