Searcharxiv⌕ Search

arXiv subjects

F. Cavaliere

Publications and source records attributed to F. Cavaliere.

71 records · Page 4Linked to original sources
arXiv2010

Planck pre-launch status: calibration of the Low Frequency Instrument flight model radiometers

The Low Frequency Instrument (LFI) on-board the ESA Planck satellite carries eleven radiometer subsystems, called Radiometer Chain Assemblies (RCAs), each composed of a pair of pseudo-correlation receivers. We describe the on-ground calibration campaign performed to qualify the flight model RCAs and to measure their pre-launch performances. Each RCA was calibrated in a dedicated flight-like cryogenic environment with the radiometer front-end cooled to 20K and the back-end at 300K, and with an external input load cooled to 4K. A matched load simulating a blackbody at different temperatures was placed in front of the sky horn to derive basic radiometer properties such as noise temperature, gain, and noise performance, e.g. 1/f noise. The spectral response of each detector was measured as was their susceptibility to thermal variation. All eleven LFI RCAs were calibrated. Instrumental parameters measured in these tests, such as noise temperature, bandwidth, radiometer isolation, and linearity, provide essential inputs to the Planck-LFI data analysis.

astro-ph.IM↗
arXiv2010

Cryogenic environment and performance for testing the Planck radiometers

This paper is part of the Prelaunch status LFI papers published on JINST: http://www.iop.org/EJ/journal/-page=extra.proc5/jinst The Planck LFI Radiometer Chain Assemblies (RCAs) have been calibrated in two dedicated cryogenic facilities. In this paper the facilities and the related instrumentation are described. The main satellite thermal interfaces for the single chains have to be reproduced and stability requirements have to be satisfied. Setup design, problems occurred and improving solutions implemented are discussed. Performance of the cryogenic setup are reported.

astro-ph.IM↗
arXiv2010

Planck pre-launch status: Low Frequency Instrument calibration and expected scientific performance

We give the calibration and scientific performance parameters of the Planck Low Frequency Instrument (LFI) measured during the ground cryogenic test campaign. These parameters characterise the instrument response and constitute our best pre-launch knowledge of the LFI scientific performance. The LFI shows excellent $1/f$ stability and rejection of instrumental systematic effects; measured noise performance shows that LFI is the most sensitive instrument of its kind. The set of measured calibration parameters will be updated during flight operations through the end of the mission.

astro-ph.IM↗
arXiv2010

Planck pre-launch status: Design and description of the Low Frequency Instrument

In this paper we present the Low Frequency Instrument (LFI), designed and developed as part of the Planck space mission, the ESA program dedicated to precision imaging of the cosmic microwave background (CMB). Planck-LFI will observe the full sky in intensity and polarisation in three frequency bands centred at 30, 44 and 70 GHz, while higher frequencies (100-850 GHz) will be covered by the HFI instrument. The LFI is an array of microwave radiometers based on state-of-the-art Indium Phosphide cryogenic HEMT amplifiers implemented in a differential system using blackbody loads as reference signals. The front-end is cooled to 20K for optimal sensitivity and the reference loads are cooled to 4K to minimise low frequency noise. We provide an overview of the LFI, discuss the leading scientific requirements and describe the design solutions adopted for the various hardware subsystems. The main drivers of the radiometric, optical and thermal design are discussed, including the stringent requirements on sensitivity, stability, and rejection of systematic effects. Further details on the key instrument units and the results of ground calibration are provided in a set of companion papers.

