105 research outputs found
L'ajustement microéconomique des prix des carburants en France
En utilisant des millions de relevés individuels de prix entre 2007 et 2009, cette étude décrit plusieurs faits stylisés sur l’ajustement des prix des carburants en France : ils changent en moyenne une fois par semaine ; ils sont plus souvent modifiés le mardi et le vendredi ; la concurrence accroît la fréquence des changements de prix ; la distribution des tailles de changements de prix présente peu de changements inférieurs à 2% ; taille des changements de prix et durée des prix sont corrélées ; l’inflation des prix des carburants est surtout déterminée par la part relative des stations-service augmentant ou baissant leur prix. Les modèles de coût d’ajustement incluant des rigidités informationnelles reproduisent le mieux ces faits stylisés
Designing High-Fidelity Gates for Dissipative Cat Qubits
Bosonic cat qubits stabilized with a driven two-photon dissipation are
systems with exponentially biased noise, opening the door to low-overhead,
fault-tolerant and universal quantum computing. However, current gate proposals
for such qubits induce substantial noise of the unprotected type, whose poor
scaling with the relevant experimental parameters limits their practical use.
In this work, we provide a new perspective on dissipative cat qubits by
reconsidering the reservoir mode used to engineer the tailored two-photon
dissipation, and show how it can be leveraged to mitigate gate-induced errors.
Doing so, we introduce four new designs of high-fidelity and bias-preserving
cat qubit gates, and compare them to the prevalent gate methods. These four
designs should give a broad overview of gate engineering for dissipative
systems with different and complementary ideas. In particular, we propose both
already achievable low-error gate designs and longer-term implementations.Comment: 22 pages, 12 figures. All comments on the preprint are welcom
Combined Dissipative and Hamiltonian Confinement of Cat Qubits
Quantum error correction with biased-noise qubits can drastically reduce the
hardware overhead for universal and fault-tolerant quantum computation. Cat
qubits are a promising realization of biased-noise qubits as they feature an
exponential error bias inherited from their non-local encoding in the phase
space of a quantum harmonic oscillator. To confine the state of an oscillator
to the cat qubit manifold, two main approaches have been considered so far: a
Kerr-based Hamiltonian confinement with high gate performances, and a
dissipative confinement with robust protection against a broad range of noise
mechanisms. We introduce a new combined dissipative and Hamiltonian confinement
scheme based on two-photon dissipation together with a Two-Photon Exchange
(TPE) Hamiltonian. The TPE Hamiltonian is similar to Kerr nonlinearity, but
unlike the Kerr it only induces a bounded distinction between even- and
odd-photon eigenstates, a highly beneficial feature for protecting the cat
qubits with dissipative mechanisms. Using this combined confinement scheme, we
demonstrate fast and bias-preserving gates with drastically improved
performance compared to dissipative or Hamiltonian schemes. In addition, this
combined scheme can be implemented experimentally with only minor modifications
of existing dissipative cat qubit experiments.Comment: 24 pages, 18 figure
Two-photon driven Kerr quantum oscillator with multiple spectral degeneracies
Kerr nonlinear oscillators driven by a two-photon process are promising
systems to encode quantum information and to ensure a hardware-efficient
scaling towards fault-tolerant quantum computation. In this paper, we show that
an extra control parameter, the detuning of the two-photon drive with respect
to the oscillator resonance, plays a crucial role in the properties of the
defined qubit. At specific values of this detuning, we benefit from strong
symmetries in the system, leading to multiple degeneracies in the spectrum of
the effective confinement Hamiltonian. Overall, these degeneracies lead to a
stronger suppression of bit-flip errors. We also study the combination of such
Hamiltonian confinement with colored dissipation to suppress leakage outside of
the bosonic code space. We show that the additional degeneracies allow us to
perform fast and high-fidelity gates while preserving a strong suppression of
bit-flip errors.Comment: 10 pages, 7 figure
Optimizing quantum phase estimation for the simulation of Hamiltonian eigenstates
