Effective Dark Energy from Decoherence

Inverse Compton-pair cascades are initiated when gamma-rays are absorbed on an ambient soft photon field to produce relativistic pairs, which in turn up-scatter the same soft photons to produce more gamma-rays. If the Compton scatterings take place in the deep Klein–Nishina regime, then triplet pair production ( ) becomes relevant and may even regulate the development of the cascade. We investigate the properties of pair-Compton cascades with triplet pair production in accelerating gaps, i.e., regions with an unscreened electric field. Using the method of transport equations for the particle evolution, we compute the growth rate of the pair cascade as a function of the accelerating electric field in the presence of blackbody and power-law ambient photon fields. Informed by the numerical results, we derive simple analytical expressions for the peak growth rate and the corresponding electric field. We show that for certain parameters, which can be realized in the vicinity of accreting supermassive black holes at the centers of active galactic nuclei, the pair cascade may well be regulated by inverse Compton scattering in the deep Klein–Nishina regime and triplet pair production. We present indicative examples of the escaping gamma-ray radiation from the gap, and discuss our results in application to the TeV observations of radio galaxy M87.

Context. The innermost parts of powerful jets in active galactic nuclei are surrounded by dense, high-velocity clouds from the broad-line region, which may penetrate into the jet and lead to the formation of a strong shock. Such jet-cloud interactions are expected to have measurable effects on the γ-ray emission from blazars. Aims. We characterise the dynamics of a typical cloud-jet interaction scenario, and the evolution of its radiative output in the 0.1–30 GeV energy range, to assess to what extent these interactions can contribute to the γ-ray emission in blazars. Methods. We use semi-analytical descriptions of the jet-cloud dynamics, taking into account the expansion of the cloud inside the jet and its acceleration. Assuming that electrons are accelerated in the interaction and making use of the hydrodynamical information, we then compute the high-energy radiation from the cloud, including the absorption of γ-rays in the ambient photon field through pair creation. Results. Jet-cloud interactions can lead to significant γ-ray fluxes in blazars with a broad-line region (BLR), in particular when the cloud expansion and acceleration inside the jet are taken into account. This is caused by 1) the increased shocked area in the jet, which leads to an increase in the energy budget for the non-thermal emission; 2) a more efficient inverse Compton cooling with the boosted photon field of the BLR; and 3) an increased observer luminosity due to Doppler boosting effects. Conclusions. For typical broad-line region parameters, either (i) jet-cloud interactions contribute significantly to the persistent γ-ray emission from blazars or (ii) the BLR is far from spherical or the fraction of energy deposited in non-thermal electrons is small.

Quantum correlations have long been recognized as an informational resource for quantum communication and computation. It now seems that they can also do physical work. See Letter p.61 Landauer's erasure principle, a widely accepted part of classical information theory first proposed by Rolf Landauer in 1961, asserts that it is necessary to perform work in order to erase data. This occurs when carrying out irreversible operations, thus releasing heat to the environment. For example, in electronics, heat generation is a major obstacle to circuitry miniaturization. Del Rio et al. show that the situation is completely different in the presence of quantum information about the system, and the implications of Landauer's principle are invalid. The more that is known about a system, the less it costs to erase it. An observer who is strongly correlated with a system may even gain work while erasing it, therefore cooling the environment. The quantum systems needed to experimentally demonstrate these results are, in principle, accessible with current technology.

A novel framework identifies the necessary thermodynamic resources for producing pure quantum states, connecting the third law of thermodynamics with Landauer's principle and highlighting the role of information and complexity in thermodynamics.

The Landauer principle asserts that the energy cost of erasure of one bit of information by the action of a thermal reservoir in equilibrium at temperature T is never less than kBT log 2. We discuss Landauer's principle for quantum statistical models describing a finite level quantum system \documentclass[12pt]{minimal}\begin{document}${\cal S}$\end{document}S coupled to an infinitely extended thermal reservoir \documentclass[12pt]{minimal}\begin{document}${\cal R}$\end{document}R. Using Araki's perturbation theory of KMS states and the Avron-Elgart adiabatic theorem we prove, under a natural ergodicity assumption on the joint system \documentclass[12pt]{minimal}\begin{document}${\cal S}+{\cal R}$\end{document}S+R, that Landauer's bound saturates for adiabatically switched interactions. The recent work [Reeb, D. and Wolf M. M., “(Im-)proving Landauer's principle,” preprint arXiv:1306.4352v2 (2013)] on the subject is discussed and compared.

