1,148 research outputs found
Noise-robust quantum sensing via optimal multi-probe spectroscopy
The dynamics of quantum systems are unavoidably influenced by their
environment and in turn observing a quantum system (probe) can allow one to
measure its environment: Measurements and controlled manipulation of the probe
such as dynamical decoupling sequences as an extension of the Ramsey
interference measurement allow to spectrally resolve a noise field coupled to
the probe. Here, we introduce fast and robust estimation strategies for the
characterization of the spectral properties of classical and quantum dephasing
environments. These strategies are based on filter function orthogonalization,
optimal control filters maximizing the relevant Fisher Information and
multi-qubit entanglement. We investigate and quantify the robustness of the
schemes under different types of noise such as finite-precision measurements,
dephasing of the probe, spectral leakage and slow temporal fluctuations of the
spectrum.Comment: 13 pages, 14 figure
Fisher information from stochastic quantum measurements
The unavoidable interaction between a quantum system and the external noisy
environment can be mimicked by a sequence of stochastic measurements whose
outcomes are neglected. Here we investigate how this stochasticity is reflected
in the survival probability to find the system in a given Hilbert subspace at
the end of the dynamical evolution. In particular, we analytically study the
distinguishability of two different stochastic measurement sequences in terms
of a new Fisher information measure depending on the variation of a function,
instead of a finite set of parameters. We find a novel characterization of Zeno
phenomena as the physical result of the random observation of the quantum
system, linked to the sensitivity of the survival probability with respect to
an arbitrary small perturbation of the measurement stochasticity. Finally, the
implications on the Cram\'er-Rao bound are discussed, together with a numerical
example. These results are expected to provide promising applications in
quantum metrology towards future, more robust, noise-based quantum sensing
devices.Comment: 5 pages, 3 figure
Irreversibility mitigation in unital non-Markovian quantum evolutions
The relation between thermodynamic entropy production and non-Markovian evolutions is a matter of current research. Here, we study the behavior of the stochastic entropy production in open quantum systems undergoing unital non-Markovian dynamics. In particular, for the family of Pauli channels we show that in some specific time intervals both the average entropy production and the variance can decrease, provided that the quantum dynamics fails to be positive divisible, i.e. it is essentially non-Markovian. Although the dynamics of the system is overall irreversible, our result may be interpreted as a transient tendency towards reversibility, described as a delta-peaked distribution of entropy production around zero. Finally, we also provide analytical bounds on the parameters in the generator giving rise to the quantum system dynamics, so as to ensure irreversibility mitigation of the corresponding non-Markovian evolution
Machine learning approach for quantum non-Markovian noise classification
In this paper, machine learning and artificial neural network models are
proposed for quantum noise classification in stochastic quantum dynamics. For
this purpose, we train and then validate support vector machine, multi-layer
perceptron and recurrent neural network, models with different complexity and
accuracy, to solve supervised binary classification problems. By exploiting the
quantum random walk formalism, we demonstrate the high efficacy of such tools
in classifying noisy quantum dynamics using data sets collected in a single
realisation of the quantum system evolution. In addition, we also show that for
a successful classification one just needs to measure, in a sequence of
discrete time instants, the probabilities that the analysed quantum system is
in one of the allowed positions or energy configurations, without any external
driving. Thus, neither measurements of quantum coherences nor sequences of
control pulses are required. Since in principle the training of the machine
learning models can be performed a-priori on synthetic data, our approach is
expected to find direct application in a vast number of experimental schemes
and also for the noise benchmarking of the already available noisy
intermediate-scale quantum devices.Comment: 14 pages, 3 figures, 3 table
Noise fingerprints in quantum computers: Machine learning software tools
In this paper we present the high-level functionalities of a
quantum-classical machine learning software, whose purpose is to learn the main
features (the fingerprint) of quantum noise sources affecting a quantum device,
as a quantum computer. Specifically, the software architecture is designed to
classify successfully (more than 99% of accuracy) the noise fingerprints in
different quantum devices with similar technical specifications, or distinct
