Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2412.03948 · Physical Review Materials

Spectroscopic investigations of multiple environments in Er: CaWO 4 through charge imbalance

Fabian Becker, Catherine L. Curtin, Sudip KC, Tim Schneider, Lorenz J. J. Sauerzopf, Ibrahim Elzeiny, Kai Müller

Published Jul 15, 2025• 6 citations
arXivHTMLPDF

Abstract

We present a detailed spectroscopic study of the I 13 / 2 4 and I 15 / 2 4 Er 3 + multiplets of Er: CaWO 4 grown without a co-dopant. Using photoluminescence and photoluminescence excitation measurements, we find multiple environments into which erbium ions are incorporated in the crystal. For the four most prevalent environments, we provide a complete assignment of the I 13 / 2 4 and I 15 / 2 4 sublevel energies. Polarization-dependent absorption and emission spectroscopy allow us to identify the irreducible representations of the states and determine the dipole nature of transitions. In addition, we compare the different relaxation paths within I 13 / 2 4 and I 15 / 2 4 multiplets via line broadening and lifetime measurements. Finally, spectral, lifetime, and polarization measurements indicate similarities between the studied environments.

DOI
10.1103/6srk-3k4n

Related papers

Optical Spectroscopy of Waveguide coupled Er$^{3+}$ ensembles in CaWO$_4$ and YVO$_4$

Fabian Becker, Anna Selzer, Lorenz J. J. Sauerzopf +4 more

We present an optical study of near-surface Er$^{3+}$ ensembles in waveguide-integrated CaWO$_4$ and YVO$_4$, investigating how nanophotonic coupling modifies rare-earth spectroscopy. In particular, we compare bulk excitation with evanescently coupled TE and TM waveguide modes. In Er$^{3+}$:CaWO$_4$, we observe a pronounced polarization-dependent surface effect. TE-coupled spectra closely reproduce bulk behavior. In contrast, TM coupling induces strong inhomogeneous broadening and an asymmetric low-energy shoulder of the site S1 Y1Z1 transition, with linewidths exceeding those of the bulk by more than a factor of four. Temperature-dependent measurements and surface termination studies indicate that surface charges are the dominant mechanism. Er$^{3+}$:YVO$_4$ remains largely unaffected by mode polarization, and surface termination leads only to minor spectral shifts. These observations suggest that non-charge-neutral rare-earth systems are more susceptible to surface-induced decoherence sources than charge-neutral hosts.

cond-mat.mtrl-sciCross-listedarXiv:2601.03455•Jan 8, 2026•0 citations

Spectroscopy, crystal-field, and transition intensity analyses of the C 3v (O 2− ) centre in Er 3+ doped CaF2 crystals

M. D. Moull, Jamin L.B. Martin, T.G.M. Newman +4 more

Erbium ions in crystals show considerable promise for the technologies that will form the backbone of future networked quantum information technology. Despite advances in leveraging erbium’s fibre-compatible infrared transition for classical and quantum applications, the transitions are, in general, not well understood. We present detailed absorption and laser site-selective spectroscopy of the C 3v (O 2 − ) centre in CaF 2 :Er 3 + as an interesting erbium site case study. The 4 I 15 / 2 Z 1 → 4 I 13 / 2 Y 1 transition has a low-temperature inhomogeneous linewidth of 1 GHz with hyperfine structure observable from the 167 Er isotope. A parametrized crystal-field Hamiltonian is fitted to 34 energy levels and the two ground state magnetic splitting factors. The wavefunctions are used to perform a transition intensity analysis and electric-dipole parameters are fitted to absorption oscillator strengths. Simulated spectra for the 4 I 11 / 2 → 4 I 15 / 2 and 4 I 13 / 2 → 4 I 15 / 2 inter-multiplet transitions are in excellent agreement with the experimentally measured spectra. The 4 I 13 / 2 excited state lifetime is 25.0 ms and the intensity calculation is in excellent agreement with this value. • Detailed spectroscopic study of the C 3v (O 2 − ) Centre in CaF 2 :Er 3 + . • Crystal-field fit to 34 energy levels and ground-state magnetic splitting. • Transition intensity analysis for the technologically relevant infrared transitions.

