Production Of High-fidelity Entangled Photons Exceeds 1 Million Per Second

[R. A. Hettinga]

<http://www.sciencedaily.com/print.php?url=/releases/2004/07/040720085840.htm>


Source:
University Of Illinois At Urbana-Champaign

Date:
2004-07-20

URL:
http://www.sciencedaily.com/releases/2004/07/040720085840.htm

Production Of High-fidelity Entangled Photons Exceeds 1 Million Per Second

CHAMPAIGN, Ill. - Like virtuosos tuning their violins, researchers at the
University of Illinois at Urbana-Champaign have tuned their instruments and
harmonized the production of entangled photons, pushing rates to more than
1 million pairs per second.

The brighter and purer entangled states could assist researchers in
applications involving quantum information processing - such as quantum
computation, teleportation and cryptography - and help scientists better
understand the mysterious transition from quantum mechanics to classical
physics.

"Entangled states are the quintessential feature of quantum mechanics,"
said Paul Kwiat, a John Bardeen Professor of Electrical and Computer
Engineering and Physics at Illinois. "All the manifestations of quantum
mechanics in the world around us arise from the basic but bizarre coupling
that exists between entangled particles."

For example, the properties of entangled photons are inextricably linked to
each other, even if the photons are located on opposite sides of the
galaxy. To study this "correlation at a distance," Kwiat and graduate
students Joseph Altepeter and Evan Jeffrey produce pairs of
polarization-entangled photons by passing a laser pulse through two
adjacent nonlinear crystals.

"You can think of polarization as the 'wiggle' direction of the photon -
either horizontal, vertical or diagonal," Kwiat said. "As soon as you
determine the wiggle direction of one photon in an entangled pair, you
immediately know the wiggle direction of the other photon, no matter how
far apart they are."

A major production problem, however, is that entangled photons are emitted
in many directions and with a wide range of polarization phase
relationships, each acting like an individual singer in a large choir.

"Instead of hearing a soloist hit one note, we were hearing many choir
members, some of whom were singing off-key," Kwiat said.

The trick was to come up with a way of tuning the system. "We found that we
could pass the photons through another crystal - one that has a different
phase profile - to compensate for the different phase relationships," Kwiat
said. "The dissonance is corrected and the system becomes harmonized."

In the same manner as a corrector lens in a telescope removes chromatic
aberration and improves image quality, the researchers' special
birefringent crystal removes distortions in the quality of the
entanglement. "After the compensator crystal, the photons are all entangled
in exactly the same way," Altepeter said. "We can open the iris and get
more than 1 million useful pairs per second."

Ultrabright, ultrapure sources of entangled photons are essential for
pursuing quantum computing and quantum networks, as a resource for
teleportation in quantum communication, and for sending more information
faster by means of quantum cryptography. High fidelity quantum states can
also provide researchers with a clearer picture of how the universe works
on a very fundamental level.

"Using a low-brightness source is like looking into the quantum world
through a foggy window," Altepeter said. "With a bright, pure source, we
have a very clear window that allows us to see phenomena we couldn't see
before."

The ultimate goal is to understand and develop an intuition for the quantum
nature of reality, said Kwiat, who will report the team's findings at the
International Conference on Quantum Communication, Measurement and
Computing, to be held July 25-29 in Glasgow, United Kingdom. "Higher
production rates of nearly perfectly entangled photons will help us better
understand the rules of the quantum universe, how to navigate that
universe, and how to characterize it in a very precise way."

 The work was funded by the National Science Foundation, the Army Research
Office, and the Advanced Research and Development Activity.

Editor's Note: The original news release can be found here.

This story has been adapted from a news release issued by University Of
Illinois At Urbana-Champaign.

-- 
-----------------
R. A. Hettinga <mailto: rah at ibuc.com>
The Internet Bearer Underwriting Corporation <http://www.ibuc.com/>
44 Farquhar Street, Boston, MA 02131 USA
"... however it may deserve respect for its usefulness and antiquity,
[predicting the end of the world] has not been found agreeable to
experience." -- Edward Gibbon, 'Decline and Fall of the Roman Empire'

---------------------------------------------------------------------
The Cryptography Mailing List
Unsubscribe by sending "unsubscribe cryptography" to majordomo at metzdowd.com