Quantum Phase Slips: from condensed matter to ultracold quantum gases

Quantum phase slips are the primary excitations in one-dimensional superfluids and superconductors at low temperatures. They have been well characterized in most condensed-matter systems, and signatures of their existence has been recently observed in superfluids based on quantum gases too. In this review we briefly summarize the main results obtained on the investigation of phase slips from superconductors to quantum gases. In particular we focus our attention on recent experimental results of the dissipation in one-dimensional Bose superfluids flowing along a shallow periodic potential, which show signatures of quantum phase slips.Comment: 10 pages, 6 figure

Energy project financing in the GCC region: an empirical investigation

This paper analyzes the capital structure of energy infrastructure projects in the Gulf Cooperation Council region, where energy projects form the bulk of the deal-making backload. The econometric estimation of 108 energy project finance for the period 2005–2014 valued at 258 bn USD sheds the light on the success factors for such projects in the region, confirming the relevant relationships among project size, owner concentration and debt duration. The analysis illustrates the roles that debt, equity, interest rate, and the economic crisis play in the financial structuring of infrastructure projects in rapidly growing emerging markets. First, it confirms that longer debt duration is correlated with higher debt ratio. Second, it shows that larger project size is correlated with lower debt ownership concentration. Third, the financial crisis had a different effect on debt ratio and debt duration. Fourth, project size and interest rate are negatively correlated, although regional specific patterns would emerge when comparing the effects of the 2008 financial crisis on interest rates. These findings have several multi-level implications for regulators, debt issuers and investors. For regulators, findings amplify the way in which to improve debt issuance in GCC countries. For issuers, findings suggest that they should be more concerned about the bonds' security and seniority as the firm-specific characteristics, such as size and debt and equity concentration of finance project, affect the capital structure. For investors, the study offers an analytical framework to investigate bonds' structure before investing

Velocity-dependent quantum phase slips in 1D atomic superfluids

Quantum phase slips are the primary excitations in one-dimensional superfluids and superconductors at low temperatures but their existence in ultracold quantum gases has not been demonstrated yet. We now study experimentally the nucleation rate of phase slips in one-dimensional superfluids realized with ultracold quantum gases, owing along a periodic potential. We observe a crossover between a regime of temperature-dependent dissipation at small velocity and interaction and a second regime of velocity-dependent dissipation at larger velocity and interaction. This behavior is consistent with the predicted crossover from thermally-assisted quantum phase slips to purely quantum phase slips.Comment: 7 pages, 6 figure

Observation of a disordered bosonic insulator from weak to strong interactions

We employ ultracold atoms with controllable disorder and interaction to study the paradigmatic problem of disordered bosons in the full disorder-interaction plane. Combining measurements of coherence, transport and excitation spectra, we get evidence of an insulating regime extending from weak to strong interaction and surrounding a superfluid-like regime, in general agreement with the theory. For strong interaction, we reveal the presence of a strongly-correlated Bose glass coexisting with a Mott insulator

Two-dimensional topological quantum walks in the momentum space of structured light

Quantum walks are powerful tools for quantum applications and for designing topological systems. Although they are simulated in a variety of platforms, genuine two-dimensional realizations are still challenging. Here we present an innovative approach to the photonic simulation of a quantum walk in two dimensions, where walker positions are encoded in the transverse wavevector components of a single light beam. The desired dynamics is obtained by means of a sequence of liquid-crystal devices, which apply polarization-dependent transverse "kicks" to the photons in the beam. We engineer our quantum walk so that it realizes a periodically-driven Chern insulator, and we probe its topological features by detecting the anomalous displacement of the photonic wavepacket under the effect of a constant force. Our compact, versatile platform offers exciting prospects for the photonic simulation of two-dimensional quantum dynamics and topological systems.Comment: Published version of the manuscrip