All-fiber Control of Entanglement:
Recovering Correlations via Mechanical Perturbations in a Multimode Fiber

In quantum optical communications, single photons can be used as a unit of quantum information. However, one can supercharge their capacity to carry information by encoding high-dimensional quantum dits, or qdits, into their transverse shape. They allow having more than two levels per unit of information as it is the case for bits. In fiber optical communications, it requires using multimode fibers to harness the spatial degrees of freedom to encode the qduts. However, when propagating through a real-life multimode fiber, the transverse shape of the photons gets scrambled because of mode mixing and modal interference. This scrambling of transverse shape is typically rectified using free-space spatial light modulators. But, this remedy prevents us from achieving a truly resilient all-fiber operation and requires a careful alignment and lab-graded stability hindering real-life implementation. In [R. Shekel et al., Arxiv 2306.02288 (2023)], the authors introduce an all-fiber method for controlling the shape of single photons and spatial correlations between entangled photon pairs. They do so by implementing carefully controlled mechanical perturbations to the fiber.

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Symposium – Quantum imaging
Unlocking the power of multimode optics.

June 15, 2023 - 9am to 5pm

Sorbonne University, Amhithéatre Herpin, 4 place Jussieu, 75005 Paris

Link: here

The symposium aims to explore the latest developments and applications of multimode optics in quantum imaging.

Compensating for phase drifts in holographic measurements

Digital holography allows measuring the complex amplitude of a given wavefront. We presented in detail the off-axis holography approach. However, it requires a separate reference arm. Due to air flow, vibrations, or other perturbations, the optical path length difference between the two arms can fluctuate in time, even in controlled lab experiments on a good optical table. This means that the phase of the measured wavefront is estimated up to a global phase that can randomly change over time. This is very detrimental for transmission matrix measurements as the relative phase between each column has to be precisely estimated. This is particularly true when the measurement time can take few minutes or more when using a liquid crystal spatial light modulator that has a limited frame rate. In [R. Mouthaan et al., Appl. Opt. (2022)], the authors propose a simple yet robust way to compensate for phase fluctuations, even when the phase changes completely between two frames.