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Coherent Frequency Conversion from Microwave to Optical Fields in an Erbium Doped Y2SiO5 Crystal: Towards the Single Photon Regime

Xavier Fernandez-Gonzalvo

Published Jan 1, 2017• 1 citation
OpenAlex

Abstract

In the context of quantum information technologies superconducting qubits (SQs) are very attractive devices for the manipulation of quantum states, and present themselves as one of our best candidates to build a quantum processor. They couple naturally to microwave photons, for which suitable quantum memories or a long distance propagation channel don’t exist. A way around these limitations is to turn these microwave photons into optical ones by building a quantum frequency converter: a device by which the frequency of a photon can be changed while preserving its non-classical correlations. Then, optical fibres could be used to link distant SQ-based devices together, facilitating the creation of a network of quantum computers. Moreover, SQs could then be coupled to quantum memories compatible with photons at optical frequencies, which are the most well developed kind of quantum memories at the present time. This thesis explores the possibility to convert single microwave photons into optical photons using erbium doped in a yttrium orthosilicate crystal (Er3+:Y2SiO5). Er3+:Y2SiO5 is a good candidate because it has a naturally occurring optical transition near 1536 nm close to the point where silica optical fibres show their minimum loss. A microwave transition can be found in two different ways: one way is to use the 167 isotope of erbium, which is the only stable isotope that shows hyperfine splitting as it has non-zero nuclear spin. The hyperfine structure of the ground state of 167Er3+:Y2SiO5 spans over about 5 GHz. The other possibility is to use the other stable isotopes of erbium and Zeeman split their ground state using an external magnetic field. A microwave transition near 5 GHz can be achieved with moderate magnetic fields due to the high 𝑔-factors of Er3+:Y2SiO5. The physical process of interest is a three wave mixing process involving two fields at optical frequencies and one field at microwave frequencies. In order to boost the efficiency of the frequency conversion process the Er3+:Y2SiO5 crystal is placed inside a microwave and an optical resonator. The problem is first explored from the theoretical point of view, where a nonlinear coefficient Λ(2) is derived (analogous to the 𝜒(2) often used in nonlinear optics), and the interaction between cavity modes and the nonlinear medium is studied. It is predicted that with a sample cooled down to millikelvin temperatures total frequency conversion between microwave and optical fields can be achieved. A preliminary hole burning spectroscopy experiment is performed with the objective of reconstructing the hyperfine structure of the excited state of 167Er3+:Y2SiO5, but the complexity of the problem makes it too difficult to achieve this goal. Then a series of experiments are shown, aimed at determining whether or not frequency conversion at the single photon level is achievable using the even isotopes of erbium in a magnetic field. These experiments are based in the Raman heterodyne spectroscopy technique, which is used in combination with electron paramagnetic resonance and optical absorption spectroscopy. In all experiments the sample is cooled down to cryogenic temperatures near 4 K. A first experiment shows that the frequency conversion process exists in Er3+:Y2SiO5, in a setup where only a microwave resonator is used, but not an optical one. A second experiment is performed in a similar setup, this time presenting a quantitative study of the properties of the frequency conversion process, and its comparison with the theoretical model previously derived. A third experiment is performed, which incorporates an optical cavity to the system. The interaction between the erbium ions and the optical cavity introduces a whole new range of experimental complications, which are studied and discussed. Then, the frequency conversion signal is studied anew, showing an unexpected highly non-linear scaling behaviour with the input powers. A hypothesis explaining this unexpected behaviour is given, referring to stray optical absorption in the inhomogeneous line of Er3+:Y2SiO5 (and in particular 167Er3+:Y2SiO5), which can be bleached out under certain circumstances due to spectral hole burning effects. The overall maximum frequency conversion efficiency observed is of 3 × 10^−4 per Watt of pump laser power. While this value is still far from the target several ways of improvement are proposed, including cooling down the system to millikelvin temperatures, increasing the dopant concentration and modifying the geometry of the resonators.

