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Zahidy M, Ribezzo D, De Lazzari C, Vagniluca I, Biagi N, Müller R, Occhipinti T, Oxenløwe LK, Galili M, Hayashi T, Cassioli D, Mecozzi A, Antonelli C, Zavatta A, Bacco D. Practical high-dimensional quantum key distribution protocol over deployed multicore fiber. Nat Commun 2024; 15:1651. [PMID: 38395964 PMCID: PMC10891113 DOI: 10.1038/s41467-024-45876-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2023] [Accepted: 02/06/2024] [Indexed: 02/25/2024] Open
Abstract
Quantum key distribution (QKD) is a secure communication scheme for sharing symmetric cryptographic keys based on the laws of quantum physics, and is considered a key player in the realm of cyber-security. A critical challenge for QKD systems comes from the fact that the ever-increasing rates at which digital data are transmitted require more and more performing sources of quantum keys, primarily in terms of secret key generation rate. High-dimensional QKD based on path encoding has been proposed as a candidate approach to address this challenge. However, while proof-of-principle demonstrations based on lab experiments have been reported in the literature, demonstrations in realistic environments are still missing. Here we report the generation of secret keys in a 4-dimensional hybrid time-path-encoded QKD system over a 52-km deployed multicore fiber link forming by looping back two cores of a 26-km 4-core optical fiber. Our results indicate that robust high-dimensional QKD can be implemented in a realistic environment by combining standard telecom equipment with emerging multicore fiber technology.
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Affiliation(s)
- Mujtaba Zahidy
- Department of Electrical and Photonics Engineering, Technical University of Denmark, Ørsteds Pl., Kgs. Lyngby, 2800, Denmark
| | - Domenico Ribezzo
- Department of Physical and Chemical Sciences, University of L'Aquila, L'Aquila, Italy
- Istituto Nazionale di Ottica, Consiglio Nazionale delle Ricerche (CNR-INO), Firenze, 50125, Italy
- University of Naples Federico II, Napoli, Italy
| | | | | | | | - Ronny Müller
- Department of Electrical and Photonics Engineering, Technical University of Denmark, Ørsteds Pl., Kgs. Lyngby, 2800, Denmark
| | | | - Leif K Oxenløwe
- Department of Electrical and Photonics Engineering, Technical University of Denmark, Ørsteds Pl., Kgs. Lyngby, 2800, Denmark
| | - Michael Galili
- Department of Electrical and Photonics Engineering, Technical University of Denmark, Ørsteds Pl., Kgs. Lyngby, 2800, Denmark
| | - Tetsuya Hayashi
- Optical Communications Laboratory, Sumitomo Electric Industries, Ltd., Yokohama, 244-8588, Japan
| | - Dajana Cassioli
- Department of Information Engineering, Computer Science and Mathematics, University of L'Aquila, L'Aquila, Italy
- National Laboratory of Advanced Optical Fibers for Photonics (FIBERS), CNIT, L'Aquila, Italy
| | - Antonio Mecozzi
- Department of Physical and Chemical Sciences, University of L'Aquila, L'Aquila, Italy
- National Laboratory of Advanced Optical Fibers for Photonics (FIBERS), CNIT, L'Aquila, Italy
| | - Cristian Antonelli
- Department of Physical and Chemical Sciences, University of L'Aquila, L'Aquila, Italy
- National Laboratory of Advanced Optical Fibers for Photonics (FIBERS), CNIT, L'Aquila, Italy
| | - Alessandro Zavatta
- Istituto Nazionale di Ottica, Consiglio Nazionale delle Ricerche (CNR-INO), Firenze, 50125, Italy
- QTI S.r.l., Firenze, 50125, Italy
| | - Davide Bacco
- QTI S.r.l., Firenze, 50125, Italy.
- Department of Physics and Astronomy, University of Florence, Via Sansone 1, Firenze, 50019, Italy.
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Bellini M, Kwon H, Biagi N, Francesconi S, Zavatta A, Kim MS. Demonstrating Quantum Microscopic Reversibility Using Coherent States of Light. Phys Rev Lett 2022; 129:170604. [PMID: 36332254 DOI: 10.1103/physrevlett.129.170604] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2022] [Revised: 09/07/2022] [Accepted: 09/08/2022] [Indexed: 06/16/2023]
Abstract
The principle of microscopic reversibility lies at the core of fluctuation theorems, which have extended our understanding of the second law of thermodynamics to the statistical level. In the quantum regime, however, this elementary principle should be amended as the system energy cannot be sharply determined at a given quantum phase space point. In this Letter, we propose and experimentally test a quantum generalization of the microscopic reversibility when a quantum system interacts with a heat bath through energy-preserving unitary dynamics. Quantum effects can be identified by noting that the backward process is less likely to happen in the existence of quantum coherence between the system's energy eigenstates. The experimental demonstration has been realized by mixing coherent and thermal states in a beam splitter, followed by heterodyne detection in an optical setup. We verify that the quantum modification for the principle of microscopic reversibility is critical in the low-temperature limit, while the quantum-to-classical transition is observed as the temperature of the thermal field gets higher.
