Is it possible for a free particle to spontaneously start spinning around a point without anything in the center of its path? The answer is yes.

Researchers at the Langevin Institute have just shown that a drop bouncing on a vertically vibrating liquid bath could remain captive to the waves it emitted during these successive bounces on the bath’s surface (see video). As in a kind of wave ballet, the drops first become walkers, propelled on the surface of the bath by the waves they emitted during their previous bounces. Then, spontaneously, they start to turn according to well-defined orbits, maintained in this perpetual movement by their past waves. It is in a way a “wave memory” that maintains them. The spontaneous emergence of a “spin” originates from the presence of a time-varying medium, the vibrating bath, which allows the emitted waves to be turned back in time and refocused on the source that initially produced them. Time-varying media are fascinating because they allow a source to be given a spatio-temporal non-locality, or more simply, to be clothed with a constantly changing past that determines its future.

Bernard-Bernardet, S., Fleury, M., & Fort, E. (2022). Spontaneous emergence of a spin state for an emitter in a time-varying medium. The European Physical Journal Plus, 137(4), 1-8.

Abstract : The back-reaction of a radiated wave on the emitting source is a general problem. In the most general case, back-reaction on moving wave sources depends on their whole history. Here we study a model system in which a pointlike source is piloted by its own memory-endowed wave field. Such a situation is implemented experimentally using a self-propelled droplet bouncing on a vertically vibrated liquid bath and driven by the waves it generates along its trajectory. The droplet and its associated wave field form an entity having an intrinsic dual particle-wave character. The wave field encodes in its interference structure the past trajectory of the droplet. In the present article we show that this object can self-organize into a spinning state in which the droplet possesses an orbiting motion without any external interaction. The rotation is driven by the wave-mediated attractive interaction of the droplet with its own past. The resulting “memory force” is investigated and characterized experimentally, numerically, and theoretically. Orbiting with a radius of curvature close to half a wavelength is shown to be a memory-induced dynamical attractor for the droplet’s motion.

Labousse, M., Perrard, S., Couder, Y., & Fort, E. (2016). Self-attraction into spinning eigenstates of a mobile wave source by its emission back-reaction. Physical Review E, 94(4), 042224.

Available on ResearchGate (Free login required)

Perrard, S., Fort, E., & Couder, Y. (2016). Wave-Based Turing Machine: Time Reversal and Information Erasing. Physical Review Letters, 117(9), 094502.

ABSTRACT

The investigation of dynamical systems has revealed a deep-rooted difference between waves and objects regarding temporal reversibility and particlelike objects. In nondissipative chaos, the dynamic of waves always remains time reversible, unlike that of particles. Here, we explore the dynamics of a wave-particle entity. It consists in a drop bouncing on a vibrated liquid bath, self-propelled and piloted by the surface waves it generates. This walker, in which there is an information exchange between the particle and the wave, can be analyzed in terms of a Turing machine with waves as the information repository. The experiments reveal that in this system, the drop can read information backwards while erasing it. The drop can thus backtrack on its previous trajectory. A transient temporal reversibility, restricted to the drop motion, is obtained in spite of the system being both dissipative and chaotic.

Available at Researchgate (requires free login)

https://www.researchgate.net/publication/307082497_Wave-Based_Turing_Machine_Time_Reversal_and_Information_Erasing

Bacot, V., Labousse, M., Eddi, A., Fink, M., & Fort, E. (2015). Revisiting time reversal and holography with spacetime transformations. arXiv preprint arXiv:1510.01277.

Wave control is usually performed by spatially engineering the properties of a medium. Because time and space play similar roles in wave propagation, manipulating time boundaries provides a complementary approach. Here, we experimentally demonstrate the relevance of this concept by introducing instantaneous time mirrors. We show with water waves that a sudden change of the effective gravity generates time-reversed waves that refocus at the source. We generalize this concept for all kinds of waves introducing a universal framework which explains the effect of any time disruption on wave propagation. We show that sudden changes of the medium properties generate instant wave sources that emerge instantaneously from the entire space at the time disruption. The time-reversed waves originate from these “Cauchy sources” which are the counterpart of Huygens virtual sources on a time boundary. It allows us to revisit the holographic method and introduce a new approach for wave control.

http://arxiv.org/ftp/arxiv/papers/1510/1510.01277.pdf

Borghesi, C., Moukhtar, J., Labousse, M., Eddi, A., Fort, E., & Couder, Y. (2014). Interaction of two walkers: Wave-mediated energy and force. Physical Review E, 90(6), 063017.

