Crossing Over from Attractive to Repulsive Interactions in a Tunneling Bosonic Josephson Junction

Abstract

We explore the interplay between tunneling and interatomic interactions in the dynamics of a bosonic Josephson junction. We tune the scattering length of an atomic 39 K Bose-Einstein condensate confined in a double-well trap to investigate regimes inaccessible to other superconducting or superfluid systems. In the limit of small-amplitude oscillations, we study the transition from Rabi to plasma oscillations by crossing over from attractive to repulsive interatomic interactions. We observe a critical slowing down in the oscillation frequency by increasing the strength of an attractive interaction up to the point of a quantum phase transition. With sufficiently large initial oscillation amplitude and repulsive interactions the system enters the macroscopic quantum self-trapping regime, where we observe coherent undamped oscillations with a self-sustained average imbalance of the relative well population. The exquisite agreement between theory and experiments enables the observation of a broad range of many body coherent dynamical regimes driven by tunable tunneling energy, interactions and external forces, with applications spanning from atomtronics to quantum metrology.

Collective excitations and tunneling dynamics in long bosonic Josephson junctions

“…In order to understand the origin of this degeneracy we look into the distribution of the tunneling current initiated by these excitations. The transverse tunneling current density can be written in the following form Inserting here the wave function (12,13) we get…”

“…These effects have been initially studied for coupled condensates in double-well traps [1][2][3][4][5][6] and coherently coupled spinor condensates [7,8]. In recent years Josephson effects were also observed and analyzed in more exotic systems such as fermionic superfluids [9], polariton condensates [10], spin-orbit coupled BECs [11,12] and condensates with attractive interaction [13].…”

Critical Transport and Vortex Dynamics in a Thin Atomic Josephson Junction

“…The coherent dynamics of atomic Josephson junctions (JJs) [10][11][12][13][14][15][16][17][18][19][20] is governed by the competition between the charging energy E C and the Josephson tunneling energy E J [10,11]. E C relates the chemical potential difference across the tunnelling barrier to the relative population imbalance between the reservoirs, and depends on interparticle interactions.…”

“…Dynamics in the T = 0 limit are simulated via the time-dependent Gross-Pitaevskii equation (GPE), extended to non-zero temperatures T 0.4 T c (where T c is the BEC critical temperature), via its coupling to a collisionless Boltzmann equation [3,37,38]. We stress that the standard twomode model [10,13] that captures both Josephson and MQST dynamics of previous experiments [16,18] is out of its validity range due to the considered values of the ratio V 0 /µ and to the thinness of the junctions [38]. Although dissipative effects can be phenomenologically modeled by damped two-mode [21,35,36] and RSJ-circuital models [7], such approaches provide limited insight into the microscopic dissipative processes.…”

Many-body quantum dynamics of an asymmetric bosonic Josephson junction

“…BJJ dynamics has been studied quite thoroughly both theoretically and experimentally [9-13, 19, 22, 29, 32-50]. Several features like Josephson oscillations [9,10,19,22,34,[44][45][46], collapse and revival cycles [11], self trapping (suppression of tunneling) [9-11, 22, 34, 44], etc have been predicted using a two-mode theory and later experimentally observed [10]. Recently, BJJ dynamics has also been studied by an in-principle numerically-exact many-body theory [47][48][49].…”