Electron quantum optics at fractional filling factor: minimal excitation states and interferometry

The emerging field of electron quantum optics aims at manipulating electrons one by one in ballistic, coherent conductors. In this way it is possible to reproduce quantum-optical experiments and setups in solid state devices, using fermionic degrees of freedom (electrons in mesoscopic systems) instead of bosonic ones (photons in waveguides and optical cavities). However, the solid state world can be heavily influenced by electron-electron interactions, differently to what happens in the traditional photonic quantum optics. In this thesis, we discuss how electron quantum optics can be extended to the fractional quantum Hall regime, where interactions give rise to exotic quasi-particles carrying a fraction of the electron charge, and whose statistical properties are neither bosonic nor fermionic, but belongs to the more general class of anyons. In particular, we discuss a strategy to excite coherent single-electron excitations in the fractional liquid by means of carefully-engineered voltage pulses applied to the conductor, and show how to detect such a unique quantum state in a fermionic Hanbury-Brown and Twiss experiment. We also analyze collisions of identical excitations in the fractional quantum Hall regime, in the spirit of the celebrated Hong-Ou-Mandel experiment, highlighting analogies and differences with respect to ordinary fermionic systems

Phonon-decoupled di-chromatic pumping scheme for highly efficient and indistinguishable single-photon sources

A key problem within single-photon sources engineering is to achieve population inversion of a quantum emitter on-demand and with the highest possible fidelity, without resorting to resonant laser pulses. A non-resonant pumping signal has the advantage of being separated in frequency from the single photons, but it typically triggers -- or makes active use of -- incoherent phonon-assisted scattering events, which preclude near unity fidelity in the population inversion and deteriorate the quality of the emitted photons. Here, we theoretically show that a coherent di-chromatic pumping scheme using short laser pulses and moderately large detuning effectively decouples the emitter from its phonon bath, allowing for population inversion arbitrarily close to unity. When considering a micropillar single-photon source driven with this scheme, we calculate very high photon emission into the cavity mode (0.953 photons per pulse), together with excellent indistinguishability (0.975). Such values are uniquely bounded by decoherence in the emission dynamics or practical considerations, and not by the excitation scheme.Comment: 5 pages main text + Supplemental Materia

Current enhancement through a time dependent constriction in fractional topological insulators

We analyze the backscattering current induced by a time dependent constriction as a tool to probe fractional topological insulators. We demonstrate an enhancement of the total current for a fractional topological insulator induced by the dominant tunneling excitation, contrary to the decreasing present in the integer case for not too strong interactions. This feature allows to unambiguously identify fractional quasiparticles. Furthermore, the dominant tunneling processes, which may involve one or two quasiparticles depending on the interactions, can be clearly determined.Comment: 6 pages, 3 figure

Interference induced thermoelectric switching and heat rectification in quantum Hall junctions

Interference represents one of the most striking manifestation of quantum physics in low-dimensional systems. Despite evidences of quantum interference in charge transport have been known for a long time, only recently signatures of interference induced thermal properties have been reported, paving the way for the phase-coherent manipulation of heat in mesoscopic devices. In this work we show that anomalous thermoelectric properties and efficient heat rectification can be achieved by exploiting the phase-coherent edge states of quantum Hall systems. By considering a tunneling geometry with multiple quantum point contacts, we demonstrate that the interference paths effectively break the electron-hole symmetry, allowing for a thermoelectric charge current flowing either from hot to cold or viceversa, depending on the details of the tunnel junction. Correspondingly, an interference induced heat current is predicted, and we are able to explain these results in terms of an intuitive physical picture. Moreover, we show that heat rectification can be achieved by coupling two quantum Hall systems with different filling factors, and that this effect can be enhanced by exploiting the interference properties of the tunnel junction.Comment: 9 pages, 7 figure

Minimal excitation states for heat transport in driven quantum Hall systems

We investigate minimal excitation states for heat transport into a fractional quantum Hall system driven out of equilibrium by means of time-periodic voltage pulses. A quantum point contact allows for tunneling of fractional quasi-particles between opposite edge states, thus acting as a beam splitter in the framework of the electron quantum optics. Excitations are then studied through heat and mixed noise generated by the random partitioning at the barrier. It is shown that levitons, the single-particle excitations of a filled Fermi sea recently observed in experiments, represent the cleanest states for heat transport, since excess heat and mixed shot noise both vanish only when Lorentzian voltage pulses carrying integer electric charge are applied to the conductor. This happens in the integer quantum Hall regime and for Laughlin fractional states as well, with no influence of fractional physics on the conditions for clean energy pulses. In addition, we demonstrate the robustness of such excitations to the overlap of Lorentzian wavepackets. Even though mixed and heat noise have nonlinear dependence on the voltage bias, and despite the non-integer power-law behavior arising from the fractional quantum Hall physics, an arbitrary superposition of levitons always generates minimal excitation states.Comment: 15 pages, 7 figure

