Path-Dependent Climate Policy: The History and Future of Emissions Trading in Europe

At the end of the 1990s, the EU was still sceptical towards emissions trading, but in 2003 it adopted a directive that enables such trading in the EU from 2005 onwards. Instead of presenting ad hoc explanations, we develop and apply the path dependence approach to clarify this remarkable attitude change. Sunk costs, switching costs and learning explain why politicians were initially tempted to add credit trading to existing, sub-optimal policy. Permit trading, however, is more efficient and effective. An institutional lock-in was bound to occur, but attitudes changed as a result of internal pressures, such as the pioneering role of the European Commission, and external shocks, such as the withdrawal of the US from the Kyoto Protocol. A full-scale institutional break-out towards efficiency is not guaranteed, though, because elements of credit trading can still enter the permit trading directive. The risk is that these elements become locked in, from which it may be difficult to escape

Observation of Goos-H\"{a}nchen shifts in metallic reflection

We report the first observation of the Goos-H$\rm \ddot{\textbf{a}}$nchen shift of a light beam incident on a metal surface. This phenomenon is particularly interesting because the Goos-H$\rm \ddot{\textbf{a}}$nchen shift for $p$ polarized light in metals is negative and much bigger than the positive shift for $s$ polarized light. The experimental result for the measured shifts as a function of the angle of incidence is in excellent agreement with theoretical predictions. In an energy-flux interpretation, our measurement shows the existence of a backward energy flow at the bare metal surface when this is excited by a $p$ polarized beam of light.Comment: The parer was published on Optics Express. The new version is modified according to the reviewers suggestion

Fiber transport of spatially entangled photons

Entanglement in the spatial degrees of freedom of photons is an interesting resource for quantum information. For practical distribution of such entangled photons it is desireable to use an optical fiber, which in this case has to support multiple transverse modes. Here we report the use of a hollow-core photonic crystal fiber to transport spatially entangled qubits.Comment: 4 pages, 4 figure

Experimental demonstration of fractional orbital angular momentum entanglement of two photons

The singular nature of a non-integer spiral phase plate allows easy manipulation of spatial degrees of freedom of photon states. Using two such devices, we have observed very high dimensional (D > 3700) spatial entanglement of twin photons generated by spontaneous parametric down-conversion.Comment: submitted to Phys. Rev. Let

Pulsed Doppler-free two-photon spectroscopy of polyatomic molecules

Doppler-free two-photon electronic spectra of a large polyatomic molecule are recorded for the first time with pulsed laser radiation of near Fourier-transform limited bandwidth (Δvnot, vert, similar100 MHz). The resolution obtained is sufficient to resolve individual rotational lines. Due to the high density of these rotational transitions a strong Doppler-broadened background is observed, which is, however, subtantially reduced by suitable choice of photon polarizations. Different vibronic bands of benzene (C6H6) are investigated and very accurate rotational constants are found

Shannon dimensionality of quantum channels and its application to photon entanglement

We introduce the concept of Shannon dimensionality D as a new way to quantify bipartite entanglement as measured in an experiment. This is applied to orbital-angular-momentum entanglement of two photons, using two state analyzers composed of a rotatable angular-sector phase plate that is lens-coupled to a single-mode fiber. We can deduce the value of D directly from the observed two-photon coincidence fringe. In our experiment, D varies between 2 and 6, depending on the experimental conditions. We predict how the Shannon dimensionality evolves when the number of angular sectors imprinted in the phase plate is increased and anticipate that D = 50 is experimentally within reach.Comment: 4 pages, 3 figures, accepted for Physical Review Letter