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| 2. |
- Thomas, HS, et al.
(author)
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- 2019
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swepub:Mat__t
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| 3. |
- Anwer, Hammad, et al.
(author)
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Experimental Characterization of Unsharp Qubit Observables and Sequential Measurement Incompatibility via Quantum Random Access Codes
- 2020
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 125:8
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Journal article (peer-reviewed)abstract
- Unsharp measurements are increasingly important for foundational insights in quantum theory and quantum information applications. Here, we report an experimental implementation of unsharp qubit measurements in a sequential communication protocol, based on a quantum random access code. The protocol involves three parties; the first party prepares a qubit system, the second party performs operations that return both a classical and quantum outcome, and the latter is measured by the third party. We demonstrate a nearly optimal sequential quantum random access code that outperforms both the best possible classical protocol and any quantum protocol that utilizes only projective measurements. Furthermore, while only assuming that the involved devices operate on qubits and that detected events constitute a fair sample, we demonstrate the noise-robust characterization of unsharp measurements based on the sequential quantum random access code. We apply this characterization towards quantifying the degree of incompatibility of two sequential pairs of quantum measurements.
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| 4. |
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| 5. |
- Anwer, Hammad, et al.
(author)
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Experimental test of maximal tripartite nonlocality using an entangled state and local measurements that are maximally incompatible
- 2019
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In: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - 2469-9926 .- 2469-9934. ; 100:2
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Journal article (peer-reviewed)abstract
- 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 vertical bar S >. Here we report the results of an experiment for preparing vertical bar 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 vertical bar 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.
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| 7. |
- Anwer, Hammad, 1983-
(author)
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Photonic Multipartite Communication : Complexity, measurements and Bell inequalities
- 2021
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Doctoral thesis (other academic/artistic)abstract
- The interdisciplinary field of quantum communication and quantum information processing merges quantum mechanics, optics, photonics, information processing, and electronics to solve information and communication tasks that are impossible to solve efficiently with classical resources. Here in this thesis experimental demonstrations of some of such tasks are presented. In particular, using a single qubit system and quantum Zeno effect we investigated a class of communication complexity problems (CCP) for multi-parties. As solutions, three different quantum strategies are evaluated by proof of concept experimental demonstrations. Our results go beyond the classical limits. Furthermore, the same single qubit system is used to show that preparation contextuality can be shared among multiple observers through a quantum state ensemble while implementing sequential unsharp measurement. We showed that this is possible for any amount of white noise and presented experimental demonstration for three parties. In addition, characterization of unsharp measurements based on quantum random access code and quantifying the degree of incompatibility of sequential measurements in a wide range of sharpness parameters are also presented.Finally, I present the experimental generation of multi-photon entanglement to meet the basic requirement of modern quantum information processing.Using this source we produced a state with high fidelity that can violate a tight Bell inequality maximally with maximally incompatible local measurements.
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| 8. |
- Tavakoli, Armin, et al.
(author)
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Quantum communication complexity using the quantum Zeno effect
- 2015
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 92:1
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Journal article (peer-reviewed)abstract
- The quantum Zeno effect (QZE) is the phenomenon in which the unitary evolution of a quantum state is suppressed, e.g., due to frequent measurements. Here, we investigate the use of the QZE in a class of communication complexity problems (CCPs). Quantum entanglement is known to solve certain CCPs beyond classical constraints. However, recent developments have yielded CCPs for which superclassical results can be obtained using only communication of a single d-level quantum state (qudit) as a resource. In the class of CCPs considered here, we show quantum reduction of complexity in three ways: using (i) entanglement and the QZE, (ii) a single qudit and the QZE, and (iii) a single qudit. We have performed a proof of concept experimental demonstrations of three party CCP protocol based on single-qubit communication with and without QZE.
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