IQUIST Seminar: Alan Dibos, Argonne National Laboratory

 Tailoring the interaction between optical emitters and their electromagnetic environment is of both fundamental scientific interest and practical relevance for applications such as quantum communication and quantum information processing. By tuning the photonic density of states, one can drastically modify the emission properties of these emitters, a phenomenon that underpins the thriving research area of cavity quantum electrodynamics. In this talk, we will first present our rare earth doped nanocavity platform that is being pursued for future quantum optical memory devices operating at cryogenic temperatures. Our spin qubit system consists of Er3+ ions with a natural optical transition in the telecom (~1520 nm), but the long optical lifetime of these ions (order of milliseconds) necessitates the use of an optical cavity to greatly enhance the emission rate. More specifically, we grow thin film Er3+-doped titanium dioxide (TiO2) atop silicon-on-insulator wafers and fabricate small mode volume photonic crystal cavities via etching through both the TiO2 and Si device layers. We have thus far demonstrated that when the optical cavity is resonant with optical transition of the Er3+ions, the optical lifetime can show an enhancement (Purcell factor) up to several hundred [1]. However, in addition to quantum communication applications, we can use the long optical lifetimes of rare-earth ions for more fundamental optical decay modification experiments [2]. For our system, the ensemble of Er3+ emitters that couples to the cavity exhibit a much broader inhomogeneous linewidth than the cavity. When the optical cavity is tuned through the Er3+ inhomogeneous distribution, the resultant Purcell factor exhibits an anomalous slowing of the decay when the cavity is resonant with the center of the distribution. We will examine the experimental Purcell factor dependence on resonant laser pump power, as well as the spectral dependence of the PLE emission. We will discuss our attempts to capture qualitative aspects of this decay rate suppression using a semi-classical model of non-interacting emitters mediated by a common cavity. Finally, we will discuss a recent material synthesis development to make our Er3+:TiO2 system potentially more scalable for foundry-level deployment [3].

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