77 research outputs found
Quantum state tomography with non-instantaneous measurements, imperfections and decoherence
Tomography of a quantum state is usually based on positive operator-valued
measure (POVM) and on their experimental statistics. Among the available
reconstructions, the maximum-likelihood (MaxLike) technique is an efficient
one. We propose an extension of this technique when the measurement process
cannot be simply described by an instantaneous POVM. Instead, the tomography
relies on a set of quantum trajectories and their measurement records. This
model includes the fact that, in practice, each measurement could be corrupted
by imperfections and decoherence, and could also be associated with the record
of continuous-time signals over a finite amount of time. The goal is then to
retrieve the quantum state that was present at the start of this measurement
process. The proposed extension relies on an explicit expression of the
likelihood function via the effective matrices appearing in quantum smoothing
and solutions of the adjoint quantum filter. It allows to retrieve the initial
quantum state as in standard MaxLike tomography, but where the traditional POVM
operators are replaced by more general ones that depend on the measurement
record of each trajectory. It also provides, aside the MaxLike estimate of the
quantum state, confidence intervals for any observable. Such confidence
intervals are derived, as the MaxLike estimate, from an asymptotic expansion of
multi-dimensional Laplace integrals appearing in Bayesian Mean estimation. A
validation is performed on two sets of experimental data: photon(s) trapped in
a microwave cavity subject to quantum non-demolition measurements relying on
Rydberg atoms; heterodyne fluorescence measurements of a superconducting qubit.Comment: 11 pages, 4 figures, submitte
Exponential convergence of a dissipative quantum system towards finite-energy grid states of an oscillator
Based on the stabilizer formalism underlying Quantum Error Correction (QEC),
the design of an original Lindblad master equation for the density operator of
a quantum harmonic oscillator is proposed. This Lindblad dynamics stabilizes
exactly the finite-energy grid states introduced in 2001 by Gottesman, Kitaev
and Preskill for quantum computation. Stabilization results from an exponential
Lyapunov function with an explicit lower-bound on the convergence rate.
Numerical simulations indicate the potential interest of such autonomous QEC in
presence of non-negligible photon-losses.Comment: Submitted, 15 pages, 1 figure
Advanced Planning and Scheduling system: An overview of gaps and potential sample solutions
13 pagesInternational audienceThis paper intends to take up an overview of gaps existing in Advanced Planning Scheduling system (APS). Even if APS system provide a number of solution approaches for several practical problems (inventory and global costs reduction, customer service level increase, pertinent decision making), improvement ways still emerge. Firstly, we have led a functional analysis, to identify some gaps about supply chain management activities (financial aspect and Engineering To Order concept). Then, we made a literature review to identify works have been done in these areas. This review allowed us to outline a second kind of weakness liked to the functional range of some modules too (demand forecasting, proposition of lots sizing, reactivity). So, gaps and potential solutions proposed in the scientist literature, are presented in this paper. We conclude by underlining another type of problem, concerning the management needed to install correctly an APS system
Advanced Planning and Scheduling system: An overview of gaps and potential sample solutions
This paper intends to take up an overview of gaps existing in Advanced Planning Scheduling system (APS). Even if APS system provide a number of solution approaches for several practical problems (inventory and global costs reduction, customer service level increase, pertinent decision making), improvement ways still emerge. Firstly, we have led a functional analysis, to identify some gaps about supply chain management activities (financial aspect and Engineering To Order concept). Then, we made a literature review to identify works have been done in these areas. This review allowed us to outline a second kind of weakness liked to the functional range of some modules too (demand forecasting, proposition of lots sizing, reactivity). So, gaps and potential solutions proposed in the scientist literature, are presented in this paper. We conclude by underlining another type of problem, concerning the management needed to install correctly an APS system.Advanced Planning and Scheduling system, Supply Chain Management, APS gaps, functional analysis
Detection of Skin Disbond in Honeycombs and Coating Detachment by Laser Tapping Technique
Peer reviewed: YesNRC publication: Ye
Applications of Laser-Ultrasonics and Laser Tapping to Aerospace Composite Structures
Peer reviewed: YesNRC publication: Ye
Laser-ultrasonic and laser-tapping techniques for probing aerospace composite structures
Peer reviewed: YesNRC publication: Ye
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
Structural determinants of specific DNA-recognition by the THAP zinc finger
Human THAP1 is the prototype of a large family of cellular factors sharing an original THAP zinc-finger motif responsible for DNA binding. Human THAP1 regulates endothelial cell proliferation and G1/S cell-cycle progression, through modulation of pRb/E2F cell-cycle target genes including rrm1. Recently, mutations in THAP1 have been found to cause DYT6 primary torsion dystonia, a human neurological disease. We report here the first 3D structure of the complex formed by the DNA-binding domain of THAP1 and its specific DNA target (THABS) found within the rrm1 target gene. The THAP zinc finger uses its double-stranded β-sheet to fill the DNA major groove and provides a unique combination of contacts from the β-sheet, the N-terminal tail and surrounding loops toward the five invariant base pairs of the THABS sequence. Our studies reveal unprecedented insights into the specific DNA recognition mechanisms within this large family of proteins controlling cell proliferation, cell cycle and pluripotency
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