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arXiv:2309.02688 · Physical review. B./Physical review. B

High resolution spectroscopy of thulium atoms implanted in solid noble gas crystals

Vinod Gaire, Mi Y., Yiting Pei, Anthony Semenova, Colin Parker

Published Dec 8, 2023• 7 citations
arXivHTMLPDF

Abstract

Optically active defects in solid-state systems have many applications in quantum information and sensing. However, unlike free atoms, which have fixed optical transition frequencies, the inhomogeneous broadening of the transitions in solid-state environments limit their use as identical scatterers for such applications. Here we show that crystals of argon and neon prepared in a closed-cycle cryostat doped with thulium atoms at cryogenic temperatures are an exception. High resolution absorption and emission spectroscopy show that the 1140 nm magnetic dipole transition is split into multiple components. The origin of this splitting is likely a combination of different classes of trapping sites, crystal field effects within each site, and hyperfine interactions. The individual lines have ensemble widths as small as $0.6\phantom{\rule{4.pt}{0ex}}\text{GHz}$, which temperature dependence and pump-probe spectroscopy indicate is likely a homogeneous effect, suggesting inhomogeneity is well below the GHz scale.

DOI
10.1103/physrevb.108.214101

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The excitation, emission spectra, and decay curves of the emission intensity of thulium atoms implanted in liquid and solid helium were observed in the presence and absence of an external magnetic field. The observed narrow line (width $\ensuremath{\sim}0.1$ nm) of the excitation spectrum at 590.60 nm is assigned as a zero-phonon transition from the electronic ground state ${4f}^{13}{(}^{2}{F}_{7/2}^{o}{)6s}^{2}$, which indicates that the transition between the inner shells is weakly perturbed by surrounding helium atoms. The pressure dependence of the emission wavelength suggests that the symmetry of helium atoms distributed around a thulium atom in the solid phase is similar to that in the liquid phase. The emission intensity was stable and large in the solid phase since thulium atoms were trapped at a density of 10${}^{10}$--10${}^{11}$ atoms/cm${}^{3}$. The lifetime of the excited state was measured to be $7.09\ifmmode\pm\else\textpm\fi{}0.04$ $\ensuremath{\mu}$s, which was longer than that of the ${4f}^{12}{(}^{3}{H}_{6}{)5d}_{5/2}{6s}^{2}$ ${(6,5/2)}_{7/2}$ state of free thulium atoms. The excited state is expected to be a mixed state of the ${4f}^{12}{5d6s}^{2}$ and ${4f}^{13}6s6p$ configurations. The metastable state ${4f}^{13}{(}^{2}{F}_{5/2}^{o}{)6s}^{2}$ is populated by a radiative transition from this excited state and relaxes to the ground state through a magnetic dipole transition. The lifetime of the metastable state of a neutral thulium atom was measured to be $75\ifmmode\pm\else\textpm\fi{}3$ ms.

