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Frontiers in Optics

Entangled Tangles of Phase Singularities

Jacquiline Romero, Jonathan Leach, Barry Jack, Mark R. Dennis, Sonja Franke‐Arnold, Stephen Mark Barnett, Miles J. Padgett

Published Jan 1, 2010• 0 citations
Publisher

Abstract

We holographically measure entangled tangles of phase singularity lines in light generated via spontaneous parametric down-conversion. This type of entanglement is interesting because it is between topological features that extend over finite, macroscopic, isolated volumes.
DOI
10.1364/fio.2010.ftug5

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We report the entanglement of topological features, namely, isolated, linked optical vortex loops in the light from spontaneous parametric down-conversion (SPDC). In three dimensions, optical vortices are lines of phase singularity and vortices of energy flow which percolate through all optical fields. This example of entanglement is between features that extend over macroscopic and finite volumes, furthermore, topological features are robust to perturbation . The entanglement of photons in complex three-dimensional(3D) topological states suggests the possibility of entanglement of similar structures in other quantum systems describable by complex scalar functions, such as superconductors, superfluids and Bose-Einstein condensates.
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Entangled-photon beams, generated for example by spontaneous parametric down-conversion from a nonlinear crystal, may be used to implement holography based on quantum interferometry. One beam is split into a probe component that illuminates the object and another serving as a reference, and is detected with no spatial resolution. The other beam is measured with full spatial resolution. The rate of two-photon coincidence contains full holographic information on the object. Since the beams are not monochromatic, this is a form of higher-order white light holography.
An optical vortex (OV) beam is a singular beam with a helical wavefront and a spatially varying phase profile, whereas spontaneous parametric down conversion (SPDC) is a well-established process of generating two-photon state of light. Here, we report photon generation via SPDC using a supercontinuum (SC) beam and a SC OV beam as pump. Specifically, we report generation of an integer charge SC OV beam with a spectral range of 420-480 nm by illuminating a narrow-band spiral phase plate (SPP) designed for 467 nm with a SC light beam of 390-500 nm spectral range. The broad bandwidth of the generated SC OV beam is confirmed using bandpass filters, and cylindrical lens based measurement is adapted to estimate the topological charge of the beam. The mode purity of the generated SC OV beam is determined by analysing its complex field, measured using a Mach–Zehnder interferometer. Besides, generation of fractional OV beam is observed around 400 nm, and the results are compared to the case of using a CW laser operating at 405 nm. In addition, we report generation of photon pairs via SPDC by pumping a β-BBO crystal with the SC beam and the integer charge SC OV beam. The down-conversion of the SC beam with a spectral range of 60 nm is confirmed using bandpass filters in the pump beam and recording the SPDC signal. A similar measurement is also conducted using the generated CW fractional OV beam. This investigation is expected to be useful in quantum imaging applications, where exploring new ways of generating photons and entanglement is of increasing interest.