Photon-efficient imaging with a single-photon camera.

Reconstructing a scene's 3D structure and reflectivity accurately with an active imaging system operating in low-light-level conditions has wide-ranging applications, spanning biological imaging to remote sensing. Here we propose and experimentally demonstrate a depth and reflectivity imaging system with a single-photon camera that generates high-quality images from ∼1 detected signal photon per pixel. Previous achievements of similar photon efficiency have been with conventional raster-scanning data collection using single-pixel photon counters capable of ∼10-ps time tagging.

Classical imaging with undetected photons.

Barreto Lemos et al. [Nature 512, 409-412 (2014)] reported an experiment in which a non-degenerate parametric downconverter and a non-degenerate optical parametric amplifier--used as a wavelength-converting phase conjugator--were employed to image object transparencies in a manner akin to ghost imaging. Their experiment, however, relied on single-photon detection, rather than the photon-coincidence measurements employed in ghost imaging with a parametric downconverter source.

Ghost imaging without discord.

Ragy and Adesso argue that quantum discord is involved in the formation of a pseudothermal ghost image. We show that quantum discord plays no role in spatial light modulator ghost imaging, i.e.

Classical far-field phase-sensitive ghost imaging.

We report the first (to our knowledge) far-field ghost images formed with phase-sensitive classical-state light and compare them with ghost images of the same object formed with conventional phase-insensitive classical-state light. To generate signal and reference beams with phase-sensitive cross correlation, we used a pair of synchronized spatial light modulators that imposed random, spatially varying, anticorrelated phase modulation on the outputs from 50-50 beam splitting of a laser beam. In agreement with theory, we found the phase-sensitive image to be inverted, whereas the phase-insensitive image is erect, with both having comparable spatial resolutions and signal-to-noise ratios.

Experimental realization of phase-conjugate optical coherence tomography.

We demonstrate phase-conjugate optical coherence tomography (PC-OCT) using a classical source of phase-sensitive cross-correlated beams to achieve measurement improvements shared by quantum OCT (Q-OCT): a factor-of-2 enhancement in axial resolution and even-order dispersion cancellation. Compared with coincidence counting used in Q-OCT, PC-OCT employs standard photodetection that results in much faster data acquisitions. This work belongs to a new class of classical techniques inspired by quantum methods that have advantages once thought to be exclusively quantum mechanical.

Classical low-coherence interferometry based on broadband parametric fluorescence and amplification.

We demonstrate that single-mode broadband amplified spontaneous parametric downconversion, combined with optical parametric amplification, can be used as a classical source of phase-sensitive cross-correlated beams. We first study the single spatial mode emission and the spectral brightness properties of the parametric fluorescence, produced in periodically poled MgO-doped lithium niobate. Using the same single-pass bulk-crystal configuration for a pulsed optical parametric amplifier, we achieve a gain of approximately 20 dB at an average pump power of 2W, and explain the pulse narrowing observed at the output of both parametric fluorescence and amplification in the regime of high gain.