BEGIN:VCALENDAR VERSION:2.0 PRODID:Icfo X-PUBLISHED-TTL:P1W BEGIN:VEVENT UID:69d289e70ed21 DTSTART:20230626T080000Z SEQUENCE:0 TRANSP:OPAQUE LOCATION:ICFO Auditorium and Online (Teams) SUMMARY:ICFO | JELENA RAKONJAC CLASS:PUBLIC DESCRIPTION:Future networks for quantum communication will require a new fo rm of technology in order to operate over long distances. The no-cloning t heorem precludes the use of amplification\, so quantum repeater schemes ha ve been proposed to achieve long-distance quantum communication through th e distribution of entanglement. A key device for this setup is a quantum m emory\, which is required in order to store entanglement and synchronise i ts distribution.\nAmong the many physical systems than can be used as a qu antum memory\, rare-earth ion-doped crystals stand out due to their long c oherence times and potential for multiplexing and integration. This thesis reports the use of one such system\, Pr3+:Y2SiO5\, as a quantum memory us ing the atomic frequency comb (AFC) protocol. Building on previous work\, we improved the performance of the memory to be able to demonstrate light- matter entanglement with a telecommunications wavelength photon and the qu antum memory\, for both a bulk memory and an integrated version.\nTo measu re light-matter entanglement\, we use photon pairs generated through cavit y-enhanced spontaneous parametric down conversion\, where one photon (the signal) is stored in the memory and the other (the idler) is at a telecomm unications wavelength. These photon pairs exhibit energy-time entanglement \, which we analyse in the time basis using fibre- and AFC-based Mach-Zehn der interferometers.\nIn the first experiment\, we demonstrate light-matte r entanglement where the bulk quantum memory is used with on-demand retrie val via storage in a spin-wave. We measure interference fringes with avera ge visibilities of 89(2)% for AFC storage\, and 70(3)% for spin-wave stora ge\, sufficient to demonstrate entanglement. This is the first such demons tration using an on-demand multimode solid-state memory and telecom photon . We show that entanglement is maintained for up to 47.7 &mu\;s of storage . These results were made possible through improvements in the AFC efficie ncy and the noise filtering. Furthermore\, we perform on-demand storage an d retrieval of up to 30 temporal modes.\nWe take the next step towards imp lementing our system in a real world scenario by measuring entanglement ov er a distance. To do so\, we send the idler photons through both optical f ibre spools and deployed fibre in the metropolitan area of Barcelona\, Spa in\, while the photon detection still occurs in the same lab. The resultin g visibilities (80% or higher) demonstrate that the photonic qubit does no t decohere during transmission through the optical fibre. We then decouple the photon creation and detection by measuring non-classical correlations between signal photons detected in the lab\, and idler photons detected 1 6 km away (44 km in fibre) in a different location.\nThe final experiment uses a fibre-integrated memory for light-matter entanglement. We use a Pr3 +:Y2SiO5 crystal containing a Type I laser-written waveguide\, interfaced directly with optical fibre. The fibre-integration allows for improved tra nsmission and AFC efficiency compared to a free-space coupled waveguide me mory. To analyse the performance of the memory\, we demonstrate non-classi cal correlations for storage times up to 28 &mu\;s. We perform qubit tomog raphy in the time basis for storage times of 3 and 10 &mu\;s\, measuring t wo-qubit fidelities of 86(2)% and 86(4)%\, respectively\, demonstrating st orage of entanglement.\nThese experiments demonstrate the potential of our system for use as part of a quantum repeater\, with many opportunities fo r further improvement to the storage time\, efficiency\, and multiplexing capability. DTSTAMP:20260405T161223Z END:VEVENT END:VCALENDAR