Ultracold quantum gases offer a controllable and microscopically accessible platform for understanding and engineering superfluidity. Yet, realizing a superleak that selectively transports the superfluid while suppressing normal flow has remained elusive. Here, we harness an optical superlattice to realize such a superleak through dynamical selectivity. The superfluid undergoes coherent Josephson transport, whereas the normal component exhibits slow, thermodynamically limited response, resulting in a flow-rate contrast of 500(49). Exploiting this contrast, we demonstrate repeated filtering of the normal component and dynamical purification of the superfluid, while sustaining coherent driven oscillations for up to 100 cycles. Our results establish a controllable atomic superleak and open possibilities for manipulating transport and thermodynamics in quantum fluids.
AI Summary
The paper asks whether an ultracold gas can implement a superleak: transport that preferentially passes the superfluid component while suppressing normal flow. It realizes a dynamical version using $^{87}$Rb gases in an optical superlattice, forming approximately 30 coupled quasi-two-dimensional layers. Ramping the energy offset between alternating sites transfers the coherent component through Josephson transport, while normal redistribution is limited by slow cross-dimensional thermalization.
Site-resolved band mapping and bimodal momentum-distribution fits distinguish the two components. Mixed samples show fast and slow transport stages, with a reported rate contrast of $500(49)$, reaching $5791(601)$ at the largest tunneling strength studied. Phase-sensitive measurements show coupled population–phase oscillations. Superfluid transport curves collapse versus $Jt/h$, whereas normal transport follows a thermalization-related scaling; Gross–Pitaevskii simulations and a thermalization-limited transport model reproduce the measured dynamics. Normal atoms can rapidly tunnel into initially empty wells, establishing that the selectivity depends on the initial thermodynamic configuration rather than blocked single-particle tunneling.
Combining transport with selective removal from the less-populated sites raises the condensate fraction from approximately $50\%$ to $94(1)\%$ after four cycles, retaining $57\%$ of the initial superfluid. Repeated purification maintains driven coherent oscillations for over 100 cycles. The filtering is time-window-dependent, not a stationary impermeable barrier for normal atoms. Finite-temperature removal has imperfect site selectivity and causes superfluid loss; during the prolonged driven experiment, the total atom number falls to approximately $10\%$ of its initial value.
Little sign of AI-generated textOverclaims
Error found: The normal-transport model predicts nonzero current at its own stated equilibrium because its Bose distributions omit the energy-reference adjustment required by μ_o + Δ = μ_e.
Written by gpt-6.1-sol from the paper's full text. Automated: it can be wrong.
Ultracold quantum gases offer a controllable and microscopically accessible platform for understanding and engineering superfluidity. Yet, realizing a superleak that selectively transports the superfluid while suppressing normal flow has remained elusive. Here, we harness an optical superlattice to realize such a superleak through dynamical selectivity. The superfluid undergoes coherent Josephson transport, whereas the normal component exhibits slow, thermodynamically limited response, resulting in a flow-rate contrast of 500(49). Exploiting this contrast, we demonstrate repeated filtering of the normal component and dynamical purification of the superfluid, while sustaining coherent driven oscillations for up to 100 cycles. Our results establish a controllable atomic superleak and open possibilities for manipulating transport and thermodynamics in quantum fluids.
The paper asks whether an ultracold gas can implement a superleak: transport that preferentially passes the superfluid component while suppressing normal flow. It realizes a dynamical version using 87Rb gases in an optical superlattice, forming approximately 30 coupled quasi-two-dimensional layers. Ramping the energy offset between alternating sites transfers the coherent component through Josephson transport, while normal redistribution is limited by slow cross-dimensional thermalization.
Site-resolved band mapping and bimodal momentum-distribution fits distinguish the two components. Mixed samples show fast and slow transport stages, with a reported rate contrast of 500(49), reaching 5791(601) at the largest tunneling strength studied. Phase-sensitive measurements show coupled population–phase oscillations. Superfluid transport curves collapse versus Jt/h, whereas normal transport follows a thermalization-related scaling; Gross–Pitaevskii simulations and a thermalization-limited transport model reproduce the measured dynamics. Normal atoms can rapidly tunnel into initially empty wells, establishing that the selectivity depends on the initial thermodynamic configuration rather than blocked single-particle tunneling.
