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arXiv:1909.02260 · Physical review. B./Physical review. B

Coherent optical and spin spectroscopy of nanoscale Pr3+:Y2O3

Diana Serrano, Chetan Deshmukh, Shuping Liu, Alexandre Tallaire, Alban Ferrier, Hugues de Riedmatten, Philippe Goldner

Published Oct 4, 2019• 24 citations
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Abstract

We investigate the potential for optical quantum technologies of ${\mathrm{Pr}}^{3+}:\phantom{\rule{0.28em}{0ex}}{\mathrm{Y}}_{2}{\mathrm{O}}_{3}$ in the form of monodisperse spherical nanoparticles. We measured optical inhomogeneous lines of 27 GHz and optical homogeneous linewidths of 108 and 315 kHz in particles with 400- and 150-nm average diameters, respectively, for the $^{1}D_{2}(0)\ensuremath{\leftrightarrow}^{3}H_{4}(0)$ transition at 1.4 K. Furthermore, ground-state and $^{1}D_{2}$ excited-state hyperfine structures in ${\mathrm{Y}}_{2}{\mathrm{O}}_{3}\phantom{\rule{0.16em}{0ex}}$ are here determined by spectral hole burning and modeled by complete Hamiltonian calculations. Ground-state spin transitions have energies of 5.99 and 10.42 MHz, for which we demonstrate spin inhomogeneous linewidths of 42 and 45 kHz, respectively. Spin ${T}_{2}$ up to $880\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{s}$ was obtained for the $\ifmmode\pm\else\textpm\fi{}3/2\ensuremath{\leftrightarrow}\ifmmode\pm\else\textpm\fi{}5/2$ transition at 10.42 MHz, a value which exceeds that of bulk ${\mathrm{Pr}}^{3+}$-doped crystals reported so far. These promising results confirm nanoscale ${\mathrm{Pr}}^{3+}:\phantom{\rule{0.28em}{0ex}}{\mathrm{Y}}_{2}{\mathrm{O}}_{3}\phantom{\rule{0.16em}{0ex}}$ is a very appealing candidate to integrate quantum devices. In particular, we discuss the possibility of using this material for realizing spin-photon interfaces emitting indistinguishable single photons.

DOI
10.1103/physrevb.100.144304

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Due to their narrow homogeneous linewidths, rare-earth ions in inorganic crystals at low temperatures have recently been given considerable attention as test materials for experiments in coherent quantum optics. Because these narrow linewidth transitions have been buried in a wide inhomogeneous line, the scope of experiments that could be carried out in these materials has been limited. However, here we present spectroscopic techniques, based on spectral hole burning and optical pumping, which allow hyperfine transitions that are initially buried within an inhomogeneously broadened absorption line to be studied with no background absorption from other transitions. A sequence of hole-burning pulses is used to isolate selected transitions between hyperfine levels, which makes it possible to directly study properties of the transitions, e.g., transition strengths, and gives access to information that is difficult to obtain in standard hole-burning spectroscopy, such as the ordering of hyperfine levels. The techniques introduced are applicable to absorbers in a solid with long-lived sublevels in the ground state and where the homogeneous linewidth and sublevel separations are smaller than the inhomogeneous broadening of the optical transition. In particular, this includes rare-earth ions doped into inorganic crystals and in the present work the techniques are demonstrated in spectroscopy of ${\mathrm{Pr}}^{3+}$ in ${\mathrm{Y}}_{2}{\mathrm{SiO}}_{5}$. Information on the hyperfine structure and relative transition strengths of the $^{3}H_{4}\text{\ensuremath{-}}^{1}D_{2}$ hyperfine transitions in ${\mathrm{Pr}}^{3+}:{\mathrm{Y}}_{2}{\mathrm{SiO}}_{5}$ has been obtained from frequency-resolved absorption measurements, in combination with coherent and incoherent driving of the transitions.

