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Wo KJ, Avis G, Rozpędek F, Mor-Ruiz MF, Pieplow G, Schröder T, Jiang L, Sørensen AS, Borregaard J. Resource-efficient fault-tolerant one-way quantum repeater with code concatenation. NPJ QUANTUM INFORMATION 2023; 9:123. [PMID: 38665254 PMCID: PMC11041798 DOI: 10.1038/s41534-023-00792-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/03/2023] [Accepted: 11/22/2023] [Indexed: 04/28/2024]
Abstract
One-way quantum repeaters where loss and operational errors are counteracted by quantum error-correcting codes can ensure fast and reliable qubit transmission in quantum networks. It is crucial that the resource requirements of such repeaters, for example, the number of qubits per repeater node and the complexity of the quantum error-correcting operations are kept to a minimum to allow for near-future implementations. To this end, we propose a one-way quantum repeater that targets both the loss and operational error rates in a communication channel in a resource-efficient manner using code concatenation. Specifically, we consider a tree-cluster code as an inner loss-tolerant code concatenated with an outer 5-qubit code for protection against Pauli errors. Adopting flag-based stabilizer measurements, we show that intercontinental distances of up to 10,000 km can be bridged with a minimized resource overhead by interspersing repeater nodes that each specialize in suppressing either loss or operational errors. Our work demonstrates how tailored error-correcting codes can significantly lower the experimental requirements for long-distance quantum communication.
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Grants
- NWO Gravitation Program Quantum Software Consortium - QSC024.003.037
- ARO(W911NF-23-1-0077), ARO MURI (W911NF-21-1-0325), AFOSR MURI (FA9550-19-1-0399, FA9550-21-1-0209), AFRL (FA8649- 21-P-0781), NSF (OMA-1936118, ERC-1941583, OMA-2137642), NTT Research, Packard Foundation (2020-71479), and the Marshall and Arlene Bennett Family Research Program.
- Austrian Science Fund (Fonds zur Förderung der Wissenschaftlichen Forschung)
- Finanziert von der Europäischen Union - NextGenerationEU
- Bundesministerium für Bildung und Forschung (Federal Ministry of Education and Research)
- European Research Council (ERC Starting Grant "QUREP")
- Danish Nation Research Foundation (Center of Excellence "Hy-Q," Grant No. DNRF139)
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Affiliation(s)
- Kah Jen Wo
- QuTech, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
- Centre for Quantum Technologies, National University of Singapore, Queenstown, 117543 Singapore
| | - Guus Avis
- QuTech, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
- Quantum Computer Science, EEMCS, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
- Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
- College of Information and Computer Sciences, University of Massachusetts Amherst, Amherst, MA 01003 USA
| | - Filip Rozpędek
- College of Information and Computer Sciences, University of Massachusetts Amherst, Amherst, MA 01003 USA
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL 60637 USA
| | - Maria Flors Mor-Ruiz
- Universität Innsbruck, Institut für Theoretische Physik, Technikerstraße 21a, 6020 Innsbruck, Austria
| | - Gregor Pieplow
- Department of Physics, Humboldt-Universität zu Berlin, Newtonstraße 15, 12489 Berlin, Germany
| | - Tim Schröder
- Department of Physics, Humboldt-Universität zu Berlin, Newtonstraße 15, 12489 Berlin, Germany
| | - Liang Jiang
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL 60637 USA
| | - Anders S. Sørensen
- Center for Hybrid Quantum Networks (Hy-Q), The Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, DK-2100 Copenhagen Ø, Denmark
| | - Johannes Borregaard
- QuTech, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
- Department of Physics, Harvard University, Cambridge, MA 02138 USA
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2
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Švarc V, Nováková M, Dudka M, Ježek M. Sub-0.1 degree phase locking of a single-photon interferometer. OPTICS EXPRESS 2023; 31:12562-12571. [PMID: 37157413 DOI: 10.1364/oe.480569] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
We report a single-photon Mach-Zehnder interferometer stabilized to a phase precision of 0.05 degrees over 15 hours. To lock the phase, we employ an auxiliary reference light at a different wavelength than the quantum signal. The developed phase locking operates continuously, with negligible crosstalk, and for an arbitrary phase of the quantum signal. Moreover, its performance is independent of intensity fluctuations of the reference. Since the presented method can be used in a vast majority of quantum interferometric networks it can significantly improve phase-sensitive applications in quantum communication and quantum metrology.
