Description
Quantum imaging with undetected photons (QIUP) enables image formation using photons that are never directly measured, decoupling illumination and detection wavelengths. Indistinguishable photon-pair generation pathways interfere coherently, enabling information carried by the undetected mid-infrared idler field to be transferred to the detected near-infrared signal field via phase- and amplitude-sensitive nonlinear interference. However, most demonstrations operate in the low-gain spontaneous parametric down-conversion regime, where limited photon flux restricts sensitivity, speed, and performance in lossy environments. Here, we demonstrate high-gain quantum imaging with undetected photons using a pulsed SU(1,1) nonlinear interferometer.
Using a 100 fs, 50 MHz pulsed pump source at 1040 nm with 4 W average power we generate idler light at 3200 nm which probes a sample while detecting signal light at 1540 nm , achieving parametric gains up to 7 and, after interferometer balancing, interference visibilities approaching $80\%$. We implement raster-scan imaging with a spatial resolution of $4~\mu$m. Measurements are performed on structured samples fabricated on $0.4~\text{mm}$ glass substrates and coated with a $7~\mu$m polymethyl methacrylate (PMMA) layer exhibiting C--H vibrational absorption in the $\sim 3~\mu$m region. Realistic loss conditions are emulated by imaging through an OD 1 neutral-density filter.
The results demonstrate a strong advantage of high-gain operation under high attenuation. In the low-gain regime, visibility falls to nearly zero for samples behind the OD 1 filter, preventing reliable imaging. In contrast, the high-gain system maintains visibilities of $13$--$16\%$ and resolves $\sim 3\%$ visibility changes induced by the PMMA layer. These results demonstrate enhanced robustness and sensitivity under loss, extending QIUP beyond the low-gain regime and establishing high-gain SU(1,1) interferometry as a promising platform for practical quantum imaging in lossy environments.
| I am the presenting author | Yes |
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