arXiv:cond-mat/0408515•Physical Review B•Dec 30, 2004•201 citations
We investigate the potential for optical quantum technologies of Pr3+:Y2O3{\mathrm{Pr}}^{3+}:\phantom{\rule{0.28em}{0ex}}{\mathrm{Y}}_{2}{\mathrm{O}}_{3}Pr3+:Y2​O3​ in the form of monodisperse spherical nanoparticles. We measured optical inhomogeneous lines of 27 GHz and optical homogeneous linewidths of 108 and 315 kHz in particles with 400- and 150-nm average diameters, respectively, for the 1D2(0)\ensuremath↔3H4(0)^{1}D_{2}(0)\ensuremath{\leftrightarrow}^{3}H_{4}(0)1D2​(0)\ensuremath↔3H4​(0) transition at 1.4 K. Furthermore, ground-state and 1D2^{1}D_{2}1D2​ excited-state hyperfine structures in Y2O3{\mathrm{Y}}_{2}{\mathrm{O}}_{3}\phantom{\rule{0.16em}{0ex}}Y2​O3​ are here determined by spectral hole burning and modeled by complete Hamiltonian calculations. Ground-state spin transitions have energies of 5.99 and 10.42 MHz, for which we demonstrate spin inhomogeneous linewidths of 42 and 45 kHz, respectively. Spin T2{T}_{2}T2​ up to 880\ensuremathμs880\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{s}880\ensuremathμs was obtained for the \ifmmode±\else\textpm\fi3/2\ensuremath↔\ifmmode±\else\textpm\fi5/2\ifmmode\pm\else\textpm\fi{}3/2\ensuremath{\leftrightarrow}\ifmmode\pm\else\textpm\fi{}5/2\ifmmode±\else\textpm\fi3/2\ensuremath↔\ifmmode±\else\textpm\fi5/2 transition at 10.42 MHz, a value which exceeds that of bulk Pr3+{\mathrm{Pr}}^{3+}Pr3+-doped crystals reported so far. These promising results confirm nanoscale Pr3+:Y2O3{\mathrm{Pr}}^{3+}:\phantom{\rule{0.28em}{0ex}}{\mathrm{Y}}_{2}{\mathrm{O}}_{3}\phantom{\rule{0.16em}{0ex}}Pr3+:Y2​O3​ is a very appealing candidate to integrate quantum devices. In particular, we discuss the possibility of using this material for realizing spin-photon interfaces emitting indistinguishable single photons.
Nanoscale systems possessing long-lived spins and the ability to coherently couple to light are highly demanded for quantum devices implementations. Several approaches, like NV centers in diamond, semiconductor quantum dots are intensively investigated in the field, where an outstanding challenge is to preserve properties, and especially optical and spin coherence lifetimes, at the nanoscale. In this context, chemically synthesized Eu3+ doped Y2O3 nanoparticles have demonstrated great potential for quantum technologies based on their narrow optical homogeneous linewidth, down to the 10 kHz level, and millisecond-long spin coherence time. Here, we investigate an alternative nanoscale material: Pr3+: Y2O3. We first determine the Pr3+ hyperfine structure in Y2O3 by spectral hole burning and then measure photon and spin echoes from nanoparticles down to 150 nm. Spin T2 up to 880 μs was obtained for the ±3/2↔±5/2 hyperfine transition at 10.42 MHz, a value which exceeds that of bulk Pr3+doped crystals so far reported. These promising results confirm nanoscale Pr3+:Y2O3 as a very appealing candidate to integrate quantum devices.
Most of the experiments related to quantum information applications, involving rare-earth doped inorganic crystals, are performed on yttrium orthosilicate single crystals. The work presented here is motivated by the search of new compounds which can be used in the field of quantum computing and/or quantum storage. Relaxation times and hyperfine structure of the $^{3}H_{4}(0)\ensuremath{\rightarrow}^{1}D_{2}(0)$ transition in 1.4% Pr3+:La2(WO4)3{\mathrm{Pr}}^{3+}:{\mathrm{La}}_{2}{(\mathrm{W}{\mathrm{O}}_{4})}_{3}Pr3+:La2​(WO4​)3​ at 4K4\phantom{\rule{0.3em}{0ex}}\mathrm{K}4K have been measured by photon-echo and spectral-hole-burning techniques. The hyperfine splittings of the ground 3H4(0)^{3}H_{4}(0)3H4​(0) and the excited 1D2(0)^{1}D_{2}(0)1D2​(0) states are $14.9\ifmmode\pm\else\textpm\fi{}0.1\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$, $24.6\ifmmode\pm\else\textpm\fi{}0.1\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$ and $5.0\ifmmode\pm\else\textpm\fi{}0.1\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$, $7.3\ifmmode\pm\else\textpm\fi{}0.1\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$, respectively. An inhomogeneous linewidth of $18.8\ifmmode\pm\else\textpm\fi{}0.1\phantom{\rule{0.3em}{0ex}}\mathrm{GHz}$ was measured. A homogeneous linewidth of $25.3\ifmmode\pm\else\textpm\fi{}2.0\phantom{\rule{0.3em}{0ex}}\mathrm{kHz}$ was obtained with or without an external