Structure of multiphoton quantum optics. II. Bipartite systems, physical processes, and heterodyne squeezed states

Extending the scheme developed for a single mode of the electromagnetic field in the preceding paper ``Structure of multiphoton quantum optics. I. Canonical formalism and homodyne squeezed states'', we introduce two-mode nonlinear canonical transformations depending on two heterodyne mixing angles. They are defined in terms of hermitian nonlinear functions that realize heterodyne superpositions of conjugate quadratures of bipartite systems. The canonical transformations diagonalize a class of Hamiltonians describing non degenerate and degenerate multiphoton processes. We determine the coherent states associated to the canonical transformations, which generalize the non degenerate two--photon squeezed states. Such heterodyne multiphoton squeezed are defined as the simultaneous eigenstates of the transformed, coupled annihilation operators. They are generated by nonlinear unitary evolutions acting on two-mode squeezed states. They are non Gaussian, highly non classical, entangled states. For a quadratic nonlinearity the heterodyne multiphoton squeezed states define two--mode cubic phase states. The statistical properties of these states can be widely adjusted by tuning the heterodyne mixing angles, the phases of the nonlinear couplings, as well as the strength of the nonlinearity. For quadratic nonlinearity, we study the higher-order contributions to the susceptibility in nonlinear media and we suggest possible experimental realizations of multiphoton conversion processes generating the cubic-phase heterodyne squeezed states.Comment: 16 pages, 23 figure

Optical implementation of continuous-variable quantum cloning machines

We propose an optical implementation of the Gaussian continuous-variable quantum cloning machines. We construct a symmetric N -> M cloner which optimally clones coherent states and we also provide an explicit design of an asymmetric 1 -> 2 cloning machine. All proposed cloning devices can be built from just a single non-degenerate optical parametric amplifier and several beam splitters.Comment: 4 pages, 3 figures, REVTe

Versatile engineering of multimode squeezed states by optimizing the pump spectral profile in spontaneous parametric down-conversion

We study the quantum correlations induced by spontaneous parametric down-conversion (SPDC) of a frequency comb. We derive a theoretical method to find the output state corresponding to a pump with an arbitrary spectral profile. After applying it to the relevant example of a spectrally chirped pump, we run an optimization algorithm to numerically find the pump profiles maximizing some target functions. These include the number of independently squeezed modes and the variances of nullifiers defining cluster states used in many continuous-variable quantum information protocols. To assess the advantages of pump-shaping in real experiments we take into account the physical limitations of the pulse shaper.Comment: Updated title, improved presentation and figures, added references, corrected typos. Closer to the version accepted for publicatio

The rationale for a safe asset and fiscal capacity for the Eurozone. LEQS Paper No. 144/2019 May 2019

The only way to share common liabilities in the Eurozone is to achieve full fiscal and political union, i.e. unity of liability and control. In the pursuit of that goal, there is a need to smooth the transition, avoid unnecessary strains to macroeconomic and financial stability and lighten the burden of stabilisation policies from national sovereigns and the European Central Bank, while preserving market discipline and avoiding moral hazard. Both fiscal and monetary policy face constraints linked to the high legacy debt in some countries and the zero-lower-bound, respectively, and thus introducing Eurozone ‘safe assets’ and fiscal capacity at the centre would strengthen the transmission of monetary and fiscal policies. The paper introduces a standard Mundell-Fleming framework adapted to the features of a closed monetary union, with a two-country setting comprising a ‘core’ and a ‘periphery’ country, to evaluate the response of policy and the economy in case of symmetric and asymmetric demand and supply shocks in the current situation and following the introduction of safe bonds and fiscal capacity. Under the specified assumptions, it concludes that a safe asset and fiscal capacity, better if in combination, would remove the doom loop between banks and sovereigns, reduce the loss in output for both economies and improve the stabilisation properties of fiscal policy for both countries, and thus is welfare enhancing

Protection, openness, and factor adjustment : evidence from the manufacturing sector in Uruguay

The authors use a panel of manufacturing firms to analyze the adjustment process in capital blue collar and white collar employment in Uruguay during a period of trade liberalization when average tariff protection fell from 43 to 14 percent. They calculate the desired factor levels arising from a counterfactual profit maximization in the absence of adjustment costs, generating a measure of factor shortages or surpluses. The average estimated output gap for 1982-95 is 2 percent. The authors'policy analysis shows that trade openness affected the adjustment functions of all three factors of production.Highly protected sectors adjust less when creating jobs (reducing labor shortages) than sectors with low protection. This may be due to fears of policy reversal in highly protected sectors. Also, highly protected sectors adjust more easily (than low protection sectors) when destroying jobs (reducing labor surpluses), especially in the case of blue collar labor. This suggests that trade protection may in fact destroy rather than create jobs within industries, as firms in highly protected sectors are more reluctant to hire and more ready to fire than firms in sectors with low protection. The results for capital are qualitatively similar but quantitatively smaller, suggesting that trade protection plays less of a role in explaining adjustment costs for capital. Interestingly, export-oriented sectors have lower adjustment costs for blue collar labor but not for white collar employment or capital, suggesting that export-led growth may be particularly successful in reducing blue collar unemployment.Economic Theory&Research,Labor Markets,Free Trade,Economic Growth,Educational Sciences