astro-ph.IM↗
arXiv2009

1st Roman Young Researchers Meeting Proceedings

During the last few decades scientists have been able to test the bases of the physics paradigms, where the quantum mechanics has to match the cosmological scales. Between the extremes of this scenario, biological phenomena and their complexity take place, challenging the laws we observe in the atomic and sub-atomic world. In order to explore the details of this world, new huge experimental facilities are under construction. These projects involve people coming from several countries and give physicists the opportunity to work together with chemists, biologists and other scientists. The Roman Young Researchers Meeting is a conference, organised by Ph. D. students and young postdocs connected to the Roman area. It is aimed primarily at graduate students and post-docs, working in physics. The 1st conference has been held on the 21st of July 2009 at the University of Roma Tor Vergata. It was organised in three sessions, devoted to Astrophysics and Cosmology, Soft and Condensed Matter Physics and Theoretical and Particle Physics. In this proceeding we collect the contributions which have been presented and discussed during the meeting, according to the specific topics treated.

physics.gen-ph↗
arXiv2009

Transport properties of quantum dots in the Wigner molecule regime

The transport properties of quantum dots with up to N=7 electrons ranging from the weak to the strong interacting regime are investigated via the projected Hartree-Fock technique. As interactions increase radial order develops in the dot, with the formation of ring and centered-ring structures. Subsequently, angular correlations appear, signalling the formation of a Wigner molecule state. We show striking signatures of the emergence of Wigner molecules, detected in transport. In the linear regime, conductance is exponentially suppressed as the interaction strength grows. A further suppression is observed when centered-ring structures develop, or peculiar spin textures appear. In the nonlinear regime, the formation of molecular states may even lead to a conductance enhancement.

cond-mat.mes-hall↗
arXiv2008

Phonon distributions of a single bath mode coupled to a quantum dot

The properties of an unconventional, single mode phonon bath coupled to a quantum dot, are investigated within the rotating wave approximation. The electron current through the dot induces an out of equilibrium bath, with a phonon distribution qualitatively different from the thermal one. In selected transport regimes, such a distribution is characterized by a peculiar selective population of few phonon modes and can exhibit a sub-Poissonian behavior. It is shown that such a sub-Poissonian behavior is favored by a double occupancy of the dot. The crossover from a unequilibrated to a conventional thermal bath is explored, and the limitations of the rotating wave approximation are discussed.

cond-mat.mes-hall↗
arXiv2007

Spin projected unrestricted Hartree-Fock ground states for harmonic quantum dots

We report results for the ground state energies and wave functions obtained by projecting spatially unrestricted Hartree Fock states to eigenstates of the total spin and the angular momentum for harmonic quantum dots with $N\leq 12$ interacting electrons including a magnetic field states with the correct spatial and spin symmetries have lower energies than those obtained by the unrestricted method. The chemical potential as a function of a perpendicular magnetic field is obtained. Signature of an intrinsic spin blockade effect is found.

cond-mat.mes-hall↗
arXiv2007

Spin and rotational symmetries in unrestricted Hartree Fock states of quantum dots

Ground state energies are obtained using the unrestricted Hartree Fock method for up to four interacting electrons parabolically confined in a quantum dot subject to a magnetic field. Restoring spin and rotational symmetries we recover Hund first rule. With increasing magnetic field, crossovers between ground states with different quantum numbers are found for fixed electron number that are not reproduced by the unrestricted Hartree Fock approximation. These are consistent with the ones obtained with more refined techniques. We confirm the presence of a spin blockade due to a spin mismatch in the ground states of three and four electrons.

cond-mat.mes-hall↗
arXiv2006

Anomalous suppression of the shot noise in a nanoelectromechanical system

In this paper we report a relaxation-induced suppression of the noise for a single level quantum dot coupled to an oscillator with incoherent dynamics in the sequential tunneling regime. It is shown that relaxation induces qualitative changes in the transport properties of the dot, depending on the strength of the electron-phonon coupling and on the applied voltage. In particular, critical thresholds in voltage and relaxation are found such that a suppression below 1/2 of the Fano factor is possible. Additionally, the current is either enhanced or suppressed by increasing relaxation, depending on bias being greater or smaller than the above threshold. These results exist for any strength of the electron-phonon coupling and are confirmed by a four states toy model.