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Mohageg M, Mazzarella L, Anastopoulos C, Gallicchio J, Hu BL, Jennewein T, Johnson S, Lin SY, Ling A, Marquardt C, Meister M, Newell R, Roura A, Schleich WP, Schubert C, Strekalov DV, Vallone G, Villoresi P, Wörner L, Yu N, Zhai A, Kwiat P. The deep space quantum link: prospective fundamental physics experiments using long-baseline quantum optics. EPJ QUANTUM TECHNOLOGY 2022; 9:25. [PMID: 36227029 PMCID: PMC9547810 DOI: 10.1140/epjqt/s40507-022-00143-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/09/2021] [Accepted: 09/15/2022] [Indexed: 06/16/2023]
Abstract
The National Aeronautics and Space Administration's Deep Space Quantum Link mission concept enables a unique set of science experiments by establishing robust quantum optical links across extremely long baselines. Potential mission configurations include establishing a quantum link between the Lunar Gateway moon-orbiting space station and nodes on or near the Earth. This publication summarizes the principal experimental goals of the Deep Space Quantum Link. These goals, identified through a multi-year design study conducted by the authors, include long-range teleportation, tests of gravitational coupling to quantum states, and advanced tests of quantum nonlocality.
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Affiliation(s)
- Makan Mohageg
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California USA
| | - Luca Mazzarella
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California USA
| | | | - Jason Gallicchio
- Department of Physics, Harvey Mudd College, Claremont, California USA
| | - Bei-Lok Hu
- Maryland Center for Fundamental Physics and Joint Quantum Institute, University of Maryland, College Park, Maryland USA
| | - Thomas Jennewein
- Institute for Quantum Computing and Dep. of Physics and Astronomy, University of Waterloo, Waterloo, Canada
| | - Spencer Johnson
- Department of Physics, Illinois Quantum Information Science & Technology Center, University of Illinois at Urbana-Champaign, Urbana, Illinois USA
| | - Shih-Yuin Lin
- Department of Physics, National Changhua University of Education, Changhua, Taiwan
| | - Alexander Ling
- Centre for Quantum Technologies and Department of Physics, National University of Singapore, Singapore, Singapore
| | | | - Matthias Meister
- Institute of Quantum Technologies, German Aerospace Center (DLR), Ulm, Germany
| | - Raymond Newell
- Los Alamos National Laboratory, Los Alamos, New Mexico USA
| | - Albert Roura
- Institute of Quantum Technologies, German Aerospace Center (DLR), Ulm, Germany
| | - Wolfgang P. Schleich
- Institute of Quantum Technologies, German Aerospace Center (DLR), Ulm, Germany
- Institut für Quantenphysik and Center for Integrated Quantum Science and Technology (IQst), Universität Ulm, Ulm, Germany
- Hagler Institute for Advanced Study, AgriLife Research, Institute for Quantum Science and Engineering (IQSE), and Department of Physics and Astronomy, Texas A& M University, College Station, Texas USA
| | - Christian Schubert
- Institute for Satellite Geodesy and Inertial Sensing, German Aerospace Center (DLR), Hanover, Germany
- Institute for Quantum Optics, Germany Leibniz University Hannover, Hanover, Germany
| | - Dmitry V. Strekalov
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California USA
| | - Giuseppe Vallone
- Dipartimento di Ingegneria dell’Informazione, Universitá degli Studi di Padova, Padova, Italy
- Padua Quantum Technologies Research Center, Universitá degli Studi di Padova, Padova, Italy
- Dipartimento di Fisica e Astronomia, Universitá degli Studi di Padova, Padova, Italy
| | - Paolo Villoresi
- Dipartimento di Ingegneria dell’Informazione, Universitá degli Studi di Padova, Padova, Italy
- Padua Quantum Technologies Research Center, Universitá degli Studi di Padova, Padova, Italy
