Nuclear laser spectroscopy of the 3.5 eV transition in Th-229

Abstract

PACS. 23.20.-g -Electromagnetic transitions. PACS. 42.62.Fi -Laser spectroscopy. PACS. 33.40.+f -Multiple resonances (including double and higher-order resonance processes, such as double nuclear magnetic resonance, electron double resonance, and microwave optical double resonance).Abstract. -We propose high-resolution laser spectroscopy of the 3.5 eV nuclear transition in Th-229 in isolated atoms. Laser excitation of the nucleus can be detected efficiently in a double-resonance method by probing the hyperfine structure of a transition in the electron shell. It is shown that for a suitably chosen electronic level, the frequency of the nuclear transition is independent of external magnetic fields to first order and of electric fields to second order. This makes Th-229 a possible reference for an optical clock of very high accuracy. The nuclearelectronic double-resonance method can be conveniently applied to a laser-cooled ion of 229 Th 3+ in a radiofrequency trap. Further applications of nuclear laser spectroscopy are discussed.

Nuclear clocks based on resonant excitation of γ-transitions

“…This makes nuclear transitions attractive as highly accurate frequency references with small field-induced shifts [25]. Apart from motional frequency shifts that can be well controlled e.g.…”

“…In this case, the nuclear transition frequency is independent of all mechanisms that produce level shifts depending only on the electronic quantum numbers (β, L, S, J), because these do not change and consequently the upper and the lower state of the transition are affected in the same way. To further reduce the sensitivity of the transition frequency to shifts resulting from coupling between electronic and nuclear momenta one may select electronic states with small values of J < 1 or F < 1 that eliminate some higher order and tensorial interactions, like the tensor part of the quadratic Stark effect and the interaction between the atomic quadrupole moment and electric field gradients [25]. An alternative that is applicable for all values of J is the use of stretched states with maximum values of F and |m F | as proposed in [24], because these are eigenstates in the coupled as well as in the uncoupled basis:…”

“…In a nuclear clock it may be possible to obtain narrow and unperturbed resonances from a large ensemble of atoms (N 10 10 ) in a solid, resulting in a potentially huge gain in signal to noise ratio and arXiv:1502.07322v1 [nucl-ex] 25 Feb 2015 clock stability. Mössbauer spectroscopy of nuclear resonances in solids at cryogenic temperature has yielded line Q-factors ν 0 /∆ν approaching 10 15 [3] and it seems attractive to replace the spontaneously emitted γ-radiation that is used as the source in these experiments by a coherent oscillator with the qualities of a tunable laser.…”

Band structure and decay channels of thorium‐229 low‐lying isomeric state for ensemble of thorium atoms adsorbed on calcium fluoride

“…This transition could serve as the basis of an optical frequency standard and could improve the accuracy of the existing standard on Al + ions by orders of magnitude [2]. The precise measurement of the energy of the isomeric transition will improve the accuracy of satellite navigation systems (GPS, GLONASS), directly related to the accuracy of frequency standards used; will make it possible to record the frequency dependence of the transition on the gravitational field, i.e., to measure the gravitational field of the Earth; will resolve a number of problems in fundamental physics, in particular, the measurement of the variation of some fundamental constants with high precision [3].…”

“…One of the methods consists in placing 229 Th ions into the ion trap [8]; mainly 229 Th + and 229 Th 3+ ions are used. 229 Th + ions have a complicated system of electron levels, but are relatively easy to obtain and can be used for implementing the mechanism of electron bridge to excite the isomer state [9]; 229 Th 3+ ions are the most convenient for finding the energies of the isomeric levels due to the high ionization potential (27 eV) and relatively simple system of electronic levels [3]. Another method consists in embedding 229 Th ions into a crystal [10]; the quality factor of the nuclear transition which is sensitive to the additional influence caused by the presence of crystal structure, remains, nevertheless, much larger compared to any electronic transitions [11].…”