Coherent control and single-shot readout of a rare-earth ion embedded in a nanophotonic cavity (1907.12161v1)

Abstract: Quantum networks based on optically addressable spin qubits promise to enable secure communication, distributed quantum computing, and tests of fundamental physics. Scaling up quantum networks based on solid-state luminescent centers requires coherent spin and optical transitions coupled to photonic resonators. Here we investigate single $\mathrm{{}^{171}Yb^{3+}}$ ions in yttrium orthovanadate coupled to a nanophotonic cavity. These ions possess optical and spin transitions that are first-order insensitive to magnetic field fluctuations, enabling optical linewidths less than 1 MHz and spin coherence times exceeding 30 ms for cavity-coupled ions. The cavity-enhanced optical emission rate facilitates efficient spin initialization and conditional single-shot readout with fidelity greater than 95%. These results showcase a solid-state platform based on single coherent rare-earth ions for the future quantum internet.

Coherent Control and Single-Shot Readout of a Rare-Earth Ion Embedded in a Nanophotonic Cavity

The paper presents an empirical paper on the coherent control and single-shot readout of rare-earth ions, specifically $^{171}\mathrm{Yb}$, embedded within nanophotonic cavities. The research aims to advance quantum information processes by enhancing optical properties through cavity quantum electrodynamics (QED).

Experimental Setup and Methodology

The experimental apparatus is centered around yttrium orthovanadate (YVO) crystals and optimized nanophotonic cavity designs using focused-ion-beam milling. The paper involves controlling light interaction with $^{171}\mathrm{Yb}$ ions at cryogenic temperatures, utilizing signal reflection techniques to assure purity of ion addressing. Through detailed considerations of optical and microwave systems, including acousto-optic modulators and superconducting nanowire single-photon detectors, the experiment achieves optimized light-ion coupling.

The cavity exhibits a maximal quality factor ($Q$) of $\sim1 \times 10^4$, presenting a potential coupling rate that aligns with the strong optical dipole polarized along the crystal $c$-axis. The cavity structure supports measurement of decay rates and photon retrieval efficiency, taking into account rare-earth ion concentrations obtained from mass spectrometry analyses.

Key Findings and Analytical Insights

The primary objective—to isolate single $^{171}\mathrm{Yb}$ ions and to assess quantum coherence—is effectively realized. Photoluminescence excitation (PLE) scans identify potential single ions through spectroscopic fingerprinting. Post-selection techniques advance coherence time measurements, revealing potential spectral diffusion effects, which could impair photon indistinguishability. High sensitivity measurements capture unconventional strain and distribution patterns, providing insight into systematic strain effects at low temperature regimes on ion coherence and behavior.

Purcell enhancement dynamics of specific room modes underline the robust increase in emission rates, achieving a modification in optical branching ratios—a compelling theoretical element supporting high cyclicity. The cavity coupling improves cyclicity, as transitions within the cavity potentially exceed $99\%$ emission preference into the cavity modes. This intensifies photon detection efficiency and thus, supports single-shot readout of qubit states.

Spin and Coherence Probing

The paper forwards a methodical approach for spin initialization leveraging contrasting optical pumping effects. Spin lifetime analysis insinuates intricate spin dynamics, where coupling between electron and nuclear spins of vanadium and yttrium form a critical variable altering the transition coherence times. Secondly, coherent spin control exhibits substantial improvements using Carr-Purcell-Meiboom-Gill (CPMG) sequences to mitigate nuclear spin bath interactions, achieving coherence times extending to tens of milliseconds.

Implications and Future Directions

Quantum technologies stand to benefit from increased integration of rare-earth semiconductor systems within actualized quantum computing frameworks. This research demonstrates the capability of enhancing quantum systems through optical cavity implementations, pushing the boundary on photon retrieval and coherence enhancement techniques. The promising results allude to further research fostering enhanced cavity design and addressing quantum noise and inconsistency through advanced strategic models.

The paper opens a practical discourse for future theoretical and empirical challenges in quantum state stability, efficient photon detection technology, and hybrid quantum system design, contributing significantly to the evolving paradigm of rare-earth spectroscopy and quantum computing.