Single photon sources with different spatial modes

TL;DR

The paper addresses how heralded single-photon sources carrying orbital angular momentum (OAM) behave in an HBT-type experiment. It uses SPDC pumped with OAM-encoded beams and measures $g^{(2)}(0)$ for various OAM orders, employing both direct triple-coincidence measurements and an accidental-coincidence model. OAM conservation $l_i + l_s = l_p$ is exploited by selecting $l_i=0$ to obtain twisted signal photons with $l_s=l_p$. Findings show that $g^{(2)}(0)$ increases with pump power and with OAM order, driven by higher multi-pair probabilities and potential reductions in fiber coupling for higher-order modes, with implications for using OAM states in quantum information tasks.

Abstract

We study the correlation properties of single photons carrying orbital angular momentum (OAM) in a Hanbury Brown and Twiss (HBT) type experiment. We have characterized single photon sources obtained by pumping a nonlinear crystal with a laser beam carrying different OAM under same experimental conditions. For heralded twisted single photons carrying OAM, we calculate $g^{(2)}(0)$, a measurable parameter characterizing the quality of a single photon source, and observe an increment with the OAM of the single photon.

Figures (4)

• Figure 1: A simplified illustration of HBT experiment for a) an ideal single photon source where photons reaching the beam splitter through the input port will choose any of the paths $1$ or $2$ without resulting in any coincidence detection between the detectors, $D_1$$\&$$D_2$ and b) a heralded single photon source.
• Figure 2: HBT-like setup to determine the second order correlation for a heralded single photon source. The delay generator introduces electronic delay in steps of 0.5 ns between the two output ports of the beam splitter (BS) in the signal arm.
• Figure 3: The variation of second order correlation function with delay, $\tau$
• Figure 4: The variation of $g^{(2)} (0)$ with pump power