time-dependences of a noise fingerprint in single quantum machines.Comment: 9 pages, 2 figure
The role of data embedding in equivariant quantum convolutional neural networks
Geometric deep learning refers to the scenario in which the symmetries of a
dataset are used to constrain the parameter space of a neural network and thus,
improve their trainability and generalization. Recently this idea has been
incorporated into the field of quantum machine learning, which has given rise
to equivariant quantum neural networks (EQNNs). In this work, we investigate
the role of classical-to-quantum embedding on the performance of equivariant
quantum convolutional neural networks (EQCNNs) for the classification of
images. We discuss the connection between the data embedding method and the
resulting representation of a symmetry group and analyze how changing
representation affects the expressibility of an EQCNN. We numerically compare
the classification accuracy of EQCNNs with three different basis-permuted
amplitude embeddings to the one obtained from a non-equivariant quantum
convolutional neural network (QCNN). Our results show a clear dependence of
classification accuracy on the underlying embedding, especially for initial
training iterations. The improvement in classification accuracy of EQCNN over
non-equivariant QCNN may be present or absent depending on the particular
embedding and dataset used. It is expected that the results of this work can be
useful to the community for a better understanding of the importance of data
embedding choice in the context of geometric quantum machine learning.Comment: 12 pages, 9 figures. Significant changes compared to previous
version. New results adde
Effect of airborne particle abrasion on microtensile bond strength of total-etch adhesives to human dentin
Aim of this study was to investigate a specific airborne particle abrasion pretreatment on dentin and its effects on microtensile bond strengths of four commercial total-etch adhesives. Midcoronal occlusal dentin of extracted human molars was used. Teeth were randomly assigned to 4 groups according to the adhesive system used: OptiBond FL (FL), OptiBond Solo Plus (SO), Prime & Bond (PB), and Riva Bond LC (RB). Specimens from each group were further divided into two subgroups: control specimens were treated with adhesive procedures; abraded specimens were pretreated with airborne particle abrasion using 50 mu m Al2O3 before adhesion. After bonding procedures, composite crowns were incrementally built up. Specimens were sectioned perpendicular to adhesive interface to producemultiple beams, which were tested under tension until failure. Data were statistically analysed. Failure mode analysis was performed. Overall comparison showed significant increase in bond strength (p < 0.001) between abraded and no-abraded specimens, independently of brand. Intrabrand comparison showed statistical increase when abraded specimens were tested compared to no-abraded ones, with the exception of PB that did not show such difference. Distribution of failure mode was relatively uniform among all subgroups. Surface treatment by airborne particle abrasion with Al2O3 particles can increase the bond strength of total-etch adhesive
Ergodicity in randomly perturbed quantum systems
The theoretical cornerstone of statistical mechanics is the ergodic
assumption that all accessible configurations of a physical system are equally
likely. Here we show how such property arises when an open quantum system is
continuously perturbed by an external environment effectively observing the
system at random times while the system dynamics approaches the quantum Zeno
regime. In this context, by large deviation theory we analytically show how the
most probable value of the probability for the system to be in a given state
eventually deviates from the non-stochastic case when the Zeno condition is not
satisfied. We experimentally test our results with ultra-cold atoms prepared on
an atom chip.Comment: 6 pages, 5 figure
Stochastic quantum Zeno-based detection of noise correlations
A system under constant observation is practically freezed to the measurement
subspace. If the system driving is a random classical field, the survival
probability of the system in the subspace becomes a random variable described
by the Stochastic Quantum Zeno Dynamics (SQZD) formalism. Here, we study the
time and ensemble average of this random survival probability and demonstrate
how time correlations in the noisy environment determine whether the two
averages do coincide or not. These environment time correlations can
potentially generate non-Markovian dynamics of the quantum system depending on
the structure and energy scale of the system Hamiltonian. We thus propose a way
to probe this interesting property of the environment by means of the system
survival probability. This will further contribute to the development of new
schemes for quantum sensing technologies, where nanodevices may be exploited to
image external structures or biological molecules via the surface field they
generate.Comment: 9 pages, 8 figure
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