# behav: the benefit of ignorance for traffic through a random congestible network.

<< When traffic is routed through a network that is susceptible to congestion, the self-interested decisions made by individual users do not, in general, produce the optimal flow. This discrepancy is quantified by the so-called "price of anarchy." >>

AA << consider whether the traffic produced by self-interested users is made better or worse when users have uncertain knowledge about the cost functions of the links in the network, and define a parallel concept that (They) call the "price of ignorance."  >>

AA << introduce a simple model in which fast, congestible links and slow, incongestible links are mixed randomly in a large network and users plan their routes with finite uncertainty about which of the two cost functions describes each link. >>

<< One of (Their) key findings is that a small level of user ignorance universally improves traffic, regardless of the network composition. Further, there is an optimal level of ignorance which, in (the) model, causes the self-interested user behavior to coincide with the optimum. Many features of (AA) model can be understood analytically, including the optimal level of user ignorance and the existence of critical scaling near the percolation threshold for fast links, where the potential benefit of user ignorance is greatest. >>️

Alican Saray, Calvin Pozderac, et al. The benefit of ignorance for traffic through a random congestible network. arXiv: 2503.09684v1 [cond-mat.dis-nn]. Mar 12, 2025.

https://arxiv.org/abs/2503.09684

Also:  network, behav, random, uncertainty, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, networks, behavior,  randomness, uncertainty, price of anarchy, price of ignorance

# qubit: stability of classical shadows under gate-dependent noise

<< Expectation values of observables are routinely estimated using so-called classical shadows—the outcomes of randomized bases measurements on a repeatedly prepared quantum state. In order to trust the accuracy of shadow estimation in practice, it is crucial to understand the behavior of the estimators under realistic noise. >>

<< In this Letter, (AA) prove that any shadow estimation protocol involving Clifford unitaries is stable under gate-dependent noise for observables with bounded stabilizer norm—originally introduced in the context of simulating Clifford circuits. In contrast, (They) demonstrate with concrete examples that estimation of “magic” observables can lead to highly misleading results in the presence of miscalibration errors and a worst case bias scaling exponentially in the system size. >>

AA << further find that so-called robust shadows, aiming at mitigating noise, can introduce a large bias in the presence of gate-dependent noise compared to unmitigated classical shadows. Nevertheless, (AA) guarantee the functioning of robust shadows for a more general noise setting than in previous works. On a technical level, (They) identify average noise channels that affect shadow estimators and allow for a more fine-grained control of noise-induced biases. >>️

Raphael Brieger, Markus Heinrich, et al. Stability of Classical Shadows under Gate-Dependent Noise. Phys. Rev. Lett. 134, 090801. Mar 4, 2025. 

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.134.090801  arXiv: 2310.19947v3 [quant-ph]. Feb 19, 2025.   https://arxiv.org/abs/2310.19947

Also: qubit, in FonT  https://flashontrack.blogspot.com/search?q=qubit  noise, ai (artificial intell) (bot), in https://www.inkgmr.net/kwrds.html   

Keywords: qubit, noise, realistic noise, shadows, robust shadows

# gst: apropos of degeneration, the topological degeneracy induced by twisting.

<< In recent years, twisting has emerged as a new degree of freedom that plays an increasingly important role in Bloch bands of various physical systems. However, there is currently a lack of reports on the nontrivial physics of topological degeneracy in twisted systems. >>

AA << investigated the intrinsic physical correlation between twisting and topological degeneracy. (They) found that twisting not only breaks the symmetry of the system but also introduces topological degeneracy that does not exist under the original symmetric system without twisting. >>

<< Furthermore, the topological degeneracy can be easily tuned through twisting. This new twist-induced topological degeneracy gives rise to a unique polarization-degenerate birefringent medium, wherein the twist angle acts as a novel degree of freedom for dispersion and polarization management of interface states. >> 

<< Exhibiting fascinating properties and experimental feasibilities, (AA) Letter points to new possibilities in the research of various topological physics in twisted photonics. >>️

Han Peng, Qiang Wang, et al. Topological degeneracy induced by twisting. Phys. Rev. Lett. 134, 106601. Mar 11, 2025.

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.134.106601   arXiv: 2503.09048v1 [physics.optics]. https://arxiv.org/abs/2503.09048  

Also: degeneration, in FonT https://flashontrack.blogspot.com/search?q=degeneration   twisting, twist, in FonT   https://flashontrack.blogspot.com/search?q=twisting    https://flashontrack.blogspot.com/search?q=twist 

Keywords: gst, degeneration, twisting 

# qubit: communication power of a noisy qubit.

<< A fundamental limitation of quantum communication is that a single qubit can carry at most one bit of classical information. For an important class of quantum communication channels, known as entanglement breaking, this limitation holds even if the sender and receiver share entangled particles. But does this mean that, for the purpose of communicating classical messages, a noisy entanglement-breaking qubit channel can be replaced by a noisy bit channel? >>

Here AA << answer the question in the negative. (They) introduce a game, similar to the Monty Hall problem in classical statistics, where a sender assists a receiver in finding a valuable item (the “prize”) hidden in one of four possible boxes, while avoiding a hazardous item (the “bomb”) hidden in one of the remaining three boxes. (AA) show that no classical strategy using a noisy bit channel can ensure that the bomb is avoided, even if the sender and receiver share arbitrary amounts of randomness. >>

<< In contrast, communication of a qubit through a class of noisy entanglement-breaking channels, which (They) call quantum not channels, allows the players to deterministically avoid the bomb and to find the prize with a guaranteed nonzero probability. >>

AA << findings show that the communication of classical messages through a noisy entanglement-breaking qubit channel assisted by quantum entanglement cannot, in general, be simulated by communication through a noisy bit channel assisted by classical correlations. >>️

Giulio Chiribella, Saptarshi Roy, et al. Communication Power of a Noisy Qubit. Phys. Rev. Lett. 134, 080803. Feb 28, 2025. 

