Connecting Dissipation and Phase Slips in a Josephson Junction between Fermionic Superfluids

Abstract

We study the emergence of dissipation in an atomic Josephson junction between weakly coupled superfluid Fermi gases. We find that vortex-induced phase slippage is the dominant microscopic source of dissipation across the Bose-Einstein condensate-Bardeen-Cooper-Schrieffer crossover. We explore different dynamical regimes by tuning the bias chemical potential between the two superfluid reservoirs. For small excitations, we observe dissipation and phase coherence to coexist, with a resistive current followed by well-defined Josephson oscillations. We link the junction transport properties to the phase-slippage mechanism, finding that vortex nucleation is primarily responsible for the observed trends of conductance and critical current. For large excitations, we observe the irreversible loss of coherence between the two superfluids, and transport cannot be described only within an uncorrelated phase-slip picture. Our findings open new directions for investigating the interplay between dissipative and superfluid transport in strongly correlated Fermi systems, and general concepts in out-of-equilibrium quantum systems.

Collective dipole oscillations in a mixture of Bose and Fermi superfluids in the BCS–BEC crossover

“…The frequencies of Josephson oscillations calculated from the order-parameter equation is shown to be in agreement with the experimental data in the regimes from the BEC to the unitarity limit for small initial imbalance and barrier height [47]. For large initial imbalance, the phase slippage induced by vortex nucleation is found to be the dominant mechanism for emergent dissipations, which is also confirmed by the numerical simulations for the order-parameter equation [48]. However, the order-parameter equation is essentially a zero-temperature theory describing condensed fermion pairs without the fermionic degrees of freedom.…”

“…The order-parameter equation depending only on a single wave function for the condensed state has the computational advantage. Very recently, the order-parameter equation is used to interpret the experiments on Josephson effect between two fermionic superfluids [47,48]. The frequencies of Josephson oscillations calculated from the order-parameter equation is shown to be in agreement with the experimental data in the regimes from the BEC to the unitarity limit for small initial imbalance and barrier height [47].…”

Critical Transport and Vortex Dynamics in a Thin Atomic Josephson Junction

“…Similar effects have been studied in ringshaped bosonic condensates [26][27][28][29], mesoscopic structures [30,31] and lower-dimensional geometries [32][33][34]. While vortices crossing the weak link are known to yield a finite resistance [25,27,30], the relation between microscopic vortex nucleation, dynamics and macroscopic dissipative flow is still poorly understood.…”

Dynamical Thermalization of Interacting Fermionic Atoms in a Sinai Oscillator Trap

“…On the other side the Sinai-oscillator trap has been already experimentally realized with Bose-Einstein condensate of cold bosonic atoms [49][50][51]. At present cold atom techniques allow to investigate various properties of cold interacting fermionic atoms [52,53] and we argue that the investigation of dynamical thermalization of such fermionic atoms, e.g. 6 Li, in a Sinai-oscillator trap is now experimentally possible.…”

“…in the basis of oscillator eigenfunctions). The Fermi energy of the trap is then E F = (N a ω x ω y ω z ) 1/3 ≈ ωN a 1/3 [52,53]. Assuming that all these components have random amplitudes of a typical size 1/ √ we then obtain an estimate for a typical matrix element of two-body interaction between one-particle eigenstates U 2 ≈ α s ω/ 3/2 , α s = 4π(a s /a 0 ) , a 0 = /mω .…”