Dynamics of a magnetic gear with two cogging-free operation modes

The coupling of two rotating spherical magnets is investigated experimentally. For two specific angles between the input and output rotation axes, a cogging-free coupling is observed, where the driven magnet is phase-locked to the driving one. The striking difference between these two modes of operation is the reversed sense of rotation of the driven magnet. For other angles the experiments reveal a more complex dynamical behavior, which is divided in three different classes. This is done by analysing the deviation from a periodic motion of the driven magnet, and by measuring the total harmonic distortion of this rotation. The experimental results can be understood by a mathematical model based on pure dipole-dipole interaction, with the addition of adequate friction terms

The Influence of Anchoring-Group Structure on the Lubricating Properties of Brush-Forming Graft Copolymers in an Aqueous Medium

We have compared the lubricating properties of two different PEG-grafted, polycationic, brush-forming copolymers to gain a deeper understanding of the role of the polyionic backbone in the lubricating behavior of such materials, when used as additives in aqueous lubricant systems. Previously, poly(l-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) has been shown to adsorb onto oxide surfaces from aqueous solution and substantially lower frictional forces. Poly(allylamine)-graft-poly(ethylene glycol) (PAAm-g-PEG), which also has a polycationic backbone, has been synthesized in several different architectures, and its performance investigated via adsorption tests, rolling- and sliding-contact tribometry, and the surface forces apparatus. These tests show a clear reduction of friction forces with PAAm-g-PEG compared to water alone. However, when compared with PLL-g-PEG, while PAAm-g-PEG copolymers did not adsorb to the same extent or exhibit as high a lubricity in sliding geometry, they showed a similar lubricating effect under rolling conditions. The difference in the chemical structure of the backbones, especially the flexibility of the anchoring groups, appears to significantly influence both the extent and kinetics of polymer adsorption, which in turn influences lubrication behavio

Assembly of eight spherical magnets into a dotriacontapole configuration

The magnetic field of a cuboidal cluster of eight magnetic spheres is measured. It decays with the inverse seventh power of the distance. This corresponds formally to a multipole named a dotriacontapole. This strong decay is explained on the basis of dipole-dipole interaction and the symmetry of the ensuing ground state of the cuboidal cluster. A method to build such dotriacontapoles is provided

Precision manufacturing of a lightweight mirror body made by selective laser melting

This article presents a new and individual way to generate opto-mechanical components by Additive Manufacturing, embedded in an established process chain for the fabrication of metal optics. The freedom of design offered by additive techniques gives the opportunity to produce more lightweight parts with improved mechanical stability. The latter is demonstrated by simulations of several models of metal mirrors with a constant outer shape but varying mass reduction factors. The optimized lightweight mirror exhibits $63.5 \%$ of mass reduction and a higher stiffness compared to conventional designs, but it is not manufacturable by cutting techniques. Utilizing Selective Laser Melting instead, a demonstrator of the mentioned topological non-trivial design is manufactured out of AlSi12 alloy powder. It is further shown that -- like in case of a traditional manufactured mirror substrate -- optical quality can be achieved by diamond turning, electroless nickel plating, and polishing techniques, which finally results in $< 150$~nm peak-to-valley shape deviation and a roughness of $< 1$~nm rms in a measurement area of $140 \times 110$ $\mu$m${}^2$. Negative implications from the additive manufacturing are shown to be negligible. Further it is shown that surface form is maintained over a two year storage period under ambient conditions.Comment: 13 pages, 19 figures, online version (corrected proof

Measurement Error Mitigation in Quantum Computers Through Classical Bit-Flip Correction

We develop a classical bit-flip correction method to mitigate measurement errors on quantum computers. This method can be applied to any operator, any number of qubits, and any realistic bit-flip probability. We first demonstrate the successful performance of this method by correcting the noisy measurements of the ground-state energy of the longitudinal Ising model. We then generalize our results to arbitrary operators and test our method both numerically and experimentally on IBM quantum hardware. As a result, our correction method reduces the measurement error on the quantum hardware by up to one order of magnitude. We finally discuss how to pre-process the method and extend it to other errors sources beyond measurement errors. For local Hamiltonians, the overhead costs are polynomial in the number of qubits, even if multi-qubit correlations are included.Comment: 31 pages, 13 figure

Quantum spin helices more stable than the ground state: onset of helical protection

Topological magnetic structures are promising candidates for resilient information storage. An elementary example are spin helices in one-dimensional easy-plane quantum magnets. To quantify their stability, we numerically implement the stochastic Schr\"odinger equation and time-dependent perturbation theory for spin chains with fluctuating local magnetic fields. We find two classes of quantum spin helices that can reach and even exceed ground-state stability: Spin-current-maximizing helices and, for fine-tuned boundary conditions, the recently discovered "phantom helices". Beyond that, we show that the helicity itself (left- or right-rotating) is even more stable. We explain these findings by separated helical sectors and connect them to topological sectors in continuous spin systems. The resulting helical protection mechanism is a promising phenomenon towards stabilizing helical quantum structures, e.g., in ultracold atoms and solid state systems. We also identify an - up to our knowledge - previously unknown new type of phantom helices.Comment: 6+4 pages, 3 figures; version 2: minor updates, additional reference

Studying the phase diagram of the three-flavor Schwinger model in the presence of a chemical potential with measurement- and gate-based quantum computing

We propose an ansatz quantum circuit for the variational quantum eigensolver (VQE), suitable for exploring the phase structure of the multi-flavor Schwinger model in the presence of a chemical potential. Our ansatz is capable of incorporating relevant model symmetries via constrains on the parameters, and can be implemented on circuit-based as well as measurement-based quantum devices. We show via classical simulation of the VQE that our ansatz is able to capture the phase structure of the model, and can approximate the ground state to a high level of accuracy. Moreover, we perform proof-of-principle simulations on superconducting, gate-based quantum hardware. Our results show that our approach is suitable for current gate-based quantum devices, and can be readily implemented on measurement-based quantum devices once available

Detecting an Itinerant Optical Photon Twice without Destroying It

Nondestructive quantum measurements are central for quantum physics applications ranging from quantum sensing to quantum computing and quantum communication. Employing the toolbox of cavity quantum electrodynamics, we here concatenate two identical nondestructive photon detectors to repeatedly detect and track a single photon propagating through a $60\,\mathrm{m}$ long optical fiber. By demonstrating that the combined signal-to-noise ratio of the two detectors surpasses each single one by about two orders of magnitude, we experimentally verify a key practical benefit of cascaded non-demolition detectors compared to conventional absorbing devices.Comment: 8 pages, 6 figure