Related papers

Hyperfine Structure and Coherent Properties of Erbium-167-doped Yttrium Orthosilicate

Jelena V. Rakonjac

Erbium-167-doped yttrium orthosilicate (167Er3+:Y2SiO5) is a rare-earth-ion-doped crystal which possesses unique properties that would make it an ideal microwave-addressed quantum memory. It has an optical transition at 1.5 µm, which lies in the telecom C-band where much of the optical telecommunications infrastructure is already operating. It also possesses both nuclear and electron spin states, and hyperfine structure with transitions at microwave frequencies. The hyperfine structure exhibits microwave frequency transitions with or without an applied magnetic field, which would allow for a memory compatible with superconducting systems. However, the complicated hyperfine structure has prevented the transitions of 167Er3+:Y2SiO5 from being fully utilised.\nWith the recent publication of new spin Hamiltonian parameters for the ground state of 167Er3+:Y2SiO5, we can predict which transitions should have the longest coherence time at zero field. Based on calculations using these spin Hamiltonian parameters, we used Raman heterodyne spectroscopy to investigate the hyperfine structure of 167Er3+:Y2SiO5 for small magnetic fields and for energy level differences from 600 to 1200 MHz. We observed many transitions from the 4I15/2 ground state, as well as the 4I13/2 excited state that until now has had little investigation regarding its hyperfine structure.\nBy comparing our spectra to the existing ground state spin Hamiltonian parameters, and unpublished excited state parameters, we identified the origin of many of the transitions. We observed differences between the predicted transition frequencies from both sets of parameters and the experimental data. The data obtained using Raman heterodyne was used to improve both ground and excited state parameters to give a better description of the zero-field hyperfine splittings.\nIn addition, we identified transitions from both the 4I15/2 ground and 4I13/2 excited state that have a small dependence on magnetic field. These transitions, with zero field frequencies of 879.4 MHz and 896.7 MHz respectively, yielded coherence times of 67 µs and 300 µs at 3.2 K, when measured with a two-pulse spin echo sequence. By using a dynamic decoupling sequence, we extending the coherence times of the transitions at 879.4 MHz to 380 µs and for the transitions at 896.7 MHz, to 1.4 ms.\nThese coherence time measurements demonstrate an improvement of a previous zero field coherence measurement in 167Er3+:Y2SiO5. By operating at lower temperatures, reducing the 167Er3+ ion concentration or using a different transition, it should be possible to extend the coherence time of 167Er3+:Y2SiO5 even further.

•Jan 1, 2018•3 citations

Theory of Microwave to Optical Photon Upconversion Using Erbium Doped Crystals

Peter S. Barnett

The subject of this thesis is coherent conversion from microwave photons to optical photons. This has applications for quantum computing, and would allow interfacing between superconducting qubits and optical fibres. Specifically, we will focus on photon conversion via erbium ions in a doped crystal. \n\nWe model a device which has an erbium doped crystal inside overlapping microwave and optical cavities. Input microwave photons are combined with photons from an optical pump laser via interactions with the erbium ions. This will produce optical output photons carrying the same quantum information as the input microwave photons. We develop a description of the interaction between the atoms and the light fields, accounting for both loss effects in the single atoms, and inhomogeneous broadening of the ensemble. Our theory is compared with experimental data, and shows good agreement. \n \nWe explore various phenomena which arise in this system, including the effects of temperature and microwave power. \n\nIt is shown that the description of this device from earlier work is not valid in the regime where the conversion efficiency is greatest. Hence, this work is necessary to be able to predict the maximum conversion efficiency. \n\nWe develop a linearised model which is accurate in the regime where the microwave and optical fields are small, such as the regime used for quantum information. This model is used to maximise the photon number conversion efficiency of the device. We predict conversion efficiencies above 20%, far higher than has been achieved experimentally with using rare earth ions. Modifying our device should further increase the conversion efficiency to above 80%.

•Jan 1, 2020•1 citation

Coherent microwave-to-optical transduction with Yb:YSO spins strongly coupled to a 3D resonator

