1,197 research outputs found
HOME: High-Order Mixed-Moment-based Embedding for Representation Learning
Minimum redundancy among different elements of an embedding in a latent space
is a fundamental requirement or major preference in representation learning to
capture intrinsic informational structures. Current self-supervised learning
methods minimize a pair-wise covariance matrix to reduce the feature redundancy
and produce promising results. However, such representation features of
multiple variables may contain the redundancy among more than two feature
variables that cannot be minimized via the pairwise regularization. Here we
propose the High-Order Mixed-Moment-based Embedding (HOME) strategy to reduce
the redundancy between any sets of feature variables, which is to our best
knowledge the first attempt to utilize high-order statistics/information in
this context. Multivariate mutual information is minimum if and only if
multiple variables are mutually independent, which suggests the necessary
conditions of factorized mixed moments among multiple variables. Based on these
statistical and information theoretic principles, our general HOME framework is
presented for self-supervised representation learning. Our initial experiments
show that a simple version in the form of a three-order HOME scheme already
significantly outperforms the current two-order baseline method (i.e., Barlow
Twins) in terms of the linear evaluation on representation features
Demonstration of a quantum logic gate in a cryogenic surface-electrode ion trap
We demonstrate quantum control techniques for a single trapped ion in a
cryogenic, surface-electrode trap. A narrow optical transition of Sr+ along
with the ground and first excited motional states of the harmonic trapping
potential form a two-qubit system. The optical qubit transition is susceptible
to magnetic field fluctuations, which we stabilize with a simple and compact
method using superconducting rings. Decoherence of the motional qubit is
suppressed by the cryogenic environment. AC Stark shift correction is
accomplished by controlling the laser phase in the pulse sequencer, eliminating
the need for an additional laser. Quantum process tomography is implemented on
atomic and motional states using conditional pulse sequences. With these
techniques we demonstrate a Cirac-Zoller Controlled-NOT gate in a single ion
with a mean fidelity of 91(1)%.Comment: 11 pages, 5 figures, 4 table
Laser-induced charging of microfabricated ion traps
Electrical charging of metal surfaces due to photoelectric generation of
carriers is of concern in trapped ion quantum computation systems, due to the
high sensitivity of the ions' motional quantum states to deformation of the
trapping potential. The charging induced by typical laser frequencies involved
in doppler cooling and quantum control is studied here, with microfabricated
surface electrode traps made of aluminum, copper, and gold, operated at 6 K
with a single Sr ion trapped 100 m above the trap surface. The lasers
used are at 370, 405, 460, and 674 nm, and the typical photon flux at the trap
is 10 photons/cm/sec. Charging is detected by monitoring the ion's
micromotion signal, which is related to the number of charges created on the
trap. A wavelength and material dependence of the charging behavior is
observed: lasers at lower wavelengths cause more charging, and aluminum
exhibits more charging than copper or gold. We describe the charging dynamic
based on a rate equation approach.Comment: 8 pages, 8 figure
Sub-volume-based Denoising Diffusion Probabilistic Model for Cone-beam CT Reconstruction from Incomplete Data
Deep learning (DL) has emerged as a new approach in the field of computed
tomography (CT) with many applicaitons. A primary example is CT reconstruction
from incomplete data, such as sparse-view image reconstruction. However,
applying DL to sparse-view cone-beam CT (CBCT) remains challenging. Many models
learn the mapping from sparse-view CT images to the ground truth but often fail
to achieve satisfactory performance. Incorporating sinogram data and performing
dual-domain reconstruction improve image quality with artifact suppression, but
a straightforward 3D implementation requires storing an entire 3D sinogram in
memory and many parameters of dual-domain networks. This remains a major
challenge, limiting further research, development and applications. In this
paper, we propose a sub-volume-based 3D denoising diffusion probabilistic model
(DDPM) for CBCT image reconstruction from down-sampled data. Our DDPM network,
trained on data cubes extracted from paired fully sampled sinograms and
down-sampled sinograms, is employed to inpaint down-sampled sinograms. Our
method divides the entire sinogram into overlapping cubes and processes them in
parallel on multiple GPUs, successfully overcoming the memory limitation.
Experimental results demonstrate that our approach effectively suppresses
few-view artifacts while preserving textural details faithfully
One-dimensional array of ion chains coupled to an optical cavity
We present a novel hybrid system where an optical cavity is integrated with a
microfabricated planar-electrode ion trap. The trap electrodes produce a
tunable periodic potential allowing the trapping of up to 50 separate ion
chains spaced by 160 m along the cavity axis. Each chain can contain up to
20 individually addressable Yb\textsuperscript{+} ions coupled to the cavity
mode. We demonstrate deterministic distribution of ions between the sites of
the electrostatic periodic potential and control of the ion-cavity coupling.
The measured strength of this coupling should allow access to the strong
collective coupling regime with 10 ions. The optical cavity could
serve as a quantum information bus between ions or be used to generate a strong
wavelength-scale periodic optical potential.Comment: 15 pages, 6 figures, submitted to New Journal of Physic
Superconducting microfabricated ion traps
We fabricate superconducting ion traps with niobium and niobium nitride and
trap single 88Sr ions at cryogenic temperatures. The superconducting transition
is verified and characterized by measuring the resistance and critical current
using a 4-wire measurement on the trap structure, and observing change in the
rf reflection. The lowest observed heating rate is 2.1(3) quanta/sec at 800 kHz
at 6 K and shows no significant change across the superconducting transition,
suggesting that anomalous heating is primarily caused by noise sources on the
surface. This demonstration of superconducting ion traps opens up possibilities
for integrating trapped ions and molecular ions with superconducting devices.Comment: 3 pages, 2 figure
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