54,131 research outputs found
On the imaging of electron transport in semiconductor quantum structures by scanning-gate microscopy: successes and limitations
This paper presents a brief review of scanning-gate microscopy applied to the
imaging of electron transport in buried semiconductor quantum structures. After
an introduction to the technique and to some of its practical issues, we
summarise a selection of its successful achievements found in the literature,
including our own research. The latter focuses on the imaging of GaInAs-based
quantum rings both in the low magnetic field Aharonov-Bohm regime and in the
high-field quantum Hall regime. Based on our own experience, we then discuss in
detail some of the limitations of scanning-gate microscopy. These include
possible tip induced artefacts, effects of a large bias applied to the scanning
tip, as well as consequences of unwanted charge traps on the conductance maps.
We emphasize how special care must be paid in interpreting these scanning-gate
images.Comment: Special issue on (nano)characterization of semiconductor materials
and structure
Optical orbital angular momentum
We present a brief introduction to the orbital angular momentum of light, the subject of our theme issue and, in particular, to the developments in the 13 years following the founding paper by Allen et al. (Allen et al. 1992 Phys. Rev. A 45, 8185 (doi:10.1103/PhysRevA.45.8185)). The papers by our invited authors serve to bring the field up to date and suggest where developments may take us next
Introduction to high-energy gamma-ray astronomy
The present issue is the first of of a two-volume review devoted to gamma-ray
astronomy above 100 MeV which has witnessed considerable progress over the last
20 years. The motivations for research in this area are explained, the
follow-on articles of these two thematic issues are introduced and a brief
history of the field is given.Comment: 15 pages, 6 figures. Introduction to a two-volume topical issue on
Gamma-ray Astronomy above 100 MeV coordinated by the author
From retrodiction to Bayesian quantum imaging
We employ quantum retrodiction to develop a robust Bayesian algorithm for reconstructing the intensity values of an image from sparse photocount data, while also accounting for detector noise in the form of dark counts. This method yields not only a reconstructed image but also provides the full probability distribution function for the intensity at each pixel. We use simulated as well as real data to illustrate both the applications of the algorithm and the analysis options that are only available when the full probability distribution functions are known. These include calculating Bayesian credible regions for each pixel intensity, allowing an objective assessment of the reliability of the reconstructed image intensity values
Multiparameter Quantum Metrology of Incoherent Point Sources: Towards Realistic Superresolution
We establish the multiparameter quantum Cram\'er-Rao bound for simultaneously
estimating the centroid, the separation, and the relative intensities of two
incoherent optical point sources using alinear imaging system. For equally
bright sources, the Cram\'er-Rao bound is independent of the source separation,
which confirms that the Rayleigh resolution limit is just an artifact of the
conventional direct imaging and can be overcome with an adequate strategy. For
the general case of unequally bright sources, the amount of information one can
gain about the separation falls to zero, but we show that there is always a
quadratic improvement in an optimal detection in comparison with the intensity
measurements. This advantage can be of utmost important in realistic scenarios,
such as observational astronomy.Comment: 5 pages, 3 figures. Comments welcome
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
Quantum temporal imaging: application of a time lens to quantum optics
We consider application of a temporal imaging system, based on the
sum-frequency generation, to a nonclassical, in particular, squeezed optical
temporal waveform. We analyze the restrictions on the pump and the phase
matching condition in the summing crystal, necessary for preserving the quantum
features of the initial waveform. We show that modification of the notion of
the field of view in the quantum case is necessary, and that the quantum field
of view is much narrower than the classical one for the same temporal imaging
system. These results are important for temporal stretching and compressing of
squeezed fields, used in quantum-enhanced metrology and quantum communications.Comment: 9 pages, 3 figure
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