Ujjwal Gautam, Nasser Gohari Kamel, Sourabh Kumar +1 more

Microwave-to-optical quantum transducers are essential for entangling remote superconducting qubits. Among the available transduction platforms, ensembles of Er$^{3+}$ and Yb$^{3+}$ ions doped into solids have emerged as leading candidates. While external magnetic fields are needed to split the Zeeman levels of erbium ions and enable a microwave--qubit interface, superconducting qubits suffer decoherence in such fields. In contrast, ytterbium ions exhibit zero-first-order Zeeman transitions and large hyperfine splittings at zero magnetic field (when doped into inorganic crystals). Owing to its long optical and spin coherence times, Yb:YSO has been widely used as a quantum memory, yet its potential for quantum transduction remains largely unexplored. Investigating this material could enable the integration of quantum memory and transduction in a single platform. Here, we demonstrate microwave-to-optical transduction in the continuous-wave regime using a 5\,ppm doped Yb:YSO crystal. The internal transduction efficiency is $2\times10^{-8}$ with a bandwidth of 200\,kHz, achieved using a 3D loop-gap microwave resonator (LGR) and a single-pass optical configuration. We explore all the ground states that form a V-type three-level system with the first and second optical excited states and assert the use of the ground state, which provides the highest efficiency and isolated optical transition. We further establish strong spin-microwave coupling from avoided crossing measurements. With a strong microwave drive to saturate the spin transition, we estimate the spin population pumped into the excited state, close to the simulated value. Finally, we calculate target parameter values for maximum efficiency with our system and suggest using 50\,ppm doped Yb:YSO crystal. With the calculated target parameters, the internal transduction efficiency is predicted to reach up to $10^{-4}$ in the current LGR.

quant-pharXiv:2609.02226•Sep 3, 2026•0 citations

Cavity enhanced Raman heterodyne spectroscopy in Er3+: Y2SiO5 for microwave to optical signal conversion

Xavier Fernandez-Gonzalvo, Sebastian P. Horvath, Yuhui Chen +1 more

The efficiency of the frequency conversion process at the heart of Raman heterodyne spectroscopy was improved by nearly four orders of magnitude by resonant enhancement of both the pump and signal optical fields. Our results using an erbium doped Y2SiO5 crystal at temperatures near 4 K suggest that such an approach is promising for the quantum conversion of microwave to optical photons.

•Jan 1, 2018•6 citations

Spectroscopic study of hyperfine properties in Yb3+171:Y2SiO5

Alexey Tiranov, Antonio Ortu, Sacha Welinski +4 more

Rare-earth ion-doped crystals are promising systems for quantum communication and quantum information processing. In particular, paramagnetic rare-earth centers can be utilized to realize quantum coherent interfaces simultaneously for optical and microwave photons. In this paper, we study hyperfine and magnetic properties of a ${\mathrm{Y}}_{2}{\mathrm{SiO}}_{5}$ crystal doped with $^{171}\mathrm{Yb}^{3+}$ ions. This isotope is particularly interesting since it is the only rare--earth ion having electronic spin $S=\frac{1}{2}$ and nuclear spin $I=\frac{1}{2}$, which results in the simplest possible hyperfine level structure. In this work, we determine the hyperfine tensors for the ground and excited states on the optical $^{2}\mathrm{F}_{7/2}(0)\ensuremath{\longleftrightarrow}^{2}\mathrm{F}_{5/2}(0)$ transition by combining spectral hole burning and optically detected magnetic resonance techniques. The resulting spin Hamiltonians correctly predict the magnetic-field dependence of all observed optical-hyperfine transitions, from zero applied field up to fields where the Zeeman interaction is dominating the hyperfine interaction. Using the optical absorption spectrum, we can also determine the order of the hyperfine levels in both states. These results pave the way for realizing solid-state optical and microwave quantum memories based on a $^{171}\mathrm{Yb}^{3+}:{\mathrm{Y}}_{2}{\mathrm{SiO}}_{5}$ crystal.

arXiv:1712.08616•Physical review. B./Physical review. B•Nov 8, 2018•36 citations

milliKelvin ESR of rare-earth doped crystals using superconducting resonators

Gavin Dold

Rare-earth doped crystals have proven to be of considerable interest for quantum information processing, with demonstrations of quantum memories and the potential for coherent microwave–optical conversion as part of a quantum network. By interfacing these rare-earth based technologies with superconducting devices, they can complement existing technologies — which form the basis of many state-of-the-art quantum computers — forming a hybrid quantum information processing architecture exhibiting the advantages of fast superconducting processors alongside the extended coherence time and frequency conversion available from rare-earths. This thesis demonstrates the suitability of a widely used rare-earth doped crystal, yttrium orthosilicate (Y2SiO5 or YSO) doped with 145Nd or with 171Yb, as a substrate for fabrication of superconducting resonators. Designs for these resonators are presented with simulations of their electromagnetic modes, and their fabrication detailed. These devices are cooled to milliKelvin temperatures in a dilution refrigerator in order to investigate properties of the device and its coupling to electron spin transitions within the substrate where a coupling rate of the order gens/2π =1.2–7.1 MHz is observed. Dielectric loss due to two-level systems is measured with a loss-tangent tan δ = 4*10−6, and a coupling between resonator and spins is observed to have a high cooperativity C = 8–250. The superconducting resonator is then used to perform pulsed spectroscopy of electron spin resonance (ESR) transitions in the high-cooperativity regime, measuring two-pulse coherence times of T2 = (409 ± 14) μs for 200 ppm 145Nd:Y2SiO5 and T2 = (1170 ± 90) μs for 50 ppm 171Yb:Y2SiO5. Chirped pulses are used to invert spin magnetisation and drive arbitrary rotations, enabling the measurement of relaxation dynamics and Rabi oscillations. Dynamical decoupling sequences are explored as a method for extending coherence time. Experiments exploiting coherence-enhancing 'near-ZEFOZ' transitions in 171Yb are proposed, and continuous-wave measurements are used to demonstrate the working principle of such a scheme.