Combining transport with selective removal from the less-populated sites raises the condensate fraction from approximately 50% to 94(1)% after four cycles, retaining 57% of the initial superfluid. Repeated purification maintains driven coherent oscillations for over 100 cycles. The filtering is time-window-dependent, not a stationary impermeable barrier for normal atoms. Finite-temperature removal has imperfect site selectivity and causes superfluid loss; during the prolonged driven experiment, the total atom number falls to approximately 10% of its initial value.
Ultracold fermionic atomic gas with Bardeen-Cooper-Schrieffer pairing between hyperfine states is studied. It is shown that a $\ensuremath{\pi}$-Josephson contact [superfluid--normal-gas--superfluid (S∕N∕S)] can be realized in systems where the left and right banks S are superfluids and the weak link N is a normal gas with the finite mismatch in chemical potentials ${\ensuremath{\delta}}_{{\ensuremath{\mu}}_{N}}\ensuremath{\ne}0$. If such a $\ensuremath{\pi}$-junction is part of a closed superfluid ring the superfluid mass-current flows spontaneously---the ultracold atomic $\ensuremath{\pi}$--superconducting quantum interference device ($\ensuremath{\pi}$-SQUID). This situation is realized if the radius of the ring R is larger than the critical one Rc. The same effect will be realized also for ${\ensuremath{\delta}}_{{\ensuremath{\mu}}_{N}}⪢\ensuremath{\Delta}$, where $\ensuremath{\Delta}$ is the superfluid gap in S. The sensitivity of the $\ensuremath{\pi}$-SQUID to inertial effects is discussed in the case of rotational motion.
In this thesis, I present experiments on making and probing strongly correlated gases of ultracold atoms in an optical lattice with engineered potentials and dynamics. The quantum gas microscope first developed in our lab enables single-site resolution imaging and manipulation of atoms in a two-dimensional lattice, offering an ideal platform for quantum simulation of condensed matter systems. Here we demonstrate our abilities to generate optical potential with high precision and high resolution, and engineer coherent dynamics using photon assisted tunneling. We also create a system of bilayer quantum gases that brings new imaging capabilities and extends the possible range of our quantum simulation.
Ultracold atoms in optical lattices provide an extremely clean and controllable setting to explore quantum many-body phases of matter. Here we give a brief review of the strong-correlation physics that has been realized using such ultracold atoms in optical lattices ranging from the realization of Hubbard models to studies of quantum magnetism and the detection of single atoms with lattice site resolution. All this has opened up fundamentally new opportunities for the investigation of quantum many-body systems. Introduction Over the past years, ultracold atoms in optical lattices have emerged as versatile new systems to explore the physics of quantum many-body systems. On the one hand, they can be helpful in gaining a better understanding of known phases of matter and their dynamical behavior; on the other hand, they allow one to realize completely novel quantum systems that have not been studied before in nature [1, 2, 3]. Commonly, the approach of exploring quantum many-body systems in such a way is referred to as “quantum simulations.” Examples of some of the first strongly interacting many-body phases that have been realized both in lattices and in the continuum include the quantum phase transition from a superfluid to a Mott insulator [4, 5, 6], fermionic Mott insulators [7, 8], the achievement of a Tonks- Girardeau gas [9, 10], and the realization of the Bose-Einsten condensate (BEC)– Bardeen-Cooper-Schrieffer (BCS) crossover (see also Chapter 12) in Fermi gas mixture [11] using Feshbach resonances [12]. In almost all of these experiments, detection was limited to time-of-flight imaging or more refined derived techniques that mainly characterized the momentum distribution of the quantum gas [2]. For several years, researchers in the field have therefore aspired to employ in situ single-particle detection methods for the analysis of ultracold quantum gases. Only recently has it become possible to implement such imaging techniques, marking a milestone for the characterization and manipulation of ultracold quantum gases [13, 14, 15, 16, 17]. In our discussion, we will focus on one of the most successful of these techniques based on high-resolution fluorescence imaging. Despite being a rather new technique, such quantum gas microscopy has already proven to be an enabling technology for probing and manipulating quantum many-body systems. For the first time, controllable and strongly interacting many-body systems, as realized with ultracold atoms, could be observed on a local scale [17, 16].