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.134.080803     arXiv: 2405.17946v2 [quant-ph]. https://arxiv.org/abs/2405.17946  

Also: qubit, in https://flashontrack.blogspot.com/search?q=qubit  game, in  https://flashontrack.blogspot.com/search?q=game  noise, in  https://flashontrack.blogspot.com/search?q=noise 

Keywords: qubit, games, noise

# gst: dynamics of fluid-driven fractures across material heterogeneities.

<< Fracture propagation is highly sensitive to the conditions at the crack tip. In heterogeneous materials, microscale obstacles can cause propagation instabilities. Macroscopic heterogeneities modify the stress field over scales larger than the tip region. >>

 Here AA << experimentally investigate the propagation of fluid-driven fractures through multilayered materials. (They) focus on analyzing fracture profiles formed upon injection of a low-viscosity fluid into a two-layer hydrogel block. >>

<< Experimental observations highlight the influence of the originating layer on fracture dynamics. Fractures that form in the softer layer are confined, with no penetration in the stiffer layer. Conversely, fractures initiated within the stiffer layer experience rapid fluid transfer into the softer layer when reaching the interface. >>

AA << report the propagation dynamics and show that it is controlled by the toughness contrast between neighboring layers, which drives fluid flow. (They) model the coupling between elastic deformation, material toughness, and volume conservation. After a short transient regime, scaling arguments capture the dependence of the fracture geometry on material properties, injection parameters, and time. These results show that stiffness contrast can modify fracture propagation over large length scales and demonstrate the importance of macroscopic scale heterogeneities on fracture dynamics. >>

Sri Savya Tanikella, Marie C. Sigallon, Emilie Dressaire. Dynamics of fluid-driven fractures across material heterogeneities. Phys. Rev. E 111, 025504. Feb 28, 2025.   https://journals.aps.org/pre/abstract/10.1103/PhysRevE.111.025504     arXiv: 2407.10298v1 [physics.flu-dyn]. Jul 14, 2024.  https://arxiv.org/abs/2407.10298

Also: fracture, crack, elastic, 

instability, disorder, transition, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, fracture, crack, elasticity, instability, disorder, transitions

# gst: tandem droplets accelerated by continuous uniform airflow.

<< In a dense droplet environment, droplets influence each other's motion, deformation, and breakup behavior. The tandem droplet is a particularly relevant case for the study of its unsteady dynamic behavior. >>

<< A three-dimensional numerical simulation study was conducted to investigate the deformation process of tandem droplets under different conditions. >>

<< The results of the research show that under conditions of high density ratio and a significant Reynolds number, the edge morphological characteristics of droplets are predominantly influenced by the Rayleigh-Taylor instability. In the case of low density ratios, the pressure drag force on the leeward side exerts a dominant influence on the accelerated motion of the leading droplet. The shape of the droplet is significantly influenced by the vortex ring present in the recirculation region. The perturbation of the liquid edge induces the vortex ring to split into secondary vortex rings, which act back on the droplet, thereby affecting its morphological characteristics. The trailing droplet is subject to a reduction in cross-flow radius, drag coefficient, minimum length, and expansion speed of the liquid bag due to the influence of the wake of the leading droplet. The decrease in Reynolds number and relative distance leads to a stronger suppression effect, while the decrease in density ratio shortens the length of the recirculation region, thereby weakening the suppression of trailing droplets. >>

Shuting Peng, Fuzhen Chen, et al. Three-dimensional numerical simulation of tandem droplets accelerated by continuous uniform airflow. Phys. Rev. Fluids 10, 024304. Feb 25, 2025. 

https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.10.024304  

Also: droplet, instability, vortex, behav, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, droplet, instability, vortex, behavior

# gst: emergent flocking in mixtures of antialigning self-propelled particles.

FIG. 4. (c) Mean field phase diagram with disorder (green triangles), polarized moving bands (blue circles), and polarized patches (orange squares).

AA << observe a flocking mechanism, the emergence of a state with global polar order, in mixed systems of self-propelled particles with purely antialigning interactions, i.e., the ground state for any pair of particles is to be opposedly oriented. In binary mixtures, (They) find that flocking can be realized by cross-species antialigning that is dominant compared to intraspecies antialignment. >>

<< While the key mechanism can be understood within a mean-field description, beyond mean-field (AA) develop an asymptotically exact Boltzmann-scattering theory from first principles.  This theory yields analytical predictions for the flocking transition and shows excellent quantitative agreement with simulations of dilute systems. For large systems, (They) find either microphase separation or static patterns with patches or stripes that carry different polarization orientations. >>️

Rüdiger Kürsten, Jakob Mihatsch, Thomas Ihle. Emergent flocking in mixtures of antialigning self-propelled particles. Phys. Rev. E 111, L023402. Feb 21, 2025.

https://journals.aps.org/pre/abstract/10.1103/PhysRevE.111.L023402

Also: particle, flock, flocking, swarm, order, disorder, transition, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, particles, self-propelled particles, flock, flocking, swarm, order, disorder, transitions