Two-photon interference with true thermal light

Two-photon interference and “ghost” imaging with entangled light have attracted much attention since the last century because of features such as nonlocality and subwavelength effects. Recently, it has been found that pseudothermal light can mimic certain effects of entangled light. We report here the first observation of two-photon interference with true thermal light.

Figure 1

Experimental setup. HCL: hollow cathode lamp. ${\mathrm{L}}_1$: lens of focal length 10 cm. G: grating of groove width 0.08 mm and groove spacing 0.2 mm. ${\mathrm{F}}_1$, ${\mathrm{F}}_2$: interference filters transmitting about 70% at 780 nm. PBS: polarizing beam splitter. BS: nonpolarizing beam splitter. ${\mathrm{C}}_1–{\mathrm{C}}_4$: fiber collimators. Effective diameter of fiber collimators in front of the detectors is 2 mm.

Figure 2

(Color online) Single-detector counts vs position of detector ${\mathrm{D}}_2$. The solid curve is a Gaussian fit of data points.

Figure 3

Joint detection counts vs time interval of the photons detected at ${\mathrm{D}}_1$ and ${\mathrm{D}}_2$. The solid curve is a Gaussian fit of data points.

Figure 4

Normalized second-order correlation function of thermal light (a) $g^{\left(2\right)}(0,x_2)$ vs position of detector ${\mathrm{D}}_2$ with detector ${\mathrm{D}}_1$ fixed. (b) $g^{\left(2\right)}(-x_2,x_2)$ vs position of detectors ${\mathrm{D}}_1$, ${\mathrm{D}}_2$. The solid curve is calculated taking into consideration the finite size of the detectors [21].

Figure 5

Normalized second-order correlation function $g^{\left(2\right)}(x_2,x_2)$ of thermal light vs position of detectors ${\mathrm{D}}_1$, ${\mathrm{D}}_2$.