Dorian Gangloff

Tuning friction atom-by-atom in an ion-crystal simulator

A frigid simulator for friction Friction can be a friend or a foe, depending on whether we are trying to brake on a slippery road or to protect moving parts in industrial equipment. It results from the forces between atoms on the two surfaces in contact, but the details of the process are not well understood. Bylinskii et al. constructed a tunable friction simulator out of a handful of cold trapped ions that move in the potential of an optical lattice (see the Perspective by Meyer). They could vary the friction force experienced by the ions from maximal to nearly zero simply by changing the spatial arrangement of the ion array with respect to the optical lattice. Science, this issue p. 1115; see also p. 1089 An array of 174Yb+ ions moving in the potential of an optical lattice simulates friction. [Also see Perspective by Meyer] Friction between ordered, atomically smooth surfaces at the nanoscale (nanofriction) is often governed by stick-slip processes. To test long-standing atomistic models of such processes, we implemented a synthetic nanofriction interface between a laser-cooled Coulomb crystal of individually addressable ions as the moving object and a periodic light-field potential as the substrate. We show that stick-slip friction can be tuned from maximal to nearly frictionless via arrangement of the ions relative to the substrate. By varying the ion number, we also show that this strong dependence of friction on the structural mismatch, as predicted by many-particle models, already emerges at the level of two or three atoms. This model system enables a microscopic and systematic investigation of friction, potentially even into the quantum many-body regime.

Suppression of ion transport due to long-lived subwavelength localization by an optical lattice.

We report the localization of an ion by a one-dimensional optical lattice in the presence of an applied external force. The ion is confined radially by a radio frequency trap and axially by a combined electrostatic and optical-lattice potential. Using a resolved Raman sideband technique, one or several ions are cooled to a mean vibrational number =(0.1±0.1) along the optical lattice. We measure the average position of a periodically driven ion with a resolution down to λ/40, and demonstrate localization to a single lattice site for up to 10 ms. This opens new possibilities for studying many-body systems with long-range interactions in periodic potentials, as well as fundamental models of friction.

One-dimensional array of ion chains coupled to an optical cavity

We present a novel system where an optical cavity is integrated with amicrofabricatedplanar-electrode iontrap.The trapelectrodesproduceatunable periodic potential allowing the trapping of up to 50 separate ion chains aligned with the cavity and spaced by 160µm in a one-dimensional array along the cavity axis. Each chain can contain up to 20 individually addressable Yb + ions coupled to the cavity mode. We demonstrate deterministic distribution of ions between the sites of the electrostatic periodic potential and control of the ion-cavity coupling. The measured strength of this coupling should allow access to the strong collective coupling regime with .10 ions. The optical cavity could serve as a quantum information bus between ions or be used to generate a strong wavelength-scale periodic optical potential.

Observation of Aubry-type transition in finite atom chains via friction

The highly nonlinear many-body physics of a chain of mutually interacting atoms in contact with a periodic substrate gives rise to complex static and dynamical phenomena, such as structural phase transitions and friction. In the limit of an infinite chain incommensurate with the substrate, Aubry predicted a transition with increasing substrate potential, from the chains intrinsic arrangement free to slide on the substrate, to a pinned arrangement favouring the substrate pattern. So far, the Aubry transition has not been observed. Here, using spatially resolved position and friction measurements of cold trapped ions in an optical lattice, we observed a finite version of the Aubry transition and the onset of its hallmark fractal atomic arrangement. Notably, the observed critical lattice depth for few-ion chains agrees well with the infinite-chain prediction. Our results elucidate the connection between competing ordering patterns and superlubricity in nanocontacts-the elementary building blocks of friction.

Velocity tuning of friction with two trapped atoms

To study atomic-scale friction in a controlled environment, researchers used two trapped, laser-cooled ions in an additional optical potential. This set-up provides a better understanding of the interplay between thermal and structural lubricity.

Technologies for trapped-ion quantum information systems

Scaling up from prototype systems to dense arrays of ions on chip, or vast networks of ions connected by photonic channels, will require developing entirely new technologies that combine miniaturized ion trapping systems with devices to capture, transmit, and detect light, while refining how ions are confined and controlled. Building a cohesive ion system from such diverse parts involves many challenges, including navigating materials incompatibilities and undesired coupling between elements. Here, we review our recent efforts to create scalable ion systems incorporating unconventional materials such as graphene and indium tin oxide, integrating devices like optical fibers and mirrors, and exploring alternative ion loading and trapping techniques.

Preventing and reversing vacuum-induced optical losses in high-finesse tantalum (V) oxide mirror coatings.

High-finesse optical cavities placed under vacuum are foundational platforms in quantum information science with photons and atoms. We study the vacuum-induced degradation of high-finesse optical cavities with mirror coatings composed of SiO₂-Ta₂O₅ dielectric stacks, and present methods to protect these coatings and to recover their initial low loss levels. For separate coatings with reflectivities centered at 370 nm and 422 nm, a vacuum-induced continuous increase in optical loss occurs if the surface-layer coating is made of Ta₂O₅, while it does not occur if it is made of SiO₂. The incurred optical loss can be reversed by filling the vacuum chamber with oxygen at atmospheric pressure, and the recovery rate can be strongly accelerated by continuous laser illumination at 422 nm. Both the degradation and the recovery processes depend strongly on temperature. We find that a 1 nm-thick layer of SiO₂ passivating the Ta₂O₅ surface layer is sufficient to reduce the degradation rate by more than a factor of 10, strongly supporting surface oxygen depletion as the primary degradation mechanism.

Passive intrinsic-linewidth narrowing of ultraviolet extended-cavity diode laser by weak optical feedback

We present a simple method for narrowing the intrinsic Lorentzian linewidth of a commercial ultraviolet grating extended-cavity diode laser (TOPTICA DL Pro) using weak optical feedback from a long external cavity. We achieve a suppression in frequency noise spectral density of 20 dB measured at frequencies around 1 MHz, corresponding to the narrowing of the intrinsic Lorentzian linewidth from 200 kHz to 2 kHz. Provided additional active low-frequency noise suppression and long-term drift compensation, the system is suitable for experiments requiring a tunable ultraviolet laser with narrow linewidth and low high-frequency noise, such as precision spectroscopy, optical clocks, and quantum information science experiments.

Multislip Friction with a Single Ion

A trapped ion transported along a periodic potential is studied as a paradigmatic nanocontact frictional interface. The combination of the periodic corrugation potential and a harmonic trapping potential creates a one-dimensional energy landscape with multiple local minima, corresponding to multistable stick-slip friction. We measure the probabilities of slipping to the various minima for various corrugations and transport velocities. The observed probabilities show that the multislip regime can be reached dynamically at smaller corrugations than would be possible statically, and can be described by an equilibrium Boltzmann model. While a clear microscopic signature of multislip behavior is observed for the ion motion, the frictional force and dissipation are only weakly affected by the transition to multistable potentials.