NEMO: A flexible and highly scalable network EMulatOr

Evaluating novel applications and protocols in realistic scenarios has always been a very important task for all stakeholders working in the networking field. Network emulation, being a trade-off between actual deployment and simulations, represents a very powerful solution to this issue, providing a working network platform without requiring the actual deployment of all network components. We present NEMO, a flexible and scalable Java-based network emulator, which can be used to emulate either only a single link, a portion of a network, or an entire network. NEMO is able to work in both real and virtual time, depending on the tested scenarios and goals, and it can be run as either a stand-alone instance on a single machine, or distributed among different network-connected machines, leading to distributed and highly scalable emulation infrastructures. Among different features, NEMO is also capable of virtualizing the execution of third-party Java applications by running them on top of virtual nodes, possibly attached to an emulated or external network. Keywords: Network emulation, Protocol stack, Jav

Crystallization of Levitons in the fractional quantum Hall regime

Using a periodic train of Lorentzian voltage pulses, which generates soliton-like electronic excitations called Levitons, we investigate the charge density backscattered off a quantum point contact in the fractional quantum Hall regime. We find a regular pattern of peaks and valleys, reminiscent of analogous self-organization recently observed for optical solitons in non-linear environments. This crystallization phenomenon is confirmed by additional side dips in the Hong-Ou-Mandel noise, a feature that can be observed in nowadays electron quantum optics experiments.Comment: 9 pages, 4 figure

Behavioral Analysis for Virtualized Network Functions : A SOM-based Approach

In this paper, we tackle the problem of detecting anomalous behaviors in a virtualized infrastructure for network function virtualization, proposing to use self-organizing maps for analyzing historical data available through a data center. We propose a joint analysis of system-level metrics, mostly related to resource consumption patterns of the hosted virtual machines, as available through the virtualized infrastructure monitoring system, and the application-level metrics published by individual virtualized network functions through their own monitoring subsystems. Experimental results, obtained by processing real data from one of the NFV data centers of the Vodafone network operator, show that our technique is able to identify specific points in space and time of the recent evolution of the monitored infrastructure that are worth to be investigated by a human operator in order to keep the system running under expected conditions

SOM-based behavioral analysis for virtualized network functions

In this paper, we propose a mechanism based on Self-Organizing Maps for analyzing the resource consumption behaviors and detecting possible anomalies in data centers for Network Function Virtualization (NFV). Our approach is based on a joint analysis of two historical data sets available through two separate monitoring systems: system-level metrics for the physical and virtual machines obtained from the monitoring infrastructure, and application-level metrics available from the individual virtualized network functions. Experimental results, obtained by processing real data from one of the NFV data centers of the Vodafone network operator, highlight some of the capabilities of our system to identify interesting points in space and time of the evolution of the monitored infrastructure

A Lentiviral Vector-Based, Herpes Simplex Virus 1 (HSV-1) Glycoprotein B Vaccine Affords Cross-Protection against HSV-1 and HSV-2 Genital Infections

Genital herpes is caused by herpes simplex virus 1 (HSV-1) and HSV-2, and its incidence is constantly increasing in the human population. Regardless of the clinical manifestation, HSV-1 and HSV-2 infections are highly transmissible to sexual partners and enhance susceptibility to other sexually transmitted infections. An effective vaccine is not yet available. Here, HSV-1 glycoprotein B (gB1) was delivered by a feline immunodeficiency virus (FIV) vector and tested against HSV-1 and HSV-2 vaginal challenges in C57BL/6 mice. The gB1 vaccine elicited cross-neutralizing antibodies and cell-mediated responses that protected 100 and 75% animals from HSV-1- and HSV-2-associated severe disease, respectively. Two of the eight fully protected vaccinees underwent subclinical HSV-2 infection, as demonstrated by deep immunosuppression and other analyses. Finally, vaccination prevented death in 83% of the animals challenged with a HSV-2 dose that killed 78 and 100% naive and mock-vaccinated controls, respectively. Since this FLY vector can accommodate two or more HSV immunogens, this vaccine has ample potential for improvement and may become a candidate for the development of a truly effective vaccine against genital herpes