338 research outputs found
Instance-based Bird Species Identification with Undiscriminant Features Pruning
International audienceThis paper reports the participation of Inria to the audiobasedbird species identication challenge of LifeCLEF 2014 campaign.Inspired by recent works on ne-grained image classication, we introducean instance-based classication scheme based on the dense indexingof MFCC features and the pruning of the non-discriminant ones. To makesuch strategy scalable to the 30M of MFCC features extracted from thetens of thousands audio recordings of the training set, we used highdimensionalhashing techniques coupled with an ecient approximatenearest neighbors search algorithm with controlled quality. Further improvementsare obtained by (i) using a sliding classier with max pooling(ii) weighting the query features according to their semantic coherence(iii) making use of the metadata to lter incoherent species. Results showthe eectiveness of the proposed technique which ranked 3rd among the10 participating groups
On the collapse pressure of armored bubbles and drops
International audienceDrops and bubbles wrapped in dense monolayers of hydrophobic particles are known to sustain a significant decrease of their internal pressure. Through dedicated experiments we investigate the collapse behavior of such armored water drops as a function of the particle-to-drop size ratio in the range 0.02-0.2. We show that this parameter controls the behavior of the armor during the deflation: at small size ratios the drop shrinkage proceeds through the soft crumpling of the monolayer, at intermediate ratios the drop becomes faceted, and for the largest studied ratios the armor behaves like a granular arch. The results show that each of the three morphological regimes is characterized by an increasing magnitude of the collapse pressure. This increase is qualitatively modeled thanks to a mechanism involving out-of-plane deformations and particle disentanglement in the armor
Non-linear coupling between the two oscillation modes of a dc-SQUID
5 pagesInternational audienceWe make a detailed theoretical description of the two-dimensional nature of a dc-SQUID, analyzing the coupling between its two orthogonal phase oscillation modes. While it has been shown that the mode defined as ''longitudinal" can be initialized, manipulated and measured, so as to encode a quantum bit of information, the mode defined as ''transverse" is usually repelled at high frequency and does not interfere in the dynamics. We show that, using typical parameters of existing devices, the transverse mode energy can be made of the order of the longitudinal one. In this regime, we can observe a strong coupling between these modes, described by an Hamiltonian providing a wide range of interesting effects, such as conditional quantum operations and entanglement. This coupling also creates an atomic-like structure for the combined two mode states, with a V-like scheme
Etching suspended superconducting hybrid junctions from a multilayer
A novel method to fabricate large-area superconducting hybrid tunnel
junctions with a suspended central normal metal part is presented. The samples
are fabricated by combining photo-lithography and chemical etch of a
superconductor - insulator - normal metal multilayer. The process involves few
fabrication steps, is reliable and produces extremely high-quality tunnel
junctions. Under an appropriate voltage bias, a significant electronic cooling
is demonstrated
Unexpectedly allowed transition in two inductively coupled transmons
We present experimental results in which the unexpected zero-two transition
of a circuit composed of two inductively coupled transmons is observed. This
transition shows an unusual magnetic flux dependence with a clear disappearance
at zero magnetic flux. In a transmon qubit the symmetry of the wave functions
prevents this transition to occur due to selection rule. In our circuit the
Josephson effect introduces strong couplings between the two normal modes of
the artificial atom. This leads to a coherent superposition of states from the
two modes enabling such transitions to occur
Rabi-like oscillations of an anharmonic oscillator: classical versus quantum interpretation
8 pagesInternational audienceWe have observed Rabi-like oscillations in a current-biased dc SQUID presenting enhanced coherence times compared to our previous realization~\cite{Claudon_PRL04}. This Josephson device behaves as an anharmonic oscillator which can be driven into a coherent superposition of quantum states by resonant microwave flux pulses. Increasing the microwave amplitude, we study the evolution of the Rabi frequency from the 2-level regime to the regime of multilevel dynamics. When up to levels are involved, the Rabi frequency is a clear signature of quantum behavior. At higher excitation amplitude, classical and quantum predictions for the Rabi frequency converge. This result is discussed in the light of a calculation of the Wigner function. In particular, our analysis shows that pronounced quantum interferences always appear in the course of the Rabi-like oscillations
Kerr coefficients of plasma resonances in Josephson junction chains
We present an experimental and theoretical analysis of the self- and
cross-Kerr effect of extended plasma resonances in Josephson junction chains.
We calculate the Kerr coefficients by deriving and diagonalizing the
Hamiltonian of a linear circuit model for the chain and then adding the
Josephson non-linearity as a perturbation. The calculated Kerr-coefficients are
compared with the measurement data of a chain of 200 junctions. The Kerr effect
manifests itself as a frequency shift that depends linearly on the number of
photons in a resonant mode. By changing the input power on a low signal level,
we are able to measure this shift. The photon number is calibrated using the
self-Kerr shift calculated from the sample parameters. We then compare the
measured cross-Kerr shift with the theoretical prediction, using the calibrated
photon number.Comment: 10 pages, 9 figure
Understanding the saturation power of Josephson Parametric Amplifiers made from SQUIDs arrays
We report on the implementation and detailed modelling of a Josephson
Parametric Amplifier (JPA) made from an array of eighty Superconducting QUantum
Interference Devices (SQUIDs), forming a non-linear quarter-wave resonator.
This device was fabricated using a very simple single step fabrication process.
It shows a large bandwidth (45 MHz), an operating frequency tunable between 5.9
GHz and 6.8 GHz and a large input saturation power (-117 dBm) when biased to
obtain 20 dB of gain. Despite the length of the SQUID array being comparable to
the wavelength, we present a model based on an effective non-linear LC series
resonator that quantitatively describes these figures of merit without fitting
parameters. Our work illustrates the advantage of using array-based JPA since a
single-SQUID device showing the same bandwidth and resonant frequency would
display a saturation power 15 dB lower.Comment: 12 pages, 9 figures, Appendices include
A photonic crystal Josephson traveling wave parametric amplifier
An amplifier combining noise performances as close as possible to the quantum
limit with large bandwidth and high saturation power is highly desirable for
many solid state quantum technologies such as high fidelity qubit readout or
high sensitivity electron spin resonance for example. Here we introduce a new
Traveling Wave Parametric Amplifier based on Superconducting QUantum
Interference Devices. It displays a 3 GHz bandwidth, a -102 dBm 1-dB
compression point and added noise near the quantum limit. Compared to previous
state-of-the-art, it is an order of magnitude more compact, its characteristic
impedance is in-situ tunable and its fabrication process requires only two
lithography steps. The key is the engineering of a gap in the dispersion
relation of the transmission line. This is obtained using a periodic modulation
of the SQUID size, similarly to what is done with photonic crystals. Moreover,
we provide a new theoretical treatment to describe the non-trivial interplay
between non-linearity and such periodicity. Our approach provides a path to
co-integration with other quantum devices such as qubits given the low
footprint and easy fabrication of our amplifier.Comment: 6 pages, 4 figures, Appendixe
Kerr non-linearity in a superconducting Josephson metamaterial
We present a detailed experimental and theoretical analysis of the dispersion
and non-linear Kerr frequency shifts of plasma modes in a one-dimensional
Josephson junction chain containing 500 SQUIDs in the regime of weak
nonlinearity. The measured low-power dispersion curve agrees perfectly with the
theoretical model if we take into account the Kerr renormalisation of the bare
frequencies and the long-range nature of the island charge screening by a
remote ground plane. We measured the self- and cross-Kerr shifts for the
frequencies of the eight lowest modes in the chain. We compare the measured
Kerr coefficients with theory and find good agreement
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