Single-ion optical clocks have shown systematic frequency uncertainties below 10^{−18}, but typically require more than one week of averaging to achieve a corresponding statistical uncertainty. This time can be reduced with longer probe times, but comes at the cost of a higher time-dilation shift due to motional heating of the ions in the trap. We show that sympathetic ground-state cooling using electromagnetically induced transparency of an Al^{+} clock ion via a cotrapped Ca^{+} ion during clock interrogation suppresses the heating of the ions. Al^{+} can be kept close to the motional ground state, independent from the chosen interrogation time, at a relative time-dilation shift of (−1.69±0.20)×10^{−18}. The Ca^{+} cooling light introduces an additional light shift on the Al^{+} clock transition of (−9.3±1.1)×10^{−18}. We project that the uncertainty of this light shift can be further reduced by nearly an order of magnitude. This sympathetic cooling enables seconds of interrogation time with 10^{−19} motional and cooling laser-induced uncertainties for Al^{+} and can be employed in other ion clocks as well.

Advances in optical clocks motivate a redefinition of the second, requiring rigorous evaluations of systematic uncertainties and robust consistency among the clocks. Here, we report the full evaluation of the systematic frequency shifts of an ^27Al^+ single-ion clock, and the measurement of its absolute frequency and frequency ratio with a ^87Sr optical lattice clock at PTB. The evaluated total systematic fractional frequency uncertainty is 1.6×10^-18, mainly limited by the accuracy of the relevant atomic coefficients and by background gas collisions. The absolute frequency of the clock has been measured to be ν_Al^+=1 121 015 393 207 859.19(24)Hz, obtained by comparison with two primary caesium fountain clocks at PTB. The frequency ratio between the Al and Sr optical clocks has been determined to be ν_Al^+/ν_^87Sr=2.611 701 431 781 462 668(36), limited by the accuracy of the Sr clock. This ratio differs by 8.6σ and 1.2σ from the 2021 and 2025 frequency ratio published by the BACON collaboration, respectively. These results represent an important contribution toward a future redefinition of the second using optical clocks, and underscore the importance of independent measurements of clock-candidate frequency ratios across different institutions.

Nonlinearities in King plots (KP) of isotope shifts (IS) can reveal the existence of beyond-standard-model (BSM) interactions that couple electrons and neutrons. However, it is crucial to distinguish higher-order standard model (SM) effects from BSM physics. We measure the IS of the transitions ^{3}P_{0}→^{3}P_{1} in Ca^{14+} and ^{2}S_{1/2}→^{2}D_{5/2} in Ca^{+} with sub-Hz precision as well as the nuclear mass ratios with relative uncertainties below 4×10^{-11} for the five stable, even isotopes of calcium (^{40,42,44,46,48}Ca). Combined, these measurements yield a calcium KP nonlinearity with a significance of ∼10^{3}σ. Precision calculations show that the nonlinearity cannot be fully accounted for by the expected largest higher-order SM effect, the second-order mass shift, and identify the little-studied nuclear polarization as the only remaining SM contribution that may be large enough to explain it. Despite the observed nonlinearity, we improve existing KP-based constraints on a hypothetical Yukawa interaction for most of the new boson masses between 10  eV/c^{2} and 10^{7}  eV/c^{2}.

The central challenge of quantum computing is implementing high-fidelity quantum gates at scale. However, many existing approaches to qubit control suffer from a scale-performance trade-off, impeding progress towards the creation of useful devices. Here, we present a vision for an electronically controlled trapped-ion quantum computer that alleviates this bottleneck. Our architecture utilizes shared current-carrying traces and local tuning electrodes in a microfabricated chip to perform quantum gates with low noise and crosstalk regardless of device size. To verify our approach, we experimentally demonstrate low-noise site-selective single- and two-qubit gates in a seven-zone ion trap. We implement electronic single-qubit gates with fidelities ≥99.99912(8)% and demonstrate consistent performance with low crosstalk across the device. We also electronically generate two-qubit maximally entangled states with 99.97(1)% fidelity and long-term stable performance over continuous system operation. These state-of-the-art results highlight the potential of our all-electronic approach for coherent control of trapped-ion qubits in large-scale quantum computers.

