Quantum walking over rough terrain: How obstacles influence the propagation of quantum particles

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- Quantum physics allows particles to spread quadratically faster than their classical counterparts in a discrete, uniform environment. We have implemented an experimental setup that demonstrates how the dynamics drastically change, if temporal and spatial inhomogeneities are introduced. Fast fluctuations in time lead to a full suppression of the quantum behavior, forcing the particle to act entirely classically. On the other hand, spatial disorders result in a stagnation of the propagation, thus trapping the quantum particle around its initial position, which is in high contrast to
any classical description. Quantum walks serve as underlying theoretical model to explain processes in a variety of different physical systems, as for example, the energy transfer in photosynthesis. The dynamics in such biological systems are hard to measure and highly influenced by disorder and thermal fluctuations. Using controllable photonic quantum networks, we were now able to simulate similar environmental influences and carry out detailed studies of their impact on quantum systems. The experiment not only confirms the theoretical predictions, but opens up new routes for quantum simulations and information processing in mesoscopic structures based on coherent state transfer.

Medley swimming of sleeping sickness parasites.

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- Though cell locomotion has been examined almost since the discovery of the cell itself, advances in microscopy and biochemical studies have paved the way to a more fundamental understanding of cell motility. More recently, a physical, quantitative approach to understanding the world at the micron scale has gained momentum. This work is a detailed, quantitative characterization of trypanosome motility. Trypanosomes, parasites responsible for deadly disease in humans and cattle, swim with the aid of an appendage called a flagellum. The flagellum, produces rapid undulatory movements that result in cell locomotion. We followed single trypanosomes in a homogeneous environment and found that cells that swim faster also exhibit stronger fluctuations in velocity. Statistical analysis allowed us to develop a mathematical model that could reproduce the diverse trajectories followed by the trypanosomes. Finally, we were able to show that the rapid movements of the body (with time scales on the order of 0.1s) are a result of an active process (requiring energy) and thus cannot be described as simple thermal fluctuations. On the whole, such studies provide insight into basic mechanisms of motility, allow for modeling of cell movement, and may eventually even provide design ideas for artificial microswimmers.

Researchers Study the Interplay between Electric and Magnetic Modes Inside a Material … by Looking Outside

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- By examining how garnet crystals reflect and transmit light, we observed the rare occurrence of a hybrid mode where the material displays electric and magnetic characteristics simultaneously. Amazingly, evidence of the hybrid mode vanishes from the reflectivity spectra but remains strong for the transmitted light. We developed an explanation called the Adjusted Oscillator Strength Matching (AOSM) condition to describe this unique electric and magnetic behavior. A possible application of this effect is in antireflection coatings. Using a variety of complementary optical techniques, such as reflectivity, transmittance and ellipsometry, we measured the material’s dielectric permittivity and magnetic permeability in the far infrared frequency range. This work is important in furthering the understanding of when coupling between magnetic excitations such as magnons and electric excitations such as phonons occurs inside a material.