Optical parametric oscillator: Difference between revisions

Revision as of 17:09, 7 March 2007

Revision as of 01:13, 11 March 2007

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The OPO is the physical system most widely used to generate [[squeezed]] states and [[entangled]] states of light in the continuous variables regime. Many demonstrations of quantum information protocols for continuous variables were realized using OPO's<ref>J. Jing, J. Zhang, Y. Yan, F. Zhao, C. Xie, and K. Peng, Phys. Rev. Lett. 90, 167903 (2003).</ref><ref>S. Koike, H. Takahashi, H. Yonezawa, N. Takei, S. L. Braunstein, T. Aoki, and A. Furusawa, Phys. Rev. Lett. 96, 060504 (2006).</ref><ref>N. Takei, H. Yonezawa, T. Aoki, and A. Furusawa, Phys. Rev. Lett. 94, 220502 (2005).</ref><ref>S. Koike, H. Takahashi, H. Yonezawa, N. Takei, S. L. Braunstein, T. Aoki, and A. Furusawa, Phys. Rev. Lett. 96, 060504 (2006).</ref>.

The downconversion process really occurs in the single photon regime: each pump photon that is annihilated inside the cavity gives rise to a pair of photons in the signal and idler intracavity modes. This leads to a quantum correlation between the intensities of signal and idler fields, so that there is [[squeezing]] in the subtraction of intensities<ref>A. Heidmann, R. J. Horowicz, S. Reynaud, E. Giacobino, C. Fabre, and G. Camy, Phys. Rev. Lett. 59, 2555 (1987).</ref>, which motivated the name "twin beams" for the downconverted fields. The highest squeezing level ever measured was observed in this situation<ref>J. Laurat, L. Longchambon, C. Fabre, and T. Coudreau, Opt. Lett. 30, 1177 (2005).</ref>, reaching the impressive value of -9.7dB. This means that the quantum fluctuations were reduced one order of magnitude relative to the classical limit.

It turns out that the phases of the twin beams are quantum correlated as well, leading to [[entanglement]], theoretically predicted in 1988 <ref>M. D. Reid and P. D. Drummond, Phys. Rev. Lett. 60, 2731 (1988).</ref>. Below threshold, entanglement was measured for the fisrtfirst time in 1992 <ref>Z. Y. Ou, S. F. Pereira, H. J. Kimble, and K. C. Peng, Phys. Rev. Lett. 68, 3663 (1992).</ref>, and in 2005 above threshold<ref>A. S. Villar, L. S. Cruz, K. N. Cassemiro, M. Martinelli, and P. Nussenzveig, Phys. Rev. Lett. 95, 243603 (2005).</ref>.

Above threshold, the pump beam depletion makes it sensitive to the quantum phenomena happening inside the crystal. The first measurement of squeezing in the pump field after parametric interaction was done in 1997<ref>K. Kasai, J.G. Gao, and C. Fabre, Europhys. Lett. 40,

25 (1997).</ref>. Actually, it has been recently predicted that all three fields (pump, signal and idler) must be entangled<ref>A. S. Villar, M. Martinelli, C Fabre, and P. Nussenzveig, Phys. Rev. Lett. 97, 140504 (2006).</ref>.