•May 11, 2020•1 citation
In the context of quantum information technologies superconducting qubits (SQs) are very attractive devices for the manipulation of quantum states, and present themselves as one of our best candidates to build a quantum processor. They couple naturally to microwave photons, for which suitable quantum memories or a long distance propagation channel don’t exist. A way around these limitations is to turn these microwave photons into optical ones by building a quantum frequency converter: a device by which the frequency of a photon can be changed while preserving its non-classical correlations. Then, optical fibres could be used to link distant SQ-based devices together, facilitating the creation of a network of quantum computers. Moreover, SQs could then be coupled to quantum memories compatible with photons at optical frequencies, which are the most well developed kind of quantum memories at the present time. This thesis explores the possibility to convert single microwave photons into optical photons using erbium doped in a yttrium orthosilicate crystal (Er3+:Y2SiO5). Er3+:Y2SiO5 is a good candidate because it has a naturally occurring optical transition near 1536 nm close to the point where silica optical fibres show their minimum loss. A microwave transition can be found in two different ways: one way is to use the 167 isotope of erbium, which is the only stable isotope that shows hyperfine splitting as it has non-zero nuclear spin. The hyperfine structure of the ground state of 167Er3+:Y2SiO5 spans over about 5 GHz. The other possibility is to use the other stable isotopes of erbium and Zeeman split their ground state using an external magnetic field. A microwave transition near 5 GHz can be achieved with moderate magnetic fields due to the high 𝑔-factors of Er3+:Y2SiO5. The physical process of interest is a three wave mixing process involving two fields at optical frequencies and one field at microwave frequencies. In order to boost the efficiency of the frequency conversion process the Er3+:Y2SiO5 crystal is placed inside a microwave and an optical resonator. The problem is first explored from the theoretical point of view, where a nonlinear coefficient Λ(2) is derived (analogous to the 𝜒(2) often used in nonlinear optics), and the interaction between cavity modes and the nonlinear medium is studied. It is predicted that with a sample cooled down to millikelvin temperatures total frequency conversion between microwave and optical fields can be achieved. A preliminary hole burning spectroscopy experiment is performed with the objective of reconstructing the hyperfine structure of the excited state of 167Er3+:Y2SiO5, but the complexity of the problem makes it too difficult to achieve this goal. Then a series of experiments are shown, aimed at determining whether or not frequency conversion at the single photon level is achievable using the even isotopes of erbium in a magnetic field. These experiments are based in the Raman heterodyne spectroscopy technique, which is used in combination with electron paramagnetic resonance and optical absorption spectroscopy. In all experiments the sample is cooled down to cryogenic temperatures near 4 K. A first experiment shows that the frequency conversion process exists in Er3+:Y2SiO5, in a setup where only a microwave resonator is used, but not an optical one. A second experiment is performed in a similar setup, this time presenting a quantitative study of the properties of the frequency conversion process, and its comparison with the theoretical model previously derived. A third experiment is performed, which incorporates an optical cavity to the system. The interaction between the erbium ions and the optical cavity introduces a whole new range of experimental complications, which are studied and discussed. Then, the frequency conversion signal is studied anew, showing an unexpected highly non-linear scaling behaviour with the input powers. A hypothesis explaining this unexpected behaviour is given, referring to stray optical absorption in the inhomogeneous line of Er3+:Y2SiO5 (and in particular 167Er3+:Y2SiO5), which can be bleached out under certain circumstances due to spectral hole burning effects. The overall maximum frequency conversion efficiency observed is of 3 × 10^−4 per Watt of pump laser power. While this value is still far from the target several ways of improvement are proposed, including cooling down the system to millikelvin temperatures, increasing the dopant concentration and modifying the geometry of the resonators.
