Laser cooling and trapping of 224Ra+

M. Fan, Roy A. Ready, H. Li, S. Kofford, R. Kwapisz, C. A. Holliman, M. S. Ladabaum, A. N. Gaiser, J. R. Griswold, A. M. Jayich

PRR 5, 043201 (2023)

We report the first laser cooling and trapping of 224Ra+ ions. This was realized via the first loading of radium into an ion trap with two step photoionization. A robust source for 224Ra atoms, 3.6 day half-life, was realized with an effusive oven containing 228Th, 1.9 year half-life, which continuously generates 224Ra via its α-decay. We characterized the efficacy of this source and found that after depleting built up radium the thorium decay provides a continuous source of radium atoms suitable for ion trapping. The vacuum system has been sealed for more than six months and continues to trap ions on demand. We also report a measurement of the 224Ra 7s2 1S07s7p 1S1 transition frequency: 621 043 830(60) MHz, which is helpful for efficient photoionization. With this measurement and previous isotope shift measurements we recommend a correction to the same transition in 226Ra: 621 037 830(60) MHz, which is 660 MHz from the accepted value. 

Links: Physical Review A, arXiv

Ion Optical Clocks With Three Electronic States 

C. A. Holliman, M. Fan, A. M. Jayich

SPIE PC124470C (2023)

Optical clocks are the apotheosis of precision measurement, but they require frequent maintenance by scientists. The supporting laser systems are a particularly demanding component of these instruments. To reduce complexity and increase robustness we propose an optical clock with trapped alkali-like ions that use the S1/2 → D3/2 electric quadrupole transition. Compared to traditional group-II ion clocks this reduces the number of laser wavelengths required, and uses hyperfine state preparation and readout techniques enabled by the nuclear spin I = 1/2. We consider 225Ra+ as a candidate system for a clock with three electronic states, and discuss the potential to help realize a transportable optical clock. 

Links: SPIE, arXiv

 Measurement of the Ra+ 7p 2P3/2 State Lifetime

M. Fan, C. A. Holliman, A. Contractor, C. Zhang, S. F. Gebretsadken, A. M. Jayich

PRA 105, 042801 (2022)

Abstract: We report the first measurement of the radium ion’s 7p 2P3/2 state lifetime, τ=4.78(3) ns. The measured lifetime is in good agreement with theoretical calculations, and will enable a determination of the differential scalar polarizability of the narrow linewidth 7s 2S1/2 → 6d 2D5/2 optical clock transition.

Links: Physical Review A, arXiv

 Radium Ion Optical Clock

C. A. Holliman, M. Fan, A. Contractor, S. M. Brewer, A. M. Jayich

PRL 128, 033202 (2020)

Abstract: We report the first operation of a Ra+ optical clock, a promising high-performance clock candidate. The clock uses a single trapped 226Ra+ ion and operates on the 7s 2S1/2 → 6d 2D5/2 electric quadrupole transition. By self-referencing three pairs of symmetric Zeeman transitions, we demonstrate a frequency instability of 1.1 x 10-13/√τ, where τ is the averaging time in seconds. The total systematic uncertainty is evaluated to be Δν/ν = 9 x 10-16. Using the clock, we realize the first measurement of the ratio of the D5/2 state to the S1/2 state Landé g-factors: gD/gS = 0.5988053(11). A Ra+ optical clock could improve limits on the time variation of the fine structure constant in an optical frequency comparison. The ion also has several features that make it a suitable system for a transportable optical clock.

Links: Physical Review Letters, arXiv

 Optical Mass Spectrometry of Cold RaOH+ and RaOCH3+

M. Fan, C. A. Holliman, X. Shi, H. Zhang, M. W. Straus, X. Li, S W. Buechele, A. M. Jayich

PRL 126, 023002 (2021)

Abstract: We present an all-optical mass spectrometry technique to identify trapped ions. The new method uses laser-cooled ions to determine the mass of a cotrapped dark ion with a sub-dalton resolution within a few seconds. We apply the method to identify the first controlled synthesis of cold, trapped RaOH+ and RaOCH3+. These molecules are promising for their sensitivity to time and parity violations that could constrain sources of new physics beyond the standard model. The nondestructive nature of the mass spectrometry technique may help identify molecular ions or highly charged ions prior to optical spectroscopy. Unlike previous mass spectrometry techniques for small ion crystals that rely on scanning, the method uses a Fourier transform that is inherently broadband and comparatively fast. The technique’s speed provides new opportunities for studying state-resolved chemical reactions in ion traps.

Links: Physical Review Letters, arXiv

 Direct Measurement of the 7s 2S1/2 → 7p 2P3/2 Transition Frequency in 226Ra+ 

C. A. Holliman, M. Fan, A. Contractor, M. W. Straus, A. M. Jayich

PRA 102, 042822 (2020)

Abstract: We report a direct measurement of the 7s 2S1/2 → 7p 2P3/2 electric dipole transition frequency in 226Ra+. With a single laser-cooled radium ion we determine the transition frequency to be 785722.11(3) GHz by directly driving the transition with frequency-doubled light and measuring the frequency of the undoubled light with an iodine reference. This measurement addresses a discrepancy of five combined standard deviations between previously reported values.

Links: Physical Review A, arXiv

 Measurements of Electric Quadrupole Transition Frequencies in 226Ra+

C. A. Holliman, M. Fan, A. M. Jayich

PRA 100, 062512 (2019)

Abstract: We report the first driving of the 7s 2S1/2 → 6d 2D3/2 and 7s 2S1/2 → 6d 2D5/2 electric quadrupole (E2) transitions in Ra+. We measure the frequencies of both E2 transitions and two other low-lying transitions in 226Ra+ that are important for controlling the radium ion’s motional and internal states: 6d 2D3/2 → 7p 2Po3/2 and 6d 2D5/2 → 7p 2Po3/2.

Links: Physical Review A, arXiv

 Measurement of the 7p 2Po3/2 State Branching Fractions in Ra+

M. Fan, C. A. Holliman, S. G. Porsev, M. S. Safronova, A. M. Jayich

PRA 100, 062504 (2019)

Abstract: We report a measurement of the radium ion’s 7p 2Po3/2 state branching fractions and improved theoretical calculations. With a single laser-cooled radium-226 ion we measure the P3/2 branching fractions to the 7s 2S1/2 ground state 0.87678(20), the 6d 2D5/2 state 0.10759(10), and the 6d 2D3/2 state 0.01563(21).

Links: Physical Review A, arXiv

 Laser Cooling of Radium Ions

M. Fan, C. A. Holliman, A. L. Wang, A. M. Jayich

PRL 122, 223001 (2019)

Abstract: The unstable radium nucleus is appealing for probing new physics due to its high mass, octupole deformation and energy level structure. Ion traps, with long hold times and low particle numbers, are excellent for work with radioactive species, such as radium and radium-based molecular ions, where low activity, and hence low total numbers, is desirable. We address the challenges associated with the lack of stable isotopes in a table-top experiment with a low-activity (∼ 10 μCi) source where we laser-cool radium ions to form radium Wigner crystals. With a laser-cooled radium ion we measured the 7p 2Po1/2 state’s branching fractions to the ground state, 7s 2S1/2, and a metastable excited state, 6d 2D3/2, to be p = 0.9104(7) and 0.0896(7), respectively. With a nearby tellurium reference line we measured the 7s 2S1/2 → 7p 2Po1/2 transition frequency, 640.09663(6) THz.

Links: Physical Review Letters, arXiv

For a complete list of publications, posters, and talks see my Google Scholar