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arXiv:2303.09593 · Optics Express

Dynamic generation of photonic spatial quantum states with an all-fiber platform

Alvaro Alarcón, Joakim Argillander, Daniel Spegel-Lexne, GUILHERME BARRETO XAVIER

Published Feb 16, 2023• 11 citations
arXivHTMLPDF

Abstract

Photonic spatial quantum states are a subject of great interest for applications in quantum communication. One important challenge has been how to dynamically generate these states using only fiber-optical components. Here we propose and experimentally demonstrate an all-fiber system that can dynamically switch between any general transverse spatial qubit state based on linearly polarized modes. Our platform is based on a fast optical switch based on a Sagnac interferometer combined with a photonic lantern and few-mode optical fibers. We show switching times between spatial modes on the order of 5 ns and demonstrate the applicability of our scheme for quantum technologies by demonstrating a measurement-device-independent (MDI) quantum random number generator based on our platform. We run the generator continuously over 15 hours, acquiring over 13.46 Gbits of random numbers, of which we ensure that at least 60.52% are private, following the MDI protocol. Our results show the use of photonic lanterns to dynamically create spatial modes using only fiber components, which due to their robustness and integration capabilities, have important consequences for photonic classical and quantum information processing.

DOI
10.1364/oe.481974

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Photonic spatial quantum states are a subject of great interest for applications in quantum communication. One important challenge has been how to dynamically generate these states using only fiber-optical components. Here we propose and experimentally demonstrate an all-fiber system that can dynamically switch between any general transverse spatial qubit state based on linearly polarized modes. Our platform is based on a fast optical switch based on a Sagnac interferometer combined with a photonic lantern and few-mode optical fibers. We show switching times between spatial modes on the order of 5 ns and demonstrate the applicability of our scheme for quantum technologies by demonstrating a measurement-device-independent (MDI) quantum random number generator based on our platform. We run the generator continuously over 15 hours, acquiring over 13.46 Gbits of random numbers, of which we ensure that at least 60.52% are private, following the MDI protocol. Our results show the use of photonic lanterns to dynamically create spatial modes using only fiber components, which due to their robustness and integration capabilities, have important consequences for photonic classical and quantum information processing.
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.
The spatial degree of freedom (DOF) has significant applications in the emerging high-dimensional quantum information processing. Using a mode-maintaining few-mode fiber (FMF) and a dual-Sagnac-loop configuration, we generate polarization-entangled photon pairs and transform the entanglement into spatial DOF. We obtain Bell states encoded in the linearly polarized (LP) and orbital angular momentum (OAM) mode bases, respectively. The entangled photons from the FMF are in well-defined spatial modes, providing great advantages for the entanglement generation, manipulation, and transmission. The measured fidelities of the obtained entangled states are more than 97%. Our generation-and-transformation protocol can also be adopted on other integrated waveguide platforms to develop robust and miniaturized sources of spatial entanglement.
Abstract The spatial degree of freedom has enabled a wide range of applications in quantum information processing (QIP), such as increasing the capacity of quantum channels and realizing novel QIP protocols. In such applications, generating and manipulating quantum states in different spatial modes is one of the primary tasks. In this paper, by utilizing a telecom-band panda-type mode-maintaining few-mode fiber (MM-FMF) with a Sagnac loop configuration, we generate polarization-entangled photon pairs in higher-order spatial modes, namely the LP 11 modes, via intermodal spontaneous four-wave mixing process. The polarization- and spatial-mode-maintaining capabilities of the MM-FMF, combined with the automatic phase-stabilization of the Sagnac loop, provide a robust architecture for entanglement generation. We verify the polarization entanglement by two-photon interference measurements, yielding raw visibilities exceeding 76%. The visibilities are mainly limited by spontaneous Raman scattering noise, which could be reduced by cooling the fiber. The photon pairs directly emerging from MM-FMF are in a well-defined spatial mode, which greatly facilitates further manipulation and transmission of the entanglement. Our work demonstrates that the MM-FMF is a robust platform for developing devices and protocols exploiting the spatial degree of freedom in QIP applications.
Abstract Quantum random number generators (QRNGs) are based on naturally random measurement results performed on individual quantum systems. Here, we demonstrate a branching-path photonic QRNG implemented using a Sagnac interferometer with a tunable splitting ratio. The fine-tuning of the splitting ratio allows us to maximize the entropy of the generated sequence of random numbers and effectively compensate for tolerances in the components. By producing single-photons from attenuated telecom laser pulses, and employing commercially-available components we are able to generate a sequence of more than 2 gigabytes of random numbers with an average entropy of 7.99 bits/byte directly from the raw measured data. Furthermore, our sequence passes randomness tests from both the NIST and Dieharder statistical test suites, thus certifying its randomness. Our scheme shows an alternative design of QRNGs based on the dynamic adjustment of the uniformity of the produced random sequence, which is relevant for the construction of modern generators that rely on independent real-time testing of its performance.