Photonic modulation: an advance in quantum information processing

  • Published
  • By Maria Callier
  • Air Force Office of Scientific Research
ARLINGTON, Va. --  Researchers at Stanford University have potentially advanced quantum cryptography, information processing, and memory storage by being the first scientists to modulate the time profile of a single photon.

Air Force Office of Scientific Research-funded Dr. Steve Harris and his co-researchers at Stanford University have demonstrated a new technique for modulating the wavepacket of a single photon. Harris's team created an entangled photon wave packet nearly a microsecond long, using "slow light" and "electromagnetically induced transparency." Prior to this, wave packets were too short to allow their modulation.

With wave packets, it is important to know when the photon is inside the
modulating device. The particle can be located by generating two photons in
rubidium gas at slightly different frequencies and letting the slow (speed
of light) moving one, signaling the faster (1/10,000 speed of light) moving
one's arrival in the pulse-shaping device (electro-optic modulator)."

"Single photon physics provides secure communication. If I do coding with photons, eavesdropping is not possible. A person who tries to eavesdrop, destroys the photon in the process," said Harris.

In the past, single photons were created in "cavities" to have particular wave packet forms, but the modulator makes it possible to both modulate much faster and also to modulate the phase. The present work demonstrates amplitude modulation, and the next phase of Harris' research will focus on phase modulation. This has the advantage that it does not cause the loss of photons. In fact, it should be possible to show that many bits of information may be transmitted as part of the phase of a single photon.

Harris' research makes use of what is termed as "cold atoms." The technique for cooling atoms was invented by Dr. Steve Chu and colleagues, earning a Nobel Prize in 1997, and was also supported by AFOSR.