BEGIN:VCALENDAR VERSION:2.0 PRODID:Icfo X-PUBLISHED-TTL:P1W BEGIN:VEVENT UID:69d2571892cba DTSTART:20230324T093000Z SEQUENCE:0 TRANSP:OPAQUE LOCATION:ICFO Auditorium SUMMARY:ICFO | STEFANO DURANTI CLASS:PUBLIC DESCRIPTION:Quantum repeaters are the foundation of future long-distance qu antum networks. In most architectures\, their functional core is constitut ed by quantum memories\, which are devices that can store and re-emit phot onic quantum information on-demand. The goal of this thesis is to progress towards efficient quantum repeater nodes enabling quantum correlations be tween telecom photons and matter qubits. To these ends\, we performed thre e main experiments.\nIn our first work\, we built a solid-state entangleme nt photon source with embedded storage capabilities. This emissive quantum memory was implemented in a Pr3+:Y2SiO5 crystal\, by means of the atomic frequency comb (AFC) protocol. Thanks to the AFC\, we were able to adapt t he Duan-Lukin-Cirac-Zoller (DLCZ) protocol\, initially conceived for cold atoms\, to a solid-state ensemble. This experiment proved that we can prod uce light-matter entanglement between a heralding photon\, at 606 nm\, and a spin-wave excitation delocalized inside the ensemble. The matter excita tion could be read on-demand at a later time with a read pulse\, and mappe d as a second photon\, at 606 nm as well\, emitted by the memory. Quantum correlations between the two photons were measured\, enabling the violatio n of a Bell inequality\, thus demonstrating the presence of entanglement. The read-out efficiency of this experiment was low\, 1.6%\, but solutions were identified to increase this value. \;\nIn the second experiment\, we laid the groundwork for the quantum frequency conversion (QFC) of thes e photons to the telecom band. The long duration of these photons\, up to 1 µ\;s\, makes their conversion with high signal-to-noise ratio (SNR) challenging. The conversion from the visible 606 nm wavelength to the tel ecom regime (1552 nm) was achieved by difference-frequency generation (DFG ) in a PPLN waveguide using a strong pump field at 994 nm. A proof of prin ciple with weak coherent pulses showed that we can convert µ\;s-long photons with the low heralding efficiency of the previous experiment with a SNR around 2.6. This sets the stage for interfacing an AFC-DLCZ memory\, working at 606 nm\, with the telecom network and with material systems wo rking at a different wave length.\nFinally\, in the last experiment\, we i mplemented an AFC impedance-matched cavity (IMC) storage experiment. It ha s been demonstrated theoretically and experimentally that the IMC enhances the storage and read-out efficiency of the AFC protocol. We harnessed thi s cavity to store weak coherent Gaussian pulses with up to 62% efficiency. Moreover\, we stored weak coherent time-bin qubits in the same system\, a chieving 52% efficiency and\, with an additional analysis carried out by m eans of an unbalanced Mach-Zehnder AFC-based interferometer\, assessing a measured fidelity of 95% for the retrieved qubit\, leading to a quantum me mory fidelity compatible with 100%\, within uncertainty. We additionally s tudied the influence of slow-light effects in our crystal\, confirming tha t they lead to a reduction of cavity bandwidth by two orders of magnitude. Moreover\, the AFC storage time was extended up to 50 µ\;s\, to cert ify that the efficiency enhancement holds for different combs.\nThe achiev ements of this thesis represent the state of the art for the AFC efficienc y and for qubit storage in solid-state systems\, and pave the way towards efficient quantum memories. In addition\, we reported the first demonstrat ion of a solid-state photon pair source of entangled photons with embedded solid-state multimode memory. The results accomplished by this last AFC-D LCZ experiment in terms of heralding efficiency make it possible to interf ace it with our quantum frequency conversion experiment. Indeed\, the QFC experiment\, combined with the AFC-DLCZ one\, enables to establish a quant um node and to interface it with different kind of nodes via conversion to the telecom band.\n \;\nThesis Director: Prof Dr. Hugues de Riedmatte n DTSTAMP:20260405T123536Z END:VEVENT END:VCALENDAR