Current production in ring condensates with a weak link

We consider attractive and repulsive condensates in a ring trap stirred by a weak link, and analyze the spectrum of solitonic trains dragged by the link, by means of analytical expressions for the wave functions, energies and currents. The precise evolution of current production and destruction in terms of defect formation in the ring and in terms of stirring is studied. We find that any excited state can be coupled to the ground state through two proposed methods: either by adiabatically tuning the link's strength and velocity through precise cycles which avoid the critical velocities and thus unstable regions, or by keeping the link still while setting an auxiliary potential and imprinting a nonlinear phase as the potential is turned off. We also analyze hysteresis cycles through the spectrum of energies and currents.Comment: 10 pages, 6 figure

Coherent phase slips in coupled matter-wave circuits

Quantum phase slips are a dual process of particle tunneling in coherent networks. Besides being of central interest to condensed matter physics, quantum phase slips are resources that are sought to be manipulated in quantum circuits. Here, we devise a specific matter-wave circuit enlightening quantum phase slips. Specifically, we investigate the quantum many-body dynamics of two side-by-side ring-shaped neutral bosonic systems coupled through a weak link. By imparting a suitable magnetic flux, persistent currents flow in each ring with given winding numbers. We demonstrate that coherent phase slips occur as winding number transfer among the two rings, with the populations in each ring remaining nearly constant. Such a phenomenon occurs as a result of a specific entanglement of circulating states, that, as such, cannot be captured by a mean-field treatment of the system. Our work can be relevant for the observation of quantum phase slips in cold-atom experiments and their manipulation in matter-wave circuits. To make contact with the field, we show that the phenomenon has clear signatures in the momentum distribution of the system providing the time-of-flight image of the condensate.We thank G. Catelani and W. Jordan Chetcuti for discussion. A.P.-O. acknowledges financial support from Secretaria d'Universitats i Recerca del Departament d'Empresa i Coneixement de la Generalitat de Catalunya cofunded by the European Union Regional Development Fund within the ERDF Operational Program of Catalunya (project QuantumCat, Ref. No. 001-P-001644).Peer ReviewedPostprint (published version

Coherent phase slips in coupled matter-wave circuits

Quantum phase slips are a dual process of particle tunneling in coherent networks. Besides being of central interest to condensed matter physics, quantum phase slips are resources that are sought to be manipulated in quantum circuits. Here, we devise a specific matter-wave circuit enlightening quantum phase slips. Specifically, we investigate the quantum many-body dynamics of two side-by-side ring-shaped neutral bosonic systems coupled through a weak link. By imparting a suitable magnetic flux, persistent currents flow in each ring with given winding numbers. We demonstrate that coherent phase slips occur as winding number transfer among the two rings, with the populations in each ring remaining nearly constant. Such a phenomenon occurs as a result of a specific entanglement of circulating states, that, as such, cannot be captured by a mean-field treatment of the system. Our work can be relevant for the observation of quantum phase slips in cold-atom experiments and their manipulation in matter-wave circuits. To make contact with the field, we show that the phenomenon has clear signatures in the momentum distribution of the system providing the time-of-flight image of the condensate.We thank G. Catelani and W. Jordan Chetcuti for discussion. A.P.-O. acknowledges financial support from Secretaria d'Universitats i Recerca del Departament d'Empresa i Coneixement de la Generalitat de Catalunya cofunded by the European Union Regional Development Fund within the ERDF Operational Program of Catalunya (project QuantumCat, Ref. No. 001-P-001644).Peer ReviewedPostprint (published version

Current constraints on the EFT for the \Lambda N --> N N transition

The relation between the low energy constants appearing in the effective field theory description of the \Lambda N --> N N transition potential and the parameters of the one-meson-exchange model previously developed are obtained. We extract the relative importance of the different exchange mechanisms included in the meson picture by means of a comparison to the corresponding operational structures appearing in the effective approach. The ability of this procedure to obtain the weak baryon-baryon-meson couplings for a possible scalar exchange is also discussed.Comment: 10 pages, 6 figure

Non-mesonic weak decay of hypernuclei in effective field theory

[cat] En aquesta tesi hem descrit la interacció feble LambdaN->NN, la qual és la principal responsable de la desintegració d’hipernuclis pesats, en el marc de teories efectives de camps. La teoria efectiva de camps (EFT) s’ha desenvolupat fins a segon ordre en “q”, on “q” és el moment transferit entre els barions interactuants. En particular s’han calculat tots els diagrames d’intercanvi de dos pions que apareixen al segon ordre en l’expansió de moments. Els valors numèrics de les constants de baixa energia s’han obtingut de dues maneres. Primer,s’ha fet un ajust als observables de desintegració hipernuclear per a tres hipernuclis lleugers, 5-lambda/He,11-lambda/B i 12-lambda/C. Per una banda, aquest càlcul ha involucrat la EFT a primer ordre per a la transició feble LambdaN->NN, i per l’altra, una descripció adequada dels estats nuclears inicials i finals en un formalisme de molts cossos. Segon, la EFT s’ha comparat al model d’intercanvi d’un mesó que descriu la mateixa interacció. Expandint els potencials d’intercanvi d’un mesó en potències de moment, les constants de baixa energia que apareixen en la EFT s’han escrit en termes dels paràmetres dels mesons pesats. Per tal d’obtenir una descripció de la desintegració feble d’hipernuclis menys depenent de model s’ha estudiat la desintegració de l’hipernucli més lleuger, l’hipertritó, el qual pot ser descrit en el marc de teoria efectiva de camps tan en el sector feble com en el sector fort. En aquest cas, les constants de baixa energia no s’han pogut ajustar a observables hipernuclears degut a la manca de dades experimentals per a la desintegració feble de l’hipertritó. Alternativament, s’ha estudiat com el ritme de la desintegració feble de l’hipertritó depèn de les constants de baixa energia de primer ordre.[eng] In this thesis we have described the weak Lambda N to NN interaction, which is the main responsible for the decay of heavy hypernuclei, within the effective field theory (EFT) framework. The EFT is developed up to second order in “q”, where “q” is the transferred momentum between the interacting baryons. In particular, all the two-pion exchange diagrams entering at second order in the momentum expansion have been calculated. Numerical values for the leading order low-energy constants are obtained by two means. First, a fit to the hypernuclear decay observables for three light hypernuclei, 5-Lambda/He, 11-lLambda/B i 12/Lambda/C, has been performed. This calculation has involved a proper description of the initial and final nuclear states within a many-body formalism. Second, the EFT has been compared to the one-meson-exchange model describing the same interaction. By expanding the one-meson-exchange potentials in powers of momentum, the low energy constants appearing in the EFT description have been written in terms of the heavy meson parameters. In order to obtain a less model dependent description of the weak decay of hypernuclei we have studied the decay of the lightest hypernucleus, the hypertriton, which can be described within an effective field theory framework in both the strong and the weak sectors