Optical Materials X•Sep 27, 2024•1 citation

Spectroscopy, Crystal-Field, and Transition Intensity Analyses of the C$_{\rm 3v}$(O$^{2-}$) Centre in Er$^{3+}$ Doped CaF$_{2}$ Crystals

M. D. Moull, Jamin L.B. Martin, Newman, T. G. M. +4 more

Erbium ions in crystals show considerable promise for the technologies that will form the backbone of future networked quantum information technology. Despite advances in leveraging erbium's fibre-compatible infrared transition for classical and quantum applications, the transitions are, in general, not well understood. We present detailed absorption and laser site-selective spectroscopy of the C$_{\rm 3v}$(O$^{2-}$) centre in CaF$_2$:Er$^{3+}$ as an interesting erbium site case study. The $^{4}$I$_{15/2}$Z$_1 \rightarrow {^{4}}$I$_{13/2}$Y$_1$ transition has a low-temperature inhomogeneous linewidth of 1 GHz with hyperfine structure observable from the $^{167}$Er isotope. A parametrized crystal-field Hamiltonian is fitted to 34 energy levels and the two ground state magnetic splitting factors. The wavefunctions are used to perform a transition intensity analysis and electric-dipole parameters are fitted to absorption oscillator strengths. Simulated spectra for the $^{4}$I$_{11/2}\rightarrow {^{4}}$I$_{15/2}$ and $^{4}$I$_{13/2} \rightarrow {^{4}}$I$_{15/2}$ inter-multiplet transitions are in excellent agreement with the experimentally measured spectra. The $^{4}$I$_{13/2}$ excited state lifetime is 25.0\,ms and the intensity calculation is in excellent agreement with this value.

arXiv:2409.15622•Sep 23, 2024•0 citations

Spectroscopy of the 3-µm laser transitions in YAlO3:Er

M. Stalder, W. Luthy, H. P. Weber

Temporal sequences of different spectral components of the 4/11/2 → 4/13/2 manifold in YAlO3:Er have been analyzed in a laser operated at 300 K. Several lines can oscillate in a spiking train. Their position in the pulse is discussed in terms of population inversion, laser linewidth, and resonant ion-ion interaction. Erbium crystals with dopant concentrations of 10, 20, and 50% have been used in the experiments. The wavelengths of the 3-µm transitions range from 2.71 to 2.92 µm. They are strongly dependent on the crystal orientation with respect to the polarization of the laser light. The polarization dependence of the most prominent emission lines has been determined for laser crystals oriented with their axes along the crystallographic a and b directions. The bandwidth of the laser lines has been measured with a resolution of 0.12 nm using a grating spectrometer in combination with an image converter. The bandwidth ranges from 0.3 nm at 2.73µm up to 2.6 nm at 2.92 µm.

Annual Meeting Optical Society of America•Jan 1, 1987•0 citations

Coupling between CaWO$_4$ phonons and Er$^{3+}$ dopants

Mikhael T. Sayat, Federico Pisani, Hin Lok Chang +8 more

We investigate the lattice dynamics of CaWO$_4$, a promising host crystal for erbium-based quantum memories, using inelastic neutron scattering together with density-functional perturbation theory. The measured phonon dispersion along the (100), (001), and (101) reciprocal space direction reveals phonon bands extending up to 130 meV, with a gap between 60 and 80 meV, in good agreement with our calculations. From a symmetry analysis of the phonon eigenmodes, we identify eight Raman-active modes that can couple directly to the Er$^{3+}$ crystal-field operators, including a low-energy $B_g$ mode at 9.1 meV that is expected to play a dominant role in phonon-assisted spin-lattice relaxation. These results provide a microscopic description of the phonon bath in CaWO$_4$ and establish a basis for engineering phononic environments to mitigate the loss of stored quantum states and optimize Er-doped CaWO$_4$ for quantum-memory applications.

cond-mat.mtrl-sciCross-listedarXiv:2602.08525•Feb 10, 2026•0 citations

A Pathway to Er Sites in Si with Long Spin and Optical Coherence Times

Alexey Lyasota, Ian R. Berkman, Gabriele G. de Boo +9 more

Rare-earth ions in solid-state hosts exhibit low homogeneous broadening and long spin coherence at cryogenic temperatures thus making them a promising candidate for optical quantum memories [1], optical-microwave transducers [2] and single dopant-based devices such as single photon emitters operating at the telecommunication wavelengths [3]. Here, we present an overview of the spin and optical properties of Er ensembles in Si accessed via resonant photoluminescence excitation (PLE) spectroscopy [4]. Samples were positioned directly on top of tailor-fabricated superconducting single photon detectors, placed in a dilution refrigerator unit and resonantly excited using fiber optics. Our method provided high collection efficiency and allowed spectral measurements of low Er density samples. The observed Er PLE spectra were strongly affected by the presence of co-dopants such as O, B or P reflecting their influence on the formation of optically active Er sites and corresponding Er optical transition energies. Higher O densities resulted in especially rich PLE spectra suggesting that a variety of Er-O complexes formed due to O doping. Lowering the O concentration, we achieved PLE spectra dominated by a single Er site in P doped samples. Interestingly, the Er spin relaxation and optical coherence properties were barely affected by the employed co-dopants and mainly depended on the Er concentration. By lowering the Er concentration from relatively high (1018cm-3) to low densities (1016cm-3), we were able to increase Er spin lifetimes from ~0.1 s to ~30 s. Long spin relaxation times allowed us to identify PLE spectra of new Er sites in Si. In both concentration regimes, we observed sub-MHz transient spectral holes suggesting long optical coherence times. Furthermore, we observed sub-MHz spin transitions in both natural and isotopically purified Si and achieved spin coherence times above 1 ms in isotopically purified Si. Narrow optical linewidths and long transverse and longitudinal spin relaxation times show that Er in Si is an excellent candidate for future quantum information and communication applications.

Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)•Jun 26, 2023•0 citations
We present a detailed spectroscopic study of the I 13 / 2 4 and I 15 / 2 4 Er 3 + multiplets of Er: CaWO 4 grown without a co-dopant. Using photoluminescence and photoluminescence excitation measurements, we find multiple environments into which erbium ions are incorporated in the crystal. For the four most prevalent environments, we provide a complete assignment of the I 13 / 2 4 and I 15 / 2 4 sublevel energies. Polarization-dependent absorption and emission spectroscopy allow us to identify the irreducible representations of the states and determine the dipole nature of transitions. In addition, we compare the different relaxation paths within I 13 / 2 4 and I 15 / 2 4 multiplets via line broadening and lifetime measurements. Finally, spectral, lifetime, and polarization measurements indicate similarities between the studied environments.
Optical Spectroscopy of Waveguide coupled Er3+^{3+}3+ ensembles in CaWO4_44​ and YVO4_44​
We present an optical study of near-surface Er3+^{3+}3+ ensembles in waveguide-integrated CaWO4_44​ and YVO4_44​, investigating how nanophotonic coupling modifies rare-earth spectroscopy. In particular, we compare bulk excitation with evanescently coupled TE and TM waveguide modes. In Er3+^{3+}3+:CaWO4_44​, we observe a pronounced polarization-dependent surface effect. TE-coupled spectra closely reproduce bulk behavior. In contrast, TM coupling induces strong inhomogeneous broadening and an asymmetric low-energy shoulder of the site S1 Y1Z1 transition, with linewidths exceeding those of the bulk by more than a factor of four. Temperature-dependent measurements and surface termination studies indicate that surface charges are the dominant mechanism. Er3+^{3+}3+:YVO4_44​ remains largely unaffected by mode polarization, and surface termination leads only to minor spectral shifts. These observations suggest that non-charge-neutral rare-earth systems are more susceptible to surface-induced decoherence sources than charge-neutral hosts.
Erbium ions in crystals show considerable promise for the technologies that will form the backbone of future networked quantum information technology. Despite advances in leveraging erbium’s fibre-compatible infrared transition for classical and quantum applications, the transitions are, in general, not well understood. We present detailed absorption and laser site-selective spectroscopy of the C 3v (O 2 − ) centre in CaF 2 :Er 3 + as an interesting erbium site case study. The 4 I 15 / 2 Z 1 → 4 I 13 / 2 Y 1 transition has a low-temperature inhomogeneous linewidth of 1 GHz with hyperfine structure observable from the 167 Er isotope. A parametrized crystal-field Hamiltonian is fitted to 34 energy levels and the two ground state magnetic splitting factors. The wavefunctions are used to perform a transition intensity analysis and electric-dipole parameters are fitted to absorption oscillator strengths. Simulated spectra for the 4 I 11 / 2 → 4 I 15 / 2 and 4 I 13 / 2 → 4 I 15 / 2 inter-multiplet transitions are in excellent agreement with the experimentally measured spectra. The 4 I 13 / 2 excited state lifetime is 25.0 ms and the intensity calculation is in excellent agreement with this value. • Detailed spectroscopic study of the C 3v (O 2 − ) Centre in CaF 2 :Er 3 + . • Crystal-field fit to 34 energy levels and ground-state magnetic splitting. • Transition intensity analysis for the technologically relevant infrared transitions.
Spectroscopy, Crystal-Field, and Transition Intensity Analyses of the C3v_{\rm 3v}3v​(O2−^{2-}2−) Centre in Er3+^{3+}3+ Doped CaF2_{2}2​ Crystals
Erbium ions in crystals show considerable promise for the technologies that will form the backbone of future networked quantum information technology. Despite advances in leveraging erbium's fibre-compatible infrared transition for classical and quantum applications, the transitions are, in general, not well understood. We present detailed absorption and laser site-selective spectroscopy of the C3v_{\rm 3v}3v​(O2−^{2-}2−) centre in CaF2_22​:Er3+^{3+}3+ as an interesting erbium site case study. The 4^{4}4I15/2_{15/2}15/2​Z1→4_1 \rightarrow {^{4}}1​→4I13/2_{13/2}13/2​Y1_11​ transition has a low-temperature inhomogeneous linewidth of 1 GHz with hyperfine structure observable from the 167^{167}167Er isotope. A parametrized crystal-field Hamiltonian is fitted to 34 energy levels and the two ground state magnetic splitting factors. The wavefunctions are used to perform a transition intensity analysis and electric-dipole parameters are fitted to absorption oscillator strengths. Simulated spectra for the 4^{4}4I11/2→4_{11/2}\rightarrow {^{4}}11/2​→4I15/2_{15/2}15/2​ and 4^{4}4I13/2→4_{13/2} \rightarrow {^{4}}13/2​→4I15/2_{15/2}15/2​ inter-multiplet transitions are in excellent agreement with the experimentally measured spectra. The 4^{4}4I13/2_{13/2}13/2​ excited state lifetime is 25.0\,ms and the intensity calculation is in excellent agreement with this value.
