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1,079 results on '"Liu, Ruifeng"'

2. Single-pixel transmission matrix recovery via 2-photon fluorescence

Author

Zhao, Shupeng, Rauer, Bernhard, Valzania, Lorenzo, Dong, Jonathan, Liu, Ruifeng, Li, Fuli, Gigan, Sylvain, and de Aguiar, Hilton B.

Subjects
Physics - Optics
Abstract

Imaging at depth in opaque materials has long been a challenge. Recently, wavefront shaping has enabled significant advance for deep imaging. Nevertheless, most non-invasive wavefront shaping methods require cameras, lack the sensitivity for deep imaging under weak optical signals, or can only focus on a single "guidestar". Here, we retrieve the transmission matrix (TM) non-invasively using two-photon fluorescence exploiting a general single-pixel detection framework, allowing to achieve single-target focus on multiple guidestars spread beyond the memory effect range. In addition, if we assume memory effect correlations exist in the transmission matrix, we are able to significantly reduce the number of measurements needed.

Published
2023

27. Efficient quantum state tomography with auxiliary Hilbert space

Author

Liu, Ruifeng, Long, Junling, Zhang, Pei, Lake, Russell E., Gao, Hong, Pappas, David P., and Li, Fuli

Subjects
Quantum Physics, Physics - Optics
Abstract

Quantum state tomography is an important tool for quantum communication, computation, metrology, and simulation. Efficient quantum state tomography on a high dimensional quantum system is still a challenging problem. Here, we propose a novel quantum state tomography method, auxiliary Hilbert space tomography, to avoid pre-rotations before measurement in a quantum state tomography experiment. Our method requires projective measurements in a higher dimensional space that contains the subspace that includes the prepared states. We experimentally demonstrate this method with orbital angular momentum states of photons. In our experiment, the quantum state tomography measurements are as simple as taking a photograph with a camera. We experimentally verify our method with near-pure- and mixed-states of orbital angular momentum with dimension up to $d=13$, and achieve greater than 95 % state fidelities for all states tested. This method dramatically reduces the complexity of measurements for full quantum state tomography, and shows potential application in various high dimensional quantum information tasks., Comment: 10 pages, 4 figures, and 1 table

Published
2019

39. Enhancement of spatial resolution of ghost imaging via localizing and thresholding

Author

Wang, Yunlong, Zhou, Yingnan, Wang, Shaoxiong, Wang, Feiran, Liu, Ruifeng, Zhang, Pei, Gao, Hong, and Li, Fuli

Subjects
Physics - Optics
Abstract

In ghost imaging scheme, an illuminated light is split into test and reference beams which pass through two different optical systems respectively and an image is constructed by the second-order correlation between the two light beams. Since both the two light beams are all diffracted when passing through the optical systems, spatial resolution of ghost imaging is in general lower than that of a corresponding conventional imaging system. When Gaussian-shaped light spots are used to illuminate an object, randomly scanning across the object plane, in ghost imaging scheme, we show that by localizing central positions of the spots of the reference light beam, the resolution can be enhanced by a factor of $\sqrt{2}$ same as that of the corresponding conventional imaging system. We also find that the resolution can be further enhanced by setting an appropriate threshold to the bucket measurement of ghost imaging.

Published
2018
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43. Investigation of the Bonding Mechanism of Al Powder Particles through Pulse Current Sintering Technology.

Author

Lv, Zhou and Liu, Ruifeng

Subjects
SINTERING, TECHNOLOGICAL innovations, INTERFACIAL bonding, TEMPERATURE distribution, POWDERS, POWDER metallurgy
Abstract

Compared with traditional powder metallurgy, pulse current sintering is an advanced powder-forming technology, but its bonding mechanism is still an open topic for debate. In this paper, pulse current sintering is used as the connection technology and millimeter-sized Al particles are used as the research object. In the whole sintering process, no pressure was loaded; the function of the pulse current was the only source of heat with which to achieve the bonding of Al particles. The bonding mechanism of pulse current sintering was investigated from the perspective of material connection behavior. The results show that the pulse current density of the particle surface reaches 3.48 × 105 A/m2 instantly, while the current density of the particle center is only 8187 A/m2 at the initial stage, which is the main difference between pulse current sintering and traditional powder metallurgy sintering. With the densification process, the current density and temperature distribution in the contact region as well as the center of Al particles contact region tend to be more consistent. Finally, dense interfacial bonding was obtained, and the contact region of Al particles also demonstrated a high hardness value of 0.6385 GPa and yield strength value of 212.83 MPa. The whole process can be considered as a comprehensive action of melting (evaporation), diffusion, and plastic deformation. Based on the above results, a new technology, named high-frequency pulse current sintering, was proposed. [ABSTRACT FROM AUTHOR]

Published
2024
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44. Intermittent Stimulation of the Nucleus Basalis of Meynert Improves Working Memory in Adult Monkeys.

Author

Liu, Ruifeng, Crawford, Jonathan, Callahan, Patrick, Terry, Alvin, Constantinidis, Christos, and Blake, David

Subjects
Alzheimer’s, Nucleus Basalis of Meynert, deep brain stimulation, executive function, nonhuman primate, working memory, Animals, Basal Nucleus of Meynert, Electric Stimulation, Female, Macaca mulatta, Male, Memory, Short-Term
Abstract

Acetylcholine in the neocortex is critical for executive function [1-3]. Degeneration of cholinergic neurons in aging and Alzheimers dementia is commonly treated with cholinesterase inhibitors [4-7]; however, these are modestly effective and are associated with side effects that preclude effective dosing in many patients [8]. Electrical activation of the nucleus basalis (NB) of Meynert, the source of neocortical acetylcholine [9, 10], provides a potential method of improving cholinergic activation [11, 12]. Here we tested whether NB stimulation would improve performance of a working memory task in a nonhuman primate model. Unexpectedly, intermittent stimulation proved to be most beneficial (60 pulses per second, for 20 s every minute), whereas continuous stimulation often impaired performance. Pharmacological experiments confirmed that the effects depended on cholinergic activation. Donepezil, a cholinesterase inhibitor, restored performance in animals impaired by continuous stimulation but did not improve performance further during intermittent stimulation. Intermittent stimulation was rendered ineffective by either nicotinic or muscarinic receptor antagonists. In the months after stimulation began, performance also improved in sessions without stimulation. Our results reveal that intermittent NB stimulation can improve working memory, a finding that has implications for restoring cognitive function in aging and Alzheimers dementia.

Published
2017

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