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Register a new userCoherent and dissipative transport in a Josephson junction between fermionic superfluids of $^6$Li atoms
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Quantum systems out of equilibrium offer the possibility of understanding intriguing and challenging problems in modern physics. Studying transport properties is not only valuable to unveil fundamental properties of quantum matter but it is also an excellent tool for developing new quantum devices which inherently employ quantum-mechanical effects. In this contribution, we present our experimental studies on quantum transport using ultracold Fermi gases of $^6$Li atoms. We realize the analogous of a Josephson junction by bisecting fermionic superfluids by a thin optical barrier. We observe coherent dynamics in both the population and in the relative phase between the two reservoirs. For critical parameters, the superfluid dynamics exhibits both coherent and resistive flow due to phase-slippage events manifesting as vortices propagating into the bulk. We uncover also a regime of strong dissipation where the junction operation is irreversibly affected by vortex proliferation. Our studies open new directions for investigating dissipation and superfluid transport in strongly correlated fermionic systems.
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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 BEC-BCS 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-equlibrium quantum systems.
We report an experimental study of peak and phase-space density of a two-stage magneto-optical trap (MOT) of 6-Li atoms, which exploits the narrower $2S_{1/2}rightarrow 3P_{3/2}$ ultra-violet (UV) transition at 323 nm following trapping and cooling on the more common D2 transition at 671 nm. The UV MOT is loaded from a red MOT and is compressed to give a high phase-space density up to $3times 10^{-4}$. Temperatures as low as 33 $mu$K are achieved on the UV transition. We study the density limiting factors and in particular find a value for the light-assisted collisional loss coefficient of $1.3 pm0.4times10^{-10},textrm{cm}^3/textrm{s}$ for low repumping intensity.
Coherent transport by adiabatic passage has recently been suggested as a high-fidelity technique to engineer the centre-of-mass state of single atoms in inhomogenous environments. While the basic theory behind this process is well understood, several conceptual challenges for its experimental observation have still to be addressed. One of these is the difficulty that currently available optical or magnetic micro-trap systems have in adjusting the tunneling rate time-dependently while keeping resonance between the asymptotic trapping states at all times. Here we suggest that both requirements can be fulfilled to a very high degree in an experimentally realistic setup based on radio frequency traps on atom chips. We show that operations with close to 100% fidelity can be achieved and that these systems also allow significant improvements for performing adiabatic passage with interacting atomic clouds.
We present spectroscopic measurements of seven vibrational levels $v=29-35$ of the $A(1^1Sigma_u^+)$ excited state of Li$_2$ molecules by the photoassociation of a degenerate Fermi gas of $^6$Li atoms. The absolute uncertainty of our measurements is $pm 0.00002$ cm$^{-1}$ ($pm 600$ kHz) and we use these new data to further refine an analytic potential for this state. This work provides high accuracy photo-association resonance locations essential for the eventual high resolution mapping of the $X(1^1Sigma_g^+)$ state enabling further improvements to the s-wave scattering length determination of Li and enabling the eventual creation of ultra-cold ground state $^6$Li$_2$ molecules.
We investigate the dipole mediated transport of Rydberg impurities through an ultracold gas of atoms excited to an auxiliary Rydberg state. In one experiment we continuously probe the system by coupling the auxiliary Rydberg state to a rapidly decaying state which realizes a dissipative medium. In-situ imaging of the impurities reveals diffusive spreading controlled by the intensity of the probe laser. By preparing the same density of hopping partners but then switching off the dressing fields the spreading is effectively frozen. This is consistent with numerical simulations which indicate the coherently evolving system enters a non-ergodic extended phase due to disorder. This opens the way to study transport and localization phenomena in systems with long-range hopping and controllable dissipation.
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