Erbium-167-doped yttrium orthosilicate (167Er3+:Y2SiO5) is a rare-earth-ion-doped crystal which possesses unique properties that would make it an ideal microwave-addressed quantum memory. It has an optical transition at 1.5 µm, which lies in the telecom C-band where much of the optical telecommunications infrastructure is already operating. It also possesses both nuclear and electron spin states, and hyperfine structure with transitions at microwave frequencies. The hyperfine structure exhibits microwave frequency transitions with or without an applied magnetic field, which would allow for a memory compatible with superconducting systems. However, the complicated hyperfine structure has prevented the transitions of 167Er3+:Y2SiO5 from being fully utilised.\nWith the recent publication of new spin Hamiltonian parameters for the ground state of 167Er3+:Y2SiO5, we can predict which transitions should have the longest coherence time at zero field. Based on calculations using these spin Hamiltonian parameters, we used Raman heterodyne spectroscopy to investigate the hyperfine structure of 167Er3+:Y2SiO5 for small magnetic fields and for energy level differences from 600 to 1200 MHz. We observed many transitions from the 4I15/2 ground state, as well as the 4I13/2 excited state that until now has had little investigation regarding its hyperfine structure.\nBy comparing our spectra to the existing ground state spin Hamiltonian parameters, and unpublished excited state parameters, we identified the origin of many of the transitions. We observed differences between the predicted transition frequencies from both sets of parameters and the experimental data. The data obtained using Raman heterodyne was used to improve both ground and excited state parameters to give a better description of the zero-field hyperfine splittings.\nIn addition, we identified transitions from both the 4I15/2 ground and 4I13/2 excited state that have a small dependence on magnetic field. These transitions, with zero field frequencies of 879.4 MHz and 896.7 MHz respectively, yielded coherence times of 67 µs and 300 µs at 3.2 K, when measured with a two-pulse spin echo sequence. By using a dynamic decoupling sequence, we extending the coherence times of the transitions at 879.4 MHz to 380 µs and for the transitions at 896.7 MHz, to 1.4 ms.\nThese coherence time measurements demonstrate an improvement of a previous zero field coherence measurement in 167Er3+:Y2SiO5. By operating at lower temperatures, reducing the 167Er3+ ion concentration or using a different transition, it should be possible to extend the coherence time of 167Er3+:Y2SiO5 even further.
The subject of this thesis is coherent conversion from microwave photons to optical photons. This has applications for quantum computing, and would allow interfacing between superconducting qubits and optical fibres. Specifically, we will focus on photon conversion via erbium ions in a doped crystal. \n\nWe model a device which has an erbium doped crystal inside overlapping microwave and optical cavities. Input microwave photons are combined with photons from an optical pump laser via interactions with the erbium ions. This will produce optical output photons carrying the same quantum information as the input microwave photons. We develop a description of the interaction between the atoms and the light fields, accounting for both loss effects in the single atoms, and inhomogeneous broadening of the ensemble. Our theory is compared with experimental data, and shows good agreement. \n \nWe explore various phenomena which arise in this system, including the effects of temperature and microwave power. \n\nIt is shown that the description of this device from earlier work is not valid in the regime where the conversion efficiency is greatest. Hence, this work is necessary to be able to predict the maximum conversion efficiency. \n\nWe develop a linearised model which is accurate in the regime where the microwave and optical fields are small, such as the regime used for quantum information. This model is used to maximise the photon number conversion efficiency of the device. We predict conversion efficiencies above 20%, far higher than has been achieved experimentally with using rare earth ions. Modifying our device should further increase the conversion efficiency to above 80%.
Microwave-to-optical quantum transducers are essential for entangling remote superconducting qubits. Among the available transduction platforms, ensembles of Er3+^{3+}3+ and Yb3+^{3+}3+ ions doped into solids have emerged as leading candidates. While external magnetic fields are needed to split the Zeeman levels of erbium ions and enable a microwave--qubit interface, superconducting qubits suffer decoherence in such fields. In contrast, ytterbium ions exhibit zero-first-order Zeeman transitions and large hyperfine splittings at zero magnetic field (when doped into inorganic crystals). Owing to its long optical and spin coherence times, Yb:YSO has been widely used as a quantum memory, yet its potential for quantum transduction