516 research outputs found
Tomography of a displacement photon counter for discrimination of single-rail optical qubits
We investigate the performance of a Kennedy receiver, which is known as a
beneficial tool in optical coherent communications, to the quantum state
discrimination of the two superpositions of vacuum and single photon states
corresponding to the eigenstates in the single-rail encoding of
photonic qubits. We experimentally characterize the Kennedy receiver in
vacuum-single photon two-dimensional space using quantum detector tomography
and evaluate the achievable discrimination error probability from the
reconstructed measurement operators. We furthermore derive the minimum error
rate obtainable with Gaussian transformations and homodyne detection. Our proof
of principle experiment shows that the Kennedy receiver can achieve a
discrimination error surpassing homodyne detection
Assessments of macroscopicity for quantum optical states
With the slow but constant progress in the coherent control of quantum
systems, it is now possible to create large quantum superpositions. There has
therefore been an increased interest in quantifying any claims of
macroscopicity. We attempt here to motivate three criteria which we believe
should enter in the assessment of macroscopic quantumness: The number of
quantum fluctuation photons, the purity of the states, and the ease with which
the branches making up the state can be distinguished
Architecture and noise analysis of continuous variable quantum gates using two-dimensional cluster states
Due to its unique scalability potential, continuous variable quantum optics
is a promising platform for large scale quantum computing and quantum
simulation. In particular, very large cluster states with a two-dimensional
topology that are suitable for universal quantum computing and quantum
simulation can be readily generated in a deterministic manner, and routes
towards fault-tolerance via bosonic quantum error-correction are known. In this
article we propose a complete measurement-based quantum computing architecture
for the implementation of a universal set of gates on the recently generated
two-dimensional cluster states [1,2]. We analyze the performance of the various
quantum gates that are executed in these cluster states as well as in other
two-dimensional cluster states (the bilayer-square lattice and quad-rail
lattice cluster states [3,4]) by estimating and minimizing the associated
stochastic noise addition as well as the resulting gate error probability. We
compare the four different states and find that, although they all allow for
universal computation, the quad-rail lattice cluster state performs better than
the other three states which all exhibit similar performance
Super sensitivity and super resolution with quantum teleportation
We propose a method for quantum enhanced phase estimation based on continuous
variable (CV) quantum teleportation. The phase shift probed by a coherent state
can be enhanced by repeatedly teleporting the state back to interact with the
phase shift again using a supply of two-mode squeezed vacuum states. In this
way, both super resolution and super sensitivity can be obtained due to the
coherent addition of the phase shift. The protocol enables Heisenberg limited
sensitivity and super- resolution given sufficiently strong squeezing. The
proposed method could be implemented with current or near-term technology of CV
teleportation.Comment: 5 pagers, 3 figure
The capacity to maintain ion and water homeostasis underlies interspecific variation in Drosophila cold tolerance
Many insects, including Drosophila, succumb to the physiological effects of chilling at temperatures well above those causing freezing. Low temperature causes a loss of extracellular ion and water homeostasis in such insects, and chill injuries accumulate. Using an integrative and comparative approach, we examined the role of ion and water balance in insect chilling susceptibility/ tolerance. The Malpighian tubules (MT), of chill susceptible Drosophila species lost [Na+] and [K+] selectivity at low temperatures, which contributed to a loss of Na+ and water balance and a deleterious increase in extracellular [K+]. By contrast, the tubules of chill tolerant Drosophila species maintained their MT ion selectivity, maintained stable extracellular ion concentrations, and thereby avoided injury. The most tolerant species were able to modulate ion balance while in a cold-induced coma and this ongoing physiological acclimation process allowed some individuals of the tolerant species to recover from chill coma during low temperature exposure. Accordingly, differences in the ability to maintain homeostatic control of water and ion balance at low temperature may explain large parts of the wide intra- and interspecific variation in insect chilling tolerance
Hybrid quantum information processing
The development of quantum information processing has traditionally followed
two separate and not immediately connected lines of study. The main line has
focused on the implementation of quantum bit (qubit) based protocols whereas
the other line has been devoted to implementations based on high-dimensional
Gaussian states (such as coherent and squeezed states). The separation has been
driven by the experimental difficulty in interconnecting the standard
