Papers by Mohamed Nawareg
Minimal informationally complete positive operator-valued measures (MIC-POVMs) are a special kind... more Minimal informationally complete positive operator-valued measures (MIC-POVMs) are a special kind of measurements in quantum theory that have the property that the statistics of their d2-outcomes are enough to reconstruct any d-dimensional quantum state. For this reason, MIC-POVMs are referred to as "standard" measurements for quantum information, and are of the utmost interest in quantum information theory and applications, where they have been shown to be the ultimate tools for quantum state tomography [1], quantum key distribution [2] and randomness certification [3], among other fields. We report on an experiment with entangled photon pairs that certifies for the first time a MIC-POVM for qubits following a device-independent protocol. That is, modeling the state preparation and the measurement devices as black boxes and using only the statistics of the inputs and outputs.
Physical Review A
The multiqubit bound entangled states that are uniformly mixed over the subspaces complementary t... more The multiqubit bound entangled states that are uniformly mixed over the subspaces complementary to unextendible product bases (UPBs) are interesting members from the peculiar family of bound entangled states. Their entanglement is delocalized and they look separable with respect to any partition into a single party and all remaining parties. Only one example of quantifying the entanglement of this type of states in the case of three-qubit states has been studied [C. Branciard, H. Zhu, L. Chen, and V. Scarani, Evaluation of two different entanglement measures on a bound entangled state, Phys. Rev. A 82, 012327 (2010)]. We provide a systematic procedure for generating decompositions of such states in terms of minimally entangled states. This procedure enables us to measure entanglement in terms of the concurrence for a wide range of families of these bound entangled (BE) states with each family containing an infinite number of states. In particular, we study one family of three-qubit states in addition to six inequivalent families of four-qubit bound entangled states. These studied families are examples that represent all the known 1446 families of four-qubit UPB-based bound entangled states, which means that our method is applicable to all the 1446 families. In addition, a discussion on the matter of applicability of the proposed strategy to additional families is provided. Specifically, the proposed method looks promising for measuring entanglement of other families of UPB-based BE states in addition to some families of symmetric multipartite positive under partial transposition BE states.
Symmetric, informationally complete, positive operator-valued measurements (SIC-POVM) are fundame... more Symmetric, informationally complete, positive operator-valued measurements (SIC-POVM) are fundamental in quantum information and foundations of quantum theory[1]. For example, SIC-POVMs are crucial for optimal quantum state tomography, quantum key distribution with optimal trade-off between security and key rate, device-independent certification of optimal randomness from one bit of entanglement, and information-based interpretations and operational reconstructions of quantum theory. Experimentally, photonic experiments of qubit and qutrit tomography, and quantum key distribution[2] have aimed for SIC-POVMs. However, these experiments rely on specific models for parts of the experimental setups and do not allow us to test whether the target measurements are truly SIC-POVMs in a "device independent" (DI) way that is, without relying on any modelling of the devices.
Journal of the Optical Society of America B
Studying beam propagation through different types of media is an active topic in scientific resea... more Studying beam propagation through different types of media is an active topic in scientific research due to its great importance for a variety of technological and industrial applications. In this current paper, we derive a general theoretical model for describing beam propagation though uniaxial crystals at an arbitrary angle with the crystal’s optical axis. In addition, we show that our model goes to the previously solved cases at the particular angles of propagation 0° and 90° with the optical axis. We then apply the derived model to the propagation of a quasi-Gaussian beam through rutile crystal at different angles with the crystal axis. In particular, we compare its propagation at different crystal’s thicknesses and at angles (0°, 45°, 70°) with the optical axis. The results show big changes in both the polarization and spatial structure of the light beam by propagating through the uniaxial crystal at different angles.
Indian Journal of Physics
In this paper, Newton’s rings interferometer was used for radius of curvature and sub-micrometric... more In this paper, Newton’s rings interferometer was used for radius of curvature and sub-micrometric film thickness determination by varying the wavelength of the illuminating source. This was performed by using a partially reflecting spherical surface placed on a partially reflecting plane surface. The illuminating source was a halogen lamp followed by a monochromator in order to select a desired wavelength. By plotting a relation between values of wavelengths and rings’ radii for different interference orders, the radius of curvature for the used spherical surface was retrieved. In addition, the system was used to determine the thickness of a sub-micrometric thin film. This was done by depositing the film on half of the glass plane surface. The step made by the presence of the film was employed in measuring the film’s thickness. By measuring the rings’ radii in both thin film and film-free regions for different interference orders and wavelengths, we succeeded in determining the film thickness by an accurate, simple and straightforward method with a nano-metric accuracy.
