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:2308.16291 · Physical Review A

Solid-state Th229 nuclear laser with two-photon pumping

Haowei Xu, Hao Tang, Guoqing Wang, Changhao Li, Boning Li, Paola Cappellaro, Ju Li

Published Aug 24, 2023• 9 citations
arXivHTMLPDF

Abstract

The authors leverage the recently proposed optonuclear quadrupolar effect to develop a two-photon pumping scheme for the isomeric state of ${}^{229}$Th, an exotic nucleus with an ultralow excitation energy of 8.3 eV. Additionally, the authors demonstrate that the lasing between nuclear states, which has been pursued for decades, may be realized based on the two-photon pumping scheme in ultrawide-band-gap compounds like ThF${}_{4}$, Na${}_{2}$ThF${}_{6}$, or K${}_{2}$ThF${}_{6}$.

DOI
10.1103/physreva.108.l021502

Related papers

Colloquium: Nuclear clocks

Andrei Derevianko, R. Elwell, Eric R. Hudson

The Th-229 nuclear isomeric state has the lowest energy of all known nuclear excited states, placing it within the reach of current table-top laser technology. This extraordinary property has made this nuclear isomer an attractive candidate for a nuclear optical clock of incredibly high precision and accuracy, both as isolated trapped Th-229 ions and embedded into solid-state platforms. Activity around Th-229 has surged in recent years, driven by breakthroughs in its direct laser excitation. The underlying nuclear physics that gives rise to this unique isomer will be elucidated, as well as the nearly half-century of efforts that led to its direct excitation. The design and systematics of a Th-229 nuclear clock will be discussed, both in ion traps and in the solid-state. These systematics, such as frequency shifts and quenching channels, can be leveraged both to probe the local chemical environment, and as a control knob during clock operation. Finally, the nuclear clock's high sensitivity to the variations of fundamental constants will be discussed.

physics.atom-phCross-listedarXiv:2606.11048•Jun 10, 2026

Two-Photon Interface of Nuclear Spins Based on the Optonuclear Quadrupolar Effect

Haowei Xu, Changhao Li, Guoqing Wang +5 more

A proposed mechanism for efficiently coupling optical photons and nuclear spins opens the door to hybridizing these two building blocks of quantum technology and to a number of novel device applications.

arXiv:2302.09616•Physical Review X•Feb 14, 2023•5 citations

Laser Cooling of Nuclear Magnons

Haowei Xu, Guoqing Wang, Changhao Li +5 more

The initialization of nuclear spin to its ground state is challenging due to its small energy scale compared with thermal energy, even at cryogenic temperature. In this Letter, we propose an optonuclear quadrupolar effect, whereby two-color optical photons can efficiently interact with nuclear spins. Leveraging such an optical interface, we demonstrate that nuclear magnons, the collective excitations of nuclear spin ensemble, can be cooled down optically. Under feasible experimental conditions, laser cooling can suppress the population and entropy of nuclear magnons by more than 2 orders of magnitude, which could facilitate the application of nuclear spins in quantum information science.

arXiv:2302.09615•Physical Review Letters•Feb 9, 2023•4 citations

Two-Photon Mechanism of the Excitation of Exciton States in Noble Gas Cryocrystals

D. A. Myzin, P. V. Borisyuk, K. L. Gubskii +9 more

The results of an experiment on the two-photon excitation of exciton states in krypton cryocrystals by the fifth harmonic of 209-nm laser radiation have been presented. It has been shown that the two-photon excitation mechanism allows reaching a density of 1016 cm−3 of free excitons with an excitation energy of ~8.4 eV at a focal radiation intensity of $$ \approx {{10}^{{11}}}{\kern 1pt} $$ W/cm2. The observed broad photoluminescence line arising from the relaxation of excited exciton states covers the $$3{\text{/}}{{2}^{ + }}(8.4{\kern 1pt} \;{\text{eV}}) \to 5{\text{/}}{{2}^{ + }}(0.0)$$ low-energy nuclear isomeric transition in 229Th. Analytical estimates showing that two-photon laser generation of exciton states in noble gas crystals can be used as a new method for the excitation of the nuclear isomeric state of thorium at a pump intensity of ~1011 W/cm2 have been provided.

Journal of Experimental and Theoretical Physics Letters•Oct 1, 2025•1 citation

Continuous-wave laser absorption spectroscopy of the Thorium-229 nucleus

I. Morawetz, T. Riebner, L. Toscani De Col +17 more

A low-energy nuclear transition in the isotope thorium-229 has been excited in thorium-doped crystals with laser light. This opens the perspective towards a highly stable and robust solid-state optical nuclear clock. The required laser radiation at 148 nm wavelength has so far been produced using pulsed laser systems where only a small fraction of the incident photons has been resonant with the narrow nuclear transition. Here we show that the nuclear resonance can be excited with a continuous-wave narrow-bandwidth laser source with a power of less than 1 nW, and that the resonance signal can be detected in absorption rather than in fluorescence. This eliminates the slow nuclear fluorescence decay from the detection process and offers a considerable advantage for clock operation through fast signal acquisition. The VUV laser source is based on three sequential frequency doublings, starting from a diode laser at 1187 nm that is well suited for linewidth narrowing and for frequency comparisons with optical atomic clocks. We use absorption spectroscopy for the quantitative characterization of two different Th-centers in calcium fluoride crystal and measure the isomeric shift between them. One of the centers shows a very small static electric crystal field gradient 0.1 V/$Å^2$, to be compared to gradients in the range of 100 V/$Å^2$ observed earlier. This indicates a center with high symmetry of the ions surrounding the Th nucleus, promising nuclear resonance lines that are nearly independent of the lattice spacing.

