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Long-time Dynamics of Spontaneous Parametric Down-conversion and Quantum Limitations of Conversion Efficiency* Michael Fleischhauer and Oliver Veits Sektion Physik, Ludwig-Maximilians-Universität München, Theresienstraße 37, D-80333 München Z. Naturforsch. 54 a, 57-62 (1999); received June 25, 1998 We analyze the long-time quantum dynamics of degenerate parametric down-conversion from an initial sub-harmonic vacuum (spontaenous down-conversion). Standard linearization of the Heisen- berg equations of motion fails in this case, since it is based on an

article we present a local hidden variables model for all experiments involving photon pairs produced in parametric down conversion, based on the Wigner representation of the radiation field. A modification of the standard quantum theory of detection is made in order to give a local realistic explanation of the counting rates in photodetectors. This model involves the existence of a real zeropoint field, such that the vacumm level of radiation lies below the threshold of the detectors. Key words: Parametric Down Conversion; Wigner Representation; Zeropoint Field

Interferometry; Parametric Down-conversion; De Broglie Wavelength; Entanglement. It is well known that a de Broglie wavelength can be associated not only to single particles, but also to a multiparticle system. For a system of N iden­ tical particles, the resulting wavelength is given by AdB = Aj/iV, where Aj is the de Broglie wavelength associated to the individual constituent particles [1]. Normally, these particles are held together by some kind of binding force as in the experiments done with molecules by Borde et al. [2] and Chapman et al. [3]. In a recent paper

). Direct measurement and reconstruction of nonclassical features of twin beams generated in spontaneous parametric down-conversion. Physical Review A, 71 (3), 033815-033819. [15] Waks, E., Sanders, B.C., Diamanti, E., Yamamoto, Y. (2006). Highly non-classical photon statistics in parametric down-conversion. Physical Review A, 73 (3), 033814. [16] Waks, E., Diamanti, E., Sanders, B.C., Bartlett, S.D., Yamamoto, Y. (2004). Direct observation of nonclassical photon statistics in parametric downconversion. Physical Review Letters, 92 (11), 113602. [17] Haderka, O., Hamar, M


Entanglement enhancement is a key task for quantum technologies. This operation performed on states produced by parametric down-conversion sources has been the object of several recent experimental investigations. In particular, conditional preparation by photon-subtraction has been shown to improve the entanglement of these states. Here we analyse the role played by non-Gaussian and Gaussian measurements in more general entanglement concentration operations performed on a pair of two-mode squeezed vacua. We find stringent requirements for achieving an improved entanglement enhancement by measuring jointly these two resource states.


The physics that governs quantum monitoring may involve other degrees of freedom than the ones initialised and controlled for probing. In this context we address the simultaneous estimation of phase and dephasing characterizing a dispersive medium, and we explore the role of frequency correlations within a photon pair generated via parametric down-conversion, when used as a probe for the medium. We derive the ultimate quantum limits on the estimation of the two parameters, by calculating the corresponding quantum Cramér-Rao bound; we then consider a feasible estimation scheme, based on the measurement of Stokes operators, and address its absolute performances in terms of the correlation parameters, and, more fundamentally, of the role played by correlations in the simultaneous achievability of the quantum Cramér- Rao bounds for each of the two parameters.

[1] SVOZIL, K.: Are simultaneous Bell measurements possible?, New J. Phys. 8 (2006), 39. [2] ZEILINGER, A.: A foundational principle for quantum mechanics, Found. Phys. 29 (1999), 631–643. [3] EIBL, M. — GAERTNER, S. — BOURENNANE, M. — KURTSIEFER, C. — ZUKOWSKI, M. — WEINFURTER, H.: Experimental observation of four-photon entanglement from parametric down-conversion, Phys. Rev. Lett. 90 (2003

”, Phys. Rev. Lett., Vol. 57, (1986), pp. 691–694. [4] L.A. Wu, H.J. Kimble, J.L. Hall and H. Wu: “Generation of Squeezed States by Parametric Down Conversion”, Phys. Rev. Lett., Vol. 57, (1986), pp. 2520–2523. [5] P. Meystre and M.S. Zubairy: “Squeezed states in the Jaynes-Cummings model”, Phys. Lett. A, Vol. 89, (1982), pp. 390–392. [6] F.L. Li and S.Y. Gao: “Controlling nonclassical properties of the Jaynes-Cummings model by an

. Fleischhauer, M. (2005). Electromagnetically induced transparency: Optics in coherent media. Reviews of Modern Physics, 46 (2), 633-673. DOI:10.1103/ RevModPhys. 77.633 20. Chrapkiewicz, R., & Wasilewski, W. (2010). Multimode spontaneous parametric down-conversion in a lossy medium. Journal of Modern Optics, 57 (5), 345-355. DOI:10.1080/09500341003642588 21. Duan, L. M, Lukin, M. D., Cirac, J. I., & Zoller, P. (2001). Long-distance quantum communication with atomic ensembles and linear optics. Nature, 81 (6862), 5788-418. DOI:10.1038/35106500 22. Scully, M. O., & Zubairy

[1] B. Yurke “Input states for enhancement of fermion interferometer sensitivity”, Phys. Rev. Lett., Vol. 56, (1986), pp. 1515–1517. [2] L.A. Wu, H.J. Kimble, J.L. Hall and H. Wu “Generation of squeezed states by parametric down conversion”, Phys. Rev. Lett., Vol. 57, (1986), pp. 2520–2523. [3] M. Kitagawa and M. Ueda “Squeezed spin states”, Phys. Rev. A, Vol. 47, (1993), pp. 5138–5143. [4] D.J. Wineland, J.J. Bollinger, W