8,136 research outputs found
Quantum metrology and its application in biology
Quantum metrology provides a route to overcome practical limits in sensing
devices. It holds particular relevance to biology, where sensitivity and
resolution constraints restrict applications both in fundamental biophysics and
in medicine. Here, we review quantum metrology from this biological context,
focusing on optical techniques due to their particular relevance for biological
imaging, sensing, and stimulation. Our understanding of quantum mechanics has
already enabled important applications in biology, including positron emission
tomography (PET) with entangled photons, magnetic resonance imaging (MRI) using
nuclear magnetic resonance, and bio-magnetic imaging with superconducting
quantum interference devices (SQUIDs). In quantum metrology an even greater
range of applications arise from the ability to not just understand, but to
engineer, coherence and correlations at the quantum level. In the past few
years, quite dramatic progress has been seen in applying these ideas into
biological systems. Capabilities that have been demonstrated include enhanced
sensitivity and resolution, immunity to imaging artifacts and technical noise,
and characterization of the biological response to light at the single-photon
level. New quantum measurement techniques offer even greater promise, raising
the prospect for improved multi-photon microscopy and magnetic imaging, among
many other possible applications. Realization of this potential will require
cross-disciplinary input from researchers in both biology and quantum physics.
In this review we seek to communicate the developments of quantum metrology in
a way that is accessible to biologists and biophysicists, while providing
sufficient detail to allow the interested reader to obtain a solid
understanding of the field. We further seek to introduce quantum physicists to
some of the central challenges of optical measurements in biological science.Comment: Submitted review article, comments and suggestions welcom
Anisotropy in s-wave Bose-Einstein condensate collisions and its relationship to superradiance
We report the experimental realization of a single-species atomic four-wave
mixing process with BEC collisions for which the angular distribution of
scattered atom pairs is not isotropic, despite the collisions being in the
-wave regime. Theoretical analysis indicates that this anomalous behavior
can be explained by the anisotropic nature of the gain in the medium. There are
two competing anisotropic processes: classical trajectory deflections due to
the mean-field potential, and Bose enhanced scattering which bears similarity
to super-radiance. We analyse the relative importance of these processes in the
dynamical buildup of the anisotropic density distribution of scattered atoms,
and compare to optically pumped super-radiance.Comment: 13 pages, 10 figures, added a fuller discussion of timescales,
otherwise some minor changes in the text and the formatting of Figures 5-
Spin Readout Techniques of the Nitrogen-Vacancy Center in Diamond
The diamond nitrogen-vacancy (NV) center is a leading platform for quantum
information science due to its optical addressability and room-temperature spin
coherence. However, measurements of the NV center's spin state typically
require averaging over many cycles to overcome noise. Here, we review several
approaches to improve the readout performance and highlight future avenues of
research that could enable single-shot electron-spin readout at room
temperature.Comment: 21 pages, 7 figure
Obliquity Constraints on an Extrasolar Planetary-Mass Companion
We place the first constraints on the obliquity of a planetary-mass companion outside of the solar system. Our target is the directly imaged system 2MASS J01225093–2439505 (2M0122), which consists of a 120 Myr 0.4 M⊙ star hosting a 12–27 M_J companion at 50 au. We constrain all three of the system's angular-momentum vectors: how the companion spin axis, the stellar spin axis, and the orbit normal are inclined relative to our line of sight. To accomplish this, we measure projected rotation rates (v sin i) for both the star and the companion using new near-infrared high-resolution spectra with NIRSPEC at Keck Observatory. We combine these with a new stellar photometric rotation period from TESS and a published companion rotation period from Hubble Space Telescope to obtain spin-axis inclinations for both objects. We also fitted multiple epochs of astrometry, including a new observation with NIRC2/Keck, to measure 2M0122b's orbital inclination. The three line-of-sight inclinations place limits on the true de-projected companion obliquity and stellar obliquity. We find that while the stellar obliquity marginally prefers alignment, the companion obliquity tentatively favors misalignment. We evaluate possible origin scenarios. While collisions, secular spin–orbit resonances, and Kozai–Lidov oscillations are unlikely, formation by gravitational instability in a gravito-turbulent disk—the scenario favored for brown dwarf companions to stars—appears promising
X-ray imaging of spin currents and magnetisation dynamics at the nanoscale
Understanding how spins move in time and space is the aim of both fundamental
and applied research in modern magnetism. Over the past three decades, research
in this field has led to technological advances that have had a major impact on
our society, while improving the understanding of the fundamentals of spin
physics. However, important questions still remain unanswered, because it is
experimentally challenging to directly observe spins and their motion with a
combined high spatial and temporal resolution. In this article, we present an
overview of the recent advances in X-ray microscopy that allow researchers to
directly watch spins move in time and space at the microscopically relevant
scales. We discuss scanning X-ray transmission microscopy (STXM) at resonant
soft X-ray edges, which is available at most modern synchrotron light sources.
This technique measures magnetic contrast through the X-ray magnetic circular
dichroism (XMCD) effect at the resonant absorption edges, while focusing the
X-ray radiation at the nanometre scale, and using the intrinsic pulsed
structure of synchrotron-generated X-rays to create time-resolved images of
magnetism at the nanoscale. In particular, we discuss how the presence of spin
currents can be detected by imaging spin accumulation, and how the
magnetisation dynamics in thin ferromagnetic films can be directly imaged. We
discuss how a direct look at the phenomena allows for a deeper understanding of
the the physics at play, that is not accessible to other, more indirect
techniques. Finally, we present an overview of the exciting opportunities that
lie ahead to further understand the fundamentals of novel spin physics,
opportunities offered by the appearance of diffraction limited storage rings
and free electron lasers.Comment: 21 pages, 10 figure
Alzheimer’s Disease Diagnosis Using Machine Learning: A Survey
Alzheimer’s is a neurodegenerative disorder affecting the central nervous system and cognitive processes, explicitly impairing detailed mental analysis. Throughout this condition, the affected individual’s cognitive abilities to process and analyze information gradually deteriorate, resulting in mental decline. In recent years, there has been a notable increase in endeavors aimed at identifying Alzheimer’s disease and addressing its progression. Research studies have demonstrated the significant involvement of genetic factors, stress, and nutrition in developing this condition. The utilization of computer-aided analysis models based on machine learning and artificial intelligence has the potential to significantly enhance the exploration of various neuroimaging methods and non-image biomarkers. This study conducts a comparative assessment of more than 80 publications that have been published since 2017. Alzheimer’s disease detection is facilitated by utilizing fundamental machine learning architectures such as support vector machines, decision trees, and ensemble models. Furthermore, around 50 papers that utilized a specific architectural or design approach concerning Alzheimer’s disease were examined. The body of literature under consideration has been categorized and elucidated through the utilization of data-related, methodology-related, and medical-fostering components to illustrate the underlying challenges. The conclusion section of our study encompasses a discussion of prospective avenues for further investigation and furnishes recommendations for future research activities on the diagnosis of Alzheimer’s disease
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