This is a collection of some of our papers explained in a few words.

You can also find our papers in the publication section.

November 2022: World-record bounds on Lorentz violation from composite pulse Ramsey spectroscopy in a trapped ion

In attempts to unify all fundamental forces in a single quantum consistent theory it has been suggested that Lorentz symmetry is violated. We have investigated the principle of local Lorentz invariance in a single trapped Yb+ ion by comparing spatially oriented atomic orbitals. The highly relativistic 2F7/2 Zeeman manifold has been shown to be exceptionally sensitive to Lorentz violation. We have implemented a highly robust composite pulse rf sequence for accurate Ramsey spectroscopy in the eight-level system with second long interrogation time. Hereby, we exploit the most sensitive mj= ±7/2 sublevels and the exceptionally long lifetime of the 2F7/2 state (~1.6 year). With our novel scheme we reach the highest sensitivity to Lorentz violation in the electron-photon sector to date. We search for Lorentz violation with signals at the rotation period of Earth (23.9345 h) and its second harmonic. A 5-week long measurement campaign revealed no significant effect stemming from Lorentz violation, but we could set new bounds at world-record accuracy. A further improvement in sensitivity can be made in the future by scaling to multiple ions in a Coulomb crystal.

July 2017: Nanofriction in self-assembled systems using trapped ions

Publication in Nature Communications: Probing nanofriction and Aubry-type signatures in a finite self-organized system

Measuring the dynamics of two sliding surfaces on the nanoscale while it happens is nearly impossible. Model systems that emulate such system, but that can be controlled and observed in situ can help further the understanding of nanofriction. In a recent publication in Nature Communications we presented a model system using a self-assembled Coulomb crystal in an ion trap. The two-dimensional zigzag configuration is similar to two chains sliding against each other. When a local defect (kink) is present we observed signatures of the Aubry-type transition, which marks the transition of sliding system between stick-slip and smooth-sliding with reduced friction. Our model system shows similarities to biological molecules such as DNA.

English press release

Deutsche Presse Mitteilung

Experimentally observed crystals at different trapping potentials. The crossing of the Aubry-type transition is marked with the breaking of the axial mirror symmetry of the crystal. The ion positions ‘split’ in several positions, because the thermal energy of the crystal is high enough, that it can switch between multiple symmetry broken positions.
Measured (red circles) and calculated (dashed line) order parameter that quantifies the mirror symmetry. For symmetric crystals, the order parameter is zero. At a value of the trapping ratio α ≈ 6.41 the order parameter shows a sudden cusp and increases monotonically.

November 2015: Characterizing the temperature environment of the new AlN ion trap with mK precision

Publication in Metrologia: Analysis of thermal radiation in ion traps for optical frequency standards

Thermal radiation emitted by the environment of the ions shifts the frequency of the clock transition due to the ac Stark effect. Rf ion traps can heat up to 150 °C due to resistive and dielectric rf losses.  Our goal was to develop an rf ion trap which has both a low temperature rise and a well-defined temperature.  Within the frame of a European EMRP project the temperature rise of the ion trap operated with an rf amplitude of 1000 V has been measured at the Czech Metrology Institute in Prague. The measurement and the comparison to corresponding simulations of the system have shown that the temperature rise seen by the ion is (1.0 ± 0.1) K. The combination of the high heat conductivity of the AlN and two Pt100 temperature sensors integrated into the trap electrodes was crucial to obtain the low temperature uncertainty. Using this result we can reduce the uncertainty of the black-body radiation shift originating from the trap temperature uncertainty to (δυ/υ)In+ ~ 2x10-20.

Measurement of the temperature of the ion trap with an IR camera. The trap was driven with an rf amplitude of 1000 V at 15.4 MHz. The gold surfaces (light and dark blue) appear to be cold, because the gold emissivity (εAu=0.04) is lower than the AlN emissivity (εAlN=0.73).

September 2015: Controlling micromotion-induced systematic shifts to below 10-19

Publication in the Journal of Applied Physics: Precise determination of micromotion for trapped-ion optical clocks

Micromotion leeds to significant systematic frequency shifts in optical ion clocks. We have compared three methods to determine micromotion in rf ion trap with highest precision. We developed and experimentally confirmed a new model for the evaluation of photon-correlation signals in the commonly used regime of a similar linewidth and trap drive frequency (see figure). These results can help to substantially reduce this source of frequency uncertainty in ion clocks in general and will allow a precise characterization of the rf field in our multi-ion traps.


Photon-correlation signal (amplitude and phase) in dependence on laser detuning, compared to the commonly used model.

December 2014: Paper on structural phase transitions and topological defects in Coulomb crystals published

Publication in Physica B: Structural phase transitions and topological defects in ion Coulomb crystals

Our article on the study of phase transitions with Coulomb crystals and the creation and control of topological defects for investigating soliton physics has been published in Physica B: Condensed Matter.

October 2013: Yb+ spectroscopy laser stabilized to 5x10-16 with a simple 12 cm short  ULE cavity setup. New vibration insensitive design for 30 cm long reference ULE cavity evaluated.

Publication in Appl. Phys. B: Simple vibration-insensitive cavity for laser stabilization at the 10−16 level

Using a simple setup based on a 12cm long ULE cavity without vibration insensitive design, we have stabilized a diode laser at 822nm to a fractional frequency instability of sy(5s)=5x10-16, close to the cavity’s thermal noise limit. The second harmonic of this laser will be used to address the 2S1/2 to 2D5/2 transition in Yb+ to investigate and manipulate the motion of Coulomb crystals. Using this laser as a reference, we could show that our design for a 30cm long ULE cavity will not be limited by environmental vibrations at a level of 1x10-16 for averaging times >200ms, which is sufficient to operate a clock based on 100 In+ ions at its quantum projection noise limited instability.


Frequency instability of our ultra-stable laser (blue circles) and assessment of individual instability contributions at the level of 10-17.
12 cm ULE cavity with FS-mirrors and ULE compensation rings within its copper heat shield.

August 2013:Cosmology in the lab using laser-cooled ions

Publication in Nature Communications: Topological defect formation and spontaneous symmetry breaking in ion Coulomb crystals

Taking a look back at the beginning of our Universe: QUEST researchers at PTB generate and investigate symmetry breaking in ion Coulomb crystals.

Press release in English:

Pressemitteilungen auf Deutsch:

Coulomb crystals
Symmetry Breaking in Coulomb crystals

August 2011: The new clock laser works!!

For the high-precision spectroscopy we set-up a ultra-stable laser, locked to a ULE-cavity. To lower the thermal noise limitwe optically contacted fused silica mirrors and ULE compensation rings onto the ULE spacer. First measured fractional frequency instabilities are already getting below 10-15.   

Ultra Stable Laser
Optical Clock Laser

July 2011: Movies on phase transitions in Coulomb crystals

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August/September 2010:  The first 172Yb+ ion crystals in our trap!

Laser cooled ion crystals with Yb+

March 2010: Our prototype trap is ready!

We are testing UHV on-board filter electronics and rf-circuit as well as our new trap design with a rf-circuit board wafer trap:

Scalable ion trap

Story of the Lab in Pictures:

January 2009, moving in...
August 2009
Closing up the vacuum chamber
Interior of the vacuum chamber with built in ovens and wired up ion trap
September 2011: it got a lot messier...
The ion trap set-up