| | - Lisa Wörner
- Institute of Quantum Technologies, German Aerospace Center (DLR), Ulm, Germany
| | - Nan Yu
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California USA
| | - Aileen Zhai
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California USA
| | - Paul Kwiat
- Department of Physics, University of Patras, Patras, Greece
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4
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Bhattacharjee A, Joshi MK, Karan S, Leach J, Jha AK. Propagation-induced revival of entanglement in the angle-OAM bases. SCIENCE ADVANCES 2022; 8:eabn7876. [PMID: 35930646 PMCID: PMC9355354 DOI: 10.1126/sciadv.abn7876] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/21/2021] [Accepted: 06/21/2022] [Indexed: 06/15/2023]
Abstract
Although the continuous-variable position-momentum entanglement of photon pairs produced by parametric down-conversion has applicability in several quantum information applications, it is not suitable for applications involving long-distance propagation. This is because entanglement in the position-momentum bases, as seen through Einstein-Podolsky-Rosen (EPR)-correlation measurements, decays very rapidly with photons propagating away from the source. In contrast, in this article, we show that in the continuous-variable bases of angle-orbital angular momentum (OAM), the entanglement, as seen through EPR-correlation measurements, exhibits a remarkably different behavior. As with the position-momentum bases, initially, the entanglement in the angle-OAM bases also decays with propagation, and after a few centimeters of propagation, there is no angle-OAM entanglement left. However, as the photons continue to travel further away from the source, the entanglement in the angle-OAM bases revives. We theoretically and experimentally demonstrate this behavior and show that angle-OAM entanglement revives even in the presence of strong turbulence.
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Affiliation(s)
| | - Mritunjay K. Joshi
- Department of Physics, Indian Institute of Technology Kanpur, Kanpur UP 208016, India
| | - Suman Karan
- Department of Physics, Indian Institute of Technology Kanpur, Kanpur UP 208016, India
| | - Jonathan Leach
- School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK
| | - Anand K. Jha
- Department of Physics, Indian Institute of Technology Kanpur, Kanpur UP 208016, India
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5
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Appel MH, Tiranov A, Pabst S, Chan ML, Starup C, Wang Y, Midolo L, Tiurev K, Scholz S, Wieck AD, Ludwig A, Sørensen AS, Lodahl P. Entangling a Hole Spin with a Time-Bin Photon: A Waveguide Approach for Quantum Dot Sources of Multiphoton Entanglement. PHYSICAL REVIEW LETTERS 2022; 128:233602. [PMID: 35749189 DOI: 10.1103/physrevlett.128.233602] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2021] [Revised: 03/13/2022] [Accepted: 04/06/2022] [Indexed: 06/15/2023]
Abstract
Deterministic sources of multiphoton entanglement are highly attractive for quantum information processing but are challenging to realize experimentally. In this Letter, we demonstrate a route toward a scaleable source of time-bin encoded Greenberger-Horne-Zeilinger and linear cluster states from a solid-state quantum dot embedded in a nanophotonic crystal waveguide. By utilizing a self-stabilizing double-pass interferometer, we measure a spin-photon Bell state with (67.8±0.4)% fidelity and devise steps for significant further improvements. By employing strict resonant excitation, we demonstrate a photon indistinguishability of (95.7±0.8)%, which is conducive to fusion of multiple cluster states for scaling up the technology and producing more general graph states.