Optical atomic clocks are the most precise and accurate measurement devices, reaching fractional systematic uncertainties below one part in 10(-18). Their exceptional performance opens up a wide range of applications in fundamental science and technology. The extreme electronic properties of highly charged ions (HCI) make them highly sensitive probes for tests of fundamental physical theories and significantly lower sensitivity to some of the leading systematic perturbations that affect state-of-the-art optical clocks. This makes them exciting candidates for next-generation clocks. In this contribution, we will briefly review the history of optical spectroscopy of HCI and how scientific advances enabled the first coherent spectroscopy of HCI using quantum logic techniques. A first generation of optical clocks based on HCI with atom-related systematic uncertainties at the 10(-18) level and below is demonstrated. Comparisons of the isotope shift between Ar-40(13+) and Ar-36(13+) as well as g-factor measurements with theory are interpreted as a test of quantum electrodynamic (QED) theory. This demonstrates the suitability of HCI as references for high-accuracy optical clocks and to probe for physics beyond the standard model.

We present a new method for coherent control of trapped ion qubits in separate interaction regions of a multizone trap by simultaneously applying an electric field and a spin-dependent gradient. Both the phase and amplitude of the effective single-qubit rotation depend on the electric field, which can be localized to each zone. We demonstrate this interaction on a single ion using both laser-based and magnetic-field gradients in a surface-electrode ion trap, and measure the localization of the electric field.

Optical atomic clocks are the most accurate measurement devices ever constructed and have found many applications in fundamental science and technology. The use of highly charged ions (HCI) as a new class of references for highest accuracy clocks and precision tests of fundamental physics has long been motivated by their extreme atomic properties and reduced sensitivity to perturbations from external electric and magnetic fields compared to singly charged ions or neutral atoms. Here we present the first realisation of this new class of clocks, based on an optical magnetic-dipole transition in Ar$^{13+}$. Its comprehensively evaluated systematic frequency uncertainty of $2.2\times10^{-17}$ is comparable to that of many optical clocks in operation. From clock comparisons we improve by eight and nine orders of magnitude upon the uncertainties for the absolute transition frequency and isotope shift ($^{40}$Ar vs. $^{36}$Ar), respectively. These measurements allow us to probe the largely unexplored quantum electrodynamic nuclear recoil, presented as part of improved calculations of the isotope shift which reduce the uncertainty of previous theory by a factor of three. This work establishes forbidden optical transitions in HCI as references for cutting-edge optical clocks and future high-sensitivity searches for physics beyond the standard model.

Steven A. King, ∗ Lukas J. Spieß, Peter Micke, 2 Alexander Wilzewski, Tobias Leopold, José R. Crespo López-Urrutia, and Piet O. Schmidt 3 Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany Institut für Quantenoptik, Leibniz Universität Hannover, Welfengarten 1, 30167 Hannover, Germany (Dated: February 26, 2021)

Nils-Holger Rehbehn ID , ∗ Michael K. Rosner ID , Hendrik Bekker ID , 2 Julian C. Berengut ID , 1 Piet O. Schmidt ID , 5 Steven A. King ID , Peter Micke ID , 1 Ming Feng Gu, Robert Müller ID , 7 Andrey Surzhykov ID , 7, 8 and José R. Crespo López-Urrutia ID 1, † Max-Planck-Institut für Kernphysik, D–69117 Heidelberg, Germany Helmholtz-Institut Mainz, Johannes Gutenberg University, D–55128 Mainz, Germany School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia Physikalisch–Technische Bundesanstalt, D–38116 Braunschweig, Germany Leibniz Universität Hannover, D–30167 Hannover, Germany Space Science Laboratory, University of California, Berkeley, CA 94720, USA Technische Universität Braunschweig, D–38106 Braunschweig, Germany Laboratory for Emerging Nanometrology Braunschweig, D-38106 Braunschweig, Germany (Dated: March 31, 2021)

