Casimir-Polder forces between two accelerating atoms and the Unruh effect

The Casimir-Polder force between two atoms with equal uniform acceleration and separated by a constant distance R is considered. We show that, in the low-acceleration limit, while the near-zone R^{-6} behavior of the interatomic interaction energy is not changed by the acceleration of the atoms, the far-zone interaction energy decreases as R^{-5} instead of the well-known R^{-7} behavior for inertial atoms. Possibility of an indirect detection of the Unruh effect through measurements of the Casimir-Polder force between the two accelerating atoms is also suggested. We also consider a heuristic model for calculating the Casimir-Polder potential energy between the two atoms in the high-acceleration limit.Comment: Contribution to the Proceedings of the QFEXT09 Conference, Norman, Oklahoma, US

Driven Markovian Quantum Criticality

We identify a new universality class in one-dimensional driven open quantum systems with a dark state. Salient features are the persistence of both the microscopic non-equilibrium conditions as well as the quantum coherence of dynamics close to criticality. This provides a non-equilibrium analogue of quantum criticality, and is sharply distinct from more generic driven systems, where both effective thermalization as well as asymptotic decoherence ensue, paralleling classical dynamical criticality. We quantify universality by computing the full set of independent critical exponents within a functional renormalization group approach.Comment: 5+3 pages, 2 figures; published version with improved presentation of result

Casimir forces and quantum friction from Ginzburg radiation in atomic BECs

We theoretically propose an experimentally viable scheme to use an impurity atom in an atomic Bose-Einstein condensate, in order to realize condensed-matter analogs of quantum vacuum effects. In a suitable atomic level configuration, the collisional interaction between the impurity atom and the density fluctuations in the condensate can be tailored to closely reproduce the electric-dipole coupling of quantum electrodynamics. By virtue of this analogy, we recover and extend the paradigm of electromagnetic vacuum forces to the domain of cold atoms, showing in particular the emergence, at supersonic atomic speeds, of a novel power-law scaling of the Casimir force felt by the atomic impurity, as well as the occurrence of a quantum frictional force, accompanied by the Ginzburg emis- sion of Bogoliubov quanta. Observable consequences of these quantum vacuum effects in realistic spectroscopic experiments are discussed.Comment: 5 pages, 2 figures. Revised version accepted in PR

Segmentation, unity, and a church divided: a critical history of churches in Nagaland, 1947-2017

This is a study of the distinctive formation of the Christian churches in Nagaland during 1947-2017. It argues that the major clues to understanding Naga church history are to be found in the cultural milieu of Nagaland. Thus, using a cultural history methodology, the ecclesiastical events described in this research were examined in the cultural framework of the segmentary Naga society and the changing political, social and religious environment in the region, giving close attention to how they affected the contours of the ecclesiastical history. It posited that segmentation as a cultural characteristic of the Naga society effected both unity and divisiveness in the Naga churches, which subsequently shaped the beliefs and practices of the churches in the region. Archival data in the form of reports, records and minutes of meetings were collected from church and government offices. Qualitative data was collected through interviews with leaders and key eyewitnesses of various events discussed in the research. Using a semi-structured questionnaire in these interviews allowed the interviewee to tell the story in their own words. Though primary textual sources were used to establish the state of churches in Nagaland prior to 1947, the main focus of this research is limited to the period 1947 to 2017. This research retells the story of the Naga church in a state of India with Christian majority. The ethnic status the Christian faith assumed, the extent of its identification with the local culture, and the scope of the mission of the Naga churches as key stakeholders in society, offers a new angle to the history of Christianity in India. As an historical study of churches within the geographical confines of Nagaland this research is hoped to be a tool for the churches’ self-evaluation in the region and beyond

Exploring many-body localization in quantum systems coupled to an environment via Wegner-Wilson flows

Inspired by recent experiments on many-body localized systems coupled to an environment, we apply a Flow Equation method to study the problem of a disorder chain of spinless fermions, coupled via density-density interactions to a second clean chain of spinless fermions. In particular, we focus on the conditions for the onset of a many-body localized phase in the clean sector of our model by proximity to the dirty one. We find that a many-body localization proximity effect in the clean component is established when the density of dirty fermions exceeds a threshold value. From the flow equation method we find that, similar to many-body localization in a single chain, the many-body localization proximity effect is also described by an extensive set of local integrals of motion. Furthermore, by tuning the geometry of the inter-chain couplings, we show that the dynamics of the model is ruled, on intermediate time scales, by an emergent set of quasi-conserved charges.Comment: 22 pages, 7 figure

Population, Poverty and Environmental Degradation in Nagaland

Nagaland which constitutes the northern part of Indo-Myanmar ranges is well-known among conservationists and environmentalist for both its unique forest ecosystems and its alarmingly high rates of deforestation through various forms of economic activities. The environment is an essential source of livelihood on which the continued existence for poor people depends. However, denial of primary requirements results to poverty. The evaluation suggests that higher population and fertility rates were associated with higher deforestation in the tropical evergreen forest. Poverty reduction and environmental protection are two international obligations for sustainable development. The standpoint of the study has changed over time, from narrowly focusing on poverty reduction to comprehensively strengthening human-welfare. The relationship between population, poverty and environmental degradation is regionally unique or has regional uniqueness. This paper analyses the poverty level in Nagaland using below poverty line card holder, Head Count Ratio and Multidimensional Poverty Index. The finding shows that during 1987-88 the poverty rate was 34.43 per cent and the forest loss was found to be -192 sq. km which further increases to 33.83 per cent (poverty rate) and forest loss to -450 sq. km during 2016-17. The result highlights high level of poverty thereby, affecting the environment resources. The paper suggests suitable measures which can ameliorate the poverty and environmental degradation.   &nbsp