remains largely unexplored. Investigating this material could enable the integration of quantum memory and transduction in a single platform. Here, we demonstrate microwave-to-optical transduction in the continuous-wave regime using a 5\,ppm doped Yb:YSO crystal. The internal transduction efficiency is 2×10−82\times10^{-8}2×10−8 with a bandwidth of 200\,kHz, achieved using a 3D loop-gap microwave resonator (LGR) and a single-pass optical configuration. We explore all the ground states that form a V-type three-level system with the first and second optical excited states and assert the use of the ground state, which provides the highest efficiency and isolated optical transition. We further establish strong spin-microwave coupling from avoided crossing measurements. With a strong microwave drive to saturate the spin transition, we estimate the spin population pumped into the excited state, close to the simulated value. Finally, we calculate target parameter values for maximum efficiency with our system and suggest using 50\,ppm doped Yb:YSO crystal. With the calculated target parameters, the internal transduction efficiency is predicted to reach up to 10−410^{-4}10−4 in the current LGR.
Rare-earth ion-doped crystals are promising systems for quantum communication and quantum information processing. In particular, paramagnetic rare-earth centers can be utilized to realize quantum coherent interfaces simultaneously for optical and microwave photons. In this paper, we study hyperfine and magnetic properties of a Y2SiO5{\mathrm{Y}}_{2}{\mathrm{SiO}}_{5}Y2​SiO5​ crystal doped with 171Yb3+^{171}\mathrm{Yb}^{3+}171Yb3+ ions. This isotope is particularly interesting since it is the only rare--earth ion having electronic spin S=12S=\frac{1}{2}S=21​ and nuclear spin I=12I=\frac{1}{2}I=21​, which results in the simplest possible hyperfine level structure. In this work, we determine the hyperfine tensors for the ground and excited states on the optical $^{2}\mathrm{F}_{7/2}(0)\ensuremath{\longleftrightarrow}^{2}\mathrm{F}_{5/2}(0)$ transition by combining spectral hole burning and optically detected magnetic resonance techniques. The resulting spin Hamiltonians correctly predict the magnetic-field dependence of all observed optical-hyperfine transitions, from zero applied field up to fields where the Zeeman interaction is dominating the hyperfine interaction. Using the optical absorption spectrum, we can also determine the order of the hyperfine levels in both states. These results pave the way for realizing solid-state optical and microwave quantum memories based on a 171Yb3+:Y2SiO5^{171}\mathrm{Yb}^{3+}:{\mathrm{Y}}_{2}{\mathrm{SiO}}_{5}171Yb3+:Y2​SiO5​ crystal.
Rare-earth doped crystals have proven to be of considerable interest for quantum information processing, with demonstrations of quantum memories and the potential for coherent microwave–optical conversion as part of a quantum network. By interfacing these rare-earth based technologies with superconducting devices, they can complement existing technologies — which form the basis of many state-of-the-art quantum computers — forming a hybrid quantum information processing architecture exhibiting the advantages of fast superconducting processors alongside the extended coherence time and frequency conversion available from rare-earths. This thesis demonstrates the suitability of a widely used rare-earth doped crystal, yttrium orthosilicate (Y2SiO5 or YSO) doped with 145Nd or with 171Yb, as a substrate for fabrication of superconducting resonators. Designs for these resonators are presented with simulations of their electromagnetic modes, and their fabrication detailed. These devices are cooled to milliKelvin temperatures in a dilution refrigerator in order to investigate properties of the device and its coupling to electron spin transitions within the substrate where a coupling rate of the order gens/2π =1.2–7.1 MHz is observed. Dielectric loss due to two-level systems is measured with a loss-tangent tan δ = 4*10−6, and a coupling between resonator and spins is observed to have a high cooperativity C = 8–250. The superconducting resonator is then used to perform pulsed spectroscopy of electron spin resonance (ESR) transitions in the high-cooperativity regime, measuring two-pulse coherence times of T2 = (409 ± 14) μs for 200 ppm 145Nd:Y2SiO5 and T2 = (1170 ± 90) μs for 50 ppm 171Yb:Y2SiO5. Chirped pulses are used to invert spin magnetisation and drive arbitrary rotations, enabling the measurement of relaxation dynamics and Rabi oscillations. Dynamical decoupling sequences are explored as a method for extending coherence time. Experiments exploiting coherence-enhancing 'near-ZEFOZ' transitions in 171Yb are proposed, and continuous-wave measurements are used to demonstrate the working principle of such a scheme.