14 research outputs found
Quantum machine learning with adaptive linear optics
We study supervised learning algorithms in which a quantum device is used to
perform a computational subroutine - either for prediction via probability
estimation, or to compute a kernel via estimation of quantum states overlap. We
design implementations of these quantum subroutines using Boson Sampling
architectures in linear optics, supplemented by adaptive measurements. We then
challenge these quantum algorithms by deriving classical simulation algorithms
for the tasks of output probability estimation and overlap estimation. We
obtain different classical simulability regimes for these two computational
tasks in terms of the number of adaptive measurements and input photons. In
both cases, our results set explicit limits to the range of parameters for
which a quantum advantage can be envisaged with adaptive linear optics compared
to classical machine learning algorithms: we show that the number of input
photons and the number of adaptive measurements cannot be simultaneously small
compared to the number of modes. Interestingly, our analysis leaves open the
possibility of a near-term quantum advantage with a single adaptive
measurement.Comment: 16 + 5 pages, presented at AQIS2020, accepted in Quantu
Corrected Bell and Noncontextuality Inequalities for Realistic Experiments
Contextuality is a feature of quantum correlations. It is crucial from a
foundational perspective as a nonclassical phenomenon, and from an applied
perspective as a resource for quantum advantage. It is commonly defined in
terms of hidden variables, for which it forces a contradiction with the
assumptions of parameter-independence and determinism. The former can be
justified by the empirical property of non-signalling or non-disturbance, and
the latter by the empirical property of measurement sharpness. However, in
realistic experiments neither empirical property holds exactly, which leads to
possible objections to contextuality as a form of nonclassicality, and
potential vulnerabilities for supposed quantum advantages. We introduce
measures to quantify both properties, and introduce quantified relaxations of
the corresponding assumptions. We prove the continuity of a known measure of
contextuality, the contextual fraction, which ensures its robustness to noise.
We then bound the extent to which these relaxations can account for
contextuality, via corrections terms to the contextual fraction (or to any
noncontextuality inequality), culminating in a notion of genuine contextuality,
which is robust to experimental imperfections. We then show that our result is
general enough to apply or relate to a variety of established results and
experimental setups.Comment: 20 pages + 14 pages of appendices, 3 figure
Certifying dimension of quantum systems by sequential projective measurements
This work analyzes correlations arising from quantum systems subject to sequential projective measurements to certify that the system in question has a quantum dimension greater than some . We refine previous known methods and show that dimension greater than two can be certified in scenarios which are considerably simpler than the ones presented before and, for the first time in this sequential projective scenario, we certify quantum systems with dimension strictly greater than three. We also perform a systematic numerical analysis in terms of robustness and conclude that performing random projective measurements on random pure qutrit states allows a robust certification of quantum dimensions with very high probability
High photon-loss threshold quantum computing using GHZ-state measurements
We propose fault-tolerant architectures based on performing projective
measurements in the Greenberger-Horne-Zeilinger (GHZ) basis on constant-sized,
entangled resource states. We present linear-optical constructions of the
architectures, where the GHZ-state measurements are encoded to suppress the
errors induced by photon loss and the probabilistic nature of linear optics.
Simulations of our constructions demonstrate high single-photon loss thresholds
compared to the state-of-the-art linear-optical architecture realized with
encoded two-qubit fusion measurements performed on constant-sized resource
states. We believe this result shows a resource-efficient path to achieving
photonic fault-tolerant quantum computing
Etude de tests du caractÚre quantique de systÚmes de dimension supérieur à deux dans des conditions réalistes
The subject of this thesis is a study of tests of the quantum features of systems of dimension greater than two under realistic conditions. Non-locality is one of the quantum properties used in protocols in the field of quantum communications. The study on the effects of the decoherence (models ofrealistic conditions) address the issue of the conservation of non-locality in practice. Contextuality is another fundamental quantum property with a potential power in quantum information processing. A contextuality test has been developed for all dimensions of quantum systems greater than two. An experiment that considers the experimental issues of contextuality tests is also proposed.Le sujet de cette thĂšse est une Ă©tude de tests du caractĂšre quantique des systĂšmes de dimension supĂ©rieure Ă deux dans des conditions rĂ©alistes. La non-localitĂ© est une des propriĂ©tĂ©s quantiques utile pour des protocoles du domaine des communications quantiques. LâĂ©tude rĂ©alisĂ©e sur les effets de la dĂ©cohĂ©rence (modĂšles de conditions rĂ©alistes) permet de rendre compte des moyens Ă mettre en oeuvre afin dâoptimiser la conservation de la non-localitĂ© en pratique. La contextualitĂ© est une autre propriĂ©tĂ© quantique fondamentale avec un potentiel dans le domaine de traitement dâinformation quantique. Un test de contextualitĂ© a Ă©tĂ© dĂ©veloppĂ© pour toutes les dimensions de systĂšmes quantiques supĂ©rieures Ă deux. Une expĂ©rience prenant en compte les enjeux expĂ©rimentaux des tests de contextualitĂ© est aussi proposĂ©e
Study of access of quantum features of high dimensional systems under realistic conditions
Le sujet de cette thĂšse est une Ă©tude de tests du caractĂšre quantique des systĂšmes de dimension supĂ©rieure Ă deux dans des conditions rĂ©alistes. La non-localitĂ© est une des propriĂ©tĂ©s quantiques utile pour des protocoles du domaine des communications quantiques. LâĂ©tude rĂ©alisĂ©e sur les effets de la dĂ©cohĂ©rence (modĂšles de conditions rĂ©alistes) permet de rendre compte des moyens Ă mettre en oeuvre afin dâoptimiser la conservation de la non-localitĂ© en pratique. La contextualitĂ© est une autre propriĂ©tĂ© quantique fondamentale avec un potentiel dans le domaine de traitement dâinformation quantique. Un test de contextualitĂ© a Ă©tĂ© dĂ©veloppĂ© pour toutes les dimensions de systĂšmes quantiques supĂ©rieures Ă deux. Une expĂ©rience prenant en compte les enjeux expĂ©rimentaux des tests de contextualitĂ© est aussi proposĂ©e.The subject of this thesis is a study of tests of the quantum features of systems of dimension greater than two under realistic conditions. Non-locality is one of the quantum properties used in protocols in the field of quantum communications. The study on the effects of the decoherence (models ofrealistic conditions) address the issue of the conservation of non-locality in practice. Contextuality is another fundamental quantum property with a potential power in quantum information processing. A contextuality test has been developed for all dimensions of quantum systems greater than two. An experiment that considers the experimental issues of contextuality tests is also proposed
Decoherence Effects on the Non-locality of Symmetric States
International audience<p>In this paper we analyze criteria for robustness of non-locality of symmetric states. We develop ourresearch using the recently developed extended Hardyâs paradox non-locality test. We investigatethe case of symmetric states, we show that for high numbers of qubits the non-locality of W statecan tolerate high degree of noise. We also demonstrate that the choice of the bases is, in particularcases, an important criterion for robustness independently from the bases which give high violation.We also apply our techniques to a discrimination of entanglement class.</p