Selective Optical Addressing of Nuclear Spins through Superhyperfine Interaction in Rare-Earth Doped Solids

Impact of Zeeman and hyperfine interactions on the magnetic properties of paramagnetic metal Ions: I. Local interactions of the electron spin

The anisotropic Zeeman interaction of an ion, and the strong hyperfine interaction with its own nucleus, can significantly influence its interactions with the local environment. These effects, including the reduction of the effective magnetic moment of the electron spin and the phase memory decay rate, are studied theoretically. Analytical expressions describing the mean magnetic moment of the electron spin are obtained. The results of the theoretical analysis and accompanying numerical computations show that the strong hyperfine interaction of the ion reduces its effective magnetic moment. In particular, a 7% reduction is found for the scandium endofullerene Sc2@C80(CH2Ph) under conditions typical of an X-band EPR experiment.

Dynamical Decoupling of Spin Ensembles with Strong Anisotropic Interactions

Ensembles of dopants have widespread applications in quantum technology. The miniaturization of corresponding devices is however hampered by dipolar interactions that reduce the coherence at increased dopant density. We theoretically and experimentally investigate this limitation. We find that dynamical decoupling can alleviate, but not fully eliminate, the decoherence in crystals with strong anisotropic spin-spin interactions that originate from an anisotropic g tensor. Our findings can be generalized to many quantum systems used for quantum sensing, microwave-to-optical conversion, and quantum memory.

Hyperfine spectroscopy in a quantum-limited spectrometer

We report measurements of electron-spin-echo envelope modulation (ESEEM) performed at millikelvin temperatures in a custom-built high-sensitivity spectrometer based on superconducting micro-resonators. The high quality factor and small mode volume (down to 0.2 pL) of the resonator allow us to probe a small number of spins, down to 5 × 10 2 . We measure two-pulse ESEEM on two systems: erbium ions coupled to 183 W nuclei in a natural-abundance CaWO 4 crystal and bismuth donors coupled to residual 29 Si nuclei in a silicon substrate that was isotopically enriched in the 28 Si isotope. We also measure three- and five-pulse ESEEM for the bismuth donors in silicon. Quantitative agreement is obtained for both the hyperfine coupling strength of proximal nuclei and the nuclear-spin concentration.

Sensing Individual Nuclear Spins with a Single Rare-Earth Electron Spin

Rare-earth related electron spins in crystalline hosts are unique material systems, as they can potentially provide a direct interface between telecom band photons and long-lived spin quantum bits. Specifically, their optically accessible electron spins in solids interacting with nuclear spins in their environment are valuable quantum memory resources. Detection of nearby individual nuclear spins, so far exclusively shown for few dilute nuclear spin bath host systems such as the nitrogen-vacancy center in diamond or the silicon vacancy in silicon carbide, remained an open challenge for rare earths in their host materials, which typically exhibit dense nuclear spin baths. Here, we present the electron spin spectroscopy of single Ce^{3+} ions in a yttrium orthosilicate host, featuring a coherence time of T_{2}=124  μs. This coherent interaction time is sufficiently long to isolate proximal ^{89}Y nuclear spins from the nuclear spin bath of ^{89}Y. Furthermore, it allows for the detection of a single nearby ^{29}Si nuclear spin, native to the host material with ∼5% abundance. This study opens the door to quantum memory applications in rare-earth ion related systems based on coupled environmental nuclear spins, potentially useful for quantum error correction schemes.

Optical coherent transients in 167Er3+ at telecom-band wavelength

We demonstrate optical coherent transients in a Λ-like hyperfine energy-level system of Er167³⁺ in yttrium orthosilicate (Y₂SiO₅) with telecom-band photons at a zero magnetic field. Spectral hole burning was used to study the temperature dependence of the induced spectral antihole. We find that temperatures below 3.0 K suppress population dissipation induced by electron-phonon interactions sufficiently to enable population initialization in the Λ-like system. Further, the pulse area dependence of photoluminescence (PL) from the Λ-like system was measured at 2.2 K. An optical pump power dependence of PL intensity shows Rabi oscillations that contain two full Rabi cycles at the frequency of 2π×810  kHz. A two-pulse photon echo measurement reveals an optical coherence time of 12 μs. To date, this measured optical coherence time is the longest observed for Er³⁺ in solids at zero magnetic field. These findings will facilitate optical coherent manipulation of Λ-like Er167³⁺ electronic states as a quantum memories operating at telecom-band wavelengths.

Optically Addressing Single Rare-Earth Ions in a Nanophotonic Cavity

We demonstrate optical probing of spectrally resolved single Nd^{3+} rare-earth ions in yttrium orthovanadate. The ions are coupled to a photonic crystal resonator and show strong enhancement of the optical emission rate via the Purcell effect, resulting in near radiatively limited single photon emission. The measured high coupling cooperativity between a single photon and the ion allows for the observation of coherent optical Rabi oscillations. This could enable optically controlled spin qubits, quantum logic gates, and spin-photon interfaces for future quantum networks.