We consider sequences of measurements implemented by positive operator valued measures (POVMs). Starting from the assumption that these sequences may be described as consistent and Markovian, even and especially for closed quantum systems, we identify properties of the equilibrium state that coincide with the properties of typical pure quantum states. We define a physical entropy that converges against the standard entropies in the approach to equilibrium. Furthermore, strict limits to its possible decrease are derived on the basis of Renyi entropies. It is demonstrated that Landauer's principle follows directly from these limits. Since the above assumptions are rather strong, we exemplify the fact that they may nevertheless apply by checking them numerically for some transition paths in a concrete model.

Pulsars are factories of relativistic electrons and positrons that propagate away from the pulsar, permeating later our Galaxy. The acceleration and propagation of these particles are a matter of intense debate. In the last few years, we had the opportunity to directly observing the injection of these particles into the interstellar medium through the discovery of gamma-ray halos around pulsars. This new type of gamma-ray source is produced by electrons and positrons diffusing out of the pulsar wind nebula and scattering ambient photon fields to produce gamma rays. This new field of study comes with a number of observations and constraints at different wavelengths and a variety of theoretical models explaining the characteristics of these halos. We examine the characteristics of the propagation of cosmic rays inferred from the observations of halos and their local and global implications on particle transport in the Galaxy. We also discuss the prospects for observations of these sources with facilities such as LHAASO, or CTA or SWGO in the near future.

When a star dies, it leaves a mark on its surrounding environment. The energy from the supernova explosion forms an expanding shock wave that interacts with interstellar and circumstellar material, creating what we know as a supernova remnant (SNR). If the original star has a mass that is greater than or equal to 8 solar masses, this can also lead to the formation of a rapidly rotating neutron star called a pulsar. As these objects evolve, they interact with the surrounding environment, producing non-thermal and thermal emission. For an SNR, its non-thermal emission arises from a population of relativistic particles being accelerated at the shock front of the SNR, while its thermal emission arises from the shock front heating ejecta and and swept-up interstellar medium to X-ray emitting temperatures. For pulsars, their non-thermal emission arises from relativistic particles being accelerated at the termination shock of a pulsar wind. These particles interact with surrounding magnetic fields and ambient photon fields producing synchrotron and inverse Compton emission which we observe as a pulsar wind nebula (PWN), while its thermal emission arises from the surface of the neutron star. These properties of SNRs and pulsars provide a unique window into studying the acceleration, injection, propagation and interaction of highly energetic particles called cosmic rays with the interstellar medium. In addition, they providing information about the evolution, and dynamics of these objects; properties of the shock fronts; details about the original progenitor star; and the impact that these objects have on their surroundings. The research presented here focuses on analysing the intimate connection between cosmic rays, the non-thermal emission arising from SNRs interacting with molecular clouds, and pulsar wind nebulae; as well as analysing the observational and evolutionary properties of these objects. In this thesis we model the propagation of cosmic rays through the Galaxy in an attempt to characterise a standard cosmic ray background with uncertainties, to reveal the origin of the cosmic ray electron positron anomaly. Furthermore, we analyse the gamma-ray emission from SNRs Kes 79 and MSH 11-61A, which are known to be interacting with molecular clouds, as well as the non-thermal X-ray emission arising from the PWN of PSR J1741-2054. We find that the emission from both SNRs most likely arises from the decay of neutral pions that resulted from the interaction of relativistic ions which are accelerated at the shock-front of a SNR, with ambient material. For PSR J1741-2054, we characterise the properties, minimum magnetic field and minimum energy of the particle population that produces the observed diffuse synchrotron emission that surrounds and trails the pulsar. In addition, we characterise the X-ray emission arising from Kes 79, MSH 11-61A and PSR J1741-2054, in an attempt to shed light on the origin and nature of these objects and their emission. Using X-ray data from XMM-Newton and Suzaku respectively, we probe the temperature, ionisation state, and elemental abundance of the shocked gas of each SNR. This allows us to determine their evolutionary properties, properties of the shock, and mass of the original progenitor; and constrain the density of the X-ray emitting plasma. Using Chandra, we determined the temperature of PSR J1741-2054, as well as characterised its proper motion, velocity, direction of motion, and presence of small scale structure immediately surrounding the pulsar.

