Simulating generic spin-boson models with matrix product states

The global coupling of few-level quantum systems ("spins") to a discrete set of bosonic modes is a key ingredient for many applications in quantum science, including large-scale entanglement generation, quantum simulation of the dynamics of long-range interacting spin models, and hybrid platforms for force and spin sensing. We present a general numerical framework for treating the out-of-equilibrium dynamics of such models based on matrix product states. Our approach applies for generic spin-boson systems: it treats any spatial and operator dependence of the two-body spin-boson coupling and places no restrictions on relative energy scales. We show that the full counting statistics of collective spin measurements and infidelity of quantum simulation due to spin-boson entanglement, both of which are difficult to obtain by other techniques, are readily calculable in our approach. We benchmark our method using a recently developed exact solution for a particular spin-boson coupling relevant to trapped ion quantum simulators. Finally, we show how decoherence can be incorporated within our framework using the method of quantum trajectories, and study the dynamics of an open-system spin-boson model with spatially non-uniform spin-boson coupling relevant for trapped atomic ion crystals in the presence of molecular ion impurities.Comment: 13 pages+refs. 13 figure

Multiple safety net regulators and agency problems in the EU: is Prompt Corrective Action a partial solution?

Prompt Corrective Action (PCA) provides a more efficient mechanism for dealing with problem banks operating in more than one European country. In a PCA framework, a bank’s losses are likely to be substantially reduced. This reduction in the losses to deposit insurance and governments will improve the problem of allocating those losses across the various insurance schemes and make it less likely that any deposit insurer will renege on its obligations in a cross-border banking crisis. This paper explores the institutional changes needed in Europe if PCA is to be effective in resolving the cross-border agency problems that arise in supervising and resolving cross-border banking groups. The paper identifies these changes starting with enhancements in the availability to prudential supervisors of information on banking groups’ financial condition. Next, the paper considers collective decision-making by prudential supervisors with authority to make discretionary decisions within the PCA framework as soon as a bank of a cross-border banking group falls below the minimum capital standard. Finally, the paper analyses the coordination measures that should be implemented if PCA requires the bank to be resolved.banking supervision; European Union; Prompt Corrective Action

What do premiums paid for bank M&As reflect? the case of the European Union

We analyze the takeover premiums paid for a sample of European bank mergers between 1997 and 2007. We find that acquiring banks value profitable, high-growth, and low-risk targets. We also find that the strength of bank regulation and supervision and of deposit insurance regimes in Europe has measurable effects on takeover pricing. Stricter bank regulatory regimes and stronger deposit insurance schemes lower the takeover premiums paid by acquiring banks. This result, presumably in anticipation of higher compliance costs, is mainly driven by domestic deals. Also, we find no conclusive evidence that bidders seek to extract benefits from regulators either by paying a premium for deals in less regulated regimes or becoming too big to fail.

The solar map as a knowledge base for solar energy use

Our existing urban environment has a significant potential to increase the use of renewable energy, mainly by using solar irradiation for heat and electricity. Quantification of the solar potential by means of a solar map is the first step in the acceleration process for using more solar energy in our urban environments. A solar map is a GIS system providing the annual solar irradiation on building surfaces, mostly accompanied by information of the output of solar thermal or photovoltaic systems. Many solar maps are already in place today; almost all of them are however using different approaches. In this paper, an analysis is done of current solar maps in order to see on which principles the solar maps were based upon

Measuring out-of-time-order correlations and multiple quantum spectra in a trapped ion quantum magnet

Controllable arrays of ions and ultra-cold atoms can simulate complex many-body phenomena and may provide insights into unsolved problems in modern science. To this end, experimentally feasible protocols for quantifying the buildup of quantum correlations and coherence are needed, as performing full state tomography does not scale favorably with the number of particles. Here we develop and experimentally demonstrate such a protocol, which uses time reversal of the many-body dynamics to measure out-of-time-order correlation functions (OTOCs) in a long-range Ising spin quantum simulator with more than 100 ions in a Penning trap. By measuring a family of OTOCs as a function of a tunable parameter we obtain fine-grained information about the state of the system encoded in the multiple quantum coherence spectrum, extract the quantum state purity, and demonstrate the buildup of up to 8-body correlations. Future applications of this protocol could enable studies of many-body localization, quantum phase transitions, and tests of the holographic duality between quantum and gravitational systems.Comment: main text: 7 pages, 4 figures; supplement: 9 pages, 4 figure

Typical Values for Active Solar Energy in Urban Planning

There is an urgent need to start generating energy within cities in order to pave the way for a more sustainable and resilient society. Renewable energy by means of active solar energy systems (solar thermal, ST and/or photovoltaics, PV) can be generated using roofs and facades of buildings. In this study, the annual solar energy potential of typical Swedish city blocks was analysed in order to develop guidelines for urban planners and architects. The results show that the design of the city blocks has a significant effect (up to 50%) on the total annual solar energy production. The study also shows that the contribution from active solar energy can be significant even in the urban environment, but shading by adjacent buildings may greatly limit the total amount of energy produced