Measurement of the Isotope Shifts in the 3s²3p^{2 3}P₁ → 3s²3p¹4s^{1 3}P₀ Transition of Silicon

Laser cooling and trapping of neutral atoms requires precise knowledge of atomic transition frequencies. However, different isotopes of the same element have different energies associated with the same transition, which presents an additional challenge to laser cooling. Despite this, isotope shifts also provide the opportunity to isolate specific isotopes in the cooling and trapping process. Isolation of ³¹Si would mark an important practical step in the construction of a Kane quantum computer, which proposes utilization of spin-1/2 ³¹P nuclei, the stable decay product of ³¹Si, as physical qubits. Consequently, we elected to utilize a slightly tunable 252.4 nm laser to explore the differences in transition frequencies of the 3s²3p^{2 3}P₁ → 3s²3p¹4s^{1 3}P₀ transition in ²⁸Si, ²⁹Si, and ³⁰Si, the stable silicon isotopes. Measuring the isotope shift between these stable isotopes, the isotope shift for the radioactive 31Si can be predicted. To do so, silicon powder is heated to 1800 K in a vaccum chamber, and effused through small aperatures (4.8 mm, 3.2 mm, or 1.6 mm) to form an atomic beam. The laser intersects the atomic beam perpendicularly and we measure the flouresence by a photomultiplier tube above the intersection of the atomic and laser beams. With this apparatus, we measure the shift between ²⁸Si and ²⁹Si as 170.47±0.16 MHz, the shift between ²⁸Si and ³⁰Si as 308.6±0.2 MHz, and we estimated the shift between ²⁸Si and ³¹Si to be 457±7 MHz.

PA#: USAFA-DF-2023-586