There are many formalisms to describe quantum decoherence. However, many of them give a non-general and ad hoc definition of ‘pointer basis’ or ‘moving preferred basis’ , and this fact is a problem for the decoherence program. In this paper, we will consider quantum systems under a general theoretical framework for decoherence and we will present a tentative definition of the moving preferred basis. These ideas are implemented in a well-known open system model. The obtained decoherence and the relaxation times are defined and compared with those of the literature for the Lee–Friedrichs model.This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘Quantum physics with non-Hermitian operators’.

The travelling salesman problem (TSP) is a popular NP-hard combinatorial optimization problem that requires finding the optimal way for a salesman to travel through different cities once and return to the initial city. The existing methods of solving TSPs on quantum systems are either gate-based or binary variable-based encoding. Both approaches are resource-expensive in terms of the number of qubits, while performing worse compared to existing classical algorithms, even for small-sized problems.
A novel encoding scheme is needed to map the TSP problem onto a quantum system, which is addressed in this work.
We introduce a distinct geometric approach to encode the TSP on a single qubit and present a quantum-inspired algorithm to solve the problem by invoking the principle of \textit{quantum superposition}.
The cities are represented as quantum states on the Bloch sphere, while the preparation of superposition states allows us to traverse multiple paths at once. The underlying framework of our algorithm is a quantum-inspired version of the classical Brachistochrone approach.
Optimal control methods are employed to create a selective superposition of the quantum states to find the shortest route of a given TSP.
The numerical simulations solve a sample of four to nine cities for which exact solutions are obtained. The algorithm can be implemented on any quantum platform capable of efficiently rotating a qubit and allowing state tomography measurements. For the TSP problem sizes considered in this work, our algorithm is more resource-efficient and accurate than existing quantum algorithms, with the potential for scalability.

Various approaches of defining and determining work performed on a quantum system are compared. Any operational definition of work, however, must allow for two facts: first, that work characterizes a process rather than an instantaneous state of a system and, second, that quantum systems are sensitive to the interactions with a measurement apparatus. We compare different measurement scenarios on the basis of the resulting postmeasurement states and the according probabilities for finding a particular work value. In particular, we analyze a recently proposed work meter for the case of a Gaussian pointer state and compare it with the results obtained by two projective and, alternatively, two Gaussian measurements. In the limit of a strong effective measurement strength the work distribution of projective two energy measurements can be recovered. In the opposite limit the average of work becomes independent of any measurement. Yet the fluctuations about this value diverge. The performance of the work meter is illustrated by the example of a spin in a suddenly changing magnetic field.

In this paper, we study the interaction between the time-dependent field and a two-level atom with one mode electromagnetic field. We consider that the field of photons is assumed to be coupled with modulated coupling parameter which depends explicitly on time. It is shown that the considered model can be reduced to a well-known form of the time-dependent generalized Jaynes–Cummings model. Under special initial conditions, in which the atom and the field are prepared in the excited and the coherent states, respectively, the explicit time evolution of the wave function of the entire system is analytically obtained. Our proposal has many advantages over the previous optical schemes and can be realized in several multiple experiments, such as trapped ions and quantum electrodynamics cavity. The influence of the time-dependent field parameter on the collapses-revivals, the normal squeezing of the radiation, the anti-bunching of photons and the entanglement phenomena for the considered atomic system is examined. The linear entropy, the von Neumann entropy are used to quantify entanglement in the quantum systems. We noticed that these phenomena are affected by the existence of both the time-dependent coupling field and detuning parameters.

