Gauging a quantum heat bath with dissipative Landau-Zener transitions

We calculate the exact Landau-Zener transitions probabilities for a qubit with arbitrary linear coupling to a bath at zero temperature. The final quantum state exhibits a peculiar entanglement between the qubit and the bath. In the special case of a diagonal coupling, the bath does not influence the transition probability, whatever the speed of the Landau-Zener sweep. It is proposed to use Landau-Zener transitions to determine both the reorganization energy and the integrated spectral density of the bath. Possible applications include circuit QED and molecular nanomagnets.Comment: 4 pages, 1 figur

Dissipative Landau-Zener transitions of a qubit: bath-specific and universal behavior

We study Landau-Zener transitions in a qubit coupled to a bath at zero temperature. A general formula is derived that is applicable to models with a non-degenerate ground state. We calculate exact transition probabilities for a qubit coupled to either a bosonic or a spin bath. The nature of the baths and the qubit-bath coupling is reflected in the transition probabilities. For diagonal coupling, when the bath causes energy fluctuations of the diabatic qubit states but no transitions between them, the transition probability coincides with the standard LZ probability of an isolated qubit. This result is universal as it does not depend on the specific type of bath. For pure off-diagonal coupling, by contrast, the tunneling probability is sensitive to the coupling strength. We discuss the relevance of our results for experiments on molecular nanomagnets, in circuit QED, and for the fast-pulse readout of superconducting phase qubits.Comment: 16 pages, 8 figure

If cooperation is likely punish mildly: Insights from economic experiments based on the snowdrift game

Punishment may deter antisocial behavior. Yet to punish is costly, and the costs often do not offset the gains that are due to elevated levels of cooperation. However, the effectiveness of punishment depends not only on how costly it is, but also on the circumstances defining the social dilemma. Using the snowdrift game as the basis, we have conducted a series of economic experiments to determine whether severe punishment is more effective than mild punishment. We have observed that severe punishment is not necessarily more effective, even if the cost of punishment is identical in both cases. The benefits of severe punishment become evident only under extremely adverse conditions, when to cooperate is highly improbable in the absence of sanctions. If cooperation is likely, mild punishment is not less effective and leads to higher average payoffs, and is thus the much preferred alternative. Presented results suggest that the positive effects of punishment stem not only from imposed fines, but may also have a psychological background. Small fines can do wonders in motivating us to chose cooperation over defection, but without the paralyzing effect that may be brought about by large fines. The later should be utilized only when absolutely necessary.Comment: 15 pages, 6 figures; accepted for publication in PLoS ON

Governing the Global Commons with Local Institutions

Most problems faced by modern human society have two characteristics in common - they are tragedy-of-the-commons type of problems, and they are global problems. Tragedy-of-the-commons type of problems are those where a commonly shared resource is overexploited by free riders at the expense of everyone sharing the resource. The exploitation of global resources such as clean air and water, political stability and peace, etc. underlies many of the most pressing human problems. Punishment of free riding behavior is one of the most frequently used strategies to combat the problem, but the spatial reach of sanctioning institutions is often more limited than the spatial effects of overexploitation. Here, we analyze a general game theoretical model to assess under what circumstances sanctioning institutions with limited reach can maintain the larger commons. We find that the effect of the spatial reach has a strong effect on whether and how the commons can be maintained, and that the transitions between those outcomes are characterized by phase transitions. The latter indicates that a small change in the reach of sanctioning systems can profoundly change the way the global commons can be managed

Dopant Spatial Distributions: Sample Independent Response Function And Maximum Entropy Reconstruction

We demonstrate the use of maximum entropy based deconvolution to reconstruct boron spatial distribution from the secondary ion mass spectrometry (SIMS) depth profiles on a system of variously spaced boron $\delta$-layers grown in silicon. Sample independent response functions are obtained using a new method which reduces the danger of incorporating real sample behaviour in the response. Although the original profiles of different primary ion energies appear quite differently, the reconstructed distributions agree well with each other. The depth resolution in the reconstructed data is increased significantly and segregation of boron at the near surface side of the $\delta$-layers is clearly shown.Comment: 5 two-columne pages, 3 postscript figures, to appear in Phys. Rev. B1

Chemical-potential standard for atomic Bose-Einstein condensates

When subject to an external time periodic perturbation of frequency $f$, a Josephson-coupled two-state Bose-Einstein condensate responds with a constant chemical potential difference $\Delta\mu=khf$, where $h$ is Planck's constant and $k$ is an integer. We propose an experimental procedure to produce ac-driven atomic Josephson devices that may be used to define a standard of chemical potential. We investigate how to circumvent some of the specific problems derived from the present lack of advanced atom circuit technology. We include the effect of dissipation due to quasiparticles, which is essential to help the system relax towards the exact Shapiro resonance, and set limits to the range of values which the various physical quantities must have in order to achieve a stable and accurate chemical potential difference between the macroscopic condensates.Comment: 13 pages, 4 figure

Poly[ethyl­enediammonium [tris­[μ3-hydrogenphosphato(2−)]dicadmium] monohydrate]

The title compound, {(C2H10N2)[Cd2(HPO4)3]·H2O}n, was synthesized under hydro­thermal conditions. The structure of this hybrid compound consists of CdO6, CdO5 and PO4 polyhedra arranged so as to build an anionic inorganic layer, namely [Cd2(HPO4)3]2−, parallel to the ab plane. The edge-sharing CdO6 octa­hedra form infinite chains running along the a axis and are linked by CdO5 and PO4 polyhedra. The ethyl­ene­diammonium cation and the water mol­ecule are located between two adjacent inorganic layers and ensure the cohesion of the structure via N—H⋯O and O—H⋯O hydrogen bonds

Landau-Zener tunnelling in dissipative circuit QED

We investigate the influence of temperature and dissipation on the Landau-Zener transition probability in circuit QED. Dissipation is modelled by coupling the transmission line to a bath of harmonic oscillators. The reduced description for the density operator is treated within Bloch-Redfield theory. A phase-space representation allows an efficient numerical implementation of the resulting master equation. It provides reliable results which are valid even for rather low temperatures. We find that the spin-flip probability as a function of temperature and dissipation strength exhibits a non-monotonic behaviour. Our numerical results are complemented by analytical solutions for zero temperature and for vanishing dissipation strength.Comment: Accepted for publicatio