161 research outputs found
Electric field excitation suppression in cold atoms
In this article, the atom excitation suppression is studied in two ways. The
first way of exploring the excitation suppression is by an external DC electric
field. The second way is to study the excitation suppression caused by electric
field generated by free charges, which are created by ionizing atoms. This
suppression is called Coulomb blockade. Here the Coulomb forces are created by
ions through ionizing atoms by a UV laser. The theory shows that the
interaction, which causes the suppression, is primarily caused by charge-dipole
interactions. Here the charge is the ion, and the dipole is an atom. In this
experiment, we use Rb atoms. The valence electron and the ion core are
the two poles of an electric dipole. The interaction potential energy between
the ion and the atom is proportional to , and the frequency
shift caused by this interaction is proportional to , where
is the distance between the ion and the dipole considered. This research can be
used for quantum information storage, remote control, creating hot plasmas
using cold atoms, as well as electronic devices.Comment: 12 pages, 7 figure
The Density Broadening in a Sodium F=2 Condensate Detected by a Pulse Train
The dipole-blockaded sodiumclock transition has been detected by high resolution microwave spectroscopy, the multiple-pulse spectroscopy. This spectroscopic technique has been first used to detect the density broadening and shifting in a Sodium Bose Einstein Condensate (BEC) by probing the sodium clock-transition. Moreover, by narrowing the pulse-width of the pulses, some of the broadening mechanisms can be partially reduced. The results reported here are essential steps toward the ground-statequantum computing, few-body spectroscopy, spin squeezing and quantum metrology
MHz Few-body Frequency Shift Detected in a Cold 85Rb Rydberg Gas
We have observed a density-dependent frequency shift of more than 4 MHz in a cold 85Rb Rydberg gas trapped in a magneto-optical trap. A one-dimensional linearly aligned four-body model is proposed to explain the experimental data, and the calculation matches the experimental data. The calculation also shows that if the energy detuning between the two coupled states, the nsnsns(n + 1)s and nsnsnpnp states in this case, is small, the lowest level of the nsnsnpnp manifold has the maximum mixing probability, causing a frequency shift instead of line broadening. The results reported may be used for few-body blockade, Rydberg single-atom imaging, studying few-body to many-body transitions and interactions, and few-body ionization as well as quantum metrology
Evidence of quadrupole-quadrupole interactions in ultracold gases
Van der Waals interactions are interactions between dipoles. Similarly,
quadrupole-quadrupole interactions are interactions between quadrupoles. In
this article, we focus on the interactions between two dipoles or two
quadrupoles. Classically, we treat one Rydberg atom as a dipole; an outer
excited electron and an ion core are the two poles of a dipole. Quantum
mechanically, we consider Rydberg transition dipoles. Therefore, dipole-dipole
interactions are the interactions between two Rydberg atoms. Rydberg atoms have
quadrupole components; consequently, the interactions between two Rydberg atoms
have quadrupole-quadrupole interaction components. In this article, we examine
the dipole-dipole and quadrupole-quadrupole contribution to the interactions
between ultracold Rydberg atoms. It is shown that the evidence of
quadrupole-blockade has been observed, which is essential for fabricating more
compact quantum computers, quantum electronics, as well as quantum sensing
Unleashing Mask: Explore the Intrinsic Out-of-Distribution Detection Capability
Out-of-distribution (OOD) detection is an indispensable aspect of secure AI
when deploying machine learning models in real-world applications. Previous
paradigms either explore better scoring functions or utilize the knowledge of
outliers to equip the models with the ability of OOD detection. However, few of
them pay attention to the intrinsic OOD detection capability of the given
model. In this work, we generally discover the existence of an intermediate
stage of a model trained on in-distribution (ID) data having higher OOD
detection performance than that of its final stage across different settings,
and further identify one critical data-level attribution to be learning with
the atypical samples. Based on such insights, we propose a novel method,
Unleashing Mask, which aims to restore the OOD discriminative capabilities of
the well-trained model with ID data. Our method utilizes a mask to figure out
the memorized atypical samples, and then finetune the model or prune it with
the introduced mask to forget them. Extensive experiments and analysis
demonstrate the effectiveness of our method. The code is available at:
https://github.com/tmlr-group/Unleashing-Mask.Comment: accepted by ICML 202
Diversified Outlier Exposure for Out-of-Distribution Detection via Informative Extrapolation
Out-of-distribution (OOD) detection is important for deploying reliable
machine learning models on real-world applications. Recent advances in outlier
exposure have shown promising results on OOD detection via fine-tuning model
with informatively sampled auxiliary outliers. However, previous methods assume
that the collected outliers can be sufficiently large and representative to
cover the boundary between ID and OOD data, which might be impractical and
challenging. In this work, we propose a novel framework, namely, Diversified
Outlier Exposure (DivOE), for effective OOD detection via informative
extrapolation based on the given auxiliary outliers. Specifically, DivOE
introduces a new learning objective, which diversifies the auxiliary
distribution by explicitly synthesizing more informative outliers for
extrapolation during training. It leverages a multi-step optimization method to
generate novel outliers beyond the original ones, which is compatible with many
variants of outlier exposure. Extensive experiments and analyses have been
conducted to characterize and demonstrate the effectiveness of the proposed
DivOE. The code is publicly available at: https://github.com/tmlr-group/DivOE.Comment: accepted by NeurIPS 202
COSST: Multi-organ Segmentation with Partially Labeled Datasets Using Comprehensive Supervisions and Self-training
Deep learning models have demonstrated remarkable success in multi-organ
segmentation but typically require large-scale datasets with all organs of
interest annotated. However, medical image datasets are often low in sample
size and only partially labeled, i.e., only a subset of organs are annotated.
Therefore, it is crucial to investigate how to learn a unified model on the
available partially labeled datasets to leverage their synergistic potential.
In this paper, we systematically investigate the partial-label segmentation
problem with theoretical and empirical analyses on the prior techniques. We
revisit the problem from a perspective of partial label supervision signals and
identify two signals derived from ground truth and one from pseudo labels. We
propose a novel two-stage framework termed COSST, which effectively and
efficiently integrates comprehensive supervision signals with self-training.
Concretely, we first train an initial unified model using two ground
truth-based signals and then iteratively incorporate the pseudo label signal to
the initial model using self-training. To mitigate performance degradation
caused by unreliable pseudo labels, we assess the reliability of pseudo labels
via outlier detection in latent space and exclude the most unreliable pseudo
labels from each self-training iteration. Extensive experiments are conducted
on one public and three private partial-label segmentation tasks over 12 CT
datasets. Experimental results show that our proposed COSST achieves
significant improvement over the baseline method, i.e., individual networks
trained on each partially labeled dataset. Compared to the state-of-the-art
partial-label segmentation methods, COSST demonstrates consistent superior
performance on various segmentation tasks and with different training data
sizes
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