Pelzer Lennart, Dietze Kai, Martínez-Lahuerta Víctor José, Krinner Ludwig, Kramer Johannes, Dawel Fabian, Spethmann Nicolas C H, Hammerer Klemens, Schmidt Piet O
<a href="https://ror.org/05r3f7h03">Physikalisch-Technische Bundesanstalt</a>, Bundesallee 100, 38116 Braunschweig, Germany.
Institut für Quantenoptik, <a href="https://ror.org/0304hq317">Leibniz Universität Hannover</a>, Welfengarten 1, 30167 Hannover, Germany.
Phys Rev Lett. 2024 Jul 19;133(3):033203. doi: 10.1103/PhysRevLett.133.033203.
We present the experimental realization of a continuous dynamical decoupling scheme which suppresses leading frequency shifts in a multi-ion frequency reference based on ^{40}Ca^{+}. By near-resonant magnetic coupling of the ^{2}S_{1/2} and ^{2}D_{5/2} Zeeman sublevels using radio-frequency dressing fields, engineered transitions with reduced sensitivity to magnetic-field fluctuations are obtained. A second stage detuned dressing field reduces the influence of amplitude noise in the first stage driving fields and decreases 2nd-rank tensor shifts, such as the electric quadrupole shift. Suppression of the quadratic dependence of the quadrupole shift to 3(2) mHz/μm^{2} and coherence times of 290(20) ms on the optical transition are demonstrated even within a laboratory environment with significant magnetic field noise. Besides removing inhomogeneous line shifts in multi-ion clocks, the demonstrated dynamical decoupling technique may find applications in quantum computing and simulation with trapped ions by a tailored design of decoherence-free subspaces.
