BEGIN:VCALENDAR VERSION:2.0 PRODID:Icfo X-PUBLISHED-TTL:P1W BEGIN:VEVENT UID:69d4ddc36eeae DTSTART:20250326T130000Z SEQUENCE:0 TRANSP:OPAQUE LOCATION:Elements Room and Online (Teams) SUMMARY:ICFO | EDUARDO BEATTIE EIZAGUIRRE CLASS:PUBLIC DESCRIPTION:Despite decades of research\, practical quantum computing and l ong-distance quantum communication remain elusive\, hindered by significan t challenges in current platforms. Single rare earth ions (SREI) in the so lid state offer a promising alternative\, with potential to form quantum c omputing nodes containing around 100 highly connected qubits capable of ph otonic networking. Nanoparticles are ideal for this system\, as they enabl e high doping concentrations for strong interactions while maintaining the required spectral distinguishability. SREI experiments benefit from optic al cavities that enhance emission via the Purcell effect. The open-access Fabry&ndash\;Perot fiber cavity\, formed by a fiber-tip micromirror and a planar or fiber mirror\, is particularly versatile: a wide range of emitte rs can be integrated on the mirror surface\, optical access is easy via th e fiber\, and three-dimensional tunability is possible. This flexibility h as enabled studies across various quantum emitters and 2D materials. This thesis presents our work developing the SREI platform using nanoparticles in fiber cavities. It begins with an introduction to quantum computing\, q uantum communication with quantum repeaters\, and rare earth ions as a bas is for quantum computers\, along with an overview of our experimental desi gn. A review of background knowledge follows\, covering optical cavities\, the Purcell effect\, the optical Bloch equations\, and single-photon ligh t statistics. The absence of commercial nanopositioners suitable for contr olling our fiber cavity led us to design our own. This positioner enabled the first detection of single ions in nanoparticles. We studied the 4I15/2 &rarr\; 4I13/2 transition at 1535 nm in 20 ppm erbium-doped 150 nm Y2O3 n anoparti[1]cles\, and identified an ion with excellent spectral stability\ , a linewidth of 3.8(3) MHz\, and a g (2)(0) compatible with a perfect sin gle emitter. We then developed a significantly improved second positioner with 2.5 pm RMS stability\, 130 µ\;m×\;130 µ\;m XY scan ran ge\, and MHz-rate cavity modulation\, all at 1.65 K in a closed-cycle cryo stat. The broad potential of fiber cavities enhances this device&rsquo\;s impact\, marking it as one of the thesis&rsquo\;s main contributions. Equi pped with this improved positioner\, we proceeded with a newexperiment to detect interactions between single ions. We studied the 3H4 &rarr\; 1D2 tr ansition at 619 nm in two sets of praseodymium-doped Y2O3 nanoparticles\, but were so far unable to observe any praseodymium emission in the cavity. To diagnose why this was happening\, we performed additional experiments with a confocal microscope\, which confirmed the presence of praseodymium in a majority of objects and found the absorption resonance near where we expected. The thesis ends with conclusions and future directions\, includi ng emission shaping and a novel microscopy technique. A closing reflection on this work and recent breakthroughs in the field paints a promising fut ure for quantum information technologies.\nWednesday March 26\, 14:00 h. E lements Room and online (Teams)\nThesis Director: Prof. Dr. Hugues de Ried matten\n \;\nJoin the meeting now\nMeeting ID: 333 757 321 630\nPassco de: 4Ca66vf6 DTSTAMP:20260407T103443Z END:VEVENT END:VCALENDAR