Optica
Minimal informationally complete positive operator-valued measures (MIC-POVMs) are special kinds ... more Minimal informationally complete positive operator-valued measures (MIC-POVMs) are special kinds of measurement in quantum theory in which the statistics of their d 2 -outcomes are enough to reconstruct any d-dimensional quantum state. For this reason, MIC-POVMs are referred to as standard measurements for quantum information. Here, we report an experiment with entangled photon pairs that certifies, for what we believe is the first time, a MIC-POVM for qubits following a device-independent protocol (i.e., modeling the state preparation and the measurement devices as black boxes, and using only the statistics of the inputs and outputs). Our certification is achieved under the assumption of freedom of choice, no communication, and fair sampling.
Science Advances
Demonstration of the superadditivity of two quantum information resources with three-partite nond... more Demonstration of the superadditivity of two quantum information resources with three-partite nondistillable entangled states.
Physical Review Letters, 2014
Contextuality 1, 2 is a fundamental concept for understanding quantum probabilities and the origi... more Contextuality 1, 2 is a fundamental concept for understanding quantum probabilities and the origin of the power of quantum systems for computation and information processing. A natural question is: Which is the simplest and cleanest version of quantum contextuality? It has been very recently found 3 that there is a version that is analog to "the simplest and cleanest" 4 version of quantum non-locality 5, 6 , but only requires single three-level quantum systems (qutrits) rather than composite systems. Here we report the first experimental observation of this "Hardy-like" quantum contextuality. We measured the correlations between the outcomes of five combinations of two compatible measurements performed sequentially, in any possible order, on heralded photonic path-encoded qutrits. The experiment adopts a novel configuration which allows for performing two sequential measurements on the same photon with a high fidelity and allows for observing the independence of the correlations with respect to the order in which measurements are performed. The experimental results match the conditions needed to define a Hardy-like argument and the predictions of quantum theory. In addition, they violate the relevant non-contextuality inequality, even when the non-contextual bound is corrected to take into account experimental imperfections. The experimental observation of this form of quantum contextuality is of fundamental importance, since it connects 3 the Kochen-Specker theorem 2 with the simplest non-contextuality inequality 7. In addition, the method introduced here opens the door to applications requiring sequential quantum measurements on photonic systems.
Physical Review A
The only known qubit states that produce maximal quantum violation of a tight Bell inequality wit... more The only known qubit states that produce maximal quantum violation of a tight Bell inequality with maximally incompatible local measurements are Bell states, Greenberger-Horne-Zeilinger states, and a recently identified three-qubit state called |S. Here we report the results of an experiment for preparing |S and testing the maximum quantum violation of the corresponding tripartite Bell inequality. Using a heralded source of three entangled photons and three tunable polarization-dependent filters, we experimentally prepare |S with 0.924 fidelity. Using maximally incompatible measurements for the three parties, we observe a value of T 26 = 7.30 ± 0.06, which clearly violates the tight Bell inequality T 26 5. In addition, we show that our setup allows preparing multipartite states that were inaccessible with previous methods and are useful for quantum information and metrology.
Why do correlations between the results of measurements performed on physical systems violate Bel... more Why do correlations between the results of measurements performed on physical systems violate Bell and non-contextuality inequalities up to some specific limits? The answer may follow from the observation that in quantum theory, unlike in other theories, whenever there is an experiment to measure $A$ simultaneously with $B$, another to measure $B$ with $C$, and another to measure $A$ with $C$, there is always an experiment to measure all of them simultaneously. This property implies that quantum theory satisfies a seemingly irrelevant restriction called the exclusivity (E) principle which, surprisingly, explains the set of quantum correlations in some fundamental scenarios. An open problem is whether the E principle explains the maximum quantum violation of the Bell-CHSH inequality. Here we show experimentally that the E principle imposes an upper bound to the violation of the Bell-CHSH inequality that matches the maximum predicted by quantum theory. For that, we use the result of an independent experiment testing a specific non-contextuality inequality. We perform both experiments: the Bell-CHSH inequality experiment on polarization entangled states of pairs of photons in Stockholm and, to demonstrate independence, the non-contextuality inequality experiment on single photons' orbital angular momentum states in Rome. The observed results provide the first experimental evidence that the E principle determines the limits of quantum correlations and prove that hypothetical super-quantum violations for either experiment would violate the E principle. This supports the conclusion that the E principle captures a fundamental limitation of nature. If this is true, much of quantum theory trivially follow from merely taking the E principle to be a fundamental truth, and various information-theoretic postulates are also simplified and/or strengthened.
Exclusivity graph of the two-city experiment. The 64 dots represent the 64 global events (ui, vj)... more Exclusivity graph of the two-city experiment. The 64 dots represent the 64 global events (ui, vj). Two dots are connected by an edge if the corresponding events are mutually exclusive. Each (ui, vj) is indicated by providing the explicit expression of ui (for instance, u0 = 1, 1|0, 0; see table ) followed by the one of vj (see table ). The 8-vertex subgraph with red edges corresponds to the correlations in W9 (see table VI). Figure courtesy of Elie Wolfe.