technologies of the two lines. However, in recent years, there has been a
significant experimental progress in refining and connecting the technologies
of the two fields which has resulted in the development and experimental
realization of numerous new hybrid protocols. In this Review, we summarize
these recent efforts on hybridizing the two types of schemes based on discrete
and continuous variables.Comment: 13 pages, 6 figure
Measurement-induced macroscopic superposition states in cavity optomechanics
We present a novel proposal for generating quantum superpositions of
macroscopically distinct states of a bulk mechanical oscillator, compatible
with existing optomechanical devices operating in the readily achievable
bad-cavity limit. The scheme is based on a pulsed cavity optomechanical quantum
non-demolition (QND) interaction, driven by displaced non-Gaussian states, and
measurement-induced feedback, avoiding the need for strong single-photon
optomechanical coupling. Furthermore, we show that single-quadrature cooling of
the mechanical oscillator is sufficient for efficient state preparation, and we
outline a three-pulse protocol comprising a sequence of QND interactions for
squeezing-enhanced cooling, state preparation, and tomography.Comment: 7 pages, 5 figure
Light rail project in Copenhagen â the Ring 21â2 corridor
The need for high class public transport service of the increasing travel across the radial urban structure of the greater Copenhagen region was examined through planning of a light rail. The exact corridor (defined as the Ring 21â2 corridor) and alignment of the light rail were documented and the locations of stops were examined through analyses of catchment areas. The timetable of the light rail was determined through travel time and correspondences with other high class public transport lines/corridors. The justification of the light rail was examined through factors like traffic impacts, operation economy, socioeconomics and strategic impacts. The light rail shows a good result on most factors. But it displays socioeconomic non-viability. However, this was expected when using the standard procedures. But the Ring 21â2 light rail shows a better socioeconomic result than many other examined light rail projects
Light rail project in Copenhagen â the Ring 21â2 corridor
The need for high class public transport service of the increasing travel across the radial urban structure of the greater Copenhagen region was examined through planning of a light rail. The exact corridor (defined as the Ring 21â2 corridor) and alignment of the light rail were documented and the locations of stops were examined through analyses of catchment areas. The timetable of the light rail was determined through travel time and correspondences with other high class public transport lines/corridors. The justification of the light rail was examined through factors like traffic impacts, operation economy, socioeconomics and strategic impacts. The light rail shows a good result on most factors. But it displays socioeconomic non-viability. However, this was expected when using the standard procedures. But the Ring 21â2 light rail shows a better socioeconomic result than many other examined light rail projects
The Psychosocial Work Environment and Perceived Stress among Seniors with Physically Demanding Jobs:The SeniorWorkingLife Study
Background: Poor psychosocial work conditions are known to foster negative health consequences. While the existing literature on this topic focus mainly on white-collar workers, the influence of different aspects of the psychosocial work environment in physically demanding jobs remain understudied. Likewise, senior workers represent a population of the workforce at increased risk of adverse health outcomes and premature exit from the labour market. This study investigates the association between psychosocial work factors and perceived stress among the senior work force. Methods: Utilizing cross-sectional findings, this study reports associations between psychosocial factors (organizational justice, cooperation and collegial support, decision latitude, clarity of tasks, and quality of leadership) and the outcome of perceived stress quantified by Cohenâs Perceived Stress Scale (CPSS). Currently employed senior workers with physically demanding jobs were included in the analyses (n = 3386). Associations were modeled using general linear models with weights to make the estimates representative. Results: For all individually adjusted psychosocial variables, the category of âgoodâ was consistently associated with lower stress scores compared to the categories of both âmoderateâ and âpoorâ (all p < 0.0001). Likewise, in the mutually adjusted analysis, the category of âgoodâ was statistically different from âpoorâ for all included variables, while the category of âmoderateâ remained different from âpoorâ for âclarity of tasksâ, âcooperation and collegial supportâ, and âdecision latitudeâ. Conclusions: Among senior workers with physically demanding jobs, poor ratings of organizational factors related to the psychosocial work environment are consistently associated with high stress scores. Blue-collar occupations focusing primarily on physical risk factors are recommended to increase awareness on psychosocial aspects that may be relevant to the local work environment
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