1,605 research outputs found
Ballistic effects in a proximity induced superconducting diffusive metal
Using a Scanning Tunneling Microscope (STM), we investigate the Local Density
of States (LDOS) of artificially fabricated normal metal nano-structures in
contact with a superconductor. Very low temperature local spectroscopic
measurements (100 mK) reveal the presence of well defined subgap peaks at
energy |E|<Delta in the LDOS at various positions of the STM tip. Although no
clear correlations between the LDOS and the shape of the samples have emerged,
some of the peak features suggest they originate from quasi-particle bound
states within the normal metal structures (De Gennes St James states).
Refocusing of electronic trajectories induced by the granular srtucture of the
samples can explain the observation of spatially uncorrelated interference
effects in a non-ballistic medium.Comment: 4 pages, 4 figure
High-gain weakly nonlinear flux-modulated Josephson parametric amplifier using a SQUID-array
We have developed and measured a high-gain quantum-limited microwave
parametric amplifier based on a superconducting lumped LC resonator with the
inductor L including an array of 8 superconducting quantum interference devices
(SQUIDs). This amplifier is parametrically pumped by modulating the flux
threading the SQUIDs at twice the resonator frequency. Around 5 GHz, a maximum
gain of 31 dB, a product amplitude-gain x bandwidth above 60 MHz, and a 1 dB
compression point of -123 dBm at 20 dB gain are obtained in the non-degenerate
mode of operation. Phase sensitive amplification-deamplification is also
measured in the degenerate mode and yields a maximum gain of 37 dB. The
compression point obtained is 18 dB above what would be obtained with a single
SQUID of the same inductance, due to the smaller nonlinearity of the SQUID
array.Comment: 7 pages, 4 figures, 23 reference
National age and coresidence patterns shape COVID-19 vulnerability
Based on harmonized census data from 81 countries, we estimate how age and coresidence patterns shape the vulnerability of countries' populations to outbreaks of coronavirus disease 2019 (COVID-19). We estimate variation in deaths arising due to a simulated random infection of 10% of the population living in private households and subsequent within-household transmission of the virus. The age structures of European and North American countries increase their vulnerability to COVID-related deaths in general. The coresidence patterns of elderly persons in Africa and parts of Asia increase these countries' vulnerability to deaths induced by within-household transmission of COVID-19. Southern European countries, which have aged populations and relatively high levels of intergenerational coresidence, are, all else equal, the most vulnerable to outbreaks of COVID-19. In a second step, we estimate to what extent avoiding primary infections for specific age groups would prevent subsequent deaths due to within-household transmission of the virus. Preventing primary infections among the elderly is the most effective in countries with small households and little intergenerational coresidence, such as France, whereas confining younger age groups can have a greater impact in countries with large and intergenerational households, such as Bangladesh
Energy flows in gesture-speech physics: The respiratory-vocal system and its coupling with hand gestures
Expressive moments in communicative hand gestures often align with emphatic stress in speech. It has recently been found that acoustic markers of emphatic stress arise naturally during steady-state phonation when upper-limb movements impart physical impulses on the body, most likely affecting acoustics via respiratory activity. In this confirmatory study, participants (N = 29) repeatedly uttered consonant-vowel (/pa/) mono-syllables while moving in particular phase relations with speech, or not moving the upper limbs. This study shows that respiration-related activity is affected by (especially high-impulse) gesturing when vocalizations occur near peaks in physical impulse. This study further shows that gesture-induced moments of bodily impulses increase the amplitude envelope of speech, while not similarly affecting the Fundamental Frequency (F0). Finally, tight relations between respiration-related activity and vocalization were observed, even in the absence of movement, but even more so when upper-limb movement is present. The current findings expand a developing line of research showing that speech is modulated by functional biomechanical linkages between hand gestures and the respiratory system. This identification of gesture-speech biomechanics promises to provide an alternative phylogenetic, ontogenetic, and mechanistic explanatory route of why communicative upper limb movements co-occur with speech in humans. ACKNOWLEDGMENT
On the number of -cycles in the assignment problem for random matrices
We continue the study of the assignment problem for a random cost matrix. We
analyse the number of -cycles for the solution and their dependence on the
