Isotope shift measurements in highly charged calcium

Highly charged ions (HCI) are promising candidates for novel optical clocks and tests of fundamental physics. For example, many HCI possess ultra-narrow optical transition that show a large sensitivity to variation of the fine-structure constant, exceeding the sensitivity of singly charged ions. They also provide additional narrow optical transitions that can be used for new physics searches using isotope shift measurements. The megakelvin temperatures needed to produce HCI usually foreclose high-resolution spectroscopy of HCI but recent experimental advances overcame those problems. In our experiment, we extract HCI from an electron beam ion trap (EBIT) and transfer them to a cryogenic linear Paul trap. There, single HCI are sympathetically cooled by laser-cooled Be ions down to millikelvin temperatures, thus enabling quantum logic state readout. This allowed to demonstrate the first optical clock based on Ar XIV, and the determination of its absolute frequency with sub-Hz uncertainty. In this thesis, we apply the developed techniques to the fine structure transition in Ca XV at a wavelength 570 nm and present isotope shift (IS) measurements between all five stable and even isotopes of calcium (40, 42, 44, 46, 48). The measurements required additional hardware for the experimental apparatus that we will present. For loading from solid targets, a laser ablation source for the EBIT system was developed and installed. For frequency stabilization of the clock laser, a vibration-insensitive cubic cavity was setup. Additionally, in parallel to the IS measurements we commissioned an updated version of the cryogenic Paul trap which was installed and characterized after the IS measurements were finished. We determine the absolute transition frequency of each isotope by an optical clock comparison with the Yb octupole clock at PTB. From those measurements we derive the isotope shifts of the transition with an uncertainty of 150 mHz. We combine these results with available isotope-shift data of singly charged Ca in a King plot. This analysis is sensitive to a new force that would couple electrons and neutrons. In this way, we tighten the bounds on the existence of such a hypothetical interaction compared to previous studies. We also discuss how far improved measurements of Ca isotope masses and isotope shifts of the will affect the King plot and the bounds on new physics that can be extracted from it

Coherent photo-thermal noise cancellation in a dual-wavelength optical cavity for narrow-linewidth laser frequency stabilisation

Optical resonators are used for the realisation of ultra-stable frequency lasers. The use of high reflectivity multi-band coatings allows the frequency locking of several lasers of different wavelengths to a single cavity. While the noise processes for single wavelength cavities are well known, the correlation caused by multi-stack coatings has as yet not been analysed experimentally. In our work, we stabilise the frequency of a 729 nm and a 1069 nm laser to one mirror pair and determine the residual-amplitude modulation (RAM) and photo-thermal noise (PTN). We find correlations in PTN between the two lasers and observe coherent cancellation of PTN for the 1069 nm coating. We show that the fractional frequency instability of the 729 nm laser is limited by RAM at 1 × 10−14. The instability of the 1069 nm laser is at 3 × 10−15 close to the thermal noise limit of 1.5 × 10−1

Coherent photo-thermal noise cancellation in a dual-wavelength optical cavity for narrow-linewidth laser frequency stabilisation

Optical resonators are used for the realisation of ultra-stable frequency lasers. The use of high reflectivity multi-band coatings allows the frequency locking of several lasers of different wavelengths to a single cavity. While the noise processes for single wavelength cavities are well known, the correlation caused by multi-stack coatings has as yet not been analysed experimentally. In our work, we stabilise the frequency of a $729\,$nm and a $1069\,$nm laser to one mirror pair and determine the residual-amplitude modulation (RAM) and photo-thermal noise (PTN). We find correlations in PTN between the two lasers and observe coherent cancellation of PTN for the $1069\,$nm coating. We show that the fractional frequency instability of the $729\,$nm laser is limited by RAM at $1\times10^{-14}$. The instability of the $1069\,$nm laser is at $3\times10^{-15}$ close to the thermal noise limit of $1.5\times10^{-15}$.Comment: 17 pages, 5 figure

An Optical Atomic Clock Based on a Highly Charged Ion

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.Comment: Main: 20 pages, 3 figures. Supplement: 19 pages, 2 figure

On the Possibility of Miniature Diamond-Based Magnetometers Using Waveguide Geometries

We propose the use of a diamond waveguide structure to enhance the sensitivity of magnetometers relying on the detection of the spin state of nitrogen-vacancy ensembles in diamond by infrared optical absorption. An optical waveguide structure allows for enhanced optical path-lengths avoiding the use of optical cavities and complicated setups. The presented design for diamond-based magnetometers enables miniaturization while maintaining high sensitivity and forms the basis for magnetic field sensors applicable in biomedical, industrial and space-related applications

Infrared laser threshold magnetometry using diamond NV centers

International audienceWe theoretically study a hybrid laser magnetometer cavity combining a semiconductor medium to obtain the optical gain and a diamond etalon containing nitrogen vacancy (NV) colored centers as magnetic field probe. This architecture avoids the issue of excited state absorption by the NV centers and could end up with equivalent magnetic field noise of 1pT/Hz^0.5. Moreover, unlike usual IR NV center magnetometry this technique does not require the use of an external frequency stabilized probe laser tuned to the IR transition. This simplification is of interest for targeting practical applications

Infrared laser threshold magnetometry with a NV doped diamond intracavity etalon

International audienceWe propose a hybrid laser system consisting of a semiconductor external cavity laser associated to an intra-cavity diamond etalon doped with nitrogen-vacancy color centers. We consider laser emission tuned to the infrared absorption line that is enhanced under the magnetic field dependent nitrogen-vacancy electron spin resonance and show that this architecture leads to a compact solid-state magnetometer that can be operated at room-temperature. The sensitivity to the magnetic field limited by the photon shot-noise of the output laser beam is estimated to be less than 1 pT/ √ Hz. Unlike usual NV center infrared magnetometry, this method would not require an external frequency stabilized laser. Since the proposed system relies on the competition between the laser threshold and an intracavity absorption, such laser-based optical sensor could be easily adapted to a broad variety of sensing applications based on absorption spectroscopy

Supplementary document for Coherent photo-thermal noise cancellation in a dual-wavelength optical cavity for narrow-linewidth laser frequency stabilisation - 6788518.pdf

Equations used for fitting to the data in Figure 2 and