2,430 research outputs found
Real-Time Polarimetry of Hyperpolarized 13C Nuclear Spins Using an Atomic Magnetometer
We introduce a method for nondestructive quantification of nuclear spin polarization, of relevance to hyperpolarized spin tracers widely used in magnetic resonance from spectroscopy to in vivo imaging. In a bias field of around 30 nT we use a high-sensitivity miniaturized 87Rb-vapor magnetometer to measure the field generated by the sample, as it is driven by a windowed dynamical decoupling pulse sequence that both maximizes the nuclear spin lifetime and modulates the polarization for easy detection. We demonstrate the procedure applied to a 0.08 M hyperpolarized [1-13C]-pyruvate solution produced by dissolution dynamic nuclear polarization, measuring polarization repeatedly during natural decay at Earth's field. Application to real-time and continuous quality monitoring of hyperpolarized substances is discussed
Cosmic Ray Processes in Galactic Ecosystems
Galaxy evolution is an important topic, and our physical understanding must be complete to establish a correct picture. This includes a thorough treatment of feedback. The effects of thermal–mechanical and radiative feedback have been widely considered; however, cosmic rays (CRs) are also powerful energy carriers in galactic ecosystems. Resolving the capability of CRs to operate as a feedback agent is therefore essential to advance our understanding of the processes regulating galaxies. The effects of CRs are yet to be fully understood, and their complex multi-channel feedback mechanisms operating across the hierarchy of galaxy structures pose a significant technical challenge. This review examines the role of CRs in galaxies, from the scale of molecular clouds to the circumgalactic medium. An overview of their interaction processes, their implications for galaxy evolution, and their observable signatures is provided and their capability to modify the thermal and hydrodynamic configuration of galactic ecosystems is discussed. We present recent advancements in our understanding of CR processes and interpretation of their signatures, and highlight where technical challenges and unresolved questions persist. We discuss how these may be addressed with upcoming opportunities
Entanglement-free Heisenberg-limited phase estimation
Measurement underpins all quantitative science. A key example is the
measurement of optical phase, used in length metrology and many other
applications. Advances in precision measurement have consistently led to
important scientific discoveries. At the fundamental level, measurement
precision is limited by the number N of quantum resources (such as photons)
that are used. Standard measurement schemes, using each resource independently,
lead to a phase uncertainty that scales as 1/sqrt(N) - known as the standard
quantum limit. However, it has long been conjectured that it should be possible
to achieve a precision limited only by the Heisenberg uncertainty principle,
dramatically improving the scaling to 1/N. It is commonly thought that
achieving this improvement requires the use of exotic quantum entangled states,
such as the NOON state. These states are extremely difficult to generate.
Measurement schemes with counted photons or ions have been performed with N <=
6, but few have surpassed the standard quantum limit and none have shown
Heisenberg-limited scaling. Here we demonstrate experimentally a
Heisenberg-limited phase estimation procedure. We replace entangled input
states with multiple applications of the phase shift on unentangled
single-photon states. We generalize Kitaev's phase estimation algorithm using
adaptive measurement theory to achieve a standard deviation scaling at the
Heisenberg limit. For the largest number of resources used (N = 378), we
estimate an unknown phase with a variance more than 10 dB below the standard
quantum limit; achieving this variance would require more than 4,000 resources
using standard interferometry. Our results represent a drastic reduction in the
complexity of achieving quantum-enhanced measurement precision.Comment: Published in Nature. This is the final versio
Piloting a parent and patient decision aid to support clinical trial decision making in childhood cancer
Objective: Families of a child with cancer can find the decision to enrol in a clinical trial challenging and often misunderstand key concepts that underpin trials. We pilot tested “Delta,” an online and booklet decision aid for parents with a child with cancer, and adolescents with cancer, deciding whether or not to enrol in a clinical trial. Methods: We developed Delta in accordance with the International Patient Decision Aid Standards. We conducted a pre-post pilot with parents with a child, and adolescents, who had enrolled in a paediatric phase III clinical trial for newly diagnosed acute lymphoblastic leukaemia. Parents (n = 37) and adolescents (n = 3) completed a questionnaire before and after using Delta (either the website or booklet, based on their preference). Results: Twenty-three parents (62.2%) and three adolescents (100%) reviewed the Delta website. Parents rated Delta as highly acceptable in regard to being clearly presented, informative, easy to read, useful, visually appealing, and easy to use. All participants reported that they would recommend Delta to others and that it would have been useful when making their decision. Parents' subjective (Mdiff=10.8, SDdiff = 15.69, P <.001) and objective (OR = 2.25, 95% CI, 1.66-3.04; P <.001) clinical trial knowledge increased significantly after reviewing Delta. Conclusions: To our knowledge, Delta is the first reported decision aid, available online and as a booklet, for parents and adolescents deciding whether or not to enrol in a paediatric oncology clinical trial. Our study suggests that Delta is acceptable, feasible, and potentially useful
