arXiv subjects

Simon Stellmer

Publications and source records attributed to Simon Stellmer.

At least 19 recordsLinked to original sources

arXiv2026

A 3D passive ring gyroscope for seismology

In seismology and related fields, the measurement of rotation in all three spatial dimensions is essential to complement the observation of translations. Access to all six degrees of freedom allows for full reconstruction of seismic wavefields and improves the understanding of complex ground motion during seismic events. In this regard, Sagnac interferometers in the form of large active ring laser systems have demonstrated remarkable performance. So-called passive ring gyroscopes offer the potential to bypass some of the limitations of active ring lasers and could represent a promising complement to existing sensor technology. Here, we present a prototype of a transportable three dimensional free-space passive ring gyroscope, reaching a sensitivity in the micro rad/s/sqrt(Hz) regime in all spatial dimensions. We demonstrate the sensor performance by reconstructing the rotational components of a simulated seismic event.

physics.optics↗

arXiv2026

Isotope shifts and hyperfine splitting of the ${}^{1}S_{0}\rightarrow{}^{3}P_{1}$ transition in zinc

We report laser-induced-fluorescence spectroscopy of the ${}^1S_0 \rightarrow {}^3P_1$ intercombination transition in neutral zinc at $307.6~\mathrm{nm}$. Isotope shifts are measured for all stable isotopes with kHz-level precision, improving previous data by about two orders of magnitude. For $^{67}\mathrm{Zn}$, we resolve the excited-state hyperfine structure and determine $\delta\nu^{67,64}_{\rm COG}=1085.933(7)~\mathrm{MHz}$, $A=608.922(3)~\mathrm{MHz}$, and $B=-18.995(10)~\mathrm{MHz}$. A King plot comparison with the ${}^1S_0 \rightarrow {}^1P_1$ 214-nm transition results in field- and mass-shift parameters of $F_{307.6,214}=1.17(5)$ and $K_{307.6,214}=-153(60)~\mathrm{GHz\ u}$. These results provide the spectroscopic basis for narrow-line cooling and precision measurements based on zinc, including the development of an optical clock.

physics.atom-ph↗

arXiv2026

Optical steering of a large ring laser

A common approach to reduce the linewidth of a laser is an increase of its resonator length. In large gas lasers, however, the frequency spacing between longitudinal modes of the resonator easily becomes significantly smaller than the Doppler-broadened width of the gain profile. As a consequence, the laser might operate on a multitude of modes simultaneously, or jump between modes. Such unstable operation cannot be tolerated in metrological or sensing applications, such as ring laser gyroscopes. Here, we propose and demonstrate a method to establish stable operation on a chosen mode index by optically steering the ring laser to a desired mode index through injection locking with an external laser. The injected mode reliably follows the external steering. Intra-cavity backscattering can even cause the counter-propagating, non-injected mode to follow the external steering as well.

physics.optics↗

arXiv2025

Magneto-optical trapping of Zinc

We report on laser cooling and magneto-optical trapping of atomic zinc. The atoms are cooled using the 213.9\,nm $^1$S$_0$ $\rightarrow$ $^1$P$_1$ transition, making this the shortest wavelength employed for magneto-optical trapping thus far. We demonstrate trapping of all stable isotopes of zinc, including the fermionic isotope $^{67}$Zn, which features a very narrow $^1$S$_0$ $\rightarrow$ $^3$P$_0$ transition that could form the basis of an optical atomic clock. We characterize the influence of various parameters on the MOT population and loading rate. The results presented here constitute the first step towards the application of zinc for high-precision optical spectroscopy and quantum information processing.

physics.atom-ph↗

arXiv2025

Probing Nuclear Interactions Through Isotope Shift Spectroscopy of Mercury

We present precision isotope shift spectroscopy of the $\mathrm{6s^{2}}\, {}^{1}\mathrm{S}_{0}{\rightarrow\,}\mathrm{6s\, 6p}\, {}^{3}\mathrm{P}_{1}$ intercombination line and the $\mathrm{6s\,6p}\, {}^{3}\mathrm{P}_{1}{\rightarrow\,}\mathrm{6s\,6d}\, {}^{3}\mathrm{D}_{J}$ ($J=1,2$) transitions in neutral mercury, performed on the five naturally abundant even isotopes, including the low-abundant isotope ${}^{196}\mathrm{Hg}$. Using laser-cooled atoms in a magneto-optical trap, we achieve uncertainties down to $20\,\mathrm{kHz}$, resolving the isotope shift to a fractional uncertainty of ${\sim}\,2{\,\times\,}10^{-6}$. A King plot analysis comparing our ${}^{1}\mathrm{S}_{0}{\rightarrow}{}^{3}\mathrm{P}_{1}$ data to previous results on the $\mathrm{6s\,6p}\,{}^{3}\mathrm{P}_{2}{\rightarrow\,}\mathrm{6s\,7s}\,{}^{3}\mathrm{S}_{1}$ line reveals a nonlinearity with $4.9\,\sigma$ significance. Our generalized King plot nonlinear decomposition analysis discusses potential contributions from quadratic ($\propto \delta\langle r^{2}\rangle^{2}$) and higher order field shifts ($\propto \delta\langle r^{4}\rangle$) also induced by nuclear deformation. These measurements yield new insights into the structure of the $\mathrm{Hg}$ nucleus and provide benchmarks for nuclear-structure models. They further establish mercury as a potential platform to search for hypothetical Yukawa-type boson-mediated forces coupling electrons to neutrons.

