Zhe-Yu Jeff Ou
Professor

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Education

B.S., Physics, Peking University, Beijing, China, 1984
M.A. Physics, University of Rochester, Rochester, NY, 1986
Ph.D., Physics, University of Rochester, Rochester, NY, 1990

Research

My research mainly concerns the quantum behavior of light with emphasis on squeezed states of light, quantum amplification processes, nonclassical interference effects, and nonlocality. In particular, we study nonclassical phenomenan the process of parametric down-conversion and its reverse process, second harmonic generation.

Fluctuations in electromagnetic fields exist even in vacuum due to the Heisenberg uncertainty principle. This noise is responsible for a number of quantum phenomena of light including spontaneous emission. However, quantum theory does not prevent us from suppressing this noise. In the squeezed state of light, fluctuations in certain phases of oscillation of the electromagnetic wave can be smaller than those in vacuum while fluctuations in other phases will be larger. A squeezed state of light can be generated in nonlinear optical processes such as parametric down-conversion, where the down-converter works as a phase-sensitive amplifier with the input vacuum noise amplified and deamplified (squeezed) depending on the phase. Application of squeezed light to quantum systems can significantly change the properties of the system.
Besides squeezed light, parametric down-conversion processes also produce nonclassical states such as a single photon state and a two-photon entangled state, which can give rise to phenomena such as sub-Poissonian photon statistics and nonclassical interference that are unexplainable by classical wave theory. These states are also associated with the famous Einstein-Podolsky-Rosen paradox of quantum theory. The problems that we are interested in are the nonlocality of single-photons and the EPR paradox with continuous variables.

A parametric down-converter can also work as a phase sensitive amplifier like a laser with excited atoms as the active medium. However, the down-converterÕs internal modes are well defined and easily accessible, allowing us to study the quantum properties of an amplifier.

Apart from the fundamental issues of quantum mechanics, we are also interested in efficient, cw, second harmonic generation using external resonators.

Publications

Lu YJ, Zhu L, and Ou Z-Y (2005)
Security Improvement of Using Modified Coherent State for Quantum Cryptograph.
Physical Review A71, 032315-(1-4).

Lu YJ, Huang F and Ou Z-Y (2005)
Preparation and Manipulation of Mode-Locked Two-Photon State.
Mod. Phys. Lett. B19, 269-293.

Ou Z-Y (2005)
Distinguishing Four Photons in Entangled State From Two Independent Pairs of Photons.
Physical Review A72, 053814-(1-6).

Shafiei F, Srinivasan P and Ou Z-Y (2004)
Generation of Three-Photon Entangled State by Quantum Interference Between a Coherent State and Parametric Down-Conversion.
Physical Review A70, 043803.

Lu YJ, Campbell RL and Ou ZY (2003)
Mode-Locked Two-Photon States.
Physical Review Letters 91, 163602-163604.

Ou ZY and Su Q (2003)
Uncertainty in Determining the Phase for an Optical Field Due to Particle Nature of Light.
Laser Physics 13, 1175-1187.

Lu YJ and Ou ZY (2002)
Observation of Nonclassical Photon Statistics due to Quantum Interference,
Phys. Rev. Lett. 88, 023601.