2,795 research outputs found
UCD Candidates in the Hydra Cluster
NGC 3311, the giant cD galaxy in the Hydra cluster (A1060), has one of the
largest globular cluster systems known. We describe new Gemini GMOS (g',i')
photometry of the NGC 3311 field which reveals that the red, metal-rich side of
its globular cluster population extends smoothly upward into the mass range
associated with the new class of Ultra-Compact Dwarfs (UCDs). We identify 29
UCD candidates with estimated masses > 6x10^6 solar masses and discuss their
characteristics. This UCD-like sequence is the most well defined one yet seen,
and reinforces current ideas that the high-mass end of the globular cluster
sequence merges continuously into the UCD sequence, which connects in turn to
the E galaxy structural sequence.Comment: 5 pages, 3 figures. Accepted for publication in ApJ Letter
Work and reversibility in quantum thermodynamics
It is a central question in quantum thermodynamics to determine how
irreversible is a process that transforms an initial state to a final
state , and whether such irreversibility can be thought of as a useful
resource. For example, we might ask how much work can be obtained by
thermalizing to a thermal state at temperature of an
ambient heat bath. Here, we show that, for different sets of resource-theoretic
thermodynamic operations, the amount of entropy produced along a transition is
characterized by how reversible the process is. More specifically, this entropy
production depends on how well we can return the state to its original
form without investing any work. At the same time, the entropy
production can be linked to the work that can be extracted along a given
transition, and we explore the consequences that this fact has for our results.
We also exhibit an explicit reversal operation in terms of the Petz recovery
channel coming from quantum information theory. Our result establishes a
quantitative link between the reversibility of thermodynamical processes and
the corresponding work gain.Comment: 14 page
Probability tree algorithm for general diffusion processes
Motivated by path-integral numerical solutions of diffusion processes,
PATHINT, we present a new tree algorithm, PATHTREE, which permits extremely
fast accurate computation of probability distributions of a large class of
general nonlinear diffusion processes
A model of ant route navigation driven by scene familiarity
In this paper we propose a model of visually guided route navigation in ants that captures the known properties of real behaviour whilst retaining mechanistic simplicity and thus biological plausibility. For an ant, the coupling of movement and viewing direction means that a familiar view specifies a familiar direction of movement. Since the views experienced along a habitual route will be more familiar, route navigation can be re-cast as a search for familiar views. This search can be performed with a simple scanning routine, a behaviour that ants have been observed to perform. We test this proposed route navigation strategy in simulation, by learning a series of routes through visually cluttered environments consisting of objects that are only distinguishable as silhouettes against the sky. In the first instance we determine view familiarity by exhaustive comparison with the set of views experienced during training. In further experiments we train an artificial neural network to perform familiarity discrimination using the training views. Our results indicate that, not only is the approach successful, but also that the routes that are learnt show many of the characteristics of the routes of desert ants. As such, we believe the model represents the only detailed and complete model of insect route guidance to date. What is more, the model provides a general demonstration that visually guided routes can be produced with parsimonious mechanisms that do not specify when or what to learn, nor separate routes into sequences of waypoints
Practicing place: Collective experience and difference in an urban online forum
Despite predictions to the contrary, place has assumed a new significance through recent innovations in digital technology. In this paper, we argue that the exchange of information and experience occurring daily on the networked urban forum Phillyblog can be usefully conceptualized as the practice of place. In adopting this terminology, we suggest particular analytic and theoretical lines which hold important implications for the way we think about information and place in online settings. Within the context of Phillyblog, the practice of place (1) publicizes and reinforces collective experiences of the city and (2) plays an active role in constructing the distinctness and diversity of its neighborhoods. In analyzing their regular interactions on Phillyblog, we hope to add to research on information practice, in particular “everyday information practices” (Savolainen, 2008 ), by suggesting their role in the social construction of place. Using this particular case, we explore how information sharing and production, in particular, may play a role in the perception, conception, and experience of place.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/78319/1/1450460264_ftp.pd
Entropic uncertainty and measurement reversibility