Pre-Thermalization in Quantum Spin Chains

The results presented in this PhD Thesis aim at understanding thermalization dynamics and, strictly speaking, pre-thermalization in both open and closed quantum spin chains driven out-of-equilibrium. In order to make analytical progress, we consider perturbations of the Quantum Ising Chain (QIC), one of the simplest integrable models, whose non-equilibrium dynamics has been studied in great details in the last few years. In Chapter 2 we introduce for the non-technical reader the main recent ideas behind quantum thermalization and relaxation in integrable and non-integrable quantum many body systems, while Chapter 3 contains an introduction to the current understanding of pre-thermalization. In Chapter 4 we start our study considering a QIC perturbed by a time dependent noise in the direction of the transverse magnetic field [6] [7]. We generalize the concept of pre-thermalization to a noisy quantum many body system driven away from equilibrium simultaneously by a quantum quench of the transverse field and by the noise, highlighting the mechanism behind pre-thermalization and the subsequent relaxation towards the thermal state in a wide class of physically relevant observables. Our main achievement is to show that pre-thermalization occurs quite generally up to time scales where the noise is dominated by the non-equilibrium dynamics induced by the quench of the transverse field, while for longer times pre-thermal plateaux disappear and the noise leaves different signatures in different observables. In Chapter 5 we consider the more challenging problem of pre-thermalization in a closed non-integrable quantum spin chain [8]. We show using a mapping of a weakly non-integrable spin chain into a hard core boson model, that pre-thermalization is successfully captured by a low-density description of the theory, which results in a integrable, bosonic model, that constitutes an excellent description for the out-of-equilibrium dynamics up to intermediate time scales. On the other hand, in order to investigate the late time dynamics we resort to a diagrammatic approach, which serves for a two-fold scope. First, we focus on the effect of the leading inelastic processes, realizing that they constitute only a sub-leading correction to the pre-thermal plateau, found within the effective low-energy description; and secondly, we show from a Quantum Boltzmann equation perspective how inelastic processes are the fundamental ingredient in order to have thermalization in the late time dynamics. The main technical tool used to derive the results in Chapter 4 and 5 is the Keldysh contour technique which is reviewed in the Appendix. This PhD Thesis is based on the following works: 1) J. Marino, A. Silva, Relaxation, pre-thermalization and diffusion in a noisy Quantum Ising Chain, Phys. Rev. B 86, 060408 (Rapid Communications) (2012). 2) M. Marcuzzi, J. Marino, A. Gambassi, A. Silva, Pre-thermalization in a non-integrable quantum spin chain after a quench, arXiv:1307.3738 (2013) (submitted to Phys. Rev. Lett.). 3) J. Marino, A. Silva, Non-Equilibrium Dynamics of a Noisy Quantum Ising Chain: statistics of the work and prethermalization after a sudden quench of the transverse field, arXiv:1309.7595 (2013) (submitted to Phys. Rev. B)

Entanglement entropy in a periodically driven quantum Ising chain

We numerically study the dynamics of entanglement entropy, induced by an oscillating time periodic driving of the transverse field, h(t), of a one-dimensional quantum Ising chain. We consider several realizations of h(t), and we find a number of results in analogy with entanglement entropy dynamics induced by a sudden quantum quench. After short-time relaxation, the dynamics of entanglement entropy synchronises with h(t), displaying an oscillatory behaviour at the frequency of the driving. Synchronisation in the dynamics of entanglement entropy, is spoiled by the appearance of quasi-revivals which fade out in the thermodynamic limit, and which we interpret using a quasi-particle picture adapted to periodic drivings. Taking the time-average of the entanglement entropy in the synchronised regime, we find that it obeys a volume law scaling with the subsystem's size. Such result is reminiscent of a thermal state or of a Generalised Gibbs ensemble of a quenched Ising chain, although the system does not heat up towards infinite temperature as a consequence of the integrability of the model.Comment: 6 pages, 3 figure

Relaxation, pre-thermalization and diffusion in a noisy Quantum Ising Chain

We study the dynamics of thermalization resulting from a time-dependent noise in a Quantum Ising Chain subject to a sudden quench of the transverse magnetic field. For weak noise the dynamics shows a pre-thermalized state at intermediate time scales, eventually drifting towards an asymptotic infinite temperature steady state characterized by diffusive behavior. By computing analytically the density of kinks, as well as the transverse and longitudinal magnetic field correlators, we characterize these two regimes, their observability and their signatures in the various physical quantities.Comment: 5 pages, 2 figures. Accepted for publication in PRB Rapid Communication