Research project B03 – SFB 1227 DQ-mat – Leibniz University Hannover

Introduction

As the systematic error budgets of ion-based frequency standards continue to improve, ever-longer measurement times are required to average over the statistical noise and obtain a measurement uncertainty that reflects the achievable accuracy. Shorter averaging times can be achieved either by reducing laser phase noise, which currently limits the spectroscopic probe time and hence the observed linewidth of many investigated atomic resonances, or by increasing the number of ions to overcome the fundamental limit on the signal-to-noise ratio of measurements on a single quantum system.

Within this project we pursue three different approaches in three different setups: linear ion chains in a precision trap will enable high-accuracy In⁺ and Yb⁺ multi-ion clocks, multiple ensembles of Yb⁺ ions in spatially separate trap zones will enable dead-time free clock readout, while we will achieve long probe times for a Al⁺/Ca⁺ quantum logic clock through pre-stabilisation of the clock laser light using an ensemble of Ca⁺ ions, realising a multi-ensemble clock. The investigated systems are therefore complementary in their goals, but synergetic in the employed quantum engineering techniques. The project contributes to all of DQ-mat’s core objectives, namely scaling quantum systems, manipulating and characterising quantum systems, composing quantum systems, enhancing quantum sensors and metrology, testing fundamental physics and exploring many-body physics.

Results

During the first two funding periods, we have investigated optimal probe times for a given number of atoms and laser noise, developed novel efficient cooling schemes for dual species clocks based on electromagnetically-induced transparency to reduce time-dilation shifts and evaluated systematic shifts of the Al⁺ system to 1 ×10⁻¹⁸. We operated an optical reference using dynamical decoupling to mitigate systematic shifts of up to five ions in a crystals, and operated an optical clock based on two Ca⁺ ions entangled in a decoherence-free sub space

Time dilation shifts due to thermal motion and micromotion are among the major challenges in controlling the dynamics of large ensembles of ions for precision spectroscopy. We therefore investigated micromotion across an ion chain, heating of the motional modes in extended 1D to 3D ion crystals and demonstrated the experimental capability of sorting mixed-species chains for reliable sympathetic cooling conditions. With this the potential of multi-ion clock operation with fractional systematic uncertainties as low as 10^-19 was successfully demonstrated. In succeeding three-cornered-hat clock comparisons a first In⁺/ Yb⁺ Coulomb crystal clock with a total systematic uncertainty of 2.5*10⁻¹⁸ for a single clock ion and first observations of reduced statistical uncertainties in measurements with up to four clock ions were demonstrated.

We have also started frequency comparisons of the Al⁺/Ca⁺ clock, the multi-ion Ca⁺ and entangled Ca⁺ reference, as well as the In⁺ multi-ion clock with the Yb⁺ single ion clocks and the Sr lattice clock in project B02 (optical clocks).

Publications

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Showing results 21 - 27 out of 27

Hannig S, Mielke J, Fenske JA, Misera M, Beev N, Ospelkaus C et al. A highly stable monolithic enhancement cavity for second harmonic generation in the ultraviolet. Review of scientific instruments. 2018 Jan;89(1):013106. Epub 2018 Jan 19. doi: 10.48550/arXiv.1709.07188, 10.1063/1.5005515, 10.15488/3075

Kozlov MG, Safronova MS, Crespo López-Urrutia JR, Schmidt PO. Highly charged ions: Optical clocks and applications in fundamental physics. Reviews of Modern Physics. 2018 Dec 4;90(4):045005. doi: 10.1103/RevModPhys.90.045005

Mehlstäubler TE, Grosche G, Lisdat C, Schmidt PO, Denker H. Atomic clocks for geodesy. Reports on Progress in Physics. 2018 Jun;81(6):064401. Epub 2018 Apr 18. doi: 10.48550/arXiv.1803.01585, 10.1088/1361-6633/aab409

Scharnhorst N, Cerrillo J, Kramer J, Leroux ID, Wübbena JB, Retzker A et al. Experimental and theoretical investigation of a multimode cooling scheme using multiple electromagnetically-induced-transparency resonances. Physical Review A. 2018 Aug;98(2):023424. Epub 2018 Aug 27. doi: 10.48550/arXiv.1711.00732, 10.1103/PhysRevA.98.023424

Beev N, Fenske JA, Hannig S, Schmidt PO. A low-drift, low-noise, multichannel dc voltage source for segmented-electrode Paul traps. Review of Scientific Instruments. 2017 May 30;88(5):054704. doi: 10.1063/1.4983925

Beev N, Keller J, Mehlstäubler TE. Note: An avalanche transistor-based nanosecond pulse generator with 25 MHz repetition rate. Review of scientific instruments. 2017 Dec 1;88(12):126105. doi: 10.1063/1.5000417

Leroux ID, Scharnhorst N, Hannig S, Kramer J, Pelzer L, Stepanova M et al. On-line estimation of local oscillator noise and optimisation of servo parameters in atomic clocks. Metrologia. 2017 Mar 5;54(3):307-321. doi: 10.1088/1681-7575/aa66e9

All publications of the Collaborative Research Centre

Overview