physics.atom-ph↗

arXiv2025

H\"ansch-Couillaud locking of a large Sagnac interferometer: advancing below the flicker floor

Large Sagnac interferometers in the form of active ring lasers have emerged as unique rotation sensors in the geosciences, where their sensitivity allows to detect geodetic and seismological signals. The passive laser gyroscope variant, however, is still at a stage of development, and thus far, only the Pound-Drever-Hall frequency stabilization technique has been explored, a method limited by residual amplitude modulation. Here, as an alternative method, we present the first H\"ansch-Couillaud locked passive laser gyroscope. We find that this method is limited by flicker noise, and we introduce a cost-effective lock-in scheme to overcome this limitation. We achieve a sensitivity of 3.1 nrad/s, corresponding to a fraction of $7.7\cdot 10^{-5}$ in the Earth's rotation rate.

physics.optics↗

arXiv2025

A tunable, continuous-wave 130-mW laser at 213 nm

We present a tunable, continuous-wave (CW) laser system emitting at 213 nm, based on the frequency quadrupling of a single Ti:sapph laser. The setup features two sequential, cavity-enhanced second-harmonic generation (SHG) stages. The first stage uses an LBO crystal and achieves a conversion efficiency of over 80%, yielding up to 3.3 W at 426 nm. The second stage employs a Brewster-cut BBO crystal with an elliptical beam waist to mitigate UV-induced degradation, producing up to 130 mW of deep UV light. The system demonstrates stable operation over several hours and is well suited for applications in atomic physics, spectroscopy, and materials science.

physics.optics↗

arXiv2025

An optical frequency shifter based on continuous-wave pump fields

Practical implementations of quantum information networks require frequency conversion of individual photons. Approaches based on a molecular gas as the nonlinear medium cover a wide range of the optical spectrum and promise high efficiency at negligible background. We present polarization-preserving frequency conversion in a hydrogen-loaded hollow core fiber using continuous-wave pump fields. We demonstrate conversion efficiency at the level of a few per mille, discuss various limitations and loss mechanisms, and present a route to increase conversion efficiency to near unity.

quant-ph↗

arXiv2025

Frequency conversion in a hydrogen-filled hollow-core fiber: power scaling, background, and bandwidth

Large-area quantum networks based on optical fibers allow photons at near-infrared wavelengths to travel with minimal loss. Quantum frequency conversion is a method to alter the wavelength of a single photon while maintaining its quantum state. Most commonly, nonlinear crystals are employed for this conversion process, where near-unity conversion efficiency at high fidelity has been demonstrated. Still, the crystal-based conversion process is plagued by strong background noise, very limited spectral bandwidth, and inhomogeneous temperature profiles at strong pump fields. In previous work, we have demonstrated frequency conversion in hydrogen-filled hollow-core fibers and claimed that this conversion process does not compromise performance at strong pump fields, is essentially free of background noise, and intrinsically broadband. Here, we demonstrate that these three claims are justified.

quant-ph↗

arXiv2024

Stabilizing the free spectral range of a large ring laser

A ring laser is defined by its perimeter, which directly enters the conversion factor between measured Sagnac frequency and the actual rotation rate. Large ring lasers employed in geodesy and fundamental physics require stability of the perimeter at or below the parts-per-billion level. We present two complementary approaches to actively control the perimeter length of such ring lasers, reaching a relative length stability of $4\times 10^{-10}$. One of these approaches is based on a phase detection between the beat of two resonances of different longitudinal mode index and a stable local oscillator. The other approach employs a highly stable wavelength meter to measure the absolute frequency of the laser light. These methods can readily be implemented and bring the stability of heterolithic devices on par with monolithic designs.

physics.optics↗

arXiv2024

Demystifying dust contamination in quantum optics labs: measurements and recommendations

Experiments in the field of quantum optics often require very low concentrations of dust particles in the laboratory, but the complexity of working routines precludes operation within a proper clean room. Research teams have established a multitude of different approaches, precaution measures, and habits to keep the delicate optics setups free of contamination. Here, we systematically quantify dust particle concentration during day-to-day operation of a quantum optics lab, assess the effectiveness of various measures, and give practical recommendations.

quant-ph↗

arXiv2024

Frequency conversion in a hydrogen-filled hollow-core fiber using continuous-wave fields