A bouncing droplet, self-propelled by its interaction with the waves it generates, forms a classical wave-particle association called a “walker.” Previous works have demonstrated that the dynamics of a single walker is driven by its global surface wave field that retains information on its past trajectory. Here, we investigate the energy stored in this wave field for two coupled walkers and how it conveys an interaction between them. For this purpose, we characterize experimentally the “promenade modes” where two walkers are bound, and propagate together. Their possible binding distances take discrete values, and the velocity of the pair depends on their mutual binding. The mean parallel motion can be either rectilinear or oscillating. The experimental results are recovered analytically with a simple theoretical framework. A relation between the kinetic energy of the droplets and the total energy of the standing waves is established.

http://arxiv.org/pdf/1412.7701.pdf

Labousse, M., Perrard, S., Couder, Y., & Fort, E. (2014). Build-up of macroscopic eigenstates in a memory-based constrained system. New Journal of Physics, 16(11), 113027.

A bouncing drop and its associated accompanying wave forms a walker. Based on previous works, we show in this article that it is possible to formulate a simple theoretical framework for the walker dynamics. It relies on a time scale decomposition corresponding to the effects successively generated when the memory effects increase. While the short time scale effect is simply responsible for the walkerʼs propulsion, the intermediate scale generates spontaneously pivotal structures endowed with angular momentum. At an even larger memory
scale, if the walker is spatially confined, the pivots become the building blocks of a self-organization into a global structure. This new theoretical framework is applied in the presence of an external harmonic potential, and reveals the underlying mechanisms leading to the emergence of the macroscopic spatial organization reported by Perrard et al (2014 Nature Commun. 5 3219).

https://hal-univ-artois.archives-ouvertes.fr/hal-01084731/document

Perrard, S., Labousse, M., Fort, E., & Couder, Y. (2014). Chaos driven by interfering memory. Physical review letters, 113(10), 104101.

The transmission of information can couple two entities of very different nature, one of them serving as a memory for the other. Here we study the situation in which information is stored in a wave field and serves as a memory that pilots the dynamics of a particle. Such a system can be implemented by a bouncing drop generating surface waves sustained by a parametric forcing. The motion of the resulting “walker” when confined in a harmonic potential well is generally disordered. Here we show that these trajectories correspond to chaotic regimes characterized by intermittent transitions between a discrete set of states. At any given time, the system is in one of these states characterized by a double quantization of size and angular momentum. A low dimensional intermittency determines their respective probabilities. They thus form an eigenstate basis of decomposition for what would be observed as a superposition of states if all measurements were intrusive

https://hal.archives-ouvertes.fr/hal-01061415/document

Perrard, S., Labousse, M., Miskin, M., Fort, E., & Couder, Y. (2014). Self-organization into quantized eigenstates of a classical wave-driven particle.Nature communications, 5.

A growing number of dynamical situations involve the coupling of particles or singularities with physical waves. In principle these situations are very far from the wave particle duality at quantum scale where the wave is probabilistic by nature. Yet some dual characteristics were observed in a system where a macroscopic droplet is guided by a pilot wave it generates. Here we investigate the behaviour of these entities when confined in a two-dimensional harmonic potential well. A discrete set of stable orbits is observed, in the shape of successive generalized Cassinian-like curves (circles, ovals, lemniscates, trefoils and so on). Along these specific trajectories, the droplet motion is characterized by a double quantization of the orbit spatial extent and of the angular momentum. We show that these trajectories are intertwined with the dynamical build-up of central wave-field modes. These dual self-organized modes form a basis of eigenstates on which more complex motions are naturally decomposed.

http://www.nature.com/ncomms/2014/140130/ncomms4219/full/ncomms4219.html

http://arxiv.org/ftp/arxiv/papers/1402/1402.1423.pdf

Quantization of trajectories of a dotwave in a harmonic potential

Perrard, S., Labousse, M., Miskin, M., Fort, E., & Couder, Y. Effets de quantification d’une association onde-particule soumise à une force centrale.Résumés des exposés de la 16e Rencontre du Non-Linéaire Paris 2013, 68.

http://nonlineaire.univ-lille1.fr/SNL/media/2012/CR/Perrard.pdf

eigenstates in circular cavity

Harris, D. M., Moukhtar, J., Fort, E., Couder, Y., & Bush, J. W. (2013). Wavelike statistics from pilot-wave dynamics in a circular corral. Physical Review E, 88(1), 011001.