Simulation calculations have been made Lo examine the modification effect of a hot X-ray photon field on a gamma-ray spectrum by the photon-photon pair production and inverse Compton scattering processes. The Cyg X-3 system was used as a paradigm. It is shown that a gamma-ray spectrum can change significantly when passing through the ambient keV X-ray photon field of an accretion binary source. For Cyg X-3, a significant amount of r-rays originated near the central source in the range of 10(2)-10(4) MeV could be absorbed by the extended X-ray photons from accretion disk corona in a high X-ray luminosity state and, on the other hand, the inverse Compton effect of secondary electrons could cause a considerable increase in intensity of gamma-rays between approximately 10 MeV and approximately 50 MeV. The relevance of the absorption effect for observations is discussed.

Purpose: Through kinetic modeling, both dynamic FLT‐PET and dynamic contrast‐enhanced CT (DCE‐CT) measure perfusion. However, the set of parameters used by the kinetic models to describe perfusion differs between the two imaging modalities. The purpose of this study was to investigate the correlations between corresponding FLT‐PET and DCE‐CT kinetic ROI and voxel parameters.Methods: Canine patients with sinonasal tumors underwent FLT‐PET and DCE‐CT on the same day. FLT‐PET uptake was modeled with a two‐compartment four‐parameter kinetic model. The DCE‐CT kinetic analysis was done by Kety, deconvolution (Decon) and distributed parameter (DP) models. All models were implemented in‐house using MATLAB. FLT K1 and k2 parameters were correlated with equivalent K1 and k2 DCE‐CT values. FLT vb was correlated with the DCE‐CT parameter blood volume ratio (BVR). ROI analysis was performed over the entire tumor volume, while voxel analysis was calculated on the largest tumor slice. Correlations were done using the population correlation coefficient (p).Results: DCE‐CT and FLT K1 displayed strong ROI correlations (DP: p=0.91, Deconvolution: p=0.87, Kety: p=0.60). The kinetic parameter vb also had high ROI correlations (p=0.82, p=0.89, p=0.89). FLT k2 correlated only marginally with the DCE‐CT models (p ∼ +/−0.50). There were no significant voxel correlations. However, increasing voxel size 128×128 to 32×32 lead to minor improvements in correlation with the most notable being K1, which increased in the distributed parameter and deconvolution models from (p=0.16, p=0.29) to (p=0.52, p=0.42). Conclusions: Significant ROI correlations were found between FLT and DCE‐CT kinetic analysis. The kinetic parameters K1 and vb had relatively high correlations between the DCE‐CT and FLT kinetic models. Even though there were no significant voxel correlations, an increase in K1 correlations with voxel size may indicate kinetic model sensitivity to noise as an important factor in kinetic parameter correlations.

Problems of detection, location, and identification of weak seismic events with a view toward a comprehensive test ban treaty have formed the main motivation for array deployment and associated research. In the past 15 yr, the large arrays LASA and NORSAR have been the main tools for this type of research. The event detection capability of arrays has proved superior to that of single stations, but event locations, while readily available, are seldom very accurate (error < 50 km) without supplementary information. The implied two-dimensional wave field sampling provided by arrays has been instrumental in understanding phenomena like the ambient seismic noise field, the extent of mantle heterogeneities, and their effect on short-period wave propagation. It is somewhat unfortunate that, due to limitations in handling the enormous amount of data involved, only a relatively small number of seismologists has had access to the high-quality array recordings; recent advances in computer technology might eliminate such problems in the near future. New technology also makes possible a new trend in array seismology, involving on the one hand world-wide deployment of small- and medium-sized arrays, and on the other hand opening up for applying array processing techniques to a global network of such stations. This paper gives an overview of past and present developments of array technology, and the associated seismological achievements. Emphasis is placed on the role of arrays in a potential comprehensive test ban treaty environment and on likely future developments in this particular field.