In large-area quantum networks based on optical fibers, photons are the fundamental carriers of information as so-called flying qubits. They may also serve as the interconnect between different components of a hybrid architecture, which might comprise atomic and solid state platforms operating at visible or near-infrared wavelengths, as well as optical links in the telecom band. Quantum frequency conversion is the pathway to change the color of a single photon while preserving its quantum state. Currently, nonlinear crystals are utilized for this process. However, their performance is limited by their acceptance bandwidth, tunability, polarization sensitivity, as well as undesired background emission. A promising alternative is based on stimulated Raman scattering in gases. Here, we demonstrate polarization-preserving frequency conversion in a hydrogen-filled anti-resonant hollow-core fiber. This approach holds promises for seamless integration into optical fiber networks and interfaces to single emitters. Disparate from related experiments that employ a pulsed pump field, we here take advantage of two coherent continuous-wave pump fields.

quant-ph↗

arXiv2024

Isotope shift measurement of the 423-nm transition in neutral Ca

We report on saturated absorption spectroscopy measurements of the $(4s^2) ^{1}S_0\rightarrow(4s4p) ^{1}P_1$ transition for the four most abundant even-mass isotopes in calcium. By referencing the laser locked to an ultralow expansion cavity and carefully investigating systematic errors, isotope shifts are determined with a precision below 100 kHz, improving previously reported values by a factor of about five. A King plot analysis employing literature values of the 729-nm transition in Ca ions shows excellent linearity. The field and mass shift parameters are determined from King plots with other transitions.

physics.atom-ph↗

arXiv2024

Frequency conversion to the telecom O-band using pressurized hydrogen

Large-scale quantum networks rely on optical fiber networks and photons as so-called flying qubits for information transport. While dispersion and absorption of optical fibers are minimum at the infrared telecom wavelengths, most atomic and solid state platforms operate at visible or near-infrared wavelengths. Quantum frequency conversion is required to bridge these two wavelength regimes, and nonlinear crystals are currently employed for this process. Here, we report on a novel approach of frequency conversion to the telecom band. This interaction is based on coherent Stokes Raman scattering (CSRS), a four-wave mixing process resonantly enhanced in a dense molecular hydrogen gas. We show the conversion of photons from \SI{863}{\nano\meter} to the telecom O-Band and demonstrate that the input polarization state is preserved. This process is intrinsically broad-band and can be adapted to any other wavelength.

quant-ph↗

arXiv2023

Hyperfine structure and isotope shifts of the $^1P_1 \leftarrow{} ^{1}S_0$ transition in atomic zinc

We report absolute frequency, isotope shift, radiative lifetime and hyperfine structure measurements of the $^1P_1 \leftarrow{} ^{1}S_0$ (213.8 nm) transition in Zn I using a cryogenic buffer gas beam. Laser-induced fluorescence is collected with two orthogonally oriented detectors to take advantage of differences in the emission pattern of the isotopes. This enables clear distinction between isotopes whose resonances are otherwise unresolved, and a measurement of the fermion hyperfine structure parameters, $A(^{67}$Zn)$=20(2)$ MHz and $B(^{67}$Zn)$=10(5)$ MHz. We reference our frequency measurements to an ultralow expansion cavity and achieve an uncertainty at the level of 1 MHz, about 1 percent of the natural linewidth of the transition.

physics.atom-ph↗

arXiv2022

Frequency Conversion in High-Pressure Hydrogen

State-preserving frequency conversion in the optical domain is a necessary component in many configurations of quantum information processing and communication. Thus far, nonlinear crystals are used for this purpose. Here, we report on a new approach based on coherent anti-Stokes Raman scattering (CARS) in a dense molecular hydrogen gas. This four-wave mixing process sidesteps the limitations imposed by crystal properties, it is intrinsically broadband and does not generate an undesired background. We demonstrate this method by converting photons from 434 nm to 370 nm and show that their polarization is preserved.

quant-ph↗

arXiv2021

Magneto-optical trapping of mercury at high phase space density

We present a realization of a magneto-optical trap of mercury atoms on the intercombination line. We report on trapping of all stable mercury isotopes. We characterize the effect of laser detuning, laser intensity, and gradient field on the trapping performance of our system. The atom number for the most abundant isotope Hg-202 is 50 million atoms. Moreover, we study the difference in cooling processes for bosonic and fermionic isotopes. We observe agreement with the Doppler cooling theory for the bosonic species and show sub-Doppler cooling for the fermionic species. We reach a phase space density of a few parts in 10^-6, which consitutes a promising starting condition for dipole trap loading and evaporative cooling.

physics.atom-ph↗

arXiv2021

Converting single photons from an InAs/GaAs quantum dot into the ultraviolet: preservation of second-order correlations

Wavelength conversion at the single-photon level is required to forge a quantum network from distinct quantum devices. Such devices include solid-state emitters of single or entangled photons, as well as network nodes based on atoms or ions. Here we demonstrate the conversion of single photons emitted from a III-V semiconductor quantum dot at 853nm via sum frequency conversion to the wavelength of the strong transition of Yb ions at 370nm. We measure the second-order correlation function of both the unconverted and of the converted photon and show that the single-photon character of the quantum dot emission is preserved during the conversion process.

quant-ph↗