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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Waveguide resonators as squeezed light sources

Michael Stefszky, Matteo Santandrea, Felix vom Bruch, Christof Eigner, Raimund Ricken, Viktor Quiring, Harald Herrmann, Christine Silberhorn

Published Jun 21, 2021• 0 citations
Publisher

Abstract

Squeezed light forms the foundation of continuous-variable quantum optics. In most experimental realisations, bulk optics resonators utilising the second-order nonlinearity serve as the source of stable, high levels of squeezing. As one would expect, there is a drive towards producing squeezed light sources in integrated platforms, as it is expected that such a transition will ease the challenges in moving toward real-world applications. However, waveguides come with their own set of challenges; they generally exhibit increased losses, and some platforms suffer from photothermal or photorefractive effects.

DOI
10.1109/cleo/europe-eqec52157.2021.9542228

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Squeezed light forms the foundation of continuous-variable quantum optics. In most experimental realisations, bulk optics resonators utilising the second-order nonlinearity serve as the source of stable, high levels of squeezing. As one would expect, there is a drive towards producing squeezed light sources in integrated platforms, as it is expected that such a transition will ease the challenges in moving toward real-world applications. However, waveguides come with their own set of challenges; they generally exhibit increased losses, and some platforms suffer from photothermal or photorefractive effects.
``Squeezed'' states of light are the fundamental building blocks for continuous-variable quantum optics, so a quantum network for optical communication would seem to require a compact, efficient source of such states. Combining clever design with recent advances in waveguide materials engineering, the authors produce a device that yields very high levels of squeezing, compared to other integrated architectures. Their innovative approach allows for rarely seen continuous-wave squeezing, paving the way for more advanced on-chip functions.
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Useful applications for squeezed states of light have been theorized for decades, however, only recently have advancements in the technology allowed for experimental investigations into applications of squeezed light. Most experiments which involve squeezing could be benefited by having a squeezing source which produces stable, highly squeezed states. This thesis investigates the generation of squeezed states of light which exhibit these properties, stability and high levels of squeezing. The key investigations are; • Initially a model is produced which estimates the expected level of squeezing in a singly or doubly resonant cavity. The properties of the cavity are altered by varying the reflectivity of one of the cavity mirrors for either the pump or seed frequencies. The effects of increasing pump power and introducing additional losses into the cavity are investigated as well as the optimum resonance conditions for maximum squeezing. • Built 3 squeezers with 3 different nonlinear mediums. A maximum squeezing value was found for each of the crystals and any effects which degraded or improved the results were investigated. Using PPKTP 5.8±0.1dB of squeezing was directly observed. Using PPSLT 4.9±0.1dB of squeezing was directly observed. PPSLT was found to have an unusually high threshold power, indicating that the crystal may have had a nonlinear coefficient much lower than expected. Using 1.7% MgO:PPSLN 1.1±0.2dB of squeezing was observed. The poor squeezing results were due to an anomaly in the material which affected its reflectivity and is investigated in the thesis. • The intra-cavity loss introduced to the system through the addition of each of the crystals was inferred from measurements of the cavity finesse, and the effect of this loss is explored. • Demonstrated the usefulness of a wedge in periodically poled materials to reach the optimum resonance condition in the squeezing setup. It is shown that the wedge is capable of cancelling the dispersion introduced in a round trip of the cavity, with no discernible negative effects. These investigations are used to comment on the suitability of each of these crystals for future experiments involving squeezing and possible modifications to improve the results.