1,840 research outputs found
Work and Quantum Phase Transitions: Is there Quantum Latency?
We study the physics of quantum phase transitions from the perspective of
non-equilibrium thermodynamics. For first order quantum phase transitions, we
find that the average work done per quench in crossing the critical point is
discontinuous. This leads us to introduce the quantum latent work in analogy
with the classical latent heat of first order classical phase transitions. For
second order quantum phase transitions the irreversible work is closely related
to the fidelity susceptibility for weak sudden quenches of the system
Hamiltonian. We demonstrate our ideas with numerical simulations of first,
second, and infinite order phase transitions in various spin chain models.Comment: accepted in PR
Measuring quantumness via anticommutators
We introduce a method to witness the quantumness of a system. The method
relies on the fact that the anticommutator of two classical states is always
positive. We show that there is always a nonpositive anticommutator due to any
two quantum states. We notice that interference depends on the trace of the
anticommutator of two states and it is therefore more natural to detect
quantumness by looking at anticommutators of states rather than their
commutators.Comment: 7 pages, 2 figure
Studies of uncontrolled air traffic patterns, phase 1
The general aviation air traffic flow patterns at uncontrolled airports are investigated and analyzed and traffic pattern concepts are developed to minimize the midair collision hazard in uncontrolled airspace. An analytical approach to evaluate midair collision hazard probability as a function of traffic densities is established which is basically independent of path structure. Two methods of generating space-time interrelationships between terminal area aircraft are presented; one is a deterministic model to generate pseudorandom aircraft tracks, the other is a statistical model in preliminary form. Some hazard measures are presented for selected traffic densities. It is concluded that the probability of encountering a hazard should be minimized independently of any other considerations and that the number of encounters involving visible-avoidable aircraft should be maximized at the expense of encounters in other categories
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Antibiotic Treatment Expands the Resistance Reservoir and Ecological Network of the Phage Metagenome
The mammalian gut ecosystem has significant influence on host physiology1–4, but the mechanisms that sustain this complex environment in the face of different stresses remain obscure. Perturbations to this ecosystem, such as through antibiotic treatment or diet, are currently interpreted at the level of bacterial phylogeny5–7. Less is known about the contributions of the abundant population of phage to this ecological network. Here, we explore the phageome as a potential genetic reservoir for bacterial adaptation by sequencing murine fecal phage populations following antibiotic perturbation. We show that antibiotic treatment leads to the enrichment of phage-encoded genes that confer resistance via disparate mechanisms to the administered drug as well as genes that confer resistance to antibiotics unrelated to the administered drug, and we demonstrate experimentally that phage from treated mice afford aerobically cultured naïve microbiota increased resistance. Systems-wide analyses uncover post-treatment phage-encoded processes related to host colonization and growth adaptation, indicating that the phageome broadly enriches for functionally beneficial genes under stress-related conditions. We also show that antibiotic treatment expands the interactions between phage and bacterial species, leading to a more highly connected phage-bacterial network for gene exchange. Our work implicates the phageome in the emergence of multidrug resistance and indicates that the adaptive capacity of the phageome may represent a community-based mechanism for protecting the gut microflora, preserving its functional robustness during antibiotic stress
Quantum work statistics and resource theories: bridging the gap through Renyi divergences
The work performed on or extracted from a non-autonomous quantum system
described by means of a two-point projective-measurement approach takes the
form of a stochastic variable. We show that the cumulant generating function of
work can be recast in the form of quantum Renyi divergences, and by exploiting
convexity of this cumulant generating function, derive a single-parameter
family of bounds for the first moment of work. Higher order moments of work can
also be obtained from this result. In this way, we establish a link between
quantum work statistics in stochastic approaches on the one hand and resource
theories for quantum thermodynamics on the other hand, a theory in which Renyi
divergences take a central role. To explore this connection further, we
consider an extended framework involving a control switch and an auxiliary
battery, which is instrumental to reconstruct the work statistics of the
system. We compare and discuss our bounds on the work distribution to findings
on deterministic work studied in resource theoretic settings.Comment: 8 pages, minor changes, references adde
Bridging the gap through Rényi divergences
The work performed on or extracted from a nonautonomous quantum system described by means of a two-point projective-measurement approach is a stochastic variable. We show that the cumulant generating function of work can be recast in the form of quantum Rényi-α divergences, and by exploiting the convexity of this cumulant generating function, derive a single-parameter family of bounds for the first moment of work. Higher order moments of work can also be obtained from this result. In this way, we establish a link between quantum work statistics in stochastic approaches and resource theories for quantum thermodynamics, a theory in which Rényi-α divergences take a central role. To explore this connection further, we consider an extended framework involving a control switch and an auxiliary battery, which is instrumental to reconstructing the work statistics of the system. We compare and discuss our bounds on the work distribution to findings on deterministic work studied in resource-theoretic settings
Infrared spectral studies of Zn-substituted CuFeCrO4 spinel ferrite system
The spinel solid solution series Znx Cu1–x FeCrO4 with x = 0.0,0.2,0.4 and 0.6 has been studied by infrared absorption spectroscopy. The IR-spectrum showed two main absorption bands ν1 and ν2 in the range 400-600 cm-1 arising from tetrahedral (A) and octahedral (B) interstitial sites in the spinel lattice. The absence of ν4 band suggests that lattice vibrations are insignificant. No shoulder or splitting is observed around ν1 and ν2 bands confirming absence of Fe+2 ions in the system. The sharpening of band with Zn- content (x) is due to the fact that the system changes from inverse to normal spinel structure. The structural and optical properties are correlated and the bulk modulus, compressional and shear velocity values determined through IR spectral analysis are in good agreement to those obtained through ultrasonic pulse transmission technique.Author Affiliation: M C Chhantbar, U N Trivedi, P V Tanna, H J Shah, R P Vara, H H Joshi and K B Modi
Department of Physics, Saurashtra University,
Rajkot-360 005, Gujarat, India
E-mail : [email protected] of Physics, Saurashtra University,
Rajkot-360 005, Gujarat, Indi
Operational approach to open dynamics and quantifying initial correlations
A central aim of physics is to describe the dynamics of physical systems.
Schrodinger's equation does this for isolated quantum systems. Describing the
time evolution of a quantum system that interacts with its environment, in its
most general form, has proved to be difficult because the dynamics is dependent
on the state of the environment and the correlations with it. For discrete
processes, such as quantum gates or chemical reactions, quantum process
tomography provides the complete description of the dynamics, provided that the
initial states of the system and the environment are independent of each other.
However, many physical systems are correlated with the environment at the
beginning of the experiment. Here, we give a prescription of quantum process
tomography that yields the complete description of the dynamics of the system
even when the initial correlations are present. Surprisingly, our method also
gives quantitative expressions for the initial correlation.Comment: Completely re-written for clarity of presentation. 15 pages and 2
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Surface and interface study of pulsed-laser-deposited off-stoichiometric NiMnSb thin films on Si(100) substrate
We report a detailed study of surface and interface properties of
pulsed-laser deposited NiMnSb films on Si (100) substrate as a function of film
thickness. As the thickness of films is reduced below 35 nm formation of a
porous layer is observed. Porosity in this layer increases with decrease in
NiMnSb film thickness. These morphological changes of the ultra thin films are
reflected in the interesting transport and magnetic properties of these films.
On the other hand, there are no influences of compositional in-homogeneity and
surface/interface roughness on the magnetic and transport properties of the
films.Comment: 13 pages, 7 figures, Submitted to Phys. Rev.
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