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Affiliation(s)
- Martin Hayhurst Appel
- Center for Hybrid Quantum Networks (Hy-Q), The Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark
| | - Alexey Tiranov
- Center for Hybrid Quantum Networks (Hy-Q), The Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark
| | - Simon Pabst
- Center for Hybrid Quantum Networks (Hy-Q), The Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark
| | - Ming Lai Chan
- Center for Hybrid Quantum Networks (Hy-Q), The Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark
| | - Christian Starup
- Center for Hybrid Quantum Networks (Hy-Q), The Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark
| | - Ying Wang
- Center for Hybrid Quantum Networks (Hy-Q), The Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark
| | - Leonardo Midolo
- Center for Hybrid Quantum Networks (Hy-Q), The Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark
| | - Konstantin Tiurev
- Center for Hybrid Quantum Networks (Hy-Q), The Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark
| | - Sven Scholz
- Lehrstuhl für Angewandte Festkörperphysik, Ruhr-Universität Bochum, Universitätsstraße 150, 44801 Bochum, Germany
| | - Andreas D Wieck
- Lehrstuhl für Angewandte Festkörperphysik, Ruhr-Universität Bochum, Universitätsstraße 150, 44801 Bochum, Germany
| | - Arne Ludwig
- Lehrstuhl für Angewandte Festkörperphysik, Ruhr-Universität Bochum, Universitätsstraße 150, 44801 Bochum, Germany
| | - Anders Søndberg Sørensen
- Center for Hybrid Quantum Networks (Hy-Q), The Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark
| | - Peter Lodahl
- Center for Hybrid Quantum Networks (Hy-Q), The Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark
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6
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Chen C, Shapiro JH, Wong FNC. Experimental Demonstration of Conjugate-Franson Interferometry. PHYSICAL REVIEW LETTERS 2021; 127:093603. [PMID: 34506171 DOI: 10.1103/physrevlett.127.093603] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2021] [Accepted: 08/04/2021] [Indexed: 06/13/2023]
Abstract
Franson interferometry is a well-known quantum measurement technique for probing photon-pair frequency correlations that is often used to certify time-energy entanglement. We demonstrate, for the first time, the complementary technique in the time basis called conjugate-Franson interferometry. It measures photon-pair arrival-time correlations, thus providing a valuable addition to the quantum toolbox. We obtain a conjugate-Franson interference visibility of 96±1% without background subtraction for entangled photon pairs generated by spontaneous parametric down-conversion. Our measured result surpasses the quantum-classical threshold by 25 standard deviations and validates the conjugate-Franson interferometer (CFI) as an alternative method for certifying time-energy entanglement. Moreover, the CFI visibility is a function of the biphoton's joint temporal intensity, and is therefore sensitive to that state's spectral phase variation: something that is not the case for Franson interferometry or Hong-Ou-Mandel interferometry. We highlight the CFI's utility by measuring its visibilities for two different biphoton states: one without and the other with spectral phase variation, observing a 21% reduction in the CFI visibility for the latter. The CFI is potentially useful for applications in areas of photonic entanglement, quantum communications, and quantum networking.
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Affiliation(s)
- Changchen Chen
- Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Jeffrey H Shapiro
- Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Franco N C Wong
- Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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7
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Anwar A, Perumangatt C, Steinlechner F, Jennewein T, Ling A. Entangled photon-pair sources based on three-wave mixing in bulk crystals. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2021; 92:041101. [PMID: 34243479 DOI: 10.1063/5.0023103] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2020] [Accepted: 03/01/2021] [Indexed: 06/13/2023]
Abstract
Entangled photon pairs are a critical resource in quantum communication protocols ranging from quantum key distribution to teleportation. The current workhorse technique for producing photon pairs is via spontaneous parametric down conversion (SPDC) in bulk nonlinear crystals. The increased prominence of quantum networks has led to a growing interest in deployable high performance entangled photon-pair sources. This manuscript provides a review of the state-of-the-art bulk-optics-based SPDC sources with continuous wave pump and discusses some of the main considerations when building for deployment.
