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Stephan Schiller

Publications and source records attributed to Stephan Schiller.

At least 37 records · Page 2Linked to original sources
arXiv2014

A simple method for characterization of the magnetic field in an ion trap using Be+ ions

We demonstrate a simple method for the determination of the magnetic field in an ion trap using laser-cooled Be+ ions. The method is not based on magnetic resonance and thus does not require delivering radiofrequency (RF) radiation to the trap. Instead, stimulated Raman spectroscopy is used, and only an easily generated optical sideband of the laser cooling wave is required. The d.c. magnetic vector, averaged over the Be+ ion ensemble, is determined. Furthermore, the field strength can be minimized and an upper limit for the field gradient can be determined. The resolution of the method is 0.04 G at present. The relevance for precision rovibrational spectroscopy of molecular hydrogen ions is briefly discussed.

quant-ph↗
arXiv2014

Quantum Tests of the Einstein Equivalence Principle with the STE-QUEST Space Mission

We present in detail the scientific objectives in fundamental physics of the Space-Time Explorer and QUantum Equivalence Space Test (STE-QUEST) space mission. STE-QUEST was pre-selected by the European Space Agency together with four other missions for the cosmic vision M3 launch opportunity planned around 2024. It carries out tests of different aspects of the Einstein Equivalence Principle using atomic clocks, matter wave interferometry and long distance time/frequency links, providing fascinating science at the interface between quantum mechanics and gravitation that cannot be achieved, at that level of precision, in ground experiments. We especially emphasize the specific strong interest of performing equivalence principle tests in the quantum regime, i.e. using quantum atomic wave interferometry. Although STE-QUEST was finally not selected in early 2014 because of budgetary and technological reasons, its science case was very highly rated. Our aim is to expose that science to a large audience in order to allow future projects and proposals to take advantage of the STE-QUEST experience.

gr-qc↗
arXiv2014

Radiation Hardness of High-Q Silicon Nitride Microresonators for Space Compatible Integrated Optics

Integrated optics has distinct advantages for applications in space because it integrates many elements onto a monolithic, robust chip. As the development of different building blocks for integrated optics advances, it is of interest to answer the important question of their resistance with respect to ionizing radiation. Here we investigate effects of proton radiation on high-Q silicon nitride microresonators formed by a waveguide ring. We show that the irradiation with high-energy protons has no lasting effect on the linear optical losses of the microresonators.

physics.optics↗
arXiv2014

A silicon single-crystal cryogenic optical resonator

We report on the demonstration and characterization of a silicon optical resonator for laser frequency stabilization, operating in the deep cryogenic regime at temperatures as low as 1.5 K. Robust operation was achieved, with absolute frequency drift less than 20 Hz over 1 hour. This stability allowed sensitive measurements of the resonator thermal expansion coefficient ($α$). We found $α=4.6\times10^{-13}$ ${\rm K^{-1}}$ at 1.6 K. At 16.8 K $α$ vanishes, with a derivative equal to $-6\times10^{-10}$ ${\rm K}^{-2}$. The temperature of the resonator was stabilized to a level below 10 $μ$K for averaging times longer than 20 s. The sensitivity of the resonator frequency to a variation of the laser power was also studied. The corresponding sensitivities and the expected Brownian noise indicate that this system should enable frequency stabilization of lasers at the low-$10^{-17}$ level.

physics.atom-ph↗
arXiv2014

The static and dynamic polarisability, and the Stark and black-body radiation frequency shifts of the molecular hydrogen ions H2+, HD+, and D2+

We calculate the DC Stark effect for three molecular hydrogen ions in the non-relativistic approximation. The effect is calculated both in dependence on the rovibrational state and in dependence on the hyperfine state. We discuss special cases and approximations. We also calculate the AC polarisabilities for several rovibrational levels, and therefrom evaluate accurately the black-body radiation shift, including the effects of excited electronic states. The results enable the detailed evaluation of certain systematic shifts of the transitions frequencies for the purpose of ultra-high-precision optical, microwave or radio-frequency spectroscopy in ion traps.

physics.atom-ph↗
arXiv2014

Simple Molecules and Clocks

The precise measurement of transition frequencies in cold, trapped molecules has applications in fundamental physics, and extremely high accuracies are desirable. We determine suitable candidates by considering simple molecules with a single electron, for which the external-field shift coefficients can be calculated with high precision. Our calculations show that $\Htwop$ exhibits particular transitions whose fractional uncertainties may reach $2\times10^{-17}$ at room temperature. We also generalize the method of composite frequencies, introducing tailored linear combinations of individual transition frequencies that are free of the major systematic shifts, independent of the strength of the external perturbing fields. By applying this technique, the uncertainty should be reduced to the $10^{-18}$ range for both $\Htwop$ and $\HDp$. Thus, the theoretical results demonstrate that these molecules are of metrological relevance for future studies.