We revisit quantum phase estimation algorithms for the purpose of obtaining the energy levels of many-body Hamiltonians and pay particular attention to the statistical analysis of their outputs. We introduce the mean phase direction of the parent distribution associated with eigenstate inputs as a new post-processing tool. By connecting it with the unknown phase, we find that if used as its direct estimator, it exceeds the accuracy of the standard majority rule using one less bit of resolution, making evident that it can also be inverted to provide unbiased estimation. Moreover, we show how to directly use this quantity to accurately find the energy levels when the initialized state is an eigenstate of the simulated propagator during the whole time evolution, which allows for shallower algorithms. We then use IBM Q hardware to carry out the digital quantum simulation of three toy models: a two-level system, a two-spin Ising model and a two-site Hubbard model at half-filling. Methodologies are provided to implement Trotterization and reduce the variability of results in noisy intermediate scale quantum computers.RG acknowledges the INL summer student program. GC acknowledges Fundação para a Ciência e a Tecnología (FCT) for Grant No. SFRH/BD/138806/2018. JFR and GC acknowledge the FCT for Grant PTDC/FIS-NAN/4662/2014 (016656)
Cистемна організація уваги та загальні принципи її корекції як засіб оптимізації учбової та професійної діяльності
У статті викладено результати літературних та експериментальних досліджень, у яких розкриваються основні напрямки, котрі стосуються феномени уваги:механізми її виникнення, типи уваги, функції контролю та управління. Розглянуто ряд методів, котрі можуть бути використані для тренінгів, з метою збільшення об’єму уваги, ступеня її концентрації, швидкості, ступеня зосередження, переключення і розподілу
Quantum control of a cat-qubit with bit-flip times exceeding ten seconds
Binary classical information is routinely encoded in the two metastable
states of a dynamical system. Since these states may exhibit macroscopic
lifetimes, the encoded information inherits a strong protection against
bit-flips. A recent qubit - the cat-qubit - is encoded in the manifold of
metastable states of a quantum dynamical system, thereby acquiring bit-flip
protection. An outstanding challenge is to gain quantum control over such a
system without breaking its protection. If this challenge is met, significant
shortcuts in hardware overhead are forecast for quantum computing. In this
experiment, we implement a cat-qubit with bit-flip times exceeding ten seconds.
This is a four order of magnitude improvement over previous cat-qubit
implementations, and six orders of magnitude enhancement over the single photon
lifetime that compose this dynamical qubit. This was achieved by introducing a
quantum tomography protocol that does not break bit-flip protection. We prepare
and image quantum superposition states, and measure phase-flip times above 490
nanoseconds. Most importantly, we control the phase of these superpositions
while maintaining the bit-flip time above ten seconds. This work demonstrates
quantum operations that preserve macroscopic bit-flip times, a necessary step
to scale these dynamical qubits into fully protected hardware-efficient
architectures
Target enrichment sequencing coupled with GWAS identifies MdPRX10 as a candidate gene in the control of budbreak in apple
The timing of floral budbreak in apple has a significant effect on fruit production and quality. Budbreak occurs as a result of a complex molecular mechanism that relies on accurate integration of external environmental cues, principally temperature. In the pursuit of understanding this mechanism, especially with respect to aiding adaptation to climate change, a QTL at the top of linkage group (LG) 9 has been identified by many studies on budbreak, but the genes underlying it remain elusive. Here, together with a dessert apple core collection of 239 cultivars, we used a targeted capture sequencing approach to increase SNP resolution in apple orthologues of known or suspected A. thaliana flowering time-related genes, as well as approximately 200 genes within the LG9 QTL interval. This increased the 275 223 SNP Axiom® Apple 480 K array dataset by an additional 40 857 markers. Robust GWAS analyses identified MdPRX10, a peroxidase superfamily gene, as a strong candidate that demonstrated a dormancy-related expression pattern and down-regulation in response to chilling. In-silico analyses also predicted the residue change resulting from the SNP allele associated with late budbreak could alter protein conformation and likely function. Late budbreak cultivars homozygous for this SNP allele also showed significantly up-regulated expression of C-REPEAT BINDING FACTOR (CBF) genes, which are involved in cold tolerance and perception, compared to reference cultivars, such as Gala. Taken together, these results indicate a role for MdPRX10 in budbreak, potentially via redox-mediated signaling and CBF gene regulation. Moving forward, this provides a focus for developing our understanding of the effects of temperature on flowering time and how redox processes may influence integration of external cues in dormancy pathways
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