Squeezing and Einstein-Podolsky-Rosen correlation in the mirrorless optical parametric oscillator

Abstract

This work analyses the temporal coherence and correlation of counterpropagating twin photons generated in a quasi-phase matched nonlinear cristal by spontaneous parametric-down conversion. We find out different pictures depending on the pump pulse duration relative to two characteristic temporal scales, determined respectively by the temporal separation between the counterpropagating and the co-propagating wavepackets. When the pump duration is intermediate between the two scales, we show a transition from a highly entangled state to an almost separable state, with strongly asymmetric spectral properties of the photons.

Continuous variable entanglement of counter-propagating twin beams

“…Our quantum model for this configuration is described in Refs. [7,9,10] (see also [14], [15]). We summarize in the following the main points − A purely temporal description of the twin beams is carried out, assuming either a waveguided configuration or that a small angular bandwidth is collected.…”

“…Its inverse Ω gvs is responsible the narrow width of the spectrum of downconverted light, both below [6,7,9,14], and above the MOPO threshold [5]. The first term in the Taylor expansion (10) is by far the dominant one, so that the linear approximation for the phase mismatch in Eq. ( 11) is well justified.…”

“…The two symmetric spectral components F(Ω), F(−Ω) can be shown to represent the noise in the two sidebands modes ĉ± (Ω), and ĉ± (−Ω) [10] . As described in [10], the best squeezing is achieved by choosing the phase-angles as…”

“…Counter-propagating PDC emerged in the last years as a promising source of quantum light, with several peculiar and appealing features [6][7][8][9][10]. First of all, in contrast with the usual single-pass co-propagating geometry, this source is narrowband, so that in the spontaneous regime it has the potentiality to generate narrowband heralded single photons in almost pure states [6][7][8].…”

“…Responsible of this critical behaviour is a feedback mechanism, which in this case is established not by the cavity mirrors, but by the back-propagating wave, in combination with stimulated down-conversion [9]. A recent analysis [10] has shown that this cavityless configuration of PDC may produce the same high and stable level of squeezing and quadrature correlation as the OPO, and may thus become a robust and monolithic alternative to the cavity configuration.…”