Observing different quantum trajectories in cavity QED

The experimental observation of quantum jumps is an example of single open quantum systems that, when monitored, evolve in terms of stochastic trajectories conditioned on measurements results. Here we present a proposal that allows the experimental observation of a much larger class of quantum trajectories in cavity QED systems. In particular, our scheme allows for the monitoring of engineered thermal baths that are crucial for recent proposals for probing entanglement decay and also for entanglement protection. The scheme relies on the interaction of a three-level atom and a cavity mode that interchangeably play the roles of system and probe. If the atom is detected the evolution of the cavity fields follows quantum trajectories and vice-versa.Comment: 5 pages, 2 figure

Private Provision of Water Service in Brazil: Impacts on Access and Affordability

Brazil has been experimenting with Private Sector Participation (PSP) in the water and sanitation sector in various forms since the mid-nineties, one of the most common being concession contracts. Currently, 25% of the population is served by companies with private sector participation and this figure could grow to 36% within 10 years. This paper studies past and ongoing experiences with private provision of water services in Brazil and assesses their impact on access and affordability indicators. It also discusses the social policies in place to improve those indicators, especially those targeting the poor. It uses different estimation methods and datasets to determine whether or not there is any difference in access to water supply and ability to pay water bills between municipalities that opted to entrust the provision of water services with private operators and those that kept them public. Moreover, whenever possible, the analysis is broken down by income (GDP) deciles in an attempt to evaluate the impact of private provision on lower income families. The results obtained entail the conclusion that PSP in Brazil has delivered higher access to water services, benefiting mostly the poor. They are inconclusive regarding affordability of water services though.Water services, access, affordability, panel data, private sector participation

Phase behavior of three-component ionic fluids

We study the phase behavior of solutions consisting of positive and negative ions of valence z to which a third ionic species of valence Z>z is added. Using a discretized Debye-Hueckel theory, we analyze the phase behavior of such systems for different values of the ratio Z/z. We find, for Z/z>1.934, a three-phase coexistence region and, for Z/z>2, a closed (reentrant) coexistence loop at high temperatures. We characterize the behavior of these ternary ionic mixtures as function of charge asymmetry and temperature, and show the complete phase diagrams for the experimentally relevant cases of Z/z=2 and Z/z=3, corresponding to addition of divalent and trivalent ions to monovalent ionic fluids, respectively.Comment: 6 pages, 4 figures; to appear in the European Physical Journal

Virial expansion for charged colloids and electrolytes

Using a field-theoretic approach, we derive the first few coefficients of the exact low-density (``virial'') expansion of a binary mixture of positively and negatively charged hard spheres (two-component hard-core plasma, TCPHC). Our calculations are nonperturbative with respect to the diameters $d_+$ and $d_-$ and charge valences $q_+$ and $q_-$ of positive and negative ions. Consequently, our closed-form expressions for the coefficients of the free energy and activity can be used to treat dilute salt solutions, where typically $d_+ \sim d_-$ and $q_+ \sim q_-$, as well as colloidal suspensions, where the difference in size and valence between macroions and counterions can be very large. We show how to map the TCPHC on a one-component hard-core plasma (OCPHC) in the colloidal limit of large size and valence ratio, in which case the counterions effectively form a neutralizing background. A sizable discrepancy with the standard OCPHC with uniform, rigid background is detected, which can be traced back to the fact that the counterions cannot penetrate the colloids. For the case of electrolyte solutions, we show how to obtain the cationic and anionic radii as independent parameters from experimental data for the activity coefficient.Comment: 15 page