87 research outputs found
Demonstration of Geometric Landau-Zener Interferometry in a Superconducting Qubit
Geometric quantum manipulation and Landau-Zener interferometry have been
separately explored in many quantum systems. In this Letter, we combine these
two approaches to study the dynamics of a superconducting phase qubit. We
experimentally demonstrate Landau-Zener interferometry based on the pure
geometric phases in this solid-state qubit. We observe the interference caused
by a pure geometric phase accumulated in the evolution between two consecutive
Landau-Zener transitions, while the dynamical phase is canceled out by a
spin-echo pulse. The full controllability of the qubit state as a function of
the intrinsically robust geometric phase provides a promising approach for
quantum state manipulation.Comment: 5 pages + 3 pages supplemental Materia
A Unified Framework for Testing High Dimensional Parameters: A Data-Adaptive Approach
High dimensional hypothesis test deals with models in which the number of
parameters is significantly larger than the sample size. Existing literature
develops a variety of individual tests. Some of them are sensitive to the dense
and small disturbance, and others are sensitive to the sparse and large
disturbance. Hence, the powers of these tests depend on the assumption of the
alternative scenario. This paper provides a unified framework for developing
new tests which are adaptive to a large variety of alternative scenarios in
high dimensions. In particular, our framework includes arbitrary hypotheses
which can be tested using high dimensional -statistic based vectors. Under
this framework, we first develop a broad family of tests based on a novel
variant of the -norm with . We then combine these
tests to construct a data-adaptive test that is simultaneously powerful under
various alternative scenarios. To obtain the asymptotic distributions of these
tests, we utilize the multiplier bootstrap for -statistics. In addition, we
consider the computational aspect of the bootstrap method and propose a novel
low-cost scheme. We prove the optimality of the proposed tests. Thorough
numerical results on simulated and real datasets are provided to support our
theory
Rapid characterization of microscopic two-level systems using Landau-Zener transitions in a superconducting qubit
This is the published version. Copyright 2015 American Institute of PhysicsWe demonstrate a fast method to detect microscopic two-level systems in a superconducting phase qubit. By monitoring the population leak after sweeping the qubit bias flux, we are able to measure the two-level systems that are coupled with the qubit. Compared with the traditional method that detects two-level systems by energy spectroscopy, our method is faster and more sensitive. This method supplies a useful tool to investigate two-level systems in solid-state qubits
Building Universal Foundation Models for Medical Image Analysis with Spatially Adaptive Networks
Recent advancements in foundation models, typically trained with
self-supervised learning on large-scale and diverse datasets, have shown great
potential in medical image analysis. However, due to the significant spatial
heterogeneity of medical imaging data, current models must tailor specific
structures for different datasets, making it challenging to leverage the
abundant unlabeled data. In this work, we propose a universal foundation model
for medical image analysis that processes images with heterogeneous spatial
properties using a unified structure. To accomplish this, we propose spatially
adaptive networks (SPAD-Nets), a family of networks that dynamically adjust the
structures to adapt to the spatial properties of input images, to build such a
universal foundation model. We pre-train a spatial adaptive visual tokenizer
(SPAD-VT) and then a spatial adaptive Vision Transformer (SPAD-ViT) via masked
image modeling (MIM) on 55 public medical image datasets. The pre-training data
comprises over 9 million image slices, representing the largest, most
comprehensive, and most diverse dataset to our knowledge for pre-training
universal foundation models for medical image analysis. The experimental
results on downstream medical image classification and segmentation tasks
demonstrate the superior performance and label efficiency of our model. Our
code is available at https://github.com/function2-llx/PUMIT
Simulating the Kibble-Zurek mechanism of the Ising model with a superconducting qubit system
The Kibble-Zurek mechanism (KZM) predicts the density of topological defects
produced in the dynamical processes of phase transitions in systems ranging
from cosmology to condensed matter and quantum materials. The similarity
between KZM and the Landau-Zener transition (LZT), which is a standard tool to
describe the dynamics of some non-equilibrium physics in contemporary physics,
is being extensively exploited. Here we demonstrate the equivalence between KZM
in the Ising model and LZT in a superconducting qubit system. We develop a
time-resolved approach to study quantum dynamics of LZT with nano-second
resolution. By using this technique, we simulate the key features of KZM in the
Ising model with LZT, e.g., the boundary between the adiabatic and impulse
regions, the freeze-out phenomenon in the impulse region, especially, the
scaling law of the excited state population as the square root of the quenching
rate. Our results supply the experimental evidence of the close connection
between KZM and LZT, two textbook paradigms to study the dynamics of the
non-equilibrium phenomena.Comment: Title changed, authors added, and some experimental data update
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