100 research outputs found
Entangled collective-spin states of atomic ensembles under non-uniform atom-light interaction
We consider the optical generation and verification of entanglement in atomic
ensembles under non-uniform interaction between the ensemble and an optical
mode. We show that for a wide range of parameters a system of non-uniformly
coupled atomic spins can be described as an ensemble of uniformly coupled spins
with a reduced effective atom-light coupling and a reduced effective atom
number, with a reduction factor of order unity given by the ensemble-mode
geometry. This description is valid even for complex entangled states with
arbitrary phase-space distribution functions as long as the detection does not
resolve single spins. Furthermore, we derive an analytic formula for the
observable entanglement in the case, of relevance in practice, where the
ensemble-mode coupling differs between state generation and measurement.Comment: 5 pages, 3 figure
Vacuum spin squeezing
We investigate the generation of entanglement (spin squeezing) in an
optical-transition atomic clock through the coupling to a vacuum
electromagnetic field that is enhanced by an optical cavity. We show that if
each atom is prepared in a superposition of the ground state and a long-lived
electronic excited state, and viewed as a spin-1/2 system, then the collective
vacuum light shift entangles the atoms, resulting in a squeezed distribution of
the ensemble collective spin. This scheme reveals that even a vacuum field can
be a useful resource for entanglement and quantum manipulation. The method is
simple and robust since it requires neither the application of light nor
precise frequency control of the ultra-high-finesse cavity. Furthermore, the
scheme can be used to implement two-axis twisting by rotating the spin
direction while coupling to the vacuum, resulting in stronger squeezing
Creation of a Bose-condensed gas of rubidium 87 by laser cooling
We demonstrate direct laser cooling of a gas of rubidium 87 atoms to quantum
degeneracy. The method does not involve evaporative cooling, is fast, and
induces little atom loss. The atoms are trapped in a two-dimensional optical
lattice that enables cycles of cloud compression to increase the density,
followed by degenerate Raman sideband cooling to decrease the temperature.
Light-induced loss at high atomic density is substantially reduced by using far
red detuned optical pumping light. Starting with 2000 atoms, we prepare 1400
atoms in 300 ms at quantum degeneracy, as confirmed by the appearance of a
bimodal velocity distribution as the system crosses over from a classical gas
to a Bose-condensed, interacting one-dimensional gas with a macroscopic
population of the quantum ground state. The method should be broadly applicable
to many bosonic and fermionic species, and to systems where evaporative cooling
is not possible.Comment: 5 pages, 3 figures (main text
Strictly nonclassical behavior of a mesoscopic system
We experimentally demonstrate the strictly nonclassical behavior in a
many-atom system using a recently derived criterion [E. Kot et al., Phys. Rev.
Lett. 108, 233601 (2012)] that explicitly does not make use of quantum
mechanics. We thereby show that the magnetic moment distribution measured by
McConnell et al. [R. McConnell et al., Nature 519, 439 (2015)] in a system with
a total mass of atomic mass units is inconsistent with
classical physics. Notably, the strictly nonclassical behavior affects an area
in phase space times larger than the Planck quantum .Comment: 5 page
Improving Visual Quality and Transferability of Adversarial Attacks on Face Recognition Simultaneously with Adversarial Restoration
Adversarial face examples possess two critical properties: Visual Quality and
Transferability. However, existing approaches rarely address these properties
simultaneously, leading to subpar results. To address this issue, we propose a
novel adversarial attack technique known as Adversarial Restoration
(AdvRestore), which enhances both visual quality and transferability of
adversarial face examples by leveraging a face restoration prior. In our
approach, we initially train a Restoration Latent Diffusion Model (RLDM)
designed for face restoration. Subsequently, we employ the inference process of
RLDM to generate adversarial face examples. The adversarial perturbations are
applied to the intermediate features of RLDM. Additionally, by treating RLDM
face restoration as a sibling task, the transferability of the generated
adversarial face examples is further improved. Our experimental results
validate the effectiveness of the proposed attack method.Comment: \copyright 2023 IEEE. Personal use of this material is permitted.
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this work in other work
Unique normal forms for Hopf-zero vector fields
We consider normal forms of Hopf-zero vector fields in R-3. Unique normal forms under conjugacy and orbital equivalence for the generic case are given.MathematicsSCI(E)4ARTICLE4345-34833
Improving the Transferability of Adversarial Attacks on Face Recognition with Beneficial Perturbation Feature Augmentation
Face recognition (FR) models can be easily fooled by adversarial examples,
which are crafted by adding imperceptible perturbations on benign face images.
To improve the transferability of adversarial face examples, we propose a novel
attack method called Beneficial Perturbation Feature Augmentation Attack
(BPFA), which reduces the overfitting of adversarial examples to surrogate FR
models by constantly generating new models that have the similar effect of hard
samples to craft the adversarial examples. Specifically, in the
backpropagation, BPFA records the gradients on pre-selected features and uses
the gradient on the input image to craft the adversarial example. In the next
forward propagation, BPFA leverages the recorded gradients to add perturbations
(i.e., beneficial perturbations) that can be pitted against the adversarial
example on their corresponding features. The optimization process of the
adversarial example and the optimization process of the beneficial
perturbations added on the features correspond to a minimax two-player game.
Extensive experiments demonstrate that BPFA can significantly boost the
transferability of adversarial attacks on FR
Carving Complex Many-Atom Entangled States by Single-Photon Detection
We propose a versatile and efficient method to generate a broad class of complex entangled states of many atoms via the detection of a single photon. For an atomic ensemble contained in a strongly coupled optical cavity illuminated by weak single- or multifrequency light, the atom-light interaction entangles the frequency spectrum of a transmitted photon with the collective spin of the atomic ensemble. Simple time-resolved detection of the transmitted photon then projects the atomic ensemble into a desired pure entangled state. This method can be implemented with existing technology, yields high success probability per trial, and can generate complex entangled states such as mesoscopic superposition states of coherent spin states with high fidelity.National Science Foundation (U.S.)United States. Defense Advanced Research Projects Agency. Quantum-Assisted Sensing and Readout (QuASAR) ProgramUnited States. Air Force Office of Scientific Research. Multidisciplinary University Research InitiativeUnited States. Army Research Office. Multidisciplinary University Research InitiativeNatural Sciences and Engineering Research Council of Canad
Calibrating the absorption imaging of cold atoms under high magnetic fields
We develop a theoretical model for calibrating the absorption imaging of cold
atoms under high magnetic fields. Comparing to zero or low magnetic fields, the
efficiency of the absorption imaging becomes lower while it requires an
additional correction factor to obtain the absolute atom number under the
Beer-Lambert law. Our model is based on the rate equations and can account many
experimental imperfections such as Zeeman level crossing, failures of hyperfine
structures, off-resonant couplings, and low repumping efficiency, etc. Based on
this method, we can precisely calculate the correction factor for atom number
measurement without any empirical or fitting parameters. Meanwhile, we use a
cold-atom apparatus of rubidium-85 to experimentally verify our model. Besides
these, we find our work can also serve as a benchmark to measure the
polarization impurity of a circular-polarized laser beam with high
sensitivities. We believe this work will bring convenience for most of
cold-atom experiments using absorption imaging.Comment: 9 pages, 5 figure
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