Philip J. T. Woodburn

Effects of fabrication methods on spin relaxation and crystallite quality in Tm-doped powders studied using spectral hole burning

High-quality rare-earth-ion (REI) doped materials are a prerequisite for many applications such as quantum memories, ultra-high-resolution optical spectrum analyzers and information processing. Compared to bulk materials, REI doped powders offer low-cost fabrication and a greater range of accessible material systems. Here we show that crystal properties, such as nuclear spin lifetime, are strongly affected by mechanical treatment, and that spectral hole burning can serve as a sensitive method to characterize the quality of REI doped powders. We focus on the specific case of thulium doped (Tm:YAG). Different methods for obtaining the powders are compared and the influence of annealing on the spectroscopic quality of powders is investigated on a few examples. We conclude that annealing can reverse some detrimental effects of powder fabrication and, in certain cases, the properties of the bulk material can be reached. Our results may be applicable to other impurities and other crystals, including color centers in nano-structured diamond. Graphical Abstract

Characterization of ^(171)Yb^(3+):YVO_4 for photonic quantum technologies

Rare-earth ions in crystals are a proven solid-state platform for quantum technologies in the ensemble regime and attractive for new opportunities at the single-ion level. Among the trivalent rare earths, ^(171)Yb^(3+) is unique in that it possesses a single 4f excited-state manifold and is the only paramagnetic isotope with a nuclear spin of 1/2. In this work, we present measurements of the optical and spin properties of ^(171)Yb^(3+):YVO_4 to assess whether this distinct energy-level structure can be harnessed for quantum interfaces. The material was found to possess large optical absorption compared to other rare-earth-doped crystals owing to the combination of narrow inhomogeneous broadening and a large transition oscillator strength. In moderate magnetic fields, we measure optical linewidths less than 3 kHz and nuclear spin linewidths less than 50 Hz. We characterize the excited-state hyperfine and Zeeman interactions in this system, which enables the engineering of a Λ system and demonstration of all-optical coherent control over the nuclear-spin ensemble. Given these properties, ^(171)Yb^(3+):YVO_4 has significant potential for building quantum interfaces such as ensemble-based memories, microwave-to-optical transducers, and optically addressable single rare-earth-ion spin qubits.

Solid-state laser cooling of optically levitated particles

Ultra-high sensitivity sensors can be achieved with optically levitated particles in ultra-high vacuum (UHV). Trapped particles act as high-Q harmonic oscillators, whose amplitude, position, and frequency can be monitored to provide high sensitivity measurements of the particle’s acceleration. Larger particles (10-30 microns in diameter) provide higher sensitivity, but they are difficult to trap in UHV without particle loss. To overcome the radiometric forces that lead to particle loss, rare earth (RE) ion dopants can be incorporated into the particles to enable solid-state laser cooling of the particle’s internal temperature. The laser used for optical trapping can be tuned to a wavelength on the lower energy side of the ion absorption band, and thus also serve as the pump laser for solid-state laser cooling. Internal cooling occurs when the average energy of the photons emitted is larger than the average energy of the photons absorbed. Ions will rapidly thermalize while in the ground and the excited states to create the energy difference. Solid-state laser cooling has been realized in bulk host materials and is well understood. This technique of internal cooling for reducing loss pressure is currently being tested.