magnetic field of about 14mT14\phantom{\rule{0.3em}{0ex}}\mathrm{mT}14mT. The fluorescence dynamics of the 1D2^{1}D_{2}1D2​ level obtained by a direct excitation in the $^{3}H_{4}\ensuremath{\rightarrow}^{1}D_{2}$ transition gives a nonexponential decay which indicates energy-transfer processes. This decay can be accurately fitted by the Inokuti-Hirayama model [J. Chem. Phys. 43, 1978 (1965)] with a radiative lifetime of $61\ifmmode\pm\else\textpm\fi{}1\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{s}$ giving a minimal homogeneous linewidth of 2.6kHz2.6\phantom{\rule{0.3em}{0ex}}\mathrm{kHz}2.6kHz. The spectral-hole lifetime due to population redistribution within the ground hyperfine levels is $16\ifmmode\pm\else\textpm\fi{}2\phantom{\rule{0.3em}{0ex}}\mathrm{s}$. The results obtained for the La2(WO4)3{\mathrm{La}}_{2}{(\mathrm{W}{\mathrm{O}}_{4})}_{3}La2​(WO4​)3​ compound make this crystal an interesting host for quantum applications.
Erbium-doped solids are a promising platform for quantum technology due to the Er3+\mathrm{E}{\mathrm{r}}^{3+}Er3+ 1.5-\textmu{}m optical transition in the telecom C band that can offer long coherence times. To characterize the intrinsic C2{\mathrm{C}}_{2}C2​ site of Er3+\mathrm{E}{\mathrm{r}}^{3+}Er3+ in Y2O3{\mathrm{Y}}_{2}{\mathrm{O}}_{3}Y2​O3​ for quantum information and photonic signal-processing applications, absorption and site-selective fluorescence spectroscopy were used to assign the Er3+4I15/2\mathrm{E}{\mathrm{r}}^{3+}\phantom{\rule{4pt}{0ex}}^{4}I_{15/2}Er3+4I15/2​$\ensuremath{\leftrightarrow}$4I13/2^{4}I_{13/2}4I13/2​ transitions. The lowest-to-lowest transition occurs at 1535.608 nm and laser absorption determined an inhomogeneous linewidth of 780 MHz in a 0.005%-doped crystal at 3.4 K. Time-resolved fluorescence established an upper limit for the excited-state lifetime of 8.5 ms. Angular-dependent Zeeman absorption was used to determine ground- and excited-state ggg tensors. The C2{\mathrm{C}}_{2}C2​-site ggg tensor components for the ground state are gx=1.60{g}_{x}=1.60gx​=1.60, gy=4.71{g}_{y}=4.71gy​=4.71, and gz=11.93{g}_{z}=11.93gz​=11.93 with a tipping angle of \ensuremath{\alpha} = $2.{06}^{\ensuremath{\circ}}$, whereas for the excited state the components are gx=1.08{g}_{x}=1.08gx​=1.08, gy=4.36{g}_{y}=4.36gy​=4.36, and gz=10.07{g}_{z}=10.07gz​=10.07 with a tipping angle of \ensuremath{\alpha} = $\ensuremath{-}11.{7}^{\ensuremath{\circ}}$. Optical decoherence can be suppressed by the application of a magnetic field parallel to $\ensuremath{\langle}111\ensuremath{\rangle}$ crystal axes where all C2{\mathrm{C}}_{2}C2​ sites become nearly magnetically equivalent with large ggg values so that spin flips of neighboring Er3+\mathrm{E}{\mathrm{r}}^{3+}Er3+ ions can be simultaneously suppressed. Using this magnetic field direction, two-pulse photon echoes gave a homogeneous linewidth of 5 kHz for an applied magnetic field of 0.5 T, narrowing and saturating at 2.5 kHz at 3.5 T. Decoherence over intermediate magnetic fields was described by spectral diffusion due to $\mathrm{E}{\mathrm{r}}^{3+}\text{\ensuremath{-}}\mathrm{E}{\mathrm{r}}^{3+}$ magnetic dipole interactions driven by the direct phonon process. With Er3+\mathrm{E}{\mathrm{r}}^{3+}Er3+:Y2O3{\mathrm{Y}}_{2}{\mathrm{O}}_{3}Y2​O3​ absorption at a convenient telecom laser wavelength and the ability to fabricate waveguides, our study suggests that this is a promising material system for quantum information and spectral hole-burning signal-processing applications.
Rare Earth (RE) ion doped nanomaterials are promising candidates for a range of quantum technology applications. Among RE ions, the so-called Kramers' ions possess spin transitions in the GHz range at low magnetic fields, which allows for high-bandwidth multimode quantum storage, fast qubit operations as well as interfacing with superconducting circuits. They also present relevant optical transitions in the infrared. In particular, Er3+{\mathrm{Er}}^{3+}Er3+ has an optical transition in the telecom band, while Nd3+{\mathrm{Nd}}^{3+}Nd3+ presents a high-emission-rate transition close to 890 nm. In this paper, we measure spectroscopic properties that are of relevance to using these materials in quantum technology applications. We find the inhomogeneous linewidth to be 10.7 GHz for Er3+{\mathrm{Er}}^{3+}Er3+ and 8.2 GHz for Nd3+{\mathrm{Nd}}^{3+}Nd3+, and the