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Affiliation(s)
- Ali Anwar
- Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, S117543 Singapore, Singapore
| | - Chithrabhanu Perumangatt
- Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, S117543 Singapore, Singapore
| | - Fabian Steinlechner
- Fraunhofer Institute for Applied Optics and Precision Engineering IOF, Albert-Einstein-Straße 7, 07745 Jena, Germany
| | - Thomas Jennewein
- Institute of Quantum Computing and Department of Physics and Astronomy, University of Waterloo, 200 University Ave. W, Waterloo, Ontario N2L 3G1, Canada
| | - Alexander Ling
- Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, S117543 Singapore, Singapore
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8
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Luiz Zanin G, Jacquet MJ, Spagnolo M, Schiansky P, Calafell IA, Rozema LA, Walther P. Fiber-compatible photonic feed-forward with 99% fidelity. OPTICS EXPRESS 2021; 29:3425-3437. [PMID: 33770941 DOI: 10.1364/oe.409867] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2020] [Accepted: 12/21/2020] [Indexed: 06/12/2023]
Abstract
Both photonic quantum computation and the establishment of a quantum internet require fiber-based measurement and feed-forward in order to be compatible with existing infrastructure. Here we present a fiber-compatible scheme for measurement and feed-forward, whose performance is benchmarked by carrying out remote preparation of single-photon polarization states at telecom-wavelengths. The result of a projective measurement on one photon deterministically controls the path a second photon takes with ultrafast optical switches. By placing well-calibrated bulk passive polarization optics in the paths, we achieve a measurement and feed-forward fidelity of (99.0 ± 1)%, after correcting for other experimental errors. Our methods are useful for photonic quantum experiments including computing, communication, and teleportation.
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Yan PS, Zhou L, Zhong W, Sheng YB. Feasible time-bin entanglement purification based on sum-frequency generation. OPTICS EXPRESS 2021; 29:571-583. [PMID: 33726290 DOI: 10.1364/oe.409931] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2020] [Accepted: 12/07/2020] [Indexed: 06/12/2023]
Abstract
High quality time-bin entanglement is widely exploited to achieve the purposes of fundamental tests of physics and the implementation of quantum communication protocols both in free space and optical fiber propagation. However, the imperfect approaches of generating time-bin entangled state will degrade its quality and limit its practical application. Entanglement purification is to distill high quality entangled states from low quality entangled states. In this paper, we present the first entanglement purification protocol (EPP) for time-bin entanglement. We first explain this EPP for two-photon time-bin entangled state and then extend it to the system of multi-photon time-bin entangled state. We also design a possible realization of this EPP with practical spontaneous parametric down conversion (SPDC) source. Differ from the conventional EPPs, this EPP does not require the sophisticated controlled-not (CNOT) gate or similar operations, and it uses the feasible sum-frequency generation (SFG) to perform the purification. Moreover, the double-pair noise emitted from the SPDC source can be eliminated automatically which is the other advantage of this EPP. If we combine with the faithful entanglement swapping, this EPP may have potential to be a part of full quantum repeaters.
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Alarcón A, González P, Cariñe J, Lima G, Xavier GB. Polarization-independent single-photon switch based on a fiber-optical Sagnac interferometer for quantum communication networks. OPTICS EXPRESS 2020; 28:33731-33738. [PMID: 33115032 DOI: 10.1364/oe.408637] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2020] [Accepted: 10/06/2020] [Indexed: 06/11/2023]
Abstract
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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Švarc V, Nováková M, Mazin G, Ježek M. Fully tunable and switchable coupler for photonic routing in quantum detection and modulation. OPTICS LETTERS 2019; 44:5844-5847. [PMID: 31774794 DOI: 10.1364/ol.44.005844] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2019] [Accepted: 10/28/2019] [Indexed: 06/10/2023]
Abstract
Photonic routing is a key building block of many optical applications challenging its development. We report a $2\times 2$2×2 photonic coupler with a splitting ratio switchable by a low-voltage electronic signal with 10 GHz bandwidth and tens of nanoseconds latency. The coupler can operate at any splitting ratio ranging from 0:100 to 100:0 with the extinction ratio of 26 dB in optical bandwidth of 1.3 THz. We show sub-nanosecond switching between arbitrary coupling regimes including a balanced 50:50 beam splitter, 0:100 switch, and a photonic tap. The core of the device is based on a Mach-Zehnder interferometer in a dual-wavelength configuration allowing real-time phase lock with long-term sub-degree stability at single-photon level. Using the reported coupler, we demonstrate for the first time, to the best of our knowledge, a perfectly balanced time-multiplexed device for photon-number-resolving detectors and also the active preparation of a photonic temporal qudit state up to four time bins. Verified long-term stable operation of the coupler at the single-photon level makes it suitable for a wide application range in quantum information processing and quantum optics in general.
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