We present a novel ultrastable superconducting radio-frequency (RF) ion trap realized as a combination of an RF cavity and a linear Paul trap. Its RF quadrupole mode at 34.52 MHz reaches a quality factor of Q ≈ 2.3 × 105 at a temperature of 4.1 K and is used to radially confine ions in an ultralow-noise pseudopotential. This concept is expected to strongly suppress motional heating rates and related frequency shifts that limit the ultimate accuracy achieved in advanced ion traps for frequency metrology. Running with its low-vibration cryogenic cooling system, electron-beam ion trap, and deceleration beamline supplying highly charged ions (HCIs), the superconducting trap offers ideal conditions for optical frequency metrology with ionic species. We report its proof-of-principle operation as a quadrupole-mass filter with HCIs and trapping of Doppler-cooled 9Be+ Coulomb crystals.

We carried out a 26-day comparison of five simultaneously operated optical clocks and six atomic fountain clocks located at INRIM, LNE-SYRTE, NPL and PTB by using two satellite-based frequency comparison techniques: broadband Two-Way Satellite Time and Frequency Transfer (TWSTFT) and Global Positioning System Precise Point Positioning (GPS PPP). With an enhanced statistical analysis procedure taking into account correlations and gaps in the measurement data, combined overall uncertainties in the range of 1.8 x 10(-16)to 3.5 x 10(-16)for the optical clock comparisons were found. The comparison of the fountain clocks yields results with a maximum relative frequency difference of 6.9 x 10(-16), and combined overall uncertainties in the range of 4.8 x 10(-16)to 7.7 x 10(-16).

Precision spectroscopy of atomic systems is an invaluable tool for the advancement of our understanding of fundamental interactions and symmetries. Recently, highly charged ions (HCI) have been proposed for sensitive tests of physics beyond the Standard Model and as candidates for high-accuracy atomic clocks. However, the implementation of these ideas has been hindered by the parts-per-million level spectroscopic accuracies achieved to date. Here, we cool a trapped HCI to the lowest reported temperatures, and introduce coherent laser spectroscopy on HCI with an eight orders of magnitude leap in precision. We probe the forbidden optical transition in ^40Ar^13+ at 441 nm using quantum-logic spectroscopy and measure both its excited-state lifetime and g-factor. Our work ultimately unlocks the potential of HCI, a large, ubiquitous atomic class, for quantum information processing, novel frequency standards, and highly sensitive tests of fundamental physics, such as searching for dark matter candidates or violations of fundamental symmetries.

In vacuo cryogenic environments are ideal for applications requiring both low temperatures and extremely low particle densities. This enables reaching long storage and coherence times, for example, in ion traps, essential requirements for experiments with highly charged ions, quantum computation, and optical clocks. We have developed a novel cryostat continuously refrigerated with a pulse-tube cryocooler and providing the lowest vibration level reported for such a closed-cycle system with 1 W cooling power for a <5 K experiment. A decoupling system suppresses vibrations from the cryocooler by three orders of magnitude down to a level of 10 nm peak amplitudes in the horizontal plane. Heat loads of about 40 W (at 45 K) and 1 W (at 4 K) are transferred from an experimental chamber, mounted on an optical table, to the cryocooler through a vacuum-insulated massive 120 kg inertial copper pendulum. The 1.4 m long pendulum allows installation of the cryocooler in a separate, acoustically isolated machine room. At the experimental chamber, we measured the residual vibrations using an interferometric setup. The positioning of the 4 K elements is reproduced to better than a few micrometer after a full thermal cycle to room temperature. Extreme high vacuum on the 10-15 mbar level is achieved. In collaboration with the Max-Planck-Institut für Kernphysik, such a setup is now in operation at the Physikalisch-Technische Bundesanstalt for a next-generation optical clock experiment using highly charged ions.

