Measuring intensity correlations with a two-element superconducting nanowire single-photon detector

Second-order intensity correlation measurements were made using a two-element superconducting nanowire single photon detector (SNSPD) without the need for an optical beam splitter. This approach can be used to obtain a $50\text{‐}\mathrm{ps}$ full width at half maximum timing resolution over a wide range of visible and near-infrared wavelengths and can be extended to measure higher-order intensity correlations. Measurements of the second-order intensity correlation of a pulsed laser and an InGaAs quantum dot were made using both a two-element SNSPD and a conventional Hanbury Brown–Twiss interferometer to demonstrate the accuracy and advantages of the multielement SNSPD.

Figure 1

(Color online) (a) Experimental schematic for the IRF and PL lifetime measurements (start input connected to the trigger photodiode) and the $g^{\left(2\right)}\left(0\right)$ measurements (start input connected to the photon counter). BS, beam splitter; DBS, dichroic beam splitter. Schematic of the Hanbury Brown–Twiss setup using (b) a free-space beam splitter and two discrete SPADs and (c) a fiber-coupled two-element SNSPD. A scanning-electron micrograph of the SNSPD is shown in (d) with two of the elements highlighted for clarity. The fiber is aligned to the best two adjacent elements.

Figure 2

(Color online) Measurements of IRFs (SNSPD, black solid line; SPAD, blue dotted line) and PL lifetimes (SNSPD, black solid squares; SPAD, blue open circles). The $50\text{‐}\mathrm{ps}$-FWHM, Gaussian-shaped SNSPD IRF allows the quantum dot lifetime to be measured more accurately.

Figure 3

(Color) Measured intensity correlation histograms for the quantum dot single-photon source (a),(b) and the Ti:sapphire laser (c),(d). The measurements were made with the two-element SNSPD (solid black lines) and, subsequently, with the SPAD-based HBT setup (blue lines with solid circles). The shape and width of the peaks demonstrate that the two-element SNSPD may be used to achieve improved timing resolution, while the setup-independent ratio of counts in the zero-time-delay peak relative to the counts in the other peaks demonstrates that both detector setups can be used to accurately measure $g^{\left(2\right)}\left(0\right)$.