1,492 research outputs found
An introduction to ghost imaging: quantum and classical
Ghost imaging has been a subject of interest to the quantum optics community for the past 20 years. Initially seen as manifestation of quantum spookiness, it is now recognized as being implementable in both single- and many-photon number regimes. Beyond its scientific curiosity, it is now feeding novel imaging modalities potentially offering performance attributes that traditional approaches cannot match
Controlling induced coherence for quantum imaging
Induced coherence in parametric down-conversion between two coherently pumped
nonlinear crystals that share a common idler mode can be used as an imaging
technique. Based on the interference between the two signal modes of the
crystals, an image can be reconstructed. By obtaining an expression for the
interference pattern that is valid in both the low- and the high-gain regimes
of parametric down-conversion, we show how the coherence of the light emitted
by the two crystals can be controlled. With our comprehensive analysis we
provide deeper insight into recent discussions about the application of induced
coherence to imaging in different regimes. Moreover, we propose a scheme for
optimizing the visibility of the interference pattern so that it directly
corresponds to the degree of coherence of the light generated in the two
crystals. We find that this scheme leads in the high-gain regime to a
visibility arbitrarily close to unity.Comment: 9 pages, 4 figure
Generation of a spin-polarized electron beam by multipoles magnetic fields
The propagation of an electron beam in the presence of transverse magnetic
fields possessing integer topological charges is presented. The spin--magnetic
interaction introduces a nonuniform spin precession of the electrons that gains
a space-variant geometrical phase in the transverse plane proportional to the
field's topological charge, whose handedness depends on the input electron's
spin state. A combination of our proposed device with an electron orbital
angular momentum sorter can be utilized as a spin-filter of electron beams in a
mid-energy range. We examine these two different configurations of a partial
spin-filter generator numerically. The results of these analysis could prove
useful in the design of improved electron microscope.Comment: 7 pages, 7 figure
Generation of orbital angular momentum bell states and their verification via accessible nonlinear witnesses
Recovering full coherence in a qubit by measuring half of its environment
When quantum systems interact with the environment they lose their quantum
properties, such as coherence. Quantum erasure makes it possible to restore
coherence in a system by measuring its environment, but accessing the whole of
it may be prohibitive: realistically one might have to concentrate only on an
accessible subspace and neglect the rest. If that is the case, how good is
quantum erasure? In this work we compute the largest coherence that we can expect to recover in a qubit, as a function of
the dimension of the accessible and of the inaccessible subspaces of its
environment. We then imagine the following game: we are given a uniformly
random pure state of qubits and we are asked to compute the largest
coherence that we can retrieve on one of them by optimally measuring a certain
number of the others. We find a surprising effect around the
value : the recoverable coherence sharply transitions between 0
and 1, indicating that in order to restore full coherence on a qubit we need
access to only half of its physical environment (or in terms of degrees of
freedom to just the square root of them). Moreover, we find that the
recoverable coherence becomes a typical property of the whole ensemble as
grows.Comment: 4 pages, 5 figure
Amplification of Angular Rotations Using Weak Measurements
We present a weak measurement protocol that permits a sensitive estimation of
angular rotations based on the concept of weak-value amplification. The shift
in the state of a pointer, in both angular position and the conjugate orbital
angular momentum bases, is used to estimate angular rotations. This is done by
an amplification of both the real and imaginary parts of the weak-value of a
polarization operator that has been coupled to the pointer, which is a spatial
mode, via a spin-orbit coupling. Our experiment demonstrates the first
realization of weak-value amplification in the azimuthal degree of freedom. We
have achieved effective amplification factors as large as 100, providing a
sensitivity that is on par with more complicated methods that employ quantum
states of light or extremely large values of orbital angular momentum.Comment: 5 pages, 3 figures, contains supplementary informatio
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