Abstract
We experimentally investigate the parametric down-conversion process in a nonlinear bulk crystal, driven by two non-collinear pump modes. The experiment shows the emergence of bright hot-spots in modes shared by the two pumps, similar to the phenomenology recently observed in 2D nonlinear photonic crystals. By exploiting the spatial walk-off between the two extraordinary pump modes, we have been able to recreate a peculiar resonance condition, reported by a local enhancement of the parametric gain, which corresponds to a transition from a three-mode to a four-mode coupling. From a quantum point of view, this opens the way to the generation of multimode entangled states of light, such as tripartite or quadripartite states, in simple bulk nonlinear sources.
Highlights
Pulsed high-gain parametric down-conversion (PDC) in standard nonlinear crystals is widely used for the generation of bright squeezed vacuum, featured by perfect photon-number correlations between twin-beams [1,2,3,4,5,6]
The transition to resonance described in the previous section and the associated local intensity enhancement of the radiation, are experimentally detected and studied by spatially and spectrally resolving the shared and coupled modes and the PM curves associated with the two PDC processes
In this work we have studied the parametric down-conversion process in a nonlinear BBO crystal, stimulated by the interference pattern of two pump beams, obtained from a Mach-Zender type interferometer
Summary
Pulsed high-gain parametric down-conversion (PDC) in standard nonlinear crystals is widely used for the generation of bright squeezed vacuum, featured by perfect photon-number correlations between twin-beams [1,2,3,4,5,6]. Nonlinear photonic crystals (NPC), whose nonlinear response is artificially modulated according to a 2D pattern [10], offer a high degree of flexibility for engineering the properties of optical parametric processes because of the multiplicity of vectors of the nonlinear lattice providing quasi phase-matching These photonic crystals have shown interesting potentialities as monolithic sources of path-entangled photonic states [11,12,13], but even if they may provide novel compact schemes for continuous-variable quantum technologies [14,15,16,17], they are often difficult to realize, necessitating of lengthy poling procedures. Of particular interest for quantum technologies is the possibility, recently outlined [15,16,17], of using NPC as sources of three-mode or four-mode parametric coupling, in contrast to the more common two-mode coupling typical of the PDC process in standard configurations
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