cond-mat.mes-hall↗
arXiv2005

Negative differential conductance in quantum dots in theory and experiment

Experimental results for sequential transport through a lateral quantum dot in the regime of spin blockade induced by spin dependent tunneling are compared with theoretical results obtained by solving a master equation for independent electrons. Orbital and spin effects in electron tunneling in the presence of a perpendicular magnetic field are identified and discussed in terms of the Fock-Darwin spectrum with spin. In the nonlinear regime, a regular pattern of negative differential conductances is observed. Electrical asymmetries in tunnel rates and capacitances must be introduced in order to account for the experimental findings. Fast relaxation of the excited states in the quantum dot have to be assumed, in order to explain the absence of certain structures in the transport spectra.

cond-mat.mes-hall↗
arXiv2004

Shot noise in charge and magnetization currents of a quantum ring

The shot noise in a quantum ring, connected to leads, is studied in the presence of electron interactions in the sequential tunneling regime. Two qualitatively different noise correlations with distinctly different behaviors are identified and studied in a large range of parameters. Noise in the total current is due to the discreteness of the electron charge and can become super-Poissonian as result of electron interaction. The noise in the magnetization current is comparatively insensitive to the interaction but can be greatly enhanced if population inversion of the angular states is assumed. The characteristic time scales are studied by a Monte-Carlo simulation.

cond-mat.mes-hall↗
arXiv2004

Spin effects in transport through non-Fermi liquid quantum dots

The current-voltage characteristic of a one dimensional quantum dot connected via tunnel barriers to interacting leads is calculated in the region of sequential tunneling. The spin of the electrons is taken into account. Non-Fermi liquid correlations implying spin-charge separation are assumed to be present in the dot and in the leads. It is found that the energetic distance of the peaks in the linear conductance shows a spin-induced parity effect at zero temperature T. The temperature dependence of the positions of the peaks depends on the non-Fermi liquid nature of the system. For non-symmetric tunnel barriers negative differential conductances are predicted, which are related to the participation in the transport of collective states in the quantum dot with larger spins. Without spin-charge separation the negative differential conductances do not occur. Taking into account spin relaxation destroys the spin-induced conductance features. The possibility of observing in experiment the predicted effects are briefly discussed.

cond-mat.str-el↗
arXiv2004

Negative differential conductance induced by spin-charge separation

Spin-charge states of correlated electrons in a one-dimensional quantum dot attached to interacting leads are studied in the non-linear transport regime. With non-symmetric tunnel barriers, regions of negative differential conductance induced by spin-charge separation are found. They are due to a correlation-induced trapping of higher-spin states without magnetic field, and associated with a strong increase in the fluctuations of the electron spin.

cond-mat.str-el↗
arXiv2003

A dual output polarimeter devoted to the study of the Cosmic Microwave Background

We have developed a correlation radiometer at 33 GHz devoted to the search for residual polarization of the Cosmic Microwave Background (CMB). The two instruments`s outputs are linear combination of two Stokes Parameters (Q and U or U and V). The instrument is therefore directly sensitive to the polarized component of the radiation (respectively linear and circular). The radiometer has a beam-width oif 7 or 14 deg, but it can be coupled to a telescope increasing the resolution. The expected CMB polarization is at most a part per milion. The polarimeter has been designed to be sensitive to this faint signal, and it has been optimized to improve its long term stability, observing from the ground. In this contribution the performances of the instrument are presented, together with the preliminary test and observations.

astro-ph↗
arXiv2002

Theory of measuring the "Luttinger-g" of a one-dimensional quantum dot

We study electron transport through a quantum dot in a Tomonaga-Luttinger liquid with an inhomogeneity induced either by a non-uniform electron interaction or by the presence of tunnel resistances of contacts. The non-analytic temperature behavior of the conductance peaks show crossovers determined by the different energy scales associated with the dot and the inhomogeneity despite the Coulomb blockade remains intact. This suggests an explanation of recent findings in semiconductor quantum wires and carbon nanotubes.

cond-mat.mes-hall↗