In this habilitation-thesis a collection of 14 experiments is presented. In these experiments we have developed and used novel techniques to control ultracold gases on the quantum level. In brief, Bose-Einstein condensates (BEC) and degenerate Fermi gases of laser-cooled alkali atoms are subjected to specially designed optical and magnetic fields. The fields influence in a coherent way the behavior, properties and dynamics of the gases. On this basis we developed tools to prepare, coherently manipulate, and analyze pre-defined quantum states. With this high level of control, it was possible to investigate interesting physics phenomena, and we were able to achieve several breakthroughs in the field of ultracold atoms. Highlights of our experimental results include the demonstration of phase engineering of a BEC wavefunction where we created solitons in a BEC and studied their propagation. In another experiment we constructed a spatially resolved matter wave interferometer with which we mapped out the phase distribution on a condensate. Illuminating the BEC with a periodic pattern, i.e. an optical lattice, allowed us to study solid states physics phenomena. In a second set of experiments we demonstrated optically tuning of the interaction between atoms with optical Feshbach resonances. Employing either magnetically tunable Feshbach resonances or laser radiation, we were able to produce ground state molecules in well defined quantum states. This led to the production of the first molecular BEC. By tuning the coupling of atom pairs in a Fermi gas of atoms, we could for the first time investigate the so-called BEC-BCS crossover which describes the continuous change from a BEC superfluid to a Bardeen-Cooper Schrieffer (BCS) superfluid. Due to the excellent control on the quantum level, the developed cold atom techniques open up intriguing prospects for future applications and experiments. They represent a general tool box to investigate fundamental physical phenomena in a pure and undisturbed environment. In the future, cold atoms might serve as a testing ground for fundamental theories or as quantum simulators for complex systems.
Domain walls are carriers of spin transport whose controlled manipulation underlies a wide range of spintronic and information-processing technologies. Here we demonstrate tunable domain-wall transport in a weakly interacting nondegenerate ultracold Bose gas. We initialize a three-domain pseudo-spin-1/2 texture and observe spontaneous propagation of long-lived domain walls driven by exchange-mediated spin currents. By varying the orientation of the spin domains, we control the balance of spin currents across the walls and thereby tune their trajectories, including reversals of the initial direction of motion. Measurements reveal a crossover from an exchange-stabilized regime, in which coherent spin-exchange collisions suppress wall motion, to a diffusion-dominated regime characterized by rapid transport at thermal velocities. Numerical solutions of a quantum Boltzmann equation reproduce the observed dynamics and identify transverse phase gradients as an important control parameter governing domain-wall propagation. These results establish coherence and phase engineering as tools for programming spin transport in ultracold gases and provide a route toward controllable domain-wall dynamics in atomtronic systems.
We analyze theoretically the transport properties of a weakly interacting ultracold Bose gas enclosed in two reservoirs connected by a constriction. We assume that the transport of the superfluid part is hydrodynamic, and we describe the ballistic transport of the normal part using the Landauer-Büttiker formalism. Modeling the coupled evolution of the phase, atom number, and temperature mismatches between the reservoirs, we predict that Helmholtz (plasma) oscillations can be observed at nonzero temperatures below Tc. We show that, because of its strong compressibility, the Bose gas is characterized by a fast thermalization compared to the damping time for plasma oscillations, accompanied by a fast transfer of the normal component. This fast thermalization also affects the gas above Tc, where we present a comparison to the ideal fermionic case. Moreover, we outline the possible realization of a superleak through the inclusion of a disordered potential.