The highly forbidden S-2(1/2) -> F-2(7/2) electric octupole transition in Yb-171(+) is a potential candidate for a redefinition of the SI second. Wepresent a measurement of the absolute frequency of this optical transition, performed using a frequency link to International Atomic Time to provide traceability to the SI second. The Yb-171(+) optical frequency standard was operated for 76% of a 25-day period, with the absolute frequency measured to be 642 121 496 772 645.14(26) Hz. The fractional uncertainty of 4.0 x 10(-16) is comparable to that of the best previously reported measurement, which was made by a direct comparison to local caesium primary frequency standards.

We present a simple, robust, narrow-linewidth, frequency-doubled semiconductor laser source suitable for laser cooling and repumping of \(^9\text {Be}^+\) ions. A distributed Bragg reflector (DBR) laser diode operating at 626 nm is self-injection-locked to a frequency doubling cavity via phase-stabilised optical feedback when the laser is resonant with the cavity mode. The short-term laser instability is reduced from the MHz level to approximately 20 kHz by the injection process, thus eliminating the need for a high-bandwidth feedback loop to suppress the otherwise troublesome high-frequency laser noise. Long-term stability of the laser frequency is achieved by feeding back to the length of the enhancement cavity utilising an electro-optic frequency comb generator to produce a beatnote with a laser that is detuned by 98 GHz. Long-term injection locking and frequency stabilisation via a wavemeter are ensured using automatic relocking algorithms. This work could find applications throughout the atomic physics community as a cost-effective alternative to expensive, intrinsically narrow-linewidth lasers where cavity-enhanced frequency doubling is required.

We report a revised absolute frequency measurement of the 171Yb + electric octupole optical clock transition of 642 121 496 772 645.17(22) Hz, with a fractional uncertainty of 3.4 × 10-16. This newer value, with lower uncertainty, is achieved through additional analysis of previously reported experimental data that links the optical frequency to the SI second through international atomic time (TAI). The new step in the data analysis involves a special computation of the fractional frequency offset between the scale interval of TAI and the SI second, over a time interval more closely matched to the experimental data acquisition period.

The highly forbidden $^2$S$_{1/2} ightarrow ^2$F$_{7/2}$ electric octupole transition in $^{171}$Yb$^+$ is a potential candidate for a redefinition of the SI second. We present a measurement of the absolute frequency of this optical transition, performed using a frequency link to International Atomic Time to provide traceability to the SI second. The $^{171}$Yb$^+$ optical frequency standard was operated for 76% of a 25-day period, with the absolute frequency measured to be 642 121 496 772 645.14(26) Hz. The fractional uncertainty of $4.0 imes 10 ^{-16}$ is comparable to that of the best previously reported measurement, which was made by a direct comparison to local caesium primary frequency standards.

The highly forbidden $^2$S$_{1/2} \rightarrow ^2$F$_{7/2}$ electric octupole transition in $^{171}$Yb$^+$ is a potential candidate for a redefinition of the SI second. We present a measurement of the absolute frequency of this optical transition, performed using a frequency link to International Atomic Time to provide traceability to the SI second. The $^{171}$Yb$^+$ optical frequency standard was operated for 76% of a 25-day period, with the absolute frequency measured to be 642 121 496 772 645.14(26) Hz. The fractional uncertainty of $4.0 \times 10 ^{-16}$ is comparable to that of the best previously reported measurement, which was made by a direct comparison to local caesium primary frequency standards.

The highly forbidden ^2S_1/2→ ^2F_7/2 electric octupole transition in ^171Yb^+ is a potential candidate for a redefinition of the SI second. We present a measurement of the absolute frequency of this optical transition, performed using a frequency link to International Atomic Time to provide traceability to the SI second. The ^171Yb^+ optical frequency standard was operated for 76 measured to be 642 121 496 772 645.14(26) Hz. The fractional uncertainty of 4.0 × 10 ^-16 is comparable to that of the best previously reported measurement, which was made by a direct comparison to local caesium primary frequency standards.