Exploring the Roper wave function in Lattice QCD

Using a correlation matrix analysis consisting of a variety of smearings, the CSSM Lattice collaboration has successfully isolated states associated with the Roper resonance and other "exotic" excited states such as the $\Lambda(1405)$ on the lattice at near-physical pion masses. We explore the nature of the Roper by examining the eigenvectors that arise from the variational analysis, demonstrating that the Roper state is dominated by the $\chi_1$ nucleon interpolator and only poorly couples to $\chi_2.$ By examining the probability distribution of the Roper on the lattice, we find a structure consistent with a constituent quark model. In particular, the Roper $d$-quark wave function contains a single node consistent with a $2S$ state. A detailed comparison with constituent quark model wave functions is carried out, validating the approach of accessing these states by constructing a variational basis composed of different levels of fermion source and sink smearing.Comment: 7 pages, 5 figures; presented at the 31st International Symposium on Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013, Mainz, German

Phase separation and pair condensation in a spin-imbalanced 2D Fermi gas

We study a two-component quasi-two-dimensional Fermi gas with imbalanced spin populations. We probe the gas at different interaction strengths and polarizations by measuring the density of each spin component in the trap and the pair momentum distribution after time of flight. For a wide range of experimental parameters, we observe in-trap phase separation characterized by the appearance of a spin-balanced condensate surrounded by a polarized gas. Our momentum space measurements indicate pair condensation in the imbalanced gas even for large polarizations where phase separation vanishes, pointing to the presence of a polarized pair condensate. Our observation of zero momentum pair condensates in 2D spin-imbalanced gases opens the way to explorations of more exotic superfluid phases that occupy a large part of the phase diagram in lower dimensions

Inducing vortices in a Bose-Einstein condensate using holographically produced light beams

In this paper we demonstrate a technique that can create out-of-equilibrium vortex configurations with almost arbitrary charge and geometry in a Bose-Einstein condensate. We coherently transfer orbital angular momentum from a holographically generated light beam to a Rubidium 87 condensate using a two-photon stimulated Raman process. Using matter wave interferometry, we verify the phase pattern imprinted onto the atomic wave function for a single vortex and a vortex-antivortex pair. In addition to their phase winding, the vortices created with this technique have an associated hyperfine spin texture.Comment: 4 pages, 5 figure

Extracting Low-Lying Lambda Resonances Using Correlation Matrix Techniques

The lowest-lying negative-parity state of the Lambda is investigated in (2+1)-flavour full-QCD on the PACS-CS configurations made available through the ILDG. We show that a variational analysis using multiple source and sink smearings can extract a state lying lower than that obtained by using a standard fixed smeared source and sink operator alone.Comment: 3 pages, 1 figure, submitted to the proceedings of T(R)OPICAL QCD II, Cairns, Australia, 201

Wave Functions of the Proton Ground State in the Presence of a Uniform Background Magnetic Field in Lattice QCD

We calculate the probability distributions of quarks in the ground state of the proton, and how they are affected in the presence of a constant background magnetic field. We focus on wave functions in the Landau and Coulomb gauges. We observe the formation of a scalar u-d diquark clustering. The overall distortion of the quark probability distribution under a very large magnetic field, as demanded by the quantisation conditions on the field, is quite small. The effect is to elongate the distributions along the external field axis while localizing the remainder of the distribution.Comment: 15 pages, 18 figure

Quantum gas microscopy for single atom and spin detection

A particular strength of ultracold quantum gases are the versatile detection methods available. Since they are based on atom-light interactions, the whole quantum optics toolbox can be used to tailor the detection process to the specific scientific question to be explored in the experiment. Common methods include time-of-flight measurements to access the momentum distribution of the gas, the use of cavities to monitor global properties of the quantum gas with minimal disturbance and phase-contrast or high-intensity absorption imaging to obtain local real space information in high-density settings. Even the ultimate limit of detecting each and every atom locally has been realized in two-dimensions using so-called quantum gas microscopes. In fact, these microscopes not only revolutionized the detection, but also the control of lattice gases. Here we provide a short overview of this technique, highlighting new observables as well as key experiments that have been enabled by quantum gas microscopy.Comment: Community comments welcome

Towards a cryogenic planar ion trap for Sr-88

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2006.Includes bibliographical references (p. 105-114).This thesis describes experiments with ion traps constructed with electrodes in a single two-dimensional plane, and ion traps operated in a cryogenic environment at 77K and 4K temperatures. These two technologies address needs which arise in developing potentially scalable approaches to quantum computing using trapped ions. Traps with electrodes in a plane are challenging to load because their trap depths are usually only of order one percent that of multi-level traps of comparable dimensions. In addition, ion heating rates in these traps are higher than in multi-level traps because of the close proximity of the electrodes that is required to achieve a reasonable trap depth and the relatively resistive semiconductor electrode materials used in planar traps fabricated with standard semiconductor lithography methods. We investigate planar traps using macroscopic ions, focusing on devising techniques for loading these shallow traps and designing electrode layouts for ion movement. Using traps fabricated lithographically with copper traces on fiberglass laminate, we trap linear chains of tens of charged particles of [approx.] 400nm diameter in a rough vacuum of 15 Pa.(cont.) We perform experiments to address concerns about the low trap depth of planar ion traps and develop control electrode layouts for moving ions between trap zones. Motivated by the desire to lower the heating rates in planar traps, we design and implement an experiment trapping strontium-88 ions in a knife-edge trap in a helium cryostat. The design challenges are obtaining a long hold-time of the cryogens, lowering the residual gas pressure and loading the trap using a technique compatible with the cryogenic environment. A novel loading technique we demonstrate successfully is laser ablation loading at 4K, employing a SrC12 target. Laser cooling is applied to produce observations of ions, both in clouds transitioning into Wigner crystals, and of linear chains of up to 14 optically resolved single ions. These results set the stage for future experiments with a planar trap for strontium-88 ions designed to operate at cryogenic temperatures.by Waseem Bakr.S.B

Accessing High Momentum States In Lattice QCD

Two measures are defined to evaluate the coupling strength of smeared interpolating operators to hadronic states at a variety of momenta. Of particular interest is the extent to which strong overlap can be obtained with individual high-momentum states. This is vital to exploring hadronic structure at high momentum transfers on the lattice and addressing interesting phenomena observed experimentally. We consider a novel idea of altering the shape of the smeared operator to match the Lorentz contraction of the probability distribution of the high-momentum state, and show a reduction in the relative error of the two-point function by employing this technique. Our most important finding is that the overlap of the states becomes very sharp in the smearing parameters at high momenta and fine tuning is required to ensure strong overlap with these states.Comment: 10 page