physics.atom-phCross-listedarXiv:2604.16640•Apr 21, 2026

Nuclear Lasing via Laser-Assisted Electronic Bridge Excitation and Lasing Without Inversion in ²²⁹Th:LiSAF

Randy Gummelt

A scheme is proposed for achieving coherent emission from the 8.355 eV nuclear isomeric transition in ²²⁹Th doped into LiSrAlF₆ (LiSAF), combining laser-assisted electronic bridge excitation for isomer population with lasing without inversion via RF-driven ground-state coherence. Gain calculations show lasing threshold is achievable with cavity finesse as low as 12. Three critical unknowns are identified for experimental verification.

•May 13, 2026•0 citations
The authors leverage the recently proposed optonuclear quadrupolar effect to develop a two-photon pumping scheme for the isomeric state of 229{}^{229}229Th, an exotic nucleus with an ultralow excitation energy of 8.3 eV. Additionally, the authors demonstrate that the lasing between nuclear states, which has been pursued for decades, may be realized based on the two-photon pumping scheme in ultrawide-band-gap compounds like ThF4{}_{4}4​, Na2{}_{2}2​ThF6{}_{6}6​, or K2{}_{2}2​ThF6{}_{6}6​.
The Th-229 nuclear isomeric state has the lowest energy of all known nuclear excited states, placing it within the reach of current table-top laser technology. This extraordinary property has made this nuclear isomer an attractive candidate for a nuclear optical clock of incredibly high precision and accuracy, both as isolated trapped Th-229 ions and embedded into solid-state platforms. Activity around Th-229 has surged in recent years, driven by breakthroughs in its direct laser excitation. The underlying nuclear physics that gives rise to this unique isomer will be elucidated, as well as the nearly half-century of efforts that led to its direct excitation. The design and systematics of a Th-229 nuclear clock will be discussed, both in ion traps and in the solid-state. These systematics, such as frequency shifts and quenching channels, can be leveraged both to probe the local chemical environment, and as a control knob during clock operation. Finally, the nuclear clock's high sensitivity to the variations of fundamental constants will be discussed.
The initialization of nuclear spin to its ground state is challenging due to its small energy scale compared with thermal energy, even at cryogenic temperature. In this Letter, we propose an optonuclear quadrupolar effect, whereby two-color optical photons can efficiently interact with nuclear spins. Leveraging such an optical interface, we demonstrate that nuclear magnons, the collective excitations of nuclear spin ensemble, can be cooled down optically. Under feasible experimental conditions, laser cooling can suppress the population and entropy of nuclear magnons by more than 2 orders of magnitude, which could facilitate the application of nuclear spins in quantum information science.
The results of an experiment on the two-photon excitation of exciton states in krypton cryocrystals by the fifth harmonic of 209-nm laser radiation have been presented. It has been shown that the two-photon excitation mechanism allows reaching a density of 1016 cm−3 of free excitons with an excitation energy of ~8.4 eV at a focal radiation intensity of ≈1011 \approx {{10}^{{11}}}{\kern 1pt} ≈1011 W/cm2. The observed broad photoluminescence line arising from the relaxation of excited exciton states covers the 3/2+(8.4  eV)→5/2+(0.0)3{\text{/}}{{2}^{ + }}(8.4{\kern 1pt} \;{\text{eV}}) \to 5{\text{/}}{{2}^{ + }}(0.0)3/2+(8.4eV)→5/2+(0.0) low-energy nuclear isomeric transition in 229Th. Analytical estimates showing that two-photon laser generation of exciton states in noble gas crystals can be used as a new method for the excitation of the nuclear isomeric state of thorium at a pump intensity of ~1011 W/cm2 have been provided.
A low-energy nuclear transition in the isotope thorium-229 has been excited in thorium-doped crystals with laser light. This opens the perspective towards a highly stable and robust solid-state optical nuclear clock. The required laser radiation at 148 nm wavelength has so far been produced using pulsed laser systems where only a small fraction of the incident photons has been resonant with the narrow nuclear transition. Here we show that the nuclear resonance can be excited with a continuous-wave narrow-bandwidth laser source with a power of less than 1 nW, and that the resonance signal can be detected in absorption rather than in fluorescence. This eliminates the slow nuclear fluorescence decay from the detection process and offers a considerable advantage for clock operation through fast signal acquisition. The VUV laser source is based on three sequential frequency doublings, starting from a diode laser at 1187 nm that is well suited for linewidth narrowing and for frequency comparisons with optical atomic clocks. We use absorption spectroscopy for the quantitative characterization of two different Th-centers in calcium fluoride crystal and measure the isomeric shift between them. One of the centers shows a very small static electric crystal field gradient 0.1 V/A˚2Å^2A˚2, to be compared to gradients in the range of 100 V/A˚2Å^2A˚2 observed earlier. This indicates a center with high symmetry of the ions surrounding the Th nucleus, promising nuclear resonance lines that are nearly independent of the lattice spacing.