Description
The search for more precise and accurate frequency standards has played a key role in the development of basic science, precision measurements and technical applications. Nowadays, optical clocks with trapped ions are achieving uncertainties in the low 10$^{-18}$ range and below. One of our group’s focuses is centered on the implementation of optical clocks with trapped $^{40}$Ca$^{+}$ and $^{27}$Al$^{+}$.
Since its first measurement in 2009 by our group, the absolute frequency of the $4s$ $ ^{2}S_{1/2}\leftrightarrow 3d$ $^{2}D_{5/2}$ $^{40}Ca^{+}$ clock transition has been reported 4 more times. However, the first two of these published results (between 2009 and 2012) disagree with the latter two (between 2013 and 2017). We present the results of a new campaign to measure the absolute frequency of $^{40}Ca^{+}$ clock transition with respect to the coordinated universal time UTC at PTB by means of a GNSS link using the Precise Point Positioning (PPP) technique. After evaluation of the systematic shifts, the transition frequency is measured to be (411 042 129 776 401.3±0.6) Hz with a fractional uncertainty of 1.4 × 10$^{-15}$.
To investigate the optical transitions on the $^{27}$Al$^{+}$, we implement Quantum Logic Spectroscopy (QLS). QLS consists of the combined implementation of an auxiliary “logic” ion, which is stored together with a “spectroscopy” ion. The “logic” ion is used to cool down the initially hot “spectroscopy” ion via their Coulomb interaction and additionally allows the preparation and detection of the internal state of the “spectroscopy” ion. We performed QLS for a measurement of the $^{1}\mathrm{S}_{0}\leftrightarrow~^{3}\mathrm{P}_{1}$ intercombination transition in $^{27}$Al$^{+}$. Ramsey spectroscopy is used for probing the transition in $^{27}$Al$^{+}$ and the $4s$ $ ^{2}S_{1/2}\leftrightarrow 3d$ $^{2}D_{5/2}$ clock transition in $^{40}Ca^{+}$ in interleaved measurements. By using the precisely measured frequency of the clock transition in $^{40}Ca^{+}$ as a frequency reference we determine the frequency of the intercombination line to be 1 122 842 857 334 736(93) Hz and the Landé g-factor of the excited state to be 0.428132(2) [1]. We have also probed the $^{1}\mathrm{S}_{0}\leftrightarrow~^{3}\mathrm{P}_{0}$ $^{27}$Al$^{+}$ clock transition with a probe-time-limited width of 1 kHz. Efforts to obtain spectrally narrower lines are mostly hampered by the formation of molecular ions by reaction of the Al+ with H2 background gas molecules. Molecular ion formation limits the time that we can uninterruptedly probe the clock transition to about 15 minutes, which in combination with long Al$^{+}$ reloading times, prevent us from investigating the clock transition more thoroughly.
Our latest project focuses on the development of three different experimental techniques to investigate trapped-ion kinetics due to background-gas collisions. Background gas collisions can perturb the frequency of atomic clocks. The energy imparted during collision events affects the motional state distribution, which consequently has an effect on the time-dilation, also known as second-order Doppler shift. In Additional to this shift, any interaction during the collision can perturb the phase of the atomic superposition. The three techniques together detect a range in energy due to collisions spanning 7 orders of magnitude. The first technique uses a composite sequence of optical transitions in Ca$^{+}$ to accurately transfer information about its motional state, allowing the detection of collisions that impart a kinetic energy between 10$^{-3}$ K to 10$^{-1}$ K. The second technique is based on the detection of collisions that cause a reordering of a mixed-species ion pair and covers a range from 10$^{-1}$ K to 10 K. The third technique is based on the characterization of the re-cooling dynamics of a single calcium ion after a collision and covers a range from 10 K to 10$^{4}$ K. The experimental characterization of trapped-ion kinetics due to background-gas collisions through such a broad range opens the door to a deeper understanding of the background-gas composition and its effect on trapped ion experiments.
[1] M Guggemos et al. “Frequency measurement of the 1$^{1}\mathrm{S}_{0},F=5/2\leftrightarrow~^{3}\mathrm{P}_{1},F=7/2$ transition of $^{27}$Al$^{+}$ via quantum logic spectroscopy with $^{40}$Ca$^{+}$”. In: New Journal of Physics 21.10 (2019), p. 103003.
| Presenter name | Milena Guevara Bertsch |
|---|---|
| How will you attend ICAP-27? | I am planning on in-person attendance |
