Research Outputs

Now showing 1 - 5 of 5
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    Post-Measurement adjustment of the coincidence window in quantum optics experiments
    (IEEE Access, 2021) ;
    Gomez, Santiago A.
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    Obregon, Giannini F.
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    Gomez, Esteban S.
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    Figueroa, Miguel
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    Lima, Gustavo
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    Xavier, Guilherme
    We report on an electronic coincidence detection circuit for quantum photonic applications implemented on a field-programmable gate array (FPGA), which records each the time separation between detection events coming from single-photon detectors. We achieve a coincidence window as narrow as 500 ps with a series of optimizations on a readily-available and affordable FPGA development board. Our implementation allows real-time visualization of coincidence measurements for multiple coincidence window widths simultaneously. To demonstrate the advantage of our high-resolution visualization, we certified the generation of polarized entangled photons by collecting data from multiple coincidence windows with minimal accidental counts, obtaining a violation of the Clauser-Horne-Shimony-Holt (CHSH) Bell inequality by more than 338 standard deviations. Our results have shown the applicability of our electronic design in the field of quantum information.
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    Polarization-independent single-photon switch based on a fiber-optical Sagnac interferometer for quantum communication networks
    (Optica Publishing Group, 2020) ;
    Alarcón, A.
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    González, P.
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    Lima, G.
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    Xavier, G.
    An essential component of future quantum networks is an optical switch capable of dynamically routing single photons. Here we implement such a switch, based on a fiber-optical Sagnac interferometer design. The routing is implemented with a pair of fast electro-optical telecom phase modulators placed inside the Sagnac loop, such that each modulator acts on an orthogonal polarization component of the single photons, in order to yield polarization-independent capability that is crucial for several applications. We obtain an average extinction ratio of more than 19 dB between both outputs of the switch. Our experiment is built exclusively with commercial off-the-shelf components, thus allowing direct compatibility with current optical communication systems.
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    Maximizing quantum discord from interference in multi-port fiber beamsplitters
    (Springer Nature Limited, 2021) ;
    Asan-Srain, M.
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    Lima, G.
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    Walborn, S.
    Fourth-order interference is an information processing primitive for photonic quantum technologies, as it forms the basis of photonic controlled-logic gates, entangling measurements, and can be used to produce quantum correlations. Here, using classical weak coherent states as inputs, we study fourth-order interference in 4 × 4 multi-port beam splitters built within multi-core optical fibers, and show that quantum correlations, in the form of geometric quantum discord, can be controlled and maximized by adjusting the intensity ratio between the two inputs. Though these states are separable, they maximize the geometric discord in some instances, and can be a resource for protocols such as remote state preparation. This should contribute to the exploitation of quantum correlations in future telecommunication networks, in particular in those that exploit spatially structured fibers.
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    Publication
    Computational advantage from the quantum superposition of multiple temporal orders of photonic gates
    (American Physical Society, 2021)
    Taddei, Márcio M.
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    Martínez, Daniel
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    García, Tania
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    Guerrero, Nayda
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    Abbott, Alastair A.
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    Araújo, Mateus
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    Branciard, Cyril
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    Gómez, Esteban S.
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    Walborn, Stephen P.
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    Aolita, Leandro
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    Lima, Gustavo
    Models for quantum computation with circuit connections subject to the quantum superposition principle have recently been proposed. In them, a control quantum system can coherently determine the order in which a target quantum system undergoes N gate operations. This process, known as the quantum N-switch, is a resource for several information-processing tasks. In particular, it provides a computational advantage—over fixed-gate-order quantum circuits—for phase-estimation problems involving N unknown unitary gates. However, the corresponding algorithm requires an experimentally unfeasible target-system dimension (super)exponential in N. Here, we introduce a promise problem for which the quantum N-switch gives an equivalent computational speedup with target-system dimension as small as 2 regardless of N. We use state-of-the-art multicore optical-fiber technology to experimentally demonstrate the quantum N-switch with N = 4 gates acting on a photonic-polarization qubit. This is the first observation of a quantum superposition of more than N = 2 temporal orders, demonstrating its usefulness for efficient phase estimation.
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    Publication
    All-in-Fiber dynamically reconfigurable orbital angular momentum mode sorting
    (American Chemical Society Photonics, 2023)
    Alarcón, Alvaro
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    Gómez, Santiago
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    Spegel-Lexne, Daniel
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    Argillander, Joakim
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    Cañas, Gustavo
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    Lima, Gustavo
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    B. Xavier, Guilherme
    The orbital angular momentum (OAM) spatial degree of freedom of light has been widely explored in many applications, including telecommunications, quantum information, and light-based micromanipulation. The ability to separate and distinguish between the different transverse spatial modes is called mode sorting or mode demultiplexing, and it is essential to recover the encoded information in such applications. An ideal d mode sorter should be able to faithfully distinguish between the different d spatial modes, with minimal losses, and have d outputs and fast response times. All previous mode sorters rely on bulk optical elements, such as spatial light modulators, which cannot be quickly tuned and have additional losses if they are to be integrated with optical fiber systems. Here, we propose and experimentally demonstrate, to the best of our knowledge, the first all-in-fiber method for OAM mode sorting with ultrafast dynamic reconfigurability. Our scheme first decomposes the OAM mode in-fiber-optical linearly polarized (LP) modes and then interferometrically recombines them to determine the topological charge, thus correctly sorting the OAM mode. In addition, our setup can also be used to perform ultrafast routing of the OAM modes. These results show a novel and fiber-integrated form of optical spatial mode sorting that can be readily used for many new applications in classical and quantum information processing.