Speaker
Description
The nucleus is generally described using a number of observables, each providing a characteristic insight into nuclear properties. Two particularly interesting properties are the nuclear charge density distribution and nuclear multipole expansion. The charge density distribution is described by an expansion ($\delta\langle r^2 \rangle$, $\delta\langle r^4 \rangle$, $\delta\langle r^2 \rangle^2$...) and the nuclear multipole expansion is described similarly (magnetic dipole $\mu$, electric quadrupole $Q$, magnetic octupole $\Omega$...) [1]. Both distributions are successfully probed using Collinear Laser Spectroscopy (CLS) across the nuclear chart. However, the technique is limited in precision and can therefore only access the lowest order multipoles, $\delta\langle r^2 \rangle$, $\mu$ and $Q$.
Using ion traps, by operating in the Lamb-Dicke regime and exploiting long interaction times, allows us to improve the precision of the measurements by many orders of magnitude as compared to conventional methods used at Radioactive Ion Beam (RIB) facilities, gaining access to $\Omega$, $\delta\langle r^4 \rangle$ and $\delta\langle r^2 \rangle^2$. Despite extensive developments in ion trapping, an ion trap for high precision optical spectroscopy of short-lived radioactive isotopes has not yet been installed at an ISOL (Isotope Separator On-Line) facility [2]. This motivated the building of two ion trapping setups at KU Leuven, one aimed at high precision optical spectroscopy, the BICEPS (Bespoke Ion Cooling Experiment for Precision Spectroscopy) trap, and another focused on deceleration and trapping of radioactive ions [3]. Both traps are fully operational and actively performing measurements.
Using BICEPS, we will perform high precision Isotope Shift (IS) spectroscopy of stable bosonic Sr$^{+}$ isotopes, as well as radiofrequency spectroscopy, probing the hyperfine structure of ${}^{87}$Sr$^{+}$ to measure $\Omega$ [4]. Eventually, the IS will allow us to probe the higher order charge density moments and to put meaningful bounds on Beyond Standard Model (BSM) physics [5]. We have already performed first low-precision IS measurements on single ${}^{84}$Sr$^{+}$, ${}^{86}$Sr$^{+}$ and ${}^{88}$Sr$^{+}$ and currently performing Rabi oscillations between the two Zeeman levels of the ground state of ${}^{88}$Sr$^{+}$. This demonstrates our capacity to coherently manipulate state populations on single ions. Furthermore, in this contribution the ongoing developments of BICEPS regarding trap control and precision laser spectroscopy as well as prospects to measure nuclear observables with high precision on radioactive isotopes at an ISOL facility will be discussed.
[1] Reinhard, P. G., Nazarewicz, W., Garcia Ruiz, R. F., Phys. Rev. C, 101 (2020).
[2] Takamine, A. et al., Phys. Rev. Lett., 112, 162502 (2024).
[3] P. Imgram et al., Review of Scientific Instruments 96, 093302 (2025)
[4] Lewty, N., et al., Opt. Express, 20, 21379 (2012).
[5] Door, M., et al., Phys. Rev. Lett., 134, 063002 (2025).
| Academic level | PhD student |
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