BEGIN:VCALENDAR VERSION:2.0 PRODID:Icfo X-PUBLISHED-TTL:P1W BEGIN:VEVENT UID:69d8d52043130 DTSTART:20220429T150000Z SEQUENCE:0 TRANSP:OPAQUE LOCATION:ICFO Auditorium and Online (Teams) SUMMARY:ICFO | CHETAN DESHMUKH CLASS:PUBLIC DESCRIPTION:Encoding information into quantum mechanical properties of a sy stem can lead to applications many fields\, including computing and commun ication. Devices that will enable these applications could be part of a qu antum network in the future. Quantum networks can be implemented using nod es that have the ability to generate and store entanglement efficiently fo r long durations as well as to process quantum information. The nodes also need to be interfaced with photons\, which can faithfully carry informati on over long distances. Single rare-earth ions doped in crystals offer all these capabilities. The main goal of this thesis was to detect a single e rbium ion\, which operates in the telecommunication wavelength\, and to in vestigate its feasibility as a spin-photon interface.\nDetecting a single erbium is challenging due to its low emission rate\, but it can be aided b y Purcell-enhancing its emission via coupling to an optical cavity. In thi s thesis\, we utilize erbium ions doped into nanoparticles\, which facilit ates their integration into cavities with small mode-volumes. In addition\ , nanoparticles provide the confinement required to individually manipulat e spatially close-by single ion qubits\, which is required for dipolar qua ntum gates. We hence first study the optical coherence properties of Er:Y2 O3 nanoparticles at cryogenic temperatures. We identify the limiting mecha nisms and identify avenues for improvement in the future. We also study th e optical and spin coherence properties of Pr:Y2O3\, which is a promising alternative to erbium.\nFiber-based microcavities can achieve high Purcell factors as they can simultaneously realize high finesse and small mode-vo lume. They are also ideally suited to be coupled to nanoparticles due to t heir tuning capabilities. However\, stabilizing such a cavity inside a cry ogenic environment is challenging. We hence first describe the constructio n of a custom setup\, which enables us to stabilize the cavity while being coupled to a suitable nanoparticle. Utilizing the first iteration of this setup\, we then report on the coupling of Er:Y2O3 nanoparticles to a fibe r-based high finesse microcavity. We achieve an average Purcell factor of 14 for a small ensemble of ions\, while a small subset of ions show Purcel l factor up to 70. We explain the obtained multi-exponential decay behavio ur using a detailed model. Furthermore\, we demonstrate dynamic control of the Purcell-enhanced emission by tuning the cavity resonance on a time-sc ale faster than the spontaneous emission rate of the ions. This allows us to extract the natural lifetime of the ions as well as to shape the wavefo rm of the emitted photons. However\, we conclude that the achieved signal- to-noise ratio is not high enough to resolve single erbium ions.\nFor the final experiment\, we operate the second iteration of the setup\, which im proves our sensitivity to single erbium ions by more than a factor 50. Thi s enables us to demonstrate the first detection of a single erbium ion in a nanoparticle. The ion exhibits a Purcell factor of 60\, leading to a cav ity enhanced lifetime of 225 us\, and a homogeneous linewidth of 380 MHz. The counts received from the ion show a clear saturation and we measure th e second-order auto-correlation of the emitted photons to be 0.59\, which reduces to 0.29 after background-subtraction. This is strong evidence that the photons are emitted by a single erbium ion. Our work opens the path f or exploring single rare-earth-ions doped into nanoparticles as spin-photo n interfaces for quantum information processing.\n \;\nThesis Director : Prof Dr. Hugues de Riedmatten\n \; DTSTAMP:20260410T104656Z END:VEVENT END:VCALENDAR