Temporal sequences of different spectral components of the 4/11/2 → 4/13/2 manifold in YAlO3:Er have been analyzed in a laser operated at 300 K. Several lines can oscillate in a spiking train. Their position in the pulse is discussed in terms of population inversion, laser linewidth, and resonant ion-ion interaction. Erbium crystals with dopant concentrations of 10, 20, and 50% have been used in the experiments. The wavelengths of the 3-µm transitions range from 2.71 to 2.92 µm. They are strongly dependent on the crystal orientation with respect to the polarization of the laser light. The polarization dependence of the most prominent emission lines has been determined for laser crystals oriented with their axes along the crystallographic a and b directions. The bandwidth of the laser lines has been measured with a resolution of 0.12 nm using a grating spectrometer in combination with an image converter. The bandwidth ranges from 0.3 nm at 2.73µm up to 2.6 nm at 2.92 µm.
Coupling between CaWO4_44​ phonons and Er3+^{3+}3+ dopants
We investigate the lattice dynamics of CaWO4_44​, a promising host crystal for erbium-based quantum memories, using inelastic neutron scattering together with density-functional perturbation theory. The measured phonon dispersion along the (100), (001), and (101) reciprocal space direction reveals phonon bands extending up to 130 meV, with a gap between 60 and 80 meV, in good agreement with our calculations. From a symmetry analysis of the phonon eigenmodes, we identify eight Raman-active modes that can couple directly to the Er3+^{3+}3+ crystal-field operators, including a low-energy BgB_gBg​ mode at 9.1 meV that is expected to play a dominant role in phonon-assisted spin-lattice relaxation. These results provide a microscopic description of the phonon bath in CaWO4_44​ and establish a basis for engineering phononic environments to mitigate the loss of stored quantum states and optimize Er-doped CaWO4_44​ for quantum-memory applications.
Rare-earth ions in solid-state hosts exhibit low homogeneous broadening and long spin coherence at cryogenic temperatures thus making them a promising candidate for optical quantum memories [1], optical-microwave transducers [2] and single dopant-based devices such as single photon emitters operating at the telecommunication wavelengths [3]. Here, we present an overview of the spin and optical properties of Er ensembles in Si accessed via resonant photoluminescence excitation (PLE) spectroscopy [4]. Samples were positioned directly on top of tailor-fabricated superconducting single photon detectors, placed in a dilution refrigerator unit and resonantly excited using fiber optics. Our method provided high collection efficiency and allowed spectral measurements of low Er density samples. The observed Er PLE spectra were strongly affected by the presence of co-dopants such as O, B or P reflecting their influence on the formation of optically active Er sites and corresponding Er optical transition energies. Higher O densities resulted in especially rich PLE spectra suggesting that a variety of Er-O complexes formed due to O doping. Lowering the O concentration, we achieved PLE spectra dominated by a single Er site in P doped samples. Interestingly, the Er spin relaxation and optical coherence properties were barely affected by the employed co-dopants and mainly depended on the Er concentration. By lowering the Er concentration from relatively high (1018cm-3) to low densities (1016cm-3), we were able to increase Er spin lifetimes from ~0.1 s to ~30 s. Long spin relaxation times allowed us to identify PLE spectra of new Er sites in Si. In both concentration regimes, we observed sub-MHz transient spectral holes suggesting long optical coherence times. Furthermore, we observed sub-MHz spin transitions in both natural and isotopically purified Si and achieved spin coherence times above 1 ms in isotopically purified Si. Narrow optical linewidths and long transverse and longitudinal spin relaxation times show that Er in Si is an excellent candidate for future quantum information and communication applications.