physics.atom-ph↗
arXiv2013

The electric quadrupole moment of molecular hydrogen ions and their potential for a molecular ion clock

The systematic shifts of the transition frequencies in the molecular hydrogen ions are of relevance to ultra-high-resolution radio-frequency, microwave and optical spectroscopy of these systems, performed in ion traps. We develop the ab-initio description of the interaction of the electric quadrupole moment of this class of molecules with the static electric field gradients present in ion traps. In good approximation, it is described in terms of an effective perturbation hamiltonian. An approximate treatment is then performed in the Born-Oppenheimer approximation. We give an expression of the electric quadrupole coupling parameter valid for all hydrogen molecular ion species and evaluate it for a large number of states of H2+, HD+, and D2+. The systematic shifts can be evaluated as simple expectation values of the perturbation hamiltonian. Results on radio-frequency (M1), one-photon electric dipole (E1) and two-photon E1 transitions between hyperfine states in HD+ are reported. For two-photon E1 transitions between rotationless states the shifts vanish. For a subset of rovibrational one-photon transitions the quadrupole shifts range from 0.2 to 10 Hz for an electric field gradient of 0.1 GV/m2. We point out an experimental procedure for determining the quadrupole shift which will allow reducing its contribution to the uncertainty of unperturbed rovibrational transition frequencies to the 1.10^(-15) relative level and, for selected transitions, even below it. The combined contributions of black-body radiation, Zeeman, Stark and quadrupole effects are considered for a large set of transitions and it is estimated that the transition frequency uncertainty of selected transitions can be reduced below the 1.10^(-15) level.

physics.atom-ph↗
arXiv2013

Robust frequency stabilization of multiple spectroscopy lasers with large and tunable offset frequencies

We demonstrate a compact and robust device for simultaneous absolute frequency stabilization of three diode lasers whose carrier frequencies can be chosen freely relative to the reference. A rigid ULE multi-cavity block is employed, and, for each laser, the sideband locking technique is applied. Useful features of the system are a negligible lock error, computer control of frequency offset, wide range of frequency offset, simple construction, and robust operation. One concrete application is as a stabilization unit for the cooling and trapping lasers of a neutral atom lattice clock. The device significantly supports and improves the operation of the clock. The laser with the most stringent requirements imposed by this application is stabilized to a linewidth of 70 Hz, and a residual frequency drift less than 0.5 Hz/s. The carrier optical frequency can be tuned over 350 MHz while in lock.

physics.optics↗
arXiv2013

Proton irradiation robustness of dielectric mirrors for high-finesse Fabry-Pérot resonators in the near-infrared spectral range

We demonstrate that a proton irradiation with fluences of $3.6\times10^{10}$/cm$^{2}$ at low energy ($<$ 36 MeV) and $1.46 \times 10^{10}$/cm$^{2}$ at high energy (40 MeV and 90 MeV combined) on the dielectric mirrors of Fabry-Pérot cavities with a finesse of about 700 000 causes less than 5% change in the finesse. Furthermore, no influence on the coupling efficiency to the cavities was observed, the efficiency being approximately 70%. The irradiation was carried out with a spectrum approximating the proton energy spectrum of a highly elliptic Earth orbit with duration of 5 years, proposed for the Space-Time Explorer and Quantum Equivalence Space Test (STE-QUEST) mission [\url{http://sci.esa.int/ste-quest/}].

physics.optics↗
arXiv2013

Robust, frequency-stable and accurate mid-IR laser spectrometer based on frequency comb metrology of quantum cascade lasers up-converted in orientation-patterned GaAs

We demonstrate a robust and simple method for measurement, stabilization and tuning of the frequency of cw mid-infrared (MIR) lasers, in particular of quantum cascade lasers. The proof of principle is performed with a quantum cascade laser at 5.4 μm, which is upconverted to 1.2 μm by sum-frequency generation in orientation-patterned GaAs with the output of a standard high-power cw 1.5 μm fiber laser. Both the 1.2 μm and the 1.5 μm waves are measured by a standard Er:fiber frequency comb. Frequency measurement at the 100 kHz-level, stabilization to sub-10 kHz level, controlled frequency tuning and long-term stability are demonstrated.

