Geometric frustration emerges when local interaction energies in an ordered lattice structure cannot be simultaneously minimized, resulting in a large number of degenerate states. The numerous degenerate configurations may lead to practical applications in microelectronics, such as data storage, memory and logic. However, it is difficult to achieve very high degeneracy, especially in a two-dimensional system. Here, we showcase in situ controllable geometric frustration with high degeneracy in a two-dimensional flux-quantum system. We create this in a superconducting thin film placed underneath a reconfigurable artificial-spin-ice structure. The tunable magnetic charges in the artificial-spin-ice strongly interact with the flux quanta in the superconductor, enabling switching between frustrated and crystallized flux quanta states. The different states have measurable effects on the superconducting critical current profile, which can be reconfigured by precise selection of the spin-ice magnetic state through the application of an external magnetic field. We demonstrate the applicability of these effects by realizing a reprogrammable flux quanta diode. The tailoring of the energy landscape of interacting 'particles' using artificial-spin-ices provides a new paradigm for the design of geometric frustration, which could illuminate a path to control new functionalities in other material systems, such as magnetic skyrmions, electrons and holes in two-dimensional materials, and topological insulators, as well as colloids in soft materials.

We show that ac driven skyrmions interacting with an asymmetric substrate provide a realization of a new class of ratchet system which we call a vector ratchet that arises due to the effect of the Magnus term on the skyrmion dynamics. In a vector ratchet, the dc motion induced by the ac drive can be described as a vector that can be rotated clockwise or counterclockwise relative to the substrate asymmetry direction. Up to a full 360• rotation is possible for varied ac amplitudes or skyrmion densities. In contrast to overdamped systems, in which ratchet motion is always parallel to the substrate asymmetry direction, vector ratchets allow the ratchet motion to be in any direction relative to the substrate asymmetry. It is also possible to obtain a reversal in the direction of rotation of the vector ratchet, permitting the creation of a reversible vector ratchet. We examine vector ratchets for ac drives applied parallel or perpendicular to the substrate asymmetry direction, and show that reverse ratchet motion can be produced by collective effects. No reversals occur for an isolated skyrmion on an asymmetric substrate. Since a vector ratchet can produce motion in any direction, it could represent a new method for controlling skyrmion motion for spintronic applications.

We have demonstrated stable self-starting passive mode-locking in a diode-end-pumped Nd:YVO4 laser using a semiconductor saturable absorber mirror (SESAM). An In0.25Ga0.75As single quantum-well SESAM, which was grown by the metalorganic chemical-vapor deposition technique at low temperature, acts as a passive mode-locking device and an output coupler at the same time. Continuous-wave mode-locked transform-limited pulses were obtained at 1064 nm with a pulse duration of 2.1 ps and an average output power of 1.28 W at a repetition rate of 96.5 MHz.

We show how vortices that support Majorana fermions when placed on a periodic pinning array can be used for vortex exchange and independent braiding by performing a series of specific moves with a probe tip. Using these braiding operations, we demonstrate realizations of a Hadamard and a CNOT gate. We specifically consider the first matching field at which there is one vortex per pinning site, and we show that there are two basic dynamic operations, move and exchange, from which basic braiding operations can be constructed in order to create specific logic gates. The periodic pinning array permits both control of the world lines of the vortices and freedom for vortex manipulation using a set of specific moves of the probe during which the probe tip strength and height remain unchanged. We measure the robustness of the different moves against thermal effects and show that the three different operations produce distinct force signatures on the moving tip.Nv j=1 K 1 (r ij /λ)r ij , where K 1 is the modified Bessel function of the second kind, r ij = |r i − r j |,r ij = (r i − r j )/r ij , and r j is the position of vortex j. We measure all forces in units of f 0 = φ 2 0 /(2πµ 0 λ 3 ) where φ 0 = h/2e is the flux

We numerically examine the manipulation of superconducting vortices interacting with a moving trap representing a magnetic force tip translating across a superconducting sample containing a periodic array of pinning sites. As a function of the tip velocity and coupling strength, we find five distinct dynamic phases, including a decoupled regime where the vortices are dragged a short distance within a pinning site, an intermediate coupling regime where vortices in neighboring pinning sites exchange places, an intermediate trapping regime where individual vortices are dragged longer distances and exchange modes of vortices occur in the surrounding pins, an intermittent multiple trapping regime where the trap switches between capturing one or two vortices, and a strong coupling regime in which the trap permanently captures and drags two vortices. In some regimes we observe the counterintuitive behavior that slow moving traps couple less strongly to vortices than faster moving traps; however, the fastest moving traps are generally decoupled. The different phases can be characterized by the distances the vortices are displaced and the force fluctuations exerted on the trap. We find different types of stick-slip motion depending on whether vortices are moving into and out of pinning sites, undergoing exchange, or performing correlated motion induced by vortices outside of the trap. Our results are general to the manipulation of other types of particle-based systems interacting with periodic trap arrays, such as colloidal particles or certain types of frictional systems.

This article examines entrepreneurial identity in both the United Kingdom and China through the lenses of identity theory and social identity theory to develop a deeper and more holistic understanding of the concept of entrepreneurial identity. By examining the entrepreneur as both a role and an identity, this article explores how an entrepreneur views the role of the entrepreneur, the counter-roles to the entrepreneur, and the “self-as-entrepreneur” and seeks to understand how entrepreneurs construct their identity as an entrepreneur. By looking at the role identity in different social constructs, a more nuanced view of entrepreneurial identity can be uncovered for entrepreneurs in both the United Kingdom and China. The study argues that entrepreneurs in the United Kingdom use counter-roles to bridge the disconnect between their understanding of the entrepreneur-as-role and the self-as-entrepreneur, whereas entrepreneurs in China have less conflict reconciling the two and use the counter-role as a way to paint entrepreneurship as a “calling,” justifying their abandonment of other identities.

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The CCD-based point source centroid computation (PSCC) error under the background light is analyzed integrally in theory, numerical simulation and experiment. Furthermore, a comprehensive formula of the PSCC error caused by the diversified error sources is put forward. The optimum threshold to reduce the effects of all the error sources to a minimum is selected. The best threshold level is N(B) +3sigma(B), where N(B) is the average value of the error sources and sigma(B) is the mean-square value of the fluctuation of the error sources. The simulation and experiment results are in great accordance with the theoretical analysis.