A5075211378- Advanced Frequency and Time Standards
- Cold Atom Physics and Bose-Einstein Condensates
- Semiconductor Quantum Structures and Devices
- Atomic and Subatomic Physics Research
- Spectroscopy and Laser Applications
- GaN-based semiconductor devices and materials
- Advanced Fiber Laser Technologies
- Atomic and Molecular Physics
- Quantum Dots Synthesis And Properties
- Nanowire Synthesis and Applications
- Spectroscopy and Quantum Chemical Studies
- Quantum optics and atomic interactions
- Mechanical and Optical Resonators
- Force Microscopy Techniques and Applications
- Molecular Junctions and Nanostructures
- Scientific Measurement and Uncertainty Evaluation
- Hemodynamic Monitoring and Therapy
- ZnO doping and properties
- Quantum Information and Cryptography
Physikalisch-Technische Bundesanstalt
2016-2021
Philipps University of Marburg
2013-2015
Trapped ions are ideally suited for precision spectroscopy, as is evident from the remarkably low systematic uncertainties of single-ion clocks. The major weakness these clocks long averaging time, necessitated by signal a single atom. An increased number can overcome this limitation and allow implementation novel clock schemes. However, presents challenge to maintain excellent control over shifts particle in spatially extended strongly coupled many-body systems. We measure deduce frequency...
Friction in ordered atomistic layers plays a central role various nanoscale systems ranging from nanomachines to biological systems. It governs transport properties, wear and dissipation. Defects incommensurate lattice constants dramatically change these properties. Recently experimental have become accessible probe the dynamics of nanofriction. Here, we present model system consisting laser-cooled ions which nanofriction processes self-organized with back action can be studied atomic...
The dependence of radiative and nonradiative lifetimes on the excess carrier density in GaInN/GaN quantum wells is studied via time-resolved photoluminescence spectroscopy over a wide range excitation densities. Our results differ from predictions simple free-carrier models: independent clearly evidence excitonic nature even at room temperature. At high densities, are weakly temperature dependent proportional to inverse density, implying an excitonic, threshold-less Auger process....
Optical clocks based on trapped ions can achieve systematic frequency uncertainties below 10${}^{\ensuremath{-}18}$, enabling relativistic geodesy and precise tests of fundamental physics. However, today's single-ion require averaging times over a week to resolve frequencies at this level, no multi-ion clock has been implemented, due difficulties in controlling ion motion. The authors present an ion-trap array that confines up 100 with time-dilation shifts the low-10${}^{\ensuremath{-}19}$...
Localization effects on the optical properties of GaAs1−xBix/GaAs single quantum wells (SQWs), with Bi contents ranging from x = 1.1% to 6.0%, are investigated using continuous-wave and time-resolved photoluminescence. The temperature- excitation density dependence PL spectra systematically studied, carrier recombination mechanisms analyzed. At low temperatures, time-integrated emission is dominated by localized electron-hole pairs due varying content clustering in alloy. extracted energy...
We report on the first coherent excitation of highly forbidden ^{2}S_{1/2}→^{2}F_{7/2} electric octupole (E3) transition in a single trapped ^{172}Yb^{+} ion, an isotope without nuclear spin. Using ^{171}Yb^{+} as reference, we determine frequency to be 642 116 784 950 887.6(2.4) Hz. map out magnetic field environment using ^{2}S_{1/2}→^{2}D_{5/2} quadrupole (E2) and its 729 476 867 027 206.8(4.4) Our results are factor 1×10^{5} (3×10^{5}) more accurate for E2 compared previous measurements....
In order to improve the short-term stability of trapped-ion optical clocks, we are developing a frequency standard based on ${}^{115}$In${}^+$ / ${}^{172}$Yb${}^+$ Coulomb crystals. For this purpose, have developed scalable segmented Paul traps which allow high level control for multiple ion ensembles. article, detail our recent results regarding reduction leading sources uncertainty introduced by trap: 2nd-order Doppler shifts due micromotion and heating secular motion, as well black-body...
We investigate the normal-mode spectrum of a trapped ion chain at symmetry-breaking linear to zigzag transition and finite temperatures. For this purpose, we modulate amplitude Doppler cooling laser excite measure mode oscillations. The expected softening critical point, signature second-order transition, is not observed. Numerical simulations show that mainly due temperature chain. Inspection trajectories suggest thermal shifts can be understood by ions collectively jumping between two...
We study heating of motional modes a single ion and extended crystals trapped in linear radio frequency (rf) Paul trap with precision $Δ\dot{\bar{n}} \approx 0.2 $ phonons s$^{-1}$. Single-ion axial radial rates are consistent electric field noise has been stable over the course four years. At secular $ω_\mathrm{sec}=2π\times620$ kHz, we measure $\dot{\bar{n}} = 0.56(6)$ s$^{-1}$ per for center-of-mass (com) mode chains up to eleven ions observe no significant out-of-phase (oop) modes. By...
The efficiency droop in nitride LEDs is currently attributed to either carrier-density-dependent nonradiative recombination or carrier leakage, both being discussed terms of a single-particle picture. Our time-resolved photoluminescence results show that the radiative lifetime independent density, while scales with inverse density. This can not be understood model. By means many-particle theory approach we obtain consistent picture and Auger enhanced by excitonic electron-hole correlation....
Abstract The carrier dynamics of a Ga(AsBi)/GaAs single quantum well (SQW) with Bi content 5.5% are studied by means time‐resolved photoluminescence (PL). Random fluctuation the alloy compositions and presence clusters in QW material, lead to localized states have significant influence on mechanism PL emission. Under low excitation conditions, emission is dominated recombination electron‐hole pairs. spectra exhibit considerable blue‐shift increased intensity due filling states. At high...