Cavity-enhanced spectroscopy of a few-ion ensemble in Eu³⁺:Y₂O₃

Abstract

We report on the coupling of the emission from a single europium-doped nanocrystal to a fiber-based microcavity under cryogenic conditions. As a first step, we study the properties of nanocrystals that are relevant for cavity experiments and show that embedding them in a dielectric thin film can significantly reduce scattering loss and increase the light-matter coupling strength for dopant ions. The latter is supported by the observation of a fluorescence lifetime reduction, which is explained by an increased local field strength. We then couple an isolated nanocrystal to an optical microcavity, determine its size and ion number, and perform cavity-enhanced spectroscopy by resonantly coupling a cavity mode to a selected transition. We measure the inhomogeneous linewidth of the coherent D F 5 0 7 0 -transition and find a value that agrees with the linewidth in bulk crystals, evidencing a high crystal quality. We detect the fluorescence from an ensemble of few ions in the regime of power broadening and observe an increased fluorescence rate consistent with Purcell enhancement. The results represent an important step towards the efficient readout of single rare earth ions with excellent optical and spin coherence properties, which is promising for applications in quantum communication and distributed quantum computation.

Coherent optical and spin spectroscopy of nanoscale Pr3+:Y2O3

“…7(b)), we conclude that ξ=0.057. For a realistic cavity presenting a finesse F=10 5 , and smallest mirror separation d=2 µm as the one discussed in [19], effective Purcell factor C=340 would be expected. This is more than three times higher than expected for Eu 3+ [19], mainly because of the difference in branching ratio between Eu 3+ and Pr 3+ transitions.…”

“…For a realistic cavity presenting a finesse F=10 5 , and smallest mirror separation d=2 µm as the one discussed in [19], effective Purcell factor C=340 would be expected. This is more than three times higher than expected for Eu 3+ [19], mainly because of the difference in branching ratio between Eu 3+ and Pr 3+ transitions. With such Purcell factor, the demonstrated optical T 2 values in the 400nm-diameter and 150-nm-particles (Table III), already verify the condition to emit Fourier transform limited photons: C > 2T 1 /T 2 .…”

“…More important, optical homogeneous linewidths down to 25 kHz have been reported in these nanocrystals for the 7 F 0 ↔ 5 D 0 transition at 580.883 nm [26,25], and millisecond-long nuclear spin T 2 [27]. A disadvantage of Eu 3+ is however that it presents weak oscillator strength (∼10 −8 in Y 2 O 3 [28]) and low emission branching ratio for the 7 F 0 ↔ 5 D 0 line (∼0.016 [19]). This reduces the achievable Purcell enhancement by a factor 60 for this ion [19].…”

“…A disadvantage of Eu 3+ is however that it presents weak oscillator strength (∼10 −8 in Y 2 O 3 [28]) and low emission branching ratio for the 7 F 0 ↔ 5 D 0 line (∼0.016 [19]). This reduces the achievable Purcell enhancement by a factor 60 for this ion [19]. In these aspects, a good alternative rare-earth ion to Eu 3+ is Pr 3+ .…”

Transverse-mode coupling effects in scanning cavity microscopy

“…It can be observed in figures 2(a)-(d) that the shape of certain contours is very similar across different measurements, and that the width of the contour lines increases continuously with increasing q. Figure 2(f) shows the superposition of measurements taken at mode orders q=11, 12,14,16,22,24,28,38. Remarkably, the individual measurements combine to a consistent isocontour map.…”