217 research outputs found
On the optimal feedback control of linear quantum systems in the presence of thermal noise
We study the possibility of taking bosonic systems subject to quadratic
Hamiltonians and a noisy thermal environment to non-classical stationary states
by feedback loops based on weak measurements and conditioned linear driving. We
derive general analytical upper bounds for the single mode squeezing and
multimode entanglement at steady state, depending only on the Hamiltonian
parameters and on the number of thermal excitations of the bath. Our findings
show that, rather surprisingly, larger number of thermal excitations in the
bath allow for larger steady-state squeezing and entanglement if the efficiency
of the optimal continuous measurements conditioning the feedback loop is high
enough. We also consider the performance of feedback strategies based on
homodyne detection and show that, at variance with the optimal measurements, it
degrades with increasing temperature.Comment: 10 pages, 2 figures. v2: minor changes to the letter; better
explanation of the necessary and sufficient conditions to achieve the bounds
(in the supplemental material); v3: title changed; comparison between optimal
general-dyne strategy and homodyne strategy is discussed; supplemental
material included in the manuscript and few references added. v4: published
versio
Optimal estimation of joint parameters in phase space
We address the joint estimation of the two defining parameters of a
displacement operation in phase space. In a measurement scheme based on a
Gaussian probe field and two homodyne detectors, it is shown that both
conjugated parameters can be measured below the standard quantum limit when the
probe field is entangled. We derive the most informative Cram\'er-Rao bound,
providing the theoretical benchmark on the estimation and observe that our
scheme is nearly optimal for a wide parameter range characterizing the probe
field. We discuss the role of the entanglement as well as the relation between
our measurement strategy and the generalized uncertainty relations.Comment: 8 pages, 3 figures; v2: references added and sections added to the
supplemental material; v3: minor changes (published version
Quantum Control at the Boundary
We present a scheme for controlling the state of a quantum system by
modifying the boundary conditions. This constitutes an infinite-dimensional
control problem. We provide conditions for the existence of solutions of the
dynamics and prove that this system is approximately controllable
Detection of Torquetenovirus and Redondovirus DNA in Saliva Samples from SARS-CoV-2-Positive and -Negative Subjects
Torquetenovirus (TTV) and Redondovirus (ReDoV) are the most prevalent viruses found in the human respiratory virome in viral metagenomics studies. A large-scale epidemiological study was performed to investigate their prevalence and loads in saliva samples according to SARS-CoV-2 status
Photography as an act of collaboration
The camera is usually considered to be a passive tool under the control of the operator. This definition implicitly constrains how we use the medium, as well as how we look at â and what we see in â its interpretations of scenes, objects, events and âmomentsâ. This text will suggest another way of thinking about â and using â the photographic medium. Based on the evidence of photographic practice (mine and othersâ), I will suggest that, as a result of the ways in which the medium interprets, juxtaposes and renders the elements in front of the lens, the camera is capable of depicting scenes, events and moments that did not exist and could not have existed until brought into being by the act of photographing them. Accordingly, I will propose that the affective power of many photographs is inseparable from their âphotographicnessâ â and that the photographic medium should therefore be considered as an active collaborator in the creation of uniquely photographic images
Quantum optics in the phase space - A tutorial on Gaussian states
In this tutorial, we introduce the basic concepts and mathematical tools
needed for phase-space description of a very common class of states, whose
phase properties are described by Gaussian Wigner functions: the Gaussian
states. In particular, we address their manipulation, evolution and
characterization in view of their application to quantum information.Comment: Tutorial. 23 pages, 1 figure. Updated version accepted for
publication in EPJ - ST devoted to the memory of Federico Casagrand
SOXS: a wide band spectrograph to follow up transients
SOXS (Son Of X-Shooter) will be a spectrograph for the ESO NTT telescope
capable to cover the optical and NIR bands, based on the heritage of the
X-Shooter at the ESO-VLT. SOXS will be built and run by an international
consortium, carrying out rapid and longer term Target of Opportunity requests
on a variety of astronomical objects. SOXS will observe all kind of transient
and variable sources from different surveys. These will be a mixture of fast
alerts (e.g. gamma-ray bursts, gravitational waves, neutrino events), mid-term
alerts (e.g. supernovae, X-ray transients), fixed time events (e.g. close-by
passage of minor bodies). While the focus is on transients and variables, still
there is a wide range of other astrophysical targets and science topics that
will benefit from SOXS. The design foresees a spectrograph with a
Resolution-Slit product ~ 4500, capable of simultaneously observing over the
entire band the complete spectral range from the U- to the H-band. The limiting
magnitude of R~20 (1 hr at S/N~10) is suited to study transients identified
from on-going imaging surveys. Light imaging capabilities in the optical band
(grizy) are also envisaged to allow for multi-band photometry of the faintest
transients. This paper outlines the status of the project, now in Final Design
Phase.Comment: 12 pages, 14 figures, to be published in SPIE Proceedings 1070
Collection Development Policies in Public Libraries in Australia: A Qualitative Content Analysis
The role that public library collection development polices play inguiding selectors and informing users has been promoted as a pillar of good professional practice. While these policies purport to open up the methods and the criteria used in selection so as to promote transparency and a sense of professional objectivity, how they actually are developed and put into practice has remained largely implicit in the research literature. This analysis revealedthat policies tended to focus on local issues and remained heavily materials focused. How collections are developed to support userâs information needs and substantive issues associated with topicality are largely unarticulated
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