Quantum quenches in the many-body localized phase

Many-body localized (MBL) systems are characterized by the absence of transport and thermalization, and therefore cannot be described by conventional statistical mechanics. In this paper, using analytic arguments and numerical simulations, we study the behaviour of local observables in an isolated MBL system following a quantum quench. For the case of a global quench, we find that the local observables reach stationary, highly non-thermal values at long times as a result of slow dephasing characteristic of the MBL phase. These stationary values retain the local memory of the initial state due to the existence of local integrals of motion in the MBL phase. The temporal fluctuations around stationary values exhibit universal power-law decay in time, with an exponent set by the localization length and the diagonal entropy of the initial state. Such a power-law decay holds for any local observable and is related to the logarithmic in time growth of entanglement in the MBL phase. This behaviour distinguishes the MBL phase from both the Anderson insulator (where no stationary state is reached), and from the ergodic phase (where relaxation is expected to be exponential). For the case of a local quench, we also find a power-law approach of local observables to their stationary values when the system is prepared in a mixed state. Quench protocols considered in this paper can be naturally implemented in systems of ultra cold atoms in disordered optical lattices, and the behaviour of local observables provides a direct experimental signature of many-body localization.Comment: 11 pages, 4 figure

Interaction-tuned compressible-to-incompressible phase transitions in the quantum Hall systems

We analyze transitions between quantum Hall ground states at prominent filling factors $\nu$ in the spherical geometry by tuning the width parameter of the Zhang-Das Sarma interaction potential. We find that incompressible ground states evolve adiabatically under this tuning, whereas the compressible ones are driven through a first order phase transition. Overlap calculations show that the resulting phase is increasingly well described by appropriate analytic model wavefunctions (Laughlin, Moore-Read, Read-Rezayi). This scenario is shared by both odd ($\nu=1/3, 1/5, 3/5, 7/3, 11/5, 13/5$) and even denominator states ($\nu=1/2, 1/4, 5/2, 9/4$). In particular, the Fermi liquid-like state at $\nu=1/2$ gives way, at large enough value of the width parameter, to an incompressible state identified as the Moore-Read Pfaffian on the basis of its entanglement spectrum.Comment: 4 pages, 5 figures; modified version as appears in PR

Achieving Optimal Redundancy in a Small Business Network

Redundancy is a highly desirable element of the network, but sometimes it is not so easy to find the optimal level of redundancy that will ensure satisfactory performance of the entire network and at the same time being affordable and easy to implement. Redundancy in the network can be performed in several ways, which can be compatible and co-exist in the network, but can also be mutually exclusive. Although at first it seems that the redundancy depends only on the size of the network, this is not entirely true. One of the main factors to take into account is the complexity of the network and the importance of services and applications that serve the company’s business and its customers. Network redundancy can be achieved in various ways. STP for example is the most basic mechanism but has several major drawbacks like underutilization of some links. Also link aggregation mechanisms could be used, which usually means investing in optical transcievers which implies a certain cost, and if one is using switch stacking it will further increase costs. For gateway redundancy one of FHRP protocols can be used which is certainly desirable. This paper will describe the redundancy in Small and Medium networks with few hundred clients and one way how to ensure redundancy by using various mechanisms such as the STP protocol, link aggregation, implementation of FHRP for gateway redundancy and using stackable switches with short analysis of recovery times for these mechanisms

Tunable Electron Interactions and Fractional Quantum Hall States in Graphene

The recent discovery of fractional quantum Hall states in graphene raises the question of whether the physics of graphene and its bilayer offers any advantages over GaAs-based materials in exploring strongly-correlated states of two-dimensional electrons. Here we propose a method to continuously tune the effective electron interactions in graphene and its bilayer by the dielectric environment of the sample. Using this method, the charge gaps of prominent FQH states, including \nu=1/3 or \nu=5/2 states, can be increased several times, or reduced all the way to zero. The tunability of the interactions can be used to realize and stabilize various strongly correlated phases in the FQH regime, and to explore the transitions between them.Comment: 4.2 pages, 5 figure

Connecting Customer Locations Using Different Service Provider MPLS Networks

MPLS (Multi Protocol Label Switching) technology is de facto standard in service provider environments and most companies are connected over service provider MPLS infrastructure. Sometimes it happens that one company from a small country such as Croatia merge with another company in a small country like Slovenia. Both companies have their own network infrastructure that is connected through service providers in their respective country, but since the two companies are now one administrative domain their networks should reflect this and connect into one bigger network in order for this network to become more efficient and to better support business goals. There are simple and common solutions such as S2S VPN, but in this case it would not be long-term and optimal solution especially if there is traffic like multicast, VoIP or various datacenter traffic. The direction in which we should go is to connect the two companies into a single organization using one of the mechanisms for connecting service providers also known as carrier supporting carrier. In this paper we will describe advantages and disadvantages using carrier supporting carrier options A and B. Once two companies are connected in this manner, it is much easier to manage traffic and to implement QOS mechanisms