In order to improve the short-term stability of trapped-ion optical clocks, we are developing a frequency standard based on 115 In + / 172 Yb + Coulomb crystals. For this purpose, we have developed scalable segmented Paul traps which allow a high level of control for multiple ion ensembles. In this article, we detail on our recent results regarding the reduction of the leading sources of frequency uncertainty introduced by the ion trap: 2nd-order Doppler shifts due to micromotion and the heating of secular motion, as well as the black-body radiation shift due to warming of the trap. We show that the fractional frequency uncertainty due to each of these effects can be reduced to well below 10 -19 .
Single ion frequency standards have demonstrated in several experiments excellent results and are approaching fractional frequency uncertainties of 10^-18. As dominant contributions to the uncertainty are linked to the ion trap properties a further reduction would be possible by an improved ion trap. Due to the interrogation of a single ion these frequency standards are currently limited by the intrinsically low signal-to-noise ratio and require long averaging times on the order of several days. This limitation is critical for various applications that require a high frequency resolution on short timescales. One possibility to improve the clock stability is to increase the number of clock ions. However, this approach further increases the requirements for the ion trap. Therefore, for the realization of a multi-ion clock that aims at simultaneously reducing the frequency stability and uncertainty the control over the characteristics of the ion trap is crucial. This thesis continues previous work towards the realization of a multi-ion optical clock based on ion Coulomb crystals of 115In+ ions which are sympathetically cooled by 172Yb+ ions. The existing design for a segmented linear ion trap has been refined and a reliable trap manufacturing process for a trap based on gold coated aluminium nitride wafers has been developed. Manufacturing tolerances below 10 μm allowed to reduce the axial micromotion amplitudes substantially. For a region of more than 300 μm the uncertainty contribution of the three-dimensional micromotion amplitude is shown to be below 10^-19. Additionally the radial ion heating rate of the trap has been measured to be 1.1 phonons/s for a trap frequency of 490 kHz. The time dilation shift due to the heating rate on the radial trap axis is found to be (2.1 ± 0.3) x 10^-20 1/s. The trap design has also been optimized for a low trap temperature rise due to the applied rf voltage. Trap temperature measurements with Pt100 sensors installed on the trap showed a maximum temperature increase of 1.21 K at an rf voltage amplitude of 1 kV. By comparing the measurement results to FEM simulations the uncertainty contribution of the trap temperature to the black-body radiation shift has been deduced to be 2.4 x 10^-20. As the ion trap provides a high level of control on Coulomb crystals it also provides an ideal test bed for studying atomic many-body systems. This work presents results of the investigations on topological defects in two-dimensional Coulomb crystals. The emphasis was placed on the effects of mass defects and external electric fields on the stability of the topological defects. It is shown that these effects can be used to manipulate and create topological defects deterministically.
Clocks have been among the most accurate man-made devices for centuries. Atomic clocks, which have been defining time by means of a microwave transition in the 133Cs atom since 1967, represent a major step in this development. A redefinition of the SI unit of time based on optical atomic clocks is currently under discussion. This forthcoming redefinition requires, among other criteria, the repeated demonstration of the consistency of different optical frequency standards in the low 10−18 range. In this work, the first evaluation of the systematic shifts and their uncertainties in a 115In+–172Yb+ Coulomb crystal clock is presented. This clock utilizes the 1S0 ↔ 3P0 transition in 115In+. 172Yb+ ions are co-trapped with the 115In+ ions in a segmented Paul trap and used for sympathetic cooling. With a systematic uncertainty of 2.5×10−18 when operating with a 1In+–3Yb+ crystal and 2.6×10−18 when operating with a 2In+–4Yb+ crystal, this clock is one of the most accurate clocks in the world. In addition, the operation of the clock with multiple clock ions is the first of its kind at this level of uncertainty. Measurements with up to four clock ions show a reduction in instability from 1.6×10−15/√ τ for a single indium ion to 9.2(4)×10−16/√τ when operating with four indium ions. By using an additional quench laser, the instability in another series of measurements was reduced from a single-ion instability of 1.5×10−15/√ τ to a four-ion instability of 7.1(15)×10−16/√τ , which is consistent with the expected scaling of 1/√N with the number of clock ions N. In this work, the hyperfine structure of the 3P0 ↔ 1P1 transition used for quenching was also resolved for the first time and the hyperfine constants were determined to be AHFS = 265.42(75)MHz and BHFS = 291.4(135) MHz. In frequency comparisons with other clocks, the optical frequency ratios 115In+/171Yb+(E3) and 115In+/87Sr were determined. With a relative total uncertainty of 4.2 × 10−18, the former ratio is the most accurate frequency ratio of different species published to date. It is also the first to meet one of the requirements defined on the roadmap for redefining the SI unit of the second: Measurements of frequency ratios with relative total measurement uncertainties below 5 × 10−18. The determination of the absolute frequency results in an uncertainty of 1.3 × 10−16 for the 1S0 ↔ 3P0 transition in 115In+, which is limited by that of the cesium fountains. The results obtained summarized: ν115In+ ν171Yb+(E3) =1.973 773 591 557 215 788(8) ν115In+ ν87Sr =2.952 748 749 874 860 781(27) ν115In+ =1 267 402 452 901 038.87(16) Hz
Trapped-ion optical clocks are capable of achieving systematic fractional frequency uncertainties of
10−18 and possibly below. However, the stability of current ion clocks is fundamentally limited by the weak signal of single-ion interrogation. We present an operational, versatile platform for extending clock spectroscopy to arrays of Coulomb crystals consisting of several tens of ions, while allowing systematic shifts as low as
10−19. The concept is applicable to all clock transitions with low differential electric quadrupole moments. We observe 3D excess micromotion amplitudes of all individual ions inside a Coulomb crystal with nm resolution and prove that the related frequency shifts can be controlled simultaneously at the
10−19 level. Using this method, we demonstrate regions of
400 μm and
2 mm length in our trap array with time dilation shifts due to micromotion close to
1×10−19 and below
10−18, respectively. Further measurements of the trapping environment and cooling dynamics calculations for mixed In
+ / Yb
+ crystals show that achievable clock uncertainties due to multi-ion operation in our setup are below
1×10−19. This work will enable clock operation with multiple ions and open up the possibility of new interrogation schemes which allow optical clock stabilities beyond classical limits.
Optical clocks have garnered widespread attention due to their unparalleled precision in the fields of time-frequency standards, geodetic measurements, and fundamental physics research. Among recent advances, highly charged ion (HCI)-based optical clocks have attracted significant scientific interest owing to their remarkable insensitivity to electromagnetic perturbations and enhanced sensitivity to potential variations of the fine-structure constant $(\ensuremath{\alpha})$. Although the recent successful demonstration of an
Ar13+ optical clock has validated the feasibility of HCI-based systems,
Ni12+ (featuring an ultranarrow clock transition linewidth) stands out as a superior candidate for achieving HCI optical clocks with ${10}^{\ensuremath{-}19}$ level uncertainty and stability. In this work, we report the Coulomb crystallization of highly charged nickel ions (Ni-HCIs). Through a precise deceleration and sympathetic cooling protocol in a room-temperature linear Paul trap, high-energy Ni-HCI bunches were sympathetically cooled from megakelvin energies down to the hundred-millikelvin range using laser-cooled
Be+ ions. This work represents a pivotal step toward the realization of an optical clock based on
Ni12+ ion.