315 research outputs found
Cascade of Solitonic Excitations in a Superfluid Fermi gas: From Planar Solitons to Vortex Rings and Lines
We follow the time evolution of a superfluid Fermi gas of resonantly interacting [superscript 6]Li atoms after a phase imprint. Via tomographic imaging, we observe the formation of a planar dark soliton, its subsequent snaking, and its decay into a vortex ring, which, in turn, breaks to finally leave behind a single solitonic vortex. In intermediate stages, we find evidence for an exotic structure resembling the Φ soliton, a combination of a vortex ring and a vortex line. Direct imaging of the nodal surface reveals its undulation dynamics and its decay via the puncture of the initial soliton plane. The observed evolution of the nodal surface represents dynamics beyond superfluid hydrodynamics, calling for a microscopic description of unitary fermionic superfluids out of equilibrium.National Science Foundation (U.S.)United States. Army Research Office. Multidisciplinary University Research Initiative on AtomtronicsUnited States. Air Force Office of Scientific Research. Presidential Early Career Award for Scientists and EngineersUnited States. Air Force Office of Scientific Research. Multidisciplinary University Research Initiative on Exotic PhasesDavid & Lucile Packard Foundatio
Spin transport in polaronic and superfluid Fermi gases
We present measurements of spin transport in ultracold gases of fermionic 6Li in a mixture of two spin states at a Feshbach resonance. In particular, we study the spin-dipole mode, where the two spin components are displaced from each other against a harmonic restoring force. We prepare a highly imbalanced, or polaronic, spin mixture with a spin-dipole excitation and we observe strong, unitarity-limited damping of the spin-dipole mode. In gases with small spin imbalance, below the Pauli limit for superfluidity, we observe strongly damped spin flow even in the presence of a superfluid core. This indicates strong mutual friction between superfluid and polarized normal spins, possibly involving Andreev reflection at the superfluid–normal interface.National Science Foundation (U.S.)United States. Army Research Office (DARPA OLE program)David & Lucile Packard FoundationAlfred P. Sloan FoundationUnited States. Air Force Office of Scientific Research (AFOSR-MURI)United States. Air Force Office of Scientific Research (AFOSR-YIP)United States. Army Research Office (ARO-MURI)United States. Office of Naval ResearchUnited States. Defense Advanced Research Projects Agency (DARPA YFA
Evolution of Fermion Pairing from Three to Two Dimensions
We follow the evolution of fermion pairing in the dimensional crossover from
3D to 2D as a strongly interacting Fermi gas of Li atoms becomes confined
to a stack of two-dimensional layers formed by a one-dimensional optical
lattice. Decreasing the dimensionality leads to the opening of a gap in
radio-frequency spectra, even on the BCS-side of a Feshbach resonance. The
measured binding energy of fermion pairs closely follows the theoretical
two-body binding energy and, in the 2D limit, the zero-temperature mean-field
BEC-BCS theory.Comment: 5 pages, 4 figure
Motion of a Solitonic Vortex in the BEC-BCS Crossover
We observe a long-lived solitary wave in a superfluid Fermi gas of Li
atoms after phase-imprinting. Tomographic imaging reveals the excitation to be
a solitonic vortex, oriented transverse to the long axis of the cigar-shaped
atom cloud. The precessional motion of the vortex is directly observed, and its
period is measured as a function of the chemical potential in the BEC-BCS
crossover. The long period and the correspondingly large ratio of the inertial
to the bare mass of the vortex are in good agreement with estimates based on
superfluid hydrodynamics that we derive here using the known equation of state
in the BEC-BCS crossover
Controllable tunability of a Chern number within the electronic-nuclear spin system in diamond
Chern numbers are gaining traction as they characterize topological phases in
various physical systems. However, the resilience of the system topology to
external perturbations makes it challenging to experimentally investigate
transitions between different phases. In this study, we demonstrate the
transitions of Chern number from 0 to 3, synthesized in an electronic-nuclear
spin system associated with the nitrogen-vacancy (NV) centre in diamond. The
Chern number is characterized by the number of degeneracies enclosed in a
control Hamiltonian parameter sphere. The topological transitions between
different phases are depicted by varying the radius and offset of the sphere.
We show that the measured topological phase diagram is not only consistent with
the numerical calculations but can also be mapped onto an interacting
three-qubit system. The NV system may also allow access to even higher Chern
numbers, which can be applied to exploring exotic topology or topological
quantum information
Scanning X-ray Diffraction Microscopy for Diamond Quantum Sensing
Understanding nano- and micro-scale crystal strain in CVD diamond is crucial
to the advancement of diamond quantum technologies. In particular, the presence
of such strain and its characterization present a challenge to diamond-based
quantum sensing and information applications -- as well as for future dark
matter detectors where directional information of incoming particles is encoded
in crystal strain. Here, we exploit nanofocused scanning X-ray diffraction
microscopy to quantitatively measure crystal deformation from growth defects in
CVD diamond with high spatial and strain resolution. Combining information from
multiple Bragg angles allows stereoscopic three-dimensional reconstruction of
strained volumes; the diffraction results are validated via comparison to
optical measurements of the strain tensor based on spin-state-dependent
spectroscopy of ensembles of nitrogen vacancy (NV) centers in the diamond. Our
results open a path towards directional detection of dark matter via X-ray
measurement of crystal strain, and provide a new tool for diamond growth
analysis and improvement of defect-based sensing.Comment: 15 pages, 17 figures (incl. Supplemental Material
The classical limit for a class of quantum baker's maps
We show that the class of quantum baker's maps defined by Schack and Caves
have the proper classical limit provided the number of momentum bits approaches
infinity. This is done by deriving a semi-classical approximation to the
coherent-state propagator.Comment: 18 pages, 5 figure
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