physics.optics↗
arXiv2013

Feasibility of giant fiber-optic gyroscopes

The availability of long-distance, underground fiber-optic links opens a perspective of implementing interferometric fiber-optic gyroscopes embracing very large areas. We discuss the potential sensitivity, some disturbances and approaches to overcome them.

physics.optics↗
arXiv2012

Locking the frequency of lasers to an optical cavity at the $1.6 \times 10^{-17}$ relative instability level

We stabilized the frequencies of two independent Nd:YAG lasers to two adjacent longitudinal modes of a high-finesse Fabry-Pérot resonator and obtained a beat frequency instability of 6.3 mHz at an integration time of 40 s. Referred to a single laser, this is $1.6\times10^{-17}$ relative to the laser frequency, and $1.3\times10^{-6}$ relative to the full width at half maximum of the cavity resonance. The amplitude spectrum of the beat signal had a FWHM of 7.8 mHz. This stable frequency locking is of importance for next-generation optical clock interrogation lasers and fundamental physics tests.

physics.optics↗
arXiv2012

Thermal noise of whispering gallery resonators

By direct application of the fluctuation-dissipation theorem, we numerically calculate the fundamental dimensional fluctuations of crystalline CaF2 whispering gallery resonators in the case of structural damping, and the limit that this noise imposes on the frequency stability of such resonators at both room and cryogenic temperatures. We analyze elasto-optic noise - the effect of Brownian dimensional fluctuation on frequency via the strain-dependence of the refractive index - a noise term that has so far not been considered for whispering-gallery resonators. We find that dimensional fluctuation sets a lower limit of 1E-16 to the Allan deviation for a 10-millimeter-radius sphere at 5 K, predominantly via induced fluctuation of the refractive index.

quant-ph↗
arXiv2011

Spectrally narrow, long-term stable optical frequency reference based on a Eu$^{3+}$:Y$_{2}$SiO$_{5}$ crystal at cryogenic temperature

Using an ultrastable continuous-wave laser at 580 nm we performed spectral hole burning of Eu$^{3+}$:Y$_{2}$SiO$_{5}$ at very high spectral resolution. Essential parameters determining the usefulness as a "macroscopic" frequency reference: linewidth, temperature sensitivity, long-term stability were characterized, using a H-maser stabilized frequency comb. Spectral holes with linewidth as low as 6 kHz were observed and the upper limit of the drift of the hole frequency was determined to be on the order of 5$\pm$3 mHz/s. We discuss necessary requirements for achieving ultra-high-stability in laser frequency stabilization to these spectral holes.

physics.optics↗
arXiv2011

Demonstration of a Transportable 1 Hz-Linewidth Laser

We present the setup and test of a transportable clock laser at 698 nm for a strontium lattice clock. A master-slave diode laser system is stabilized to a rigidly mounted optical reference cavity. The setup was transported by truck over 400 km from Braunschweig to Düsseldorf, where the cavity-stabilized laser was compared to a stationary clock laser for the interrogation of ytterbium (578 nm). Only minor realignments were necessary after the transport. The lasers were compared by a Ti:Sapphire frequency comb used as a transfer oscillator. The thus generated virtual beat showed a combined linewidth below 1 Hz (at 1156 nm). The transport back to Braunschweig did not degrade the laser performance, as was shown by interrogating the strontium clock transition.

physics.optics↗
arXiv2010

Precision spectroscopy of the molecular ion HD+: control of Zeeman shifts

Precision spectroscopy on cold molecules can potentially enable novel tests of fundamental laws of physics and alternative determination of some fundamental constants. Realizing this potential requires a thorough understanding of the systematic effects that shift the energy levels of molecules. We have performed a complete ab initio calculation of the magnetic field effects for a particular system, the heteronuclear molecular hydrogen ion HD+. Different spectroscopic schemes have been considered, and numerous transitions, all accessible by modern radiation sources and exhibiting well controllable or negligible Zeeman shift, have been found to exist. Thus, HD+ is a perspective candidate for determination of the ratio of electron-to-nuclear reduced mass, and for tests of its time-independence.

physics.atom-ph↗
arXiv2008

Sympathetically cooled molecular ions: from principles to first applications

We review the current status of the field of sympathetically cooled molecular ions, i.e. the method used for cooling the translational degrees of freedom, the techniques applied for detection and analysis of the cold trapped ion ensembles produced as well as first applications. We summarize a few salient results and point out various possibilities for future developments.

quant-ph↗