Laser-based measurement and control of atomic and molecular states form the foundation
of modern quantum technology and provide deep insights into fundamental physics. Today’s most
precise clocks are based on measurements of optical transitions in atoms. To this end, transitions
with high quality factors, a low sensitivities to external perturbations, and good signal-to-noise
ratios are desired.
In this thesis, we achieve frequency-based laser spectroscopy of the 229Th nuclear clock
transition using a vacuum ultraviolet (VUV) frequency comb. The high transition frequency of
2,020,407,384,335(2) kHz (in 150 K CaF2 crystals) and a long excited state lifetime of 641(4) s
show the high intrinsic quality factor of this nuclear transition. This transition frequency is predicted
to be insensitive to external perturbations due to 1) the small electromagnetic moment of the
atomic nucleus and 2) the shielding effect of the outer electronic shell. Further, the large number
density of quantum emitters in a solid-state crystalline host promises a high signal-to-noise ratio.
Moreover, based on the different fundamental interactions involved in nuclear versus electronic
transitions, precise comparison between a nuclear clock and an atomic clock offers dramatically enhanced
sensitivity to new physics. Resolving individual nuclear quantum states in its host crystal
enables us to perform the first steps in characterizing the nuclear clock performance.
Probing the 229Th nuclear transition required new tools. Building upon previous generations
of extreme-ultraviolet (XUV) comb projects in our lab, we construct a VUV comb to perform
direct frequency comb spectroscopy of the 229Th nuclear clock transition. We calibrate the absolute
frequency by linking this comb to the JILA 87Sr atomic clock. We also present our effort on making
229Th thin-film samples for reducing the cost and radioactivity of future nuclear clocks.
Laser-based measurement and control of atomic and molecular states form the foundation
of modern quantum technology and provide deep insights into fundamental physics. Today’s most
precise clocks are based on measurements of optical transitions in atoms. To this end, transitions
with high quality factors, a low sensitivities to external perturbations, and good signal-to-noise
ratios are desired.
In this thesis, we achieve frequency-based laser spectroscopy of the 229Th nuclear clock
transition using a vacuum ultraviolet (VUV) frequency comb. The high transition frequency of
2,020,407,384,335(2) kHz (in 150 K CaF2 crystals) and a long excited state lifetime of 641(4) s
show the high intrinsic quality factor of this nuclear transition. This transition frequency is predicted
to be insensitive to external perturbations due to 1) the small electromagnetic moment of the
atomic nucleus and 2) the shielding effect of the outer electronic shell. Further, the large number
density of quantum emitters in a solid-state crystalline host promises a high signal-to-noise ratio.
Moreover, based on the different fundamental interactions involved in nuclear versus electronic
transitions, precise comparison between a nuclear clock and an atomic clock offers dramatically enhanced
sensitivity to new physics. Resolving individual nuclear quantum states in its host crystal
enables us to perform the first steps in characterizing the nuclear clock performance.
Probing the 229Th nuclear transition required new tools. Building upon previous generations
of extreme-ultraviolet (XUV) comb projects in our lab, we construct a VUV comb to perform
direct frequency comb spectroscopy of the 229Th nuclear clock transition. We calibrate the absolute
frequency by linking this comb to the JILA 87Sr atomic clock. We also present our effort on making
229Th thin-film samples for reducing the cost and radioactivity of future nuclear clocks.