Delocalized Correlations in Twin Light Beams with Orbital Angular Momentum

We generate intensity-difference-squeezed Laguerre-Gauss twin beams of light carrying orbital angular momentum by using four-wave mixing in a hot atomic vapor. The conservation of orbital angular momentum in the four-wave mixing process is studied as well as the spatial distribution of the quantum correlations obtained with different configurations of orbital angular momentum. Intensity-difference squeezing of up to $-6.7\mathrm{dB}$ is demonstrated with beams carrying orbital angular momentum. Delocalized spatial correlations between the twin beams are observed.

Figure 1

(a) Setup geometry. $\mathrm{PBS}=\mathrm{\text{polarizing beam splitter}}$, $\mathrm{SA}=\mathrm{\text{spectrum analyzer}}$. (b) 4WM level scheme.

Figure 2

Intensity distribution (upper) and phase interferogram (lower) of the probe beam at the input, the amplified probe beam at the output, and the generated conjugate beam at the output of the 4WM cell. The output probe and conjugate beams display $-6.7\mathrm{dB}$ of intensity-difference squeezing. Reproduced from Ref. 16.

Figure 3

Mandel $Q$ parameter for the intensity difference as a function of the fractional transmitted intensity as the two beams are attenuated equally. The two beams are attenuated (a) with neutral density filters, (b) with razor blades moved symmetrically with respect to the pump, (c) one with a razor blade and the other with a neutral density filter, and (d) with razor blades moved antisymmetrically.

Figure 4

Intensity distribution (upper) and phase interferogram (lower) of the amplified probe beam, the pump beam, and the generated conjugate beam at the output of the 4WM cell. The probe and conjugate beams display $-4.4\mathrm{dB}$ of intensity-difference squeezing.

Figure 5

Mandel $Q$ parameter for the intensity difference as a function of the fractional transmitted intensity for equally attenuated beams. The pump is an LG+1 beam. The two beams are attenuated (a) with neutral density filters, (b) one with a razor blade and the other with a neutral density filter, (c) with razor blades moved symmetrically with respect to the pump, and (d) with razor blades moved antisymmetrically.