We measured the ground-state electric-dipole polarizability of sodium, potassium, and rubidium using a Mach-Zehnder atom interferometer with an electric-field gradient. We find α Na = 24.11(2) stat (18) sys × 10 −24 cm 3 , α K = 43.06 (14)(33), and α Rb = 47.24(12)(42). Since these measurements were all performed in the same apparatus and subject to the same systematic errors, we can present polarizability ratios with 0.3% uncertainty. We find α Rb /α Na = 1.959(5), α K /α Na = 1.786(6), and α Rb /α K = 1.097(5). We combine our ratio measurements with the higher-precision measurement of sodium polarizability by Ekstrom et al. [Phys. Rev. A 51, 3883 (1995)] to find α K = 43.06(21) and α Rb = 47.24(21).

We have characterized the one-dimensional (1D) to three-dimensional (3D) crossover of a twocomponent spin-imbalanced Fermi gas of 6 Li atoms in a 2D optical lattice by varying the lattice tunneling and the interactions. The gas phase separates, and we detect the phase boundaries using in situ imaging of the inhomogeneous density profiles. The locations of the phases are inverted in 1D as compared to 3D, thus providing a clear signature of the crossover. By scaling the tunneling rate t with respect to the pair binding energy B , we observe a collapse of the data to a universal crossover point at a scaled tunneling value oftc = 0.025(7).PACS numbers: 67.85. Lm, 71.10.Pm, 37.10.Jk, 05.70.Fh Atomic Fermi gases prepared in two hyperfine sublevels realize a quasi-spin-1 /2 system, for which the two states may be denoted as |↑ and |↓ . Spinimbalanced Fermi gases, where the number of spinup atoms, N ↑ , exceeds the number of spin-down atoms, N ↓ , have been studied extensively in recent years, largely motivated by a search for exotic superfluid phases [1][2][3]. One such superfluid, the FuldeFerrell-Larkin-Ovchinnikov (FFLO) phase [4,5], has not been conclusively observed in three dimensions (3D) but is believed to occupy a large portion of the one-dimensional (1D) phase diagram [6,7]. Measurements have confirmed that the 1D phase diagram is consistent with theories exhibiting FFLO [8], but direct evidence for this phase remains elusive. Since the FFLO phase is expected to be more robust to quantum and thermal fluctuations in higher dimensions, attention has focused on the dimensional crossover [9][10][11][12].A crossover between 1D and 3D regimes may be realized by simply varying the confinement aspect ratio [13][14][15][16][17]. A complementary dimensional crossover occurs by varying the tunneling between tubes aligned in an array, as depicted in Fig. 1(a). Such a geometry, which may be achieved using ultracold atoms in an optical lattice, is more analogous to some material systems, such as carbon nanotube bundles [18] and spin-1 /2 magnet chains [19,20]. The bundle will cross over from an array of independent 1D tubes for small tunneling t, to a 3D system as t is increased [21,22]. We have employed this geometry to determine the crossover value of t for a spin-imbalanced Fermi gas with various interaction strengths and find a striking universality in the crossover location.Trapped Fermi gases with spin-imbalance have been observed to phase separate at low temperatures in both 3D [23][24][25][26][27] FIG. 1. (Color online) (a) Schematic of an array of 1Dcoupled tubes formed by a 2D optical lattice. The tunneling rate t between the tubes increases with decreasing optical lattice depth. (b) Schematic of phase separation for a trapped spin-imbalanced Fermi gas in 1D (top) and in 3D (bottom) at zero temperature. In 1D, the central region is an FFLO partially-polarized superfluid (SFP), with balanced superfluid (SF0) wings for small polarization P . In 3D, for P < P 3D c , a central SF0 core is surrounded by an SFP or ...

If quantum information processors are to fulfill their potential, the diverse errors that affect them must be understood and suppressed. But errors typically fluctuate over time, and the most widely used tools for characterizing them assume static error modes and rates. This mismatch can cause unheralded failures, misidentified error modes, and wasted experimental effort. Here, we demonstrate a spectral analysis technique for resolving time dependence in quantum processors. Our method is fast, simple, and statistically sound. It can be applied to time-series data from any quantum processor experiment. We use data from simulations and trapped-ion qubit experiments to show how our method can resolve time dependence when applied to popular characterization protocols, including randomized benchmarking, gate set tomography, and Ramsey spectroscopy. In the experiments, we detect instability and localize its source, implement drift control techniques to compensate for this instability, and then demonstrate that the instability has been suppressed.

We obtain the phase diagram of spin-imbalanced interacting Fermi gases from measurements of density profiles of 6 Li atoms in a harmonic trap. These results agree with, and extend, previous experimental measurements. Measurements of the critical polarization at which the balanced superfluid core vanishes generally agree with previous experimental results and with quantum Monte Carlo (QMC) calculations in the BCS and unitary regimes. We disagree with the QMC results in the BEC regime, however, where the measured critical polarizations are greater than theoretically predicted. We also measure the equation of state in the crossover regime for a gas with equal numbers of the two fermion spin states.

We study the role of particle transport and evaporation on the phase separation of an ultracold, spinpolarized atomic Fermi gas. We show that the previously observed deformation of the superfluid paired core is a result of evaporative depolarization of the superfluid due to a combination of enhanced evaporation at the center of the trap and the inhibition of spin transport at the normal-superfluid phase boundary. These factors contribute to a nonequilibrium jump in the chemical potentials at the phase boundary. Once formed, the deformed state is highly metastable, persisting for times of up to 2 s.