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., ghost-image formation based on structured illumination realized with laser light that has undergone spatial light modulation by the output from a pseudorandom number generator. Our analysis thus casts doubt on the degree to which quantum discord is necessary for ghost imaging.United States. Defense Advanced Research Projects Agency (Army Research Office Award W911NF-10-1-0404

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. In contrast, our camera’s detector array requires highly parallelized time-to-digital conversions with photon time-tagging accuracy limited to ∼ns. Thus, we develop an array-specific algorithm that converts coarsely time-binned photon detections to highly accurate scene depth and reflectivity by exploiting both the transverse smoothness and longitudinal sparsity of natural scenes. By overcoming the coarse time resolution of the array, our framework uniquely achieves high photon efficiency in a relatively short acquisition time.National Science Foundation (U.S.) (1161413)National Science Foundation (U.S.) (1422034)Lincoln LaboratorySamsung (Firm

Towards Visual Foundational Models of Physical Scenes

We describe a first step towards learning general-purpose visual representations of physical scenes using only image prediction as a training criterion. To do so, we first define "physical scene" and show that, even though different agents may maintain different representations of the same scene, the underlying physical scene that can be inferred is unique. Then, we show that NeRFs cannot represent the physical scene, as they lack extrapolation mechanisms. Those, however, could be provided by Diffusion Models, at least in theory. To test this hypothesis empirically, NeRFs can be combined with Diffusion Models, a process we refer to as NeRF Diffusion, used as unsupervised representations of the physical scene. Our analysis is limited to visual data, without external grounding mechanisms that can be provided by independent sensory modalities.Comment: TLDR: Physical scenes are equivalence classes of sufficient statistics, and can be inferred uniquely by any agent measuring the same finite data; We formalize and implement an approach to representation learning that overturns "naive realism" in favor of an analytical approach of Russell and Koenderink. NeRFs cannot capture the physical scenes, but combined with Diffusion Models they ca

Quantum-mimetic imaging

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 139-146).Many recent experiments have explored the use of nonclassical states of light to perform imaging or sensing. Although these experiments require quantum descriptions of light to explain their behavior, the advantages they claim are not necessarily unique to quantum light. This thesis explores the underlying principles behind two of those imaging techniques and realizes classical experiments that demonstrate properties similar to their quantum counterparts. The principal contributions of this thesis in the preceding quantum-mimetic imaging paradigm are the experimental implementation of phase-conjugate optical coherence tomography and phase-sensitive ghost imaging, two experiments whose quantum counterparts utilize phase-sensitive light with nonclassical strength. This thesis also explores the use of compressed sensing to further speed up acquisition of ghost imaging. Finally, a new paradigm inspired by compressed sensing is demonstrated, in which high-quality depth and reflectivity images are simultaneously captured using only the first photon arrival at each pixel. This paradigm is also extended to the case of single-photon APD arrays which may offer few-photon low-light imaging capabilities beyond what is possible with current camera technologies.by Dheera Venkatraman.Ph. D

Picosecond polarization-maintaining Er-doped fiber laser for quantum optics and the construction of a high-flux non-degenerate entangled photon pair source

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (p. 50-52).Two separate projects were undertaken to improve technology for entangled photon sources, useful for quantum optics. In one project, a pulsed, mode-locked erbium-doped fiber laser, designed to be used as a seed laser for a 390 nm source, was built using polarization-maintaining components to address polarization drift. The fiber laser operated at a center wavelength of 1560.0 nm with an output power of 1 to 2.5 mW, and mode-locked with a repetition rate of 31.1 MHz. The laser also exhibited bandwidth tunability from 0.045 to 0.095 nm, as a function of the input pump power. A commercial 5 W erbium-doped fiber amplifier and a second harmonic generation crystal were used to obtain pulses at 780 nm with an average power of 3 W. The next second harmonic generation stage, for generating the desired 390 nm output, remains to be built. In the second project, we tried to optimize the coupling efficiency of light generated from spontaneous parametric downconversion (SPDC) into single-mode optical fibers, which are useful for transporting entangled photons. Using a setup with a tunable 532 nm pump waist in a nonlinear crystal, we achieved an effective coupling efficiency of 48.8% of the 797 nm signal light into a single-mode fiber, higher than previously obtained in the laboratory. Efficient single-mode operation of SPDC would enable the construction of a high-flux fiber-coupled source of nondegenerate entangled photons at 797 nm and 1600 nm.by Dheera Venkatraman.M.Eng

An introduction to quantum error correction

Communication at high speeds, long distances, and in unknown environments often requires combatting noise that may affect or destroy data before it has reached its intended destina-tion. When designing robust, practical communication systems, it is important to take such effects into account and engineer a system to be as immune to noise as possible. Classica

Management of complexity in manufacturing (Keynote paper)

We demonstrate a new type of optical coherence tomography using only classical resources to achieve results that are typically associated with quantum-enhanced metrology: factor-of-two axial resolution enhancement and even-order dispersion cancellation

Phase-sensitive coherence and the classical-quantum boundary in ghost imaging

The theory of partial coherence has a long and storied history in classical statistical optics. The vast majority of this work addresses fields that are statistically stationary in time, hence their complex envelopes only have phase-insensitive correlations. The quantum optics of squeezed-state generation, however, depends on nonlinear interactions producing baseband field operators with phase-insensitive and phase-sensitive correlations. Utilizing quantum light to enhance imaging has been a topic of considerable current interest, much of it involving biphotons, i.e., streams of entangled-photon pairs. Biphotons have been employed for quantum versions of optical coherence tomography, ghost imaging, holography, and lithography. However, their seemingly quantum features have been mimicked with classical-state light, questioning wherein lies the classical-quantum boundary. We have shown, for the case of Gaussian-state light, that this boundary is intimately connected to the theory of phase-sensitive partial coherence. Here we present that theory, contrasting it with the familiar case of phase-insensitive partial coherence, and use it to elucidate the classical-quantum boundary of ghost imaging. We show, both theoretically and experimentally, that classical phase-sensitive light produces ghost images most closely mimicking those obtained with biphotons, and we derive the spatial resolution, image contrast, and signal-to-noise ratio of a standoff-sensing ghost imager, taking into account target-induced speckle.United States. Defense Advanced Research Projects Agency (Contract PROP. 40-15391)United States. National Aeronautics and Space AdministrationU.S. Army Research Laboratory (Grant W911NF-10-1-0404