excited state lifetime T1{T}_{1}T1​ to be 13.68 ms for Er3+{\mathrm{Er}}^{3+}Er3+ and $540\phantom{\rule{0.16em}{0ex}}\textmu{}\mathrm{s}$ for Nd3+{\mathrm{Nd}}^{3+}Nd3+. We study the dependence of homogeneous linewidth on temperature for both samples, with the narrowest linewidth being 379 kHz (T2=839{T}_{2}=839T2​=839 ns) for Er3+{\mathrm{Er}}^{3+}Er3+ measured at 3 K, and 62 kHz (${T}_{2}=5.14\phantom{\rule{4pt}{0ex}}\textmu{}\mathrm{s}$) for Nd3+{\mathrm{Nd}}^{3+}Nd3+ measured at 1.6 K. Further, we investigate time-dependent homogeneous linewidth broadening due to spectral diffusion and the dependence of the homogeneous linewidth on magnetic field to get additional clarity of mechanisms that can influence the coherence time. In light of our results, we discuss two applications: single qubit-state readout and a Fourier-limited single photon source.
Contributions to the homogeneous linewidth of the 3^{3}3H4{\mathit{H}}_{4}H4​(1)${\ensuremath{\rightarrow}}^{1}$D2{\mathit{D}}_{2}D2​(1) transition for the two crystallographic sites of Pr3+{\mathrm{Pr}}^{3+}Pr3+ in Y2{\mathrm{Y}}_{2}Y2​SiO5{\mathrm{SiO}}_{5}SiO5​ have been investigated using photon echoes. The effects of excitation-intensity-dependent dephasing or instantaneous diffusion were systematically studied to allow accurate determination of the optical resonance widths. Homogeneous linewidths of 2.8 kHz (site 1) and 1 kHz (site 2) were measured with no applied magnetic field and with sufficiently low laser intensity to minimize the effects of instantaneous diffusion. Using the same excitation intensity, widths of 2.1 kHz (site 1) and 0.85 kHz (site 2) were obtained with an applied magnetic field of 77 G, demonstrating a significant contribution of 89Y^{89}\mathrm{Y}89Y nuclear-spin fluctuations to the zero-field homogeneous linewidth. Extrapolation to zero excitation intensity yielded optical resonance widths that were only slightly narrower than the measured values. Optically detected nuclear magnetic resonance measurements determined the hyperfine structure of the 3^{3}3H4{\mathit{H}}_{4}H4​ ground state for each site; the hyperfine levels of the lowest component of the 1^{1}1D2{\mathit{D}}_{2}D2​ manifold for each site were determined using photon echo nuclear double resonance. The relatively large oscillator strength of 3\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}7}$ for a rare-earth ion, in conjunction with long dephasing times makes this material a useful candidate for demonstration of time-domain signal processing and optical data storage.
Due to their narrow homogeneous linewidths, rare-earth ions in inorganic crystals at low temperatures have recently been given considerable attention as test materials for experiments in coherent quantum optics. Because these narrow linewidth transitions have been buried in a wide inhomogeneous line, the scope of experiments that could be carried out in these materials has been limited. However, here we present spectroscopic techniques, based on spectral hole burning and optical pumping, which allow hyperfine transitions that are initially buried within an inhomogeneously broadened absorption line to be studied with no background absorption from other transitions. A sequence of hole-burning pulses is used to isolate selected transitions between hyperfine levels, which makes it possible to directly study properties of the transitions, e.g., transition strengths, and gives access to information that is difficult to obtain in standard hole-burning spectroscopy, such as the ordering of hyperfine levels. The techniques introduced are applicable to absorbers in a solid with long-lived sublevels in the ground state and where the homogeneous linewidth and sublevel separations are smaller than the inhomogeneous broadening of the optical transition. In particular, this includes rare-earth ions doped into inorganic crystals and in the present work the techniques are demonstrated in spectroscopy of Pr3+{\mathrm{Pr}}^{3+}Pr3+ in Y2SiO5{\mathrm{Y}}_{2}{\mathrm{SiO}}_{5}Y2​SiO5​. Information on the hyperfine structure and relative transition strengths of the $^{3}H_{4}\text{\ensuremath{-}}^{1}D_{2}$ hyperfine transitions in Pr3+:Y2SiO5{\mathrm{Pr}}^{3+}:{\mathrm{Y}}_{2}{\mathrm{SiO}}_{5}Pr3+:Y2​SiO5​ has been obtained from frequency-resolved absorption measurements, in combination with coherent and incoherent driving of the transitions.