3,262 research outputs found
Integration of fiber coupled high-Q silicon nitride microdisks with atom chips
Micron scale silicon nitride (SiN_x) microdisk optical resonators are
demonstrated with Q = 3.6 x 10^6 and an effective mode volume of 15 (\lambda /
n)^3 at near visible wavelengths. A hydrofluoric acid wet etch provides
sensitive tuning of the microdisk resonances, and robust mounting of a fiber
taper provides efficient fiber optic coupling to the microdisks while allowing
unfettered optical access for laser cooling and trapping of atoms. Measurements
indicate that cesium adsorption on the SiN_x surfaces significantly red-detunes
the microdisk resonances. A technique for parallel integration of multiple (10)
microdisks with a single fiber taper is also demonstrated.Comment: Published vesion. Minor change
A long-lived spin-orbit-coupled degenerate dipolar Fermi gas
We describe the creation of a long-lived spin-orbit-coupled gas of quantum
degenerate atoms using the most magnetic fermionic element, dysprosium.
Spin-orbit-coupling arises from a synthetic gauge field created by the
adiabatic following of degenerate dressed states comprised of optically coupled
components of an atomic spin. Because of dysprosium's large electronic orbital
angular momentum and large magnetic moment, the lifetime of the gas is limited
not by spontaneous emission from the light-matter coupling, as for gases of
alkali-metal atoms, but by dipolar relaxation of the spin. This relaxation is
suppressed at large magnetic fields due to Fermi statistics. We observe
lifetimes up to 400 ms, which exceeds that of spin-orbit-coupled fermionic
alkali atoms by a factor of 10-100, and is close to the value obtained from a
theoretical model. Elastic dipolar interactions are also observed to influence
the Rabi evolution of the spin, revealing an interacting fermionic system. The
long lifetime of this weakly interacting spin-orbit-coupled degenerate Fermi
gas will facilitate the study of quantum many-body phenomena manifest at longer
timescales, with exciting implications for the exploration of exotic
topological quantum liquids.Comment: 11 pages, 8 figures, one appendi
Quantum degenerate dipolar Fermi gas
The interplay between crystallinity and superfluidity is of great fundamental
and technological interest in condensed matter settings. In particular,
electronic quantum liquid crystallinity arises in the non-Fermi liquid,
pseudogap regime neighboring a cuprate's unconventional superconducting phase.
While the techniques of ultracold atomic physics and quantum optics have
enabled explorations of the strongly correlated, many-body physics inherent in,
e.g., the Hubbard model, lacking has been the ability to create a quantum
degenerate Fermi gas with interparticle interactions---such as the strong
dipole-dipole interaction---capable of inducing analogs to electronic quantum
liquid crystals. We report the first quantum degenerate dipolar Fermi gas, the
realization of which opens a new frontier for exploring strongly correlated
physics and, in particular, the quantum melting of smectics in the pristine
environment provided by the ultracold atomic physics setting. A quantum
degenerate Fermi gas of the most magnetic atom 161Dy is produced by laser
cooling to 10 uK before sympathetically cooling with ultracold, bosonic 162Dy.
The temperature of the spin-polarized 161Dy is a factor T/TF=0.2 below the
Fermi temperature TF=300 nK. The co-trapped 162Dy concomitantly cools to
approximately Tc for Bose-Einstein condensation, thus realizing a novel, nearly
quantum degenerate dipolar Bose-Fermi gas mixture.Comment: 6 pages, 3 figure
Fisher Vectors Derived from Hybrid Gaussian-Laplacian Mixture Models for Image Annotation
In the traditional object recognition pipeline, descriptors are densely
sampled over an image, pooled into a high dimensional non-linear representation
and then passed to a classifier. In recent years, Fisher Vectors have proven
empirically to be the leading representation for a large variety of
applications. The Fisher Vector is typically taken as the gradients of the
log-likelihood of descriptors, with respect to the parameters of a Gaussian
Mixture Model (GMM). Motivated by the assumption that different distributions
should be applied for different datasets, we present two other Mixture Models
and derive their Expectation-Maximization and Fisher Vector expressions. The
first is a Laplacian Mixture Model (LMM), which is based on the Laplacian
distribution. The second Mixture Model presented is a Hybrid Gaussian-Laplacian
Mixture Model (HGLMM) which is based on a weighted geometric mean of the
Gaussian and Laplacian distribution. An interesting property of the
Expectation-Maximization algorithm for the latter is that in the maximization
step, each dimension in each component is chosen to be either a Gaussian or a
Laplacian. Finally, by using the new Fisher Vectors derived from HGLMMs, we
achieve state-of-the-art results for both the image annotation and the image
search by a sentence tasks.Comment: new version includes text synthesis by an RNN and experiments with
the COCO benchmar
Atom chip microscopy: A novel probe for strongly correlated materials
Improved measurements of strongly correlated systems will enable the predicative design of the next generation of supermaterials. In this program, we are harnessing recent advances in the quantum manipulation of ultracold atomic gases to expand our ability to probe these technologically important materials in heretofore unexplored regions of temperature, resolution, and sensitivity parameter space. We are working to demonstrate the use of atom chips to enable single-shot, large area detection of magnetic flux at the 10^-7 flux quantum level and below. By harnessing the extreme sensitivity of atomic clocks and Bose-Einstein condensates (BECs) to external perturbations, the cryogenic atom chip technology developed here will provide a magnetic flux detection capability that surpasses other techniques---such as scanning SQUIDs---by a factor of 10--1000. We are testing the utility of this technique by using rubidium BECs to image the magnetic fields emanating from charge transport and magnetic domain percolation in strongly correlated materials as they undergo temperature-tuned metal--to--insulator phase transitions. Cryogenic atom chip microscopy introduces three very important features to the toolbox of high-resolution, strongly correlated material microscopy: simultaneous detection of magnetic and electric fields (down to the sub-single electron charge level); no invasive large magnetic fields or gradients; simultaneous micro- and macroscopic spatial resolution; freedom from 1/f flicker noise at low frequencies; and, perhaps most importantly, the complete decoupling of probe and sample temperatures. The first of these features will play an important role in studying the interplay between magnetic and electric domain structure. The last two are crucial for low frequency magnetic noise detection in, e.g., the cuprate pseudogap region and for precision measurements of transport in the high temperature, technologically relevant regime inaccessible to other techniques based on superconducting scanning probes. In periods 1--3 of this grant, which we now close at the University of Illinois at Urbana-Champaign and restart at Stanford University where our new lab is being built, we have demonstrated the ability to rapidly create Rb BECs and trap them within microns of a surface ina cryostat. Period 4 of this grant, to be performed at Stanford, will demonstrate the feasibility of using atom chips with a BEC to image transport features on a cryogenically cooled surface. Successful demonstration, in future funding cycles, will lead directly to the use of system for studies of transport in exotic and technologically relevant materials such as cuprate superconductors and topological insulators
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