12,983 research outputs found
Speed limits for quantum gates in multi-qubit systems
We use analytical and numerical calculations to obtain speed limits for
various unitary quantum operations in multiqubit systems under typical
experimental conditions. The operations that we consider include single-, two-,
and three-qubit gates, as well as quantum-state transfer in a chain of qubits.
We find in particular that simple methods for implementing two-qubit gates
generally provide the fastest possible implementations of these gates. We also
find that the three-qubit Toffoli gate time varies greatly depending on the
type of interactions and the system's geometry, taking only slightly longer
than a two-qubit controlled-NOT (CNOT) gate for a triangle geometry. The speed
limit for quantum-state transfer across a qubit chain is set by the maximum
spin-wave speed in the chain.Comment: 7 pages (two-column), 2 figures, 2 table
Majorana fermions in pinned vortices
Exploiting the peculiar properties of proximity-induced superconductivity on
the surface of a topological insulator, we propose a device which allows the
creation of a Majorana fermion inside the core of a pinned Abrikosov vortex.
The relevant Bogolyubov-de Gennes equations are studied analytically. We
demonstrate that in this system the zero-energy Majorana fermion state is
separated by a large energy gap, of the order of the zero-temperature
superconducting gap , from a band of single-particle non-topological
excitations. In other words, the Majorana fermion remains robust against
thermal fluctuations, as long as the temperature remains substantially lower
than the critical superconducting temperature. Experimentally, the Majorana
state may be detected by measuring the tunneling differential conductance at
the center of the Abrikosov vortex. In such an experiment, the Majorana state
manifests itself as a zero-bias anomaly separated by a gap, of the order of
, from the contributions of the nontopological excitations.Comment: 9 pages, 2 eps figures, new references are added, several typos are
correcte
Deep structure of the Tyrrhenian basin from 2-D joint refraction and reflection travel-time tomography of wide angle seismic data
Rifting of the Tyrrhenian Basin, a complex interaction among faulting , magmatism and mantle exhumation
Quantum limit of photothermal cooling
We study the problem of cooling a mechanical oscillator using the
photothermal (bolometric) force. Contrary to previous attempts to model this
system, we take into account the noise effects due to the granular nature of
photon absorption. This allows us to tackle the cooling problem down to the
noise dominated regime and to find reasonable estimates for the lowest
achievable phonon occupation in the cantilever
A novel stepwise micro-TESE approach in non obstructive azoospermia
Background: The purpose of the study was to investigate whether micro-TESE can improve sperm retrieval rate
(SRR) compared to conventional single TESE biopsy on the same testicle or to contralateral multiple TESE, by
employing a novel stepwise micro-TESE approach in a population of poor prognosis patients with non-obstructive
azoospermia (NOA).
Methods: Sixty-four poor prognosis NOA men undergoing surgical testicular sperm retrieval for ICSI, from March
2007 to April 2013, were included in this study. Patients inclusion criteria were a) previous unsuccessful TESE, b)
unfavorable histology (SCOS, MA, sclerahyalinosis), c) Klinefelter syndrome. We employed a stepwise micro-TESE
consisting three-steps: 1) single conventional TESE biopsy; 2) micro-TESE on the same testis; 3) contralateral multiple
TESE.
Results: SRR was 28.1 % (18/64). Sperm was obtained in both the initial single conventional TESE and in the
following micro-TESE. The positive or negative sperm retrieval was further confirmed by a contralateral multiple
TESE, when performed. No significant pre-operative predictors of sperm retrieval, including patients’ age, previous
negative TESE or serological markers (LH, FSH, inhibin B), were observed at univariate or multivariate analysis.
Micro-TESE (step 2) did not improve sperm retrieval as compared to single TESE biopsy on the same testicle
(step 1) or multiple contralateral TESE (step 3).
Conclusions: Stepwise micro-TESE could represent an optimal approach for sperm retrieval in NOA men. In
our view, it should be offered to NOA patients in order to gradually increase surgical invasiveness, when
necessary. Stepwise micro-TESE might also reduce the costs, time and efforts involved in surgery
Two fibre post systems luted with or without post space preparation: cement thickness analysis
INVESTIGATION ON THE ARTIFICIAL NEURAL NETWORKS PREDICTION CAPABILITIES APPLIED TO VIBRATING PLATES IN SIMILITUDE
The prediction capabilities of artificial neural networks in similitude field are investigated. They have been applied to plates in similitude with two objectives: prediction of natural frequencies and model identification. The results show that the method is able to give accurate predictions and that an experimental training set can be created if the models are well characterized
Support of Dynamic Measurements Through Similitude Formulations
Up to now, similitude methods have been used in order to overcome the typical drawbacks of experimental testing and numerical simulations by reconstructing the full-scale model behavior from that of the scaled model. The novelty of this work is the application of similitude theory not as a tool for predicting the prototype dynamic response, but for supporting, and eventually validating, experimental measurements polluted by noise. Two Aluminium Foam Sandwich (AFS) plates are analyzed with Digital Image Correlation (DIC) cameras. First, an algorithm for blind source separation problems is used to extract information about the excitation; then, SAMSARA (Similitude and Asymptotic Models for Structural-Acoustic Research Applications) similitude method is applied to both the force spectra and velocity responses of prototype and model. The reconstruction of force and velocity curves demonstrates that the similitude results are coherent with the quality of the experimental measurements: when the spatial pattern in resonance is recognizable, then the curves overlap. Instead, when the displacement field of just one model is not well identified, the reconstruction exhibits discrepancies. Therefore, similitude methods reveal to be an interesting tool for understanding if a set of measurements is reliable or not and their application should not be underestimated, especially in the light of the expanding range of approaches which can extract important information from noisy observations
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