Relativistic Nuclear Energy Density Functionals: Mean-Field and Beyond

Relativistic energy density functionals (EDF) have become a standard tool for nuclear structure calculations, providing a complete and accurate, global description of nuclear ground states and collective excitations. Guided by the medium dependence of the microscopic nucleon self-energies in nuclear matter, semi-empirical functionals have been adjusted to the nuclear matter equation of state and to bulk properties of finite nuclei, and applied to studies of arbitrarily heavy nuclei, exotic nuclei far from stability, and even systems at the nucleon drip-lines. REDF-based structure models have also been developed that go beyond the static mean-field approximation, and include collective correlations related to the restoration of broken symmetries and to fluctuations of collective variables. These models are employed in analyses of structure phenomena related to shell evolution, including detailed predictions of excitation spectra and electromagnetic transition rates.Comment: To be published in Progress in Particle and Nuclear Physic

Quantum Big Bang without fine-tuning in a toy-model

The question of possible physics before Big Bang (or after Big Crunch) is addressed via a schematic non-covariant simulation of the loss of observability of the Universe. Our model is drastically simplified by the reduction of its degrees of freedom to the mere finite number. The Hilbert space of states is then allowed time-dependent and singular at the critical time $t=t_c$. This option circumvents several traditional theoretical difficulties in a way illustrated via solvable examples. In particular, the unitary evolution of our toy-model quantum Universe is shown interruptible, without any fine-tuning, at the instant of its bang or collapse $t= t_c$.Comment: 20 pp., 1 fig., invited talk for the conference "10th Workshop on Quantization, Dualities and Integrable Systems" (April 22 - 24, 2011), http://qdis.emu.edu.tr/index.htm

Protection, Openness and Factor Adjustment: Evidence from the manufacturing sector in Uruguay

Using a panel of Uruguayan manufacturing firms we analyze the adjustment process in capital, blue collar and white collar employment. Our results confirm the lumpy nature of factor adjustment, the relevance of nonlinearities and the interdependence between factor shortages. The average annual estimated output gap due to adjustment cost for1982-1995 was 2%. Trade openness affected the adjustment functions of all three factors. Highly protected sectors adjust less when creating jobs (reducing labor shortages) than sectors with low protection. This may be due to fears of policy reversal in highly protected sectors. Also, highly protected sectors adjust more easily (than low protection sectors) when destroying jobs (reducing labor surpluses), especially in the case of blue collar labor. This suggests that trade protection may in fact destroy rather than create jobs within industries, as firms in highly protected sectors are more reluctant to hire and more ready to fire than firms in sectors with low protection. The results for capital are qualitatively similar but quantitatively smaller. Overall the impact of higher international exposure is larger for blue collar workers than white collar workers.Adjustment costs, Adjustment functions, Openness

Optical state engineering, quantum communication, and robustness of entanglement promiscuity in three-mode Gaussian states

We present a novel, detailed study on the usefulness of three-mode Gaussian states states for realistic processing of continuous-variable quantum information, with a particular emphasis on the possibilities opened up by their genuine tripartite entanglement. We describe practical schemes to engineer several classes of pure and mixed three-mode states that stand out for their informational and/or entanglement properties. In particular, we introduce a simple procedure -- based on passive optical elements -- to produce pure three-mode Gaussian states with {\em arbitrary} entanglement structure (upon availability of an initial two-mode squeezed state). We analyze in depth the properties of distributed entanglement and the origin of its sharing structure, showing that the promiscuity of entanglement sharing is a feature peculiar to symmetric Gaussian states that survives even in the presence of significant degrees of mixedness and decoherence. Next, we discuss the suitability of the considered tripartite entangled states to the implementation of quantum information and communication protocols with continuous variables. This will lead to a feasible experimental proposal to test the promiscuous sharing of continuous-variable tripartite entanglement, in terms of the optimal fidelity of teleportation networks with Gaussian resources. We finally focus on the application of three-mode states to symmetric and asymmetric telecloning, and single out the structural properties of the optimal Gaussian resources for the latter protocol in different settings. Our analysis aims to lay the basis for a practical quantum communication with continuous variables beyond the bipartite scenario.Comment: 33 pages, 10 figures (some low-res due to size constraints), IOP style; (v2) improved and reorganized, accepted for publication in New Journal of Physic