Abstract : Bouncing droplets can self-propel laterally along the surface of a vibrated fluid bath by virtue of a resonant interaction with their own wave field. The resulting walking droplets exhibit features reminiscent of microscopic quantum particles. Here we present the results of an experimental investigation of droplets walking in a circular corral. We demonstrate that a coherent wavelike statistical behavior emerges from the complex underlying dynamics and that the probability distribution is prescribed by the Faraday wave mode of the corral. The statistical behavior of the walking droplets is demonstrated to be analogous to that of electrons in quantum corrals.

http://math.mit.edu/~bush/wordpress/wp-content/uploads/2013/07/Harris-Corrals-2013.pdf

Statistical behavior of a walking droplet in a confined geometry

Eddi, A., Decelle, A., Fort, E., & Couder, Y. (2009). Archimedean lattices in the bound states of wave interacting particles. EPL (Europhysics Letters), 87(5), 56002.

http://stilton.tnw.utwente.nl/people/eddi/Papers/epl_Cristaux.pdf

Cristal lattices of bouncing droplets

Fort, E., Eddi, A., Boudaoud, A., Moukhtar, J., & Couder, Y. (2010). Path-memory induced quantization of classical orbits. Proceedings of the National Academy of Sciences, 107(41), 17515-17520.

http://stilton.tnw.utwente.nl/people/eddi/Papers/PNAS_2010.pdf

Rotating bath

Quantization of trajectories

“L’organisation du manuscrit est la suivante : dans le premier chapitre, nous rappelons les premieres experiences realisees avec les gouttes rebondissantes, en particulier les regimes ou elles sont statiques. Nous presentons egalement l’instabilite de Faraday qui permet d’expliquer le couplage entre goutte et ondes a l’origine des marcheurs. Leurs proprietes sont discutees, en particulier dans le cas des experiences de diraction. Dans un second chapitre, nous presentons le montage experimental ainsi que l’ensemble des techniques de mesure utilisees. Le troisieme chapitre est dedie a l’etude d’un analogue de l’eet tunnel pour les marcheurs. Le quatrieme est consacre a l’etude des ondes de surface generees par un marcheur, en particulier le lien avec l’instabilite de Faraday a l’origine de la memoire de chemin. Enfin, dans le chapitre cinq, nous analysons la nature des trajectoires circulaires d’un marcheur soumis a une force orthogonale au mouvement. L’in uence de la memoire de chemin sur la quantication des rayons est presentee en detail, pour comprendre comment cet analogue macroscopique des niveaux de Landau se met en place avec des marcheurs.”

Eddi, A. (2011). Marcheurs, Dualité onde-particule et Mémoire de chemin (Doctoral dissertation, Université Paris-Diderot-Paris VII).

http://tel.archives-ouvertes.fr/docs/00/57/56/26/PDF/these_A_Eddi.pdf

Eddi, A., Moukhtar, J., Perrard, S., Fort, E., & Couder, Y. (2012). Level Splitting at Macroscopic Scale. Physical Review Letters, 108(26), 264503.

http://stilton.tnw.utwente.nl/people/eddi/Papers/PhysRevLett_Zeeman.pdf

Couder, Y., Fort, E., Gautier, C. H., & Boudaoud, A. (2005). From bouncing to floating: Noncoalescence of drops on a fluid bath. Physical review letters,94(17), 177801.

http://www.lps.ens.fr/~boudaoud/Publis/Couder05Bounc.pdf

Couder, Y., Boudaoud, A., Protière, S., & Fort, E. (2007). Les gouttes marcheuses-Une forme de dualité onde-particule à échelle macroscopique?.Reflets de la physique, (5), 20-24.

http://www.refletsdelaphysique.fr/articles/refdp/pdf/2007/03/refdp20075p20.pdf

Couder, Y., & Fort, E. (2012, May). Probabilities and trajectories in a classical wave-particle duality. In Journal of Physics: Conference Series (Vol. 361, No. 1, p. 012001). IOP Publishing.

http://iopscience.iop.org/1742-6596/361/1/012001/pdf/1742-6596_361_1_012001.pdf

Eddi, A., Sultan, E., Moukhtar, J., Fort, E., Rossi, M., & Couder, Y. (2011). Information stored in faraday waves: the origin of a path memory. Journal of Fluid Mechanics, 674, 433.

http://stilton.tnw.utwente.nl/people/eddi/Papers/Walker_JFM.pdf

Eddi, A., Fort, E., Moisy, F., & Couder, Y. (2009). Unpredictable tunneling of a classical wave-particle association. Physical review letters, 102(24), 240401.

http://www.fast.u-psud.fr/~moisy/papers/eddi_prl09.pdf

Couder, Y., Fort, E., Gautier, C. H., & Boudaoud, A. (2005). From bouncing to floating: noncoalescence of drops on a fluid bath. Physical review letters,94(17), 177801..

http://www.lps.ens.fr/~boudaoud/Publis/Couder05Bounc.pdf