Interaction-based quantum metrology showing scaling beyond the Heisenberg limit
Quantum metrology studies the use of entanglement and other quantum resources
to improve precision measurement. An interferometer using N independent
particles to measure a parameter X can achieve at best the "standard quantum
limit" (SQL) of sensitivity {\delta}X \propto N^{-1/2}. The same interferometer
using N entangled particles can achieve in principle the "Heisenberg limit"
{\delta}X \propto N^{-1}, using exotic states. Recent theoretical work argues
that interactions among particles may be a valuable resource for quantum
metrology, allowing scaling beyond the Heisenberg limit. Specifically, a
k-particle interaction will produce sensitivity {\delta}X \propto N^{-k} with
appropriate entangled states and {\delta}X \propto N^{-(k-1/2)} even without
entanglement. Here we demonstrate this "super-Heisenberg" scaling in a
nonlinear, non-destructive measurement of the magnetisation of an atomic
ensemble. We use fast optical nonlinearities to generate a pairwise
photon-photon interaction (k = 2) while preserving quantum-noise-limited
performance, to produce {\delta}X \propto N^{-3/2}. We observe super-Heisenberg
scaling over two orders of magnitude in N, limited at large N by higher-order
nonlinear effects, in good agreement with theory. For a measurement of limited
duration, super-Heisenberg scaling allows the nonlinear measurement to overtake
in sensitivity a comparable linear measurement with the same number of photons.
In other scenarios, however, higher-order nonlinearities prevent this crossover
from occurring, reflecting the subtle relationship of scaling to sensitivity in
nonlinear systems. This work shows that inter-particle interactions can improve
sensitivity in a quantum-limited measurement, and introduces a fundamentally
new resource for quantum metrology
Super-resolving phase measurements with a multi-photon entangled state
Using a linear optical elements and post-selection, we construct an entangled
polarization state of three photons in the same spatial mode. This state is
analogous to a ``photon-number path entangled state'' and can be used for
super-resolving interferometry. Measuring a birefringent phase shift, we
demonstrate two- and three-fold improvements in phase resolution.Comment: 4 pages, 3 figure
Quantum states made to measure
Recent progress in manipulating quantum states of light and matter brings
quantum-enhanced measurements closer to prospective applications. The current
challenge is to make quantum metrologic strategies robust against
imperfections.Comment: 4 pages, 3 figures, Commentary for Nature Photonic
Entanglement-enhanced probing of a delicate material system
Quantum metrology uses entanglement and other quantum effects to improve the
sensitivity of demanding measurements. Probing of delicate systems demands high
sensitivity from limited probe energy and has motivated the field's key
benchmark-the standard quantum limit. Here we report the first
entanglement-enhanced measurement of a delicate material system. We
non-destructively probe an atomic spin ensemble by means of near-resonant
Faraday rotation, a measurement that is limited by probe-induced scattering in
quantum-memory and spin-squeezing applications. We use narrowband,
atom-resonant NOON states to beat the standard quantum limit of sensitivity by
more than five standard deviations, both on a per-photon and per-damage basis.
This demonstrates quantum enhancement with fully realistic loss and noise,
including variable-loss effects. The experiment opens the way to ultra-gentle
probing of single atoms, single molecules, quantum gases and living cells.Comment: 7 pages, 8 figures; Nature Photonics, advance online publication, 16
December 201
Can a falling tree make a noise in two forests at the same time?
It is a commonplace to claim that quantum mechanics supports the old idea
that a tree falling in a forest makes no sound unless there is a listener
present. In fact, this conclusion is far from obvious. Furthermore, if a
tunnelling particle is observed in the barrier region, it collapses to a state
in which it is no longer tunnelling. Does this imply that while tunnelling, the
particle can not have any physical effects? I argue that this is not the case,
and moreover, speculate that it may be possible for a particle to have effects
on two spacelike separate apparatuses simultaneously. I discuss the measurable
consequences of such a feat, and speculate about possible statistical tests
which could distinguish this view of quantum mechanics from a ``corpuscular''
one. Brief remarks are made about an experiment underway at Toronto to
investigate these issues.Comment: 9 pp, Latex, 3 figs, to appear in Proc. Obsc. Unr. Conf.; Fig 2
postscript repaired on 26.10.9
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