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Communications Materials•Oct 10, 2024•12 citations
Optically active defects in solid-state systems have many applications in quantum information and sensing. However, unlike free atoms, which have fixed optical transition frequencies, the inhomogeneous broadening of the transitions in solid-state environments limit their use as identical scatterers for such applications. Here we show that crystals of argon and neon prepared in a closed-cycle cryostat doped with thulium atoms at cryogenic temperatures are an exception. High resolution absorption and emission spectroscopy show that the 1140 nm magnetic dipole transition is split into multiple components. The origin of this splitting is likely a combination of different classes of trapping sites, crystal field effects within each site, and hyperfine interactions. The individual lines have ensemble widths as small as 0.6GHz0.6\phantom{\rule{4.pt}{0ex}}\text{GHz}0.6GHz, which temperature dependence and pump-probe spectroscopy indicate is likely a homogeneous effect, suggesting inhomogeneity is well below the GHz scale.
We investigate the 1140 nm magnetic-dipole transition of thulium atoms trapped in solid argon and neon. These solids can be straightforwardly grown on any substrate at cryogenic temperatures, making them prime targets for surface-sensing applications. Our data are well described by a splitting of the single vacuum transition into three components in both argon and neon, with each component narrower than the 0.8 nm spectrometer resolution. The lifetime of the excited states is 14.6(0.5) ms in argon and 27(3) ms in neon, shorter than in vacuum or in solid helium. We also collected visible laser-induced fluorescence spectroscopy showing broader emission features in the range of 580--600 nm. The narrow infrared features in particular suggest a range of possible applications.
Optically active defects suspended in an inert solid are an interesting system for sensing and magnetometry at the nanometer scale, in addition to being a potential source of high-density, identical quantum emitters for quantum information. Beyond their response to external fields, the optical absorption and emission spectra also reflect information about the host matrix, which is critical to understand for either application. For the particular system of thulium atoms implanted in solid argon, high resolution laser spectroscopy reveals narrow ensemble linewidths of the 1140 nm f to f ground state spin-orbit transition, which is split due to crystal field effects and hyperfine coupling. Pump-probe spectroscopy is used to identify crystal field levels in at least two stable trapping sites, and the crystal field is determined to be nearly axial in both sites. Strong selection rules indicate that this transition becomes magnetic-electric in the argon host, most likely due to dielectric effects. In the presence of mT magnetic fields, Zeeman shifts are resolvable by laser fluorescence, allowing crystal axis selective polarized spectroscopy. These results show that all-optical detection schemes for DC magnetic fields are already possible with thulium-doped argon, and point towards more informed strategies for monitoring and improving crystal growth and annealing.
We study Lambda-type electromagnetically induced transparency (EIT) in cryogenically-cooled, europium and praseodymium doped yttrium orthosilicate (Eu:YSO and Pr:YSO). We use spectral hole burning techniques to vary the optical inhomogeneous width of the sub-ensemble of atoms participating in the EIT. The effect of inhomogeneous broadening has been studied in the context of Doppler broadened gases, but less so in solids where motional effects are absent and the coherence is not limited by the transit of atoms through the optical field. Rare earth doped crystals, like many solid-state systems, exhibit spectral hole burning in which a narrowband laser field optically pumps atoms to states in the ground manifold that are dark with respect to the applied field, opening up a transparency window that persists after the pumping laser is shuttered. More complex sequences of fields at multiple frequencies can create arbitrary spectral profiles, within bounds set by the particular energy level structure of the atoms. For both Eu:YSO and Pr:YSO, there are three hyperfine ground states and three hyperfine excited states (at zero magnetic field) and all nine transitions are dipole-allowed with varying transition strengths. We use spectral hole-burning techniques to prepare a sub-ensemble of atoms in a particular frequency class and a particular ground spin state, while also pumping atoms out of another ground state to create a Lambda system. We observe the same functional dependence of the EIT width on the optical inhomogeneous width and independently calibrated control field Rabi frequency in both systems.
Rare-earth (RE) atoms, such as erbium (Er), have inner-shell optical transitions in the near-infrared, some of which are in the telecom bands. These transitions are largely insensitive to the host environment due to effective shielding by the filled outer shells. Cryogenic rare-gas (RG) solids, such as solid neon (Ne) and argon (Ar), combine high chemical purity with a nearly nuclear-spin-free environment, making them attractive solid hosts for preserving optical and spin coherence. In this work, we isolate neutral Er atoms in solid Ne and Ar at 6 K and characterize their emission by steady-state and time-resolved photoluminescence (PL) spectroscopy. In both hosts, we observe several near-infrared transitions between 1000--1500 nm, including inner-shell emission in the telecom O and E bands. The 4f→5d4f \rightarrow 5d4f→5d transition near 1299 nm forms a multiplet of narrow components, consistent with crystal-field splitting, and decays on a microsecond timescale. The 4f→4f4f \rightarrow 4f4f→4f transition near 1437 nm shows a matrix shift below 1 cm−1^{-1}−1 in both hosts. In solid Ne, its inhomogeneous linewidth is bounded by the spectrometer resolution to < 22 GHz, and its PL lifetime reaches up to 78.9 ms, close to the estimated radiative limit. Thermal annealing extends the 1437 nm lifetime in Ne and suppresses the phonon sidebands relative to the zero-phonon lines in Ar. These results identify RG solids as promising hosts for long-lived telecom-band Er emission and provide a foundation for future spin-photon interfaces and hybrid quantum architectures.
The excitation, emission spectra, and decay curves of the emission intensity of thulium atoms implanted in liquid and solid helium were observed in the presence and absence of an external magnetic field. The observed narrow line (width $\ensuremath{\sim}0.1$ nm) of the excitation spectrum at 590.60 nm is assigned as a zero-phonon transition from the electronic ground state 4f13(2F7/2o)6s2{4f}^{13}{(}^{2}{F}_{7/2}^{o}{)6s}^{2}4f13(2F7/2o​)6s2, which indicates that the transition between the inner shells is weakly perturbed by surrounding helium atoms. The pressure dependence of the emission wavelength suggests that the symmetry of helium atoms distributed around a thulium atom in the solid phase is similar to that in the liquid phase. The emission intensity was stable and large in the solid phase since thulium atoms were trapped at a density of 1010{}^{10}10--1011{}^{11}11 atoms/cm3{}^{3}3. The lifetime of the excited state was measured to be $7.09\ifmmode\pm\else\textpm\fi{}0.04$ $\ensuremath{\mu}$s, which was longer than that of the 4f12(3H6)5d5/26s2{4f}^{12}{(}^{3}{H}_{6}{)5d}_{5/2}{6s}^{2}4f12(3H6​)5d5/2​6s2 (6,5/2)7/2{(6,5/2)}_{7/2}(6,5/2)7/2​ state of free thulium atoms. The excited state is expected to be a mixed state of the 4f125d6s2{4f}^{12}{5d6s}^{2}4f125d6s2 and 4f136s6p{4f}^{13}6s6p4f136s6p configurations. The metastable state 4f13(2F5/2o)6s2{4f}^{13}{(}^{2}{F}_{5/2}^{o}{)6s}^{2}4f13(2F5/2o​)6s2 is populated by a radiative transition from this excited state and relaxes to the ground state through a magnetic dipole transition. The lifetime of the metastable state of a neutral thulium atom was measured to be $75\ifmmode\pm\else\textpm\fi{}3$ ms.
Abstract With their optical addressability of individual spins and long coherence time, nitrogen-vacancy (NV) centers in diamond are often called “atom-like solid spin-defects”. As observed with trapped atomic ions, quantum interference mediated by indistinguishable photons was demonstrated between remote NV centers. In high sensitivity DC magnetometry at room temperature, NV ensembles are potentially rivaling with alkali-atom vapor cells. However, local strain induces center-to-center variation of both optical and spin transitions of NV centers. Therefore, advanced engineering of diamond growth toward crystalline perfection is demanded. Here, we report on the synthesis of high-quality HPHT (high-pressure, high-temperature) crystals, demonstrating a small inhomogeneous broadening of the spin transitions, of T 2 * = 1.28 μs, approaching the limit for crystals with natural 13 C abundance, that we determine as T 2 * = 1.48 μs. The contribution from strain and local charges to the inhomogeneous broadening is lowered to ~17 kHz full width at half maximum for NV ensemble within a > 10 mm 3 volume. Looking at optical transitions in low nitrogen crystals, we examine the variation of zero-phonon-line optical transition frequencies at low temperatures, showing a strain contribution below 2 GHz for a large fraction of single NV centers.