Lithium niobate is a promising platform for integrated quantum optics. In this platform we aim to efficiently manipulate and detect quantum states by combining superconducting single photon detectors and modulators. The cryogenic operation of a superconducting single photon detector dictates the optimisation of the electro-optic modulators under the same operating conditions. To that end, we characterise a phase modulator, directional coupler, and polarisation converter at both ambient and cryogenic temperatures. The operation voltage Vπ/2 of these modulators increases due to the decrease of the electro-optic effect by 74% for the phase modulator, 84% for the directional coupler and 35% for the polarisation converter below 8.5 K. The phase modulator preserves its broadband nature and modulates light in the characterised wavelength range. The unbiased bar state of the directional coupler changed by a wavelength shift of 85 nm while cooling the device down to 5 K. The polarisation converter uses periodic poling to phasematch the two orthogonal polarisations. The phasematched wavelength of the used poling changes by 112 nm when cooling to 5 K.

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We demonstrate the integration of amorphous tungsten silicide superconducting nanowire single-photon detectors on titanium in-diffused lithium niobate waveguides. We show proof-of-principle detection of evanescently coupled photons of 1550 nm wavelength using bidirectional waveguide coupling for two orthogonal polarization directions. We investigate the internal detection efficiency as well as detector absorption using coupling-independent characterization measurements. Furthermore, we describe strategies to improve the yield and efficiency of these devices.

Superconducting Nanowire Single Photon Detectors (SNSPDs) have become an integral part of quantum optics in recent years because of their high performance in single photon detection. We present a method to replace the electrical input by supplying the required bias current via the photocurrent of a photodiode situated on the cold stage of the cryostat. Light is guided to the bias photodiode through an optical fibre, which enables a lower thermal conduction and galvanic isolation between room temperature and the cold stage. We show that an off-the-shelf InGaAs-InP photodiode exhibits a responsivity of at least 0.55A/W at 0.8K. Using this device to bias an SNSPD, we characterise the count rate dependent on the optical power incident on the photodiode. This configuration of the SNSPD and photodiode shows an expected plateau in the single photon count rate with an optical bias power on the photodiode above 6.8µW. Furthermore, we compare the same detector under both optical and electrical bias, and show there is no significant changes in performance. This has the advantage of avoiding an electrical input cable, which reduces the latent heat load by a factor of 100, and in principle allows for low loss RF current supply at the cold stage.

improvements to exciting optical functionality and expands the potential applications of metasurfaces in ever more directions. However, the fragile nano structures are typically highly sensitive to dust and other contaminants, which ultimately limits their wider application. Until now, there is no solution to efficiently clean or protect from the dust contamination on a metasurface that consists of specifically designed antennas. Hence, finding a feasible strategy to clean the metasurface without affecting its optical performance or damage the nanostructures is extremely promising for various practical applications. Furthermore, future development of metasurfaces entails not only continuous efforts to improve the optical performance but also accessible strategies to enhance the device adaptability and effectiveness in complex application conditions. [21][22][23] This means metasurface with enhanced optical performance, physical stability, and smarter functionality are important properties that need to be considered when one designs the device.