FIG. 4: Exclusivity graph of the two-city experiment. The 64 dots represent the 64 global events ... more FIG. 4: Exclusivity graph of the two-city experiment. The 64 dots represent the 64 global events (ui, vj). Two dots are connected by an edge if the corresponding events are mutually exclusive. Each (ui, vj) is indicated by providing the explicit expression of ui (for instance, u0 = 1, 1|0, 0; see table I) followed by the one of vj (see table II). The 8-vertex subgraph with red edges corresponds to the correlations in W9 (see table VI). Figure courtesy of Elie Wolfe.
Physical Review A, 2012
Most of known multipartite Bell inequalities involve correlation functions for all subsystems. Th... more Most of known multipartite Bell inequalities involve correlation functions for all subsystems. They are useless for entangled states without such correlations. We give a method of derivation of families of Bell inequalities for N parties, which involve, eg, only (N− 1)-partite correlations, but still are able to detect proper N-partite entanglement. We present an inequality which reveals five-partite entanglement despite using only four-partite correlations. Classes of inequalities introduced here can be put into a handy form of a single nonlinear inequality. An example is given of an N-qubit state, which strongly violates such an inequality, despite having no N-qubit correlations. This surprising property might be of potential value for quantum information tasks.
Physical review letters, 2014
Contextuality is a fundamental property of quantum theory and a critical resource for quantum com... more Contextuality is a fundamental property of quantum theory and a critical resource for quantum computation. Here, we experimentally observe the arguably cleanest form of contextuality in quantum theory [A. Cabello et al., Phys. Rev. Lett. 111, 180404 (2013)] by implementing a novel method for performing two sequential measurements on heralded photons. This method opens the door to a variety of fundamental experiments and applications.
Scientific reports, 2015
Entanglement is one of the most puzzling features of quantum theory and of great importance for t... more Entanglement is one of the most puzzling features of quantum theory and of great importance for the new field of quantum information. The determination whether a given state is entangled or not is one of the most challenging open problems of the field. Here we report on the experimental demonstration of measurement-device-independent (MDI) entanglement detection using witness method for general two qubits photon polarization systems. In the MDI settings, there is no requirement to assume perfect implementations or neither to trust the measurement devices. This experimental demonstration can be generalized for the investigation of properties of quantum systems and for the realization of cryptography and communication protocols.
Science advances, 2017
Entanglement is one of the most puzzling features of quantum theory and a principal resource for ... more Entanglement is one of the most puzzling features of quantum theory and a principal resource for quantum information processing. It is well known that in classical information theory, the addition of two classical information resources will not lead to any extra advantages. On the contrary, in quantum information, a spectacular phenomenon of the superadditivity of two quantum information resources emerges. It shows that quantum entanglement, which was completely absent in any of the two resources separately, emerges as a result of combining them together. We present the first experimental demonstration of this quantum phenomenon with two photonic three-partite nondistillable entangled states shared between three parties Alice, Bob, and Charlie, where the entanglement was completely absent between Bob and Charlie.
Journal of the Optical Society of America B, 2019
Studying beam propagation through different types of media is an active topic in scientific resea... more Studying beam propagation through different types of media is an active topic in scientific research due to its great importance for a variety of technological and industrial applications. In this current paper, we derive a general theoretical model for describing beam propagation though uniaxial crystals at an arbitrary angle with the crystal’s optical axis. In addition, we show that our model goes to the previously solved cases at the particular angles of propagation 0° and 90° with the optical axis. We then apply the derived model to the propagation of a quasi-Gaussian beam through rutile crystal at different angles with the crystal axis. In particular, we compare its propagation at different crystal’s thicknesses and at angles (0°, 45°, 70°) with the optical axis. The results show big changes in both the polarization and spatial structure of the light beam by propagating through the uniaxial crystal at different angles.
European Quantum Electronics Conference, 2019
Symmetric, informationally complete, positive operator-valued measurements (SIC-POVM) are fundame... more Symmetric, informationally complete, positive operator-valued measurements (SIC-POVM) are fundamental in quantum information and foundations of quantum theory [1]. For example, SIC-POVMs are crucial for optimal quantum state tomography, quantum key distribution with optimal trade-off between security and key rate, device-independent certification of optimal randomness from one bit of entanglement, and information-based interpretations and operational reconstructions of quantum theory. Experimentally, photonic experiments of qubit and qutrit tomography, and quantum key distribution [2] have aimed for SIC-POVMs. However, these experiments rely on specific models for parts of the experimental setups and do not allow us to test whether the target measurements are truly SIC-POVMs in a “device independent”(DI) way that is, without relying on any modelling of the devices.
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Papers by Mohamed Nawareg