Narrow optical linewidths in erbium implanted in TiO2_2

Atomic and atom-like defects in the solid-state are widely explored for quantum computers, networks and sensors. Rare earth ions are an attractive class of atomic defects that feature narrow spin and optical transitions that are isolated from the host crystal, allowing incorporation into a wide range of materials. However, the realization of long electronic spin coherence times is hampered by magnetic noise from abundant nuclear spins in the most widely studied host crystals. Here, we demonstrate that Er$^{3+}$ ions can be introduced via ion implantation into TiO$_2$, a host crystal that has not been studied extensively for rare earth ions and has a low natural abundance of nuclear spins. We observe efficient incorporation of the implanted Er$^{3+}$ into the Ti$^{4+}$ site (40% yield), and measure narrow inhomogeneous spin and optical linewidths (20 and 460 MHz, respectively) that are comparable to bulk-doped crystalline hosts for Er$^{3+}$. This work demonstrates that ion implantation is a viable path to studying rare earth ions in new hosts, and is a significant step towards realizing individually addressed rare earth ions with long spin coherence times for quantum technologies

Strong Purcell enhancement of an optical magnetic dipole transition

Engineering the local density of states with nanophotonic structures is a powerful tool to control light-matter interactions via the Purcell effect. At optical frequencies, control over the electric field density of states is typically used to couple to and manipulate electric dipole transitions. However, it is also possible to engineer the magnetic density of states to control magnetic dipole transitions. In this work, we experimentally demonstrate the optical magnetic Purcell effect using a single rare earth ion coupled to a nanophotonic cavity. We engineer a new single photon emitter, Er$^{3+}$ in MgO, where the electric dipole decay rate is strongly suppressed by the cubic site symmetry, giving rise to a nearly pure magnetic dipole optical transition. This allows the unambiguous determination of a magnetic Purcell factor $P_m=1040 \pm 30$. We further extend this technique to realize a magnetic dipole spin-photon interface, performing optical spin initialization and readout of a single Er$^{3+}$ electron spin. This work demonstrates the fundamental equivalence of electric and magnetic density of states engineering, and provides a new tool for controlling light-matter interactions for a broader class of emitters

Effects of Additives on Crystallization in Thin Organic Films

Controlling the shape and growth of crystals in molecular organic solids has ramifications impacting diverse fields, but remains challenging to fully exploit. Here, crystal shapes in organic thin films are manipulated from aspect ratios of 1 to over 50, with corresponding growth rates decreased by an order of magnitude simply by mixing a structurally dissimilar minority species into the film. These effects are mapped with composition and temperature in mixtures of two model small-molecular-weight organic compounds, revealing a continuous variation in crystal shape and growth rate. Other combinations of molecules are discussed, showing additive shape selection in multicomponent mixtures and enabling customization of crystal shape

Coherent Control of a Nuclear Spin via Interactions with a Rare-Earth Ion in the Solid State

Individually addressed Er3+ ions in solid-state hosts are promising resources for quantum repeaters, because of their direct emission in the telecom band and their compatibility with silicon photonic devices. While the Er3+ electron spin provides a spin-photon interface, ancilla nuclear spins could enable multiqubit registers with longer storage times. In this work, we demonstrate coherent coupling between the electron spin of a single Er3+ ion and a single I=1/2 nuclear spin in the solid-state host crystal, which is a fortuitously located proton (1H). We control the nuclear spin using dynamical-decoupling sequences applied to the electron spin, implementing one- and two-qubit gate operations. Crucially, the nuclear spin coherence time exceeds the electron coherence time by several orders of magnitude, because of its smaller magnetic moment. These results provide a path toward combining long-lived nuclear spin quantum registers with telecom-wavelength emitters for long-distance quantum repeaters. </p

Erbium-implanted materials for quantum communication applications

Erbium-doped materials can serve as spin-photon interfaces with optical transitions in the telecom C band, making them an exciting class of materials for long-distance quantum communication. However, the spin and optical coherence times of Er3+ ions are limited by currently available host materials, motivating the development of new Er3+-containing materials. Here we demonstrate the use of ion implantation to efficiently screen prospective host candidates, and show that disorder introduced by ion implantation can be mitigated through post-implantation thermal processing to achieve inhomogeneous linewidths comparable to bulk linewidths in as-grown samples. We present optical spectroscopy data for each host material, which allows us to determine the level structure of each site, allowing us to compare the environments of Er3+ introduced via implantation and via doping during growth. We demonstrate that implantation can generate a range of local environments for Er3+, including those observed in bulk-doped materials, and that the populations of these sites can be controlled with thermal processing