symmetry of the random matrix. We observe that for a symmetric matrix one and
two-cycles are dominant in the optimal solution. In the antisymmetric case the
situation is the opposite and the one and two-cycles are suppressed. We solve
the model for a pure random matrix (without correlations between its entries)
and give analytic arguments to explain the numerical results in the symmetric
and antisymmetric case. We show that the results can be explained to great
accuracy by a simple ansatz that connects the expected number of -cycles to
that of one and two cycles.Comment: To appear in Journal of Statistical Mechanic
Extreme value distributions and Renormalization Group
In the classical theorems of extreme value theory the limits of suitably
rescaled maxima of sequences of independent, identically distributed random
variables are studied. So far, only affine rescalings have been considered. We
show, however, that more general rescalings are natural and lead to new limit
distributions, apart from the Gumbel, Weibull, and Fr\'echet families. The
problem is approached using the language of Renormalization Group
transformations in the space of probability densities. The limit distributions
are fixed points of the transformation and the study of the differential around
them allows a local analysis of the domains of attraction and the computation
of finite-size corrections.Comment: 16 pages, 5 figures. Final versio
Storage and retrieval of microwave fields at the single-photon level in a spin ensemble
We report the storage of microwave pulses at the single-photon level in a
spin-ensemble memory consisting of NV centers in a diamond crystal
coupled to a superconducting LC resonator. The energy of the signal, retrieved
later by spin-echo techniques, reaches of the
energy absorbed by the spins, and this storage efficiency is quantitatively
accounted for by simulations. This figure of merit is sufficient to envision
first implementations of a quantum memory for superconducting qubits.Comment: 6 page
Reaching the quantum limit of sensitivity in electron spin resonance
We report pulsed electron-spin resonance (ESR) measurements on an ensemble of
Bismuth donors in Silicon cooled at 10mK in a dilution refrigerator. Using a
Josephson parametric microwave amplifier combined with high-quality factor
superconducting micro-resonators cooled at millikelvin temperatures, we improve
the state-of-the-art sensitivity of inductive ESR detection by nearly 4 orders
of magnitude. We demonstrate the detection of 1700 bismuth donor spins in
silicon within a single Hahn echo with unit signal-to-noise (SNR) ratio,
reduced to just 150 spins by averaging a single Carr-Purcell-Meiboom-Gill
sequence. This unprecedented sensitivity reaches the limit set by quantum
fluctuations of the electromagnetic field instead of thermal or technical
noise, which constitutes a novel regime for magnetic resonance.Comment: Main text : 10 pages, 4 figures. Supplementary text : 16 pages, 8
figure
Producing and Detecting Correlated atoms
We discuss experiments to produce and detect atom correlations in a
degenerate or nearly degenerate gas of neutral atoms. First we treat the atomic
analog of the celebrated Hanbury Brown Twiss experiment, in which atom
correlations result simply from interference effects without any atom
interactions.We have performed this experiment for both bosons and fermions.
Next we show how atom interactions produce correlated atoms using the atomic
analog of spontaneous four-wavemixing. Finally, we briefly mention experiments
on a one dimensional gas on an atom chip in which correlation effects due to
both interference and interactions have been observed.Comment: to appear in conference proceedings "Atomic Physics 20
Transport in metallic multi-island Coulomb blockade systems: A systematic perturbative expansion in the junction transparency
We study electronic transport through metallic multi-island Coulomb-blockade
systems. Based on a diagrammatic real-time approach, we develop a computer
algorithm that generates and calculates all transport contributions up to
second order in the tunnel-coupling strengths for arbitrary multi-island
systems. This comprises sequential and cotunneling, as well as terms
corresponding to a renormalization of charging energies and tunneling
conductances. Multi-island cotunneling processes with energy transfer between
different island are taken into account. To illustrate our approach we analyze
the current through an island in Coulomb blockade, that is electrostatically
coupled to a second island through which a large current is flowing. In this
regime both cotunneling processes involving one island only as well as
multi-island processes are important. The latter can be understood as
photon-assisted sequential tunneling in the blockaded island, where the photons
are provided by potential fluctuations due to sequential tunneling in the
second island. We compare results of our approach to a P(E)-theory for
photon-assisted tunneling in the weak coupling limit.Comment: 14 pages, 7 figures, published version; minor changes in Sec. IV
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