The entropic uncertainty relation with quantum side information (EUR-QSI) from (Berta et al 2010 Nat. Phys. 6 659) is a unifying principle relating two distinctive features of quantum mechanics: quantum uncertainty due to measurement incompatibility, and entanglement. In these relations, quantum uncertainty takes the form of preparation uncertainty where one of two incompatible measurements is applied. In particular, the 'uncertainty witness' lower bound in the EUR-QSI is not a function of a post-measurement state. An insightful proof of the EUR-QSI from (Coles et al 2012 Phys. Rev. Lett. 108 210405) makes use of a fundamental mathematical consequence of the postulates of quantum mechanics known as the non-increase of quantum relative entropy under quantum channels. Here, we exploit this perspective to establish a tightening of the EUR-QSI which adds a new state-dependent term in the lower bound, related to how well one can reverse the action of a quantum measurement. As such, this new term is a direct function of the post-measurement state and can be thought of as quantifying how much disturbance a given measurement causes. Our result thus quantitatively unifies this feature of quantum mechanics with the others mentioned above. We have experimentally tested our theoretical predictions on the IBM quantum experience and find reasonable agreement between our predictions and experimental outcomes
Entropic uncertainty relations and their applications
© 2017 American Physical Society. Heisenberg's uncertainty principle forms a fundamental element of quantum mechanics. Uncertainty relations in terms of entropies were initially proposed to deal with conceptual shortcomings in the original formulation of the uncertainty principle and, hence, play an important role in quantum foundations. More recently, entropic uncertainty relations have emerged as the central ingredient in the security analysis of almost all quantum cryptographic protocols, such as quantum key distribution and two-party quantum cryptography. This review surveys entropic uncertainty relations that capture Heisenberg's idea that the results of incompatible measurements are impossible to predict, covering both finite- and infinite-dimensional measurements. These ideas are then extended to incorporate quantum correlations between the observed object and its environment, allowing for a variety of recent, more general formulations of the uncertainty principle. Finally, various applications are discussed, ranging from entanglement witnessing to wave-particle duality to quantum cryptography
Desert Ants Learn Vibration and Magnetic Landmarks
The desert ants Cataglyphis navigate not only by path integration but also by using visual and olfactory landmarks to pinpoint the nest entrance. Here we show that Cataglyphis noda can additionally use magnetic and vibrational landmarks as nest-defining cues. The magnetic field may typically provide directional rather than positional information, and vibrational signals so far have been shown to be involved in social behavior. Thus it remains questionable if magnetic and vibration landmarks are usually provided by the ants' habitat as nest-defining cues. However, our results point to the flexibility of the ants' navigational system, which even makes use of cues that are probably most often sensed in a different context
Multipartite entanglement verification resistant against dishonest parties
Future quantum information networks will likely consist of quantum and
classical agents, who have the ability to communicate in a variety of ways with
trusted and untrusted parties and securely delegate computational tasks to
untrusted large-scale quantum computing servers. Multipartite quantum
entanglement is a fundamental resource for such a network and hence it is
imperative to study the possibility of verifying a multipartite entanglement
source in a way that is efficient and provides strong guarantees even in the
presence of multiple dishonest parties. In this work, we show how an agent of a
quantum network can perform a distributed verification of a multipartite
entangled source with minimal resources, which is, nevertheless, resistant
against any number of dishonest parties. Moreover, we provide a tight tradeoff
between the level of security and the distance between the state produced by
the source and the ideal maximally entangled state. Last, by adding the
resource of a trusted common random source, we can further provide security
guarantees for all honest parties in the quantum network simultaneously.Comment: The statement of Theorem 2 has been revised and a new proof is given.
Other results unchange
A transform of complementary aspects with applications to entropic uncertainty relations
Even though mutually unbiased bases and entropic uncertainty relations play
an important role in quantum cryptographic protocols they remain ill
understood. Here, we construct special sets of up to 2n+1 mutually unbiased
bases (MUBs) in dimension d=2^n which have particularly beautiful symmetry
properties derived from the Clifford algebra. More precisely, we show that
there exists a unitary transformation that cyclically permutes such bases. This
unitary can be understood as a generalization of the Fourier transform, which
exchanges two MUBs, to multiple complementary aspects. We proceed to prove a
lower bound for min-entropic entropic uncertainty relations for any set of
MUBs, and show that symmetry plays a central role in obtaining tight bounds.
For example, we obtain for the first time a tight bound for four MUBs in
dimension d=4, which is attained by an eigenstate of our complementarity
transform. Finally, we discuss the relation to other symmetries obtained by
transformations in discrete phase space, and note that the extrema of discrete
Wigner functions are directly related to min-entropic uncertainty relations for
MUBs.Comment: 16 pages, 2 figures, v2: published version, clarified ref [30
- …