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Affiliation(s)
- Marco Bellini
- Istituto Nazionale di Ottica (CNR-INO), Largo Enrico Fermi 6, 50125 Florence, Italy
- LENS and Department of Physics and Astronomy, University of Firenze, 50019 Sesto Fiorentino, Florence, Italy
| | - Hyukjoon Kwon
- Korea Institute for Advanced Study, Seoul 02455, South Korea
| | - Nicola Biagi
- Istituto Nazionale di Ottica (CNR-INO), Largo Enrico Fermi 6, 50125 Florence, Italy
- LENS and Department of Physics and Astronomy, University of Firenze, 50019 Sesto Fiorentino, Florence, Italy
| | - Saverio Francesconi
- Istituto Nazionale di Ottica (CNR-INO), Largo Enrico Fermi 6, 50125 Florence, Italy
- LENS and Department of Physics and Astronomy, University of Firenze, 50019 Sesto Fiorentino, Florence, Italy
| | - Alessandro Zavatta
- Istituto Nazionale di Ottica (CNR-INO), Largo Enrico Fermi 6, 50125 Florence, Italy
- LENS and Department of Physics and Astronomy, University of Firenze, 50019 Sesto Fiorentino, Florence, Italy
| | - M S Kim
- QOLS, Blackett Laboratory, Imperial College London, London SW7 2AZ, United Kingdom
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Biagi N, Francesconi S, Zavatta A, Bellini M. Coherent Superpositions of Photon Creation Operations and Their Application to Multimode States of Light. Entropy (Basel) 2021; 23:e23080999. [PMID: 34441139 PMCID: PMC8391713 DOI: 10.3390/e23080999] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/17/2021] [Revised: 07/28/2021] [Accepted: 07/28/2021] [Indexed: 12/03/2022]
Abstract
We present a concise review of recent experimental results concerning the conditional implementation of coherent superpositions of single-photon additions onto distinct field modes. Such a basic operation is seen to give rise to a wealth of interesting and useful effects, from the generation of a tunable degree of entanglement to the birth of peculiar correlations in the photon numbers and the quadratures of multimode, multiphoton, states of light. The experimental investigation of these properties will have an impact both on fundamental studies concerning, for example, the quantumness and entanglement of macroscopic states, and for possible applications in the realm of quantum-enhanced technologies.
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Affiliation(s)
- Nicola Biagi
- Istituto Nazionale di Ottica (CNR-INO), L.go E. Fermi 6, 50125 Firenze, Italy; (N.B.); (S.F.); (A.Z.)
- LENS and Department of Physics & Astronomy, University of Firenze, 50019 Sesto Fiorentino, Italy
| | - Saverio Francesconi
- Istituto Nazionale di Ottica (CNR-INO), L.go E. Fermi 6, 50125 Firenze, Italy; (N.B.); (S.F.); (A.Z.)
- LENS and Department of Physics & Astronomy, University of Firenze, 50019 Sesto Fiorentino, Italy
| | - Alessandro Zavatta
- Istituto Nazionale di Ottica (CNR-INO), L.go E. Fermi 6, 50125 Firenze, Italy; (N.B.); (S.F.); (A.Z.)
- LENS and Department of Physics & Astronomy, University of Firenze, 50019 Sesto Fiorentino, Italy
| | - Marco Bellini
- Istituto Nazionale di Ottica (CNR-INO), L.go E. Fermi 6, 50125 Firenze, Italy; (N.B.); (S.F.); (A.Z.)
- LENS and Department of Physics & Astronomy, University of Firenze, 50019 Sesto Fiorentino, Italy
- Correspondence:
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Biagi N, Bohmann M, Agudelo E, Bellini M, Zavatta A. Experimental Certification of Nonclassicality via Phase-Space Inequalities. Phys Rev Lett 2021; 126:023605. [PMID: 33512213 DOI: 10.1103/physrevlett.126.023605] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2020] [Accepted: 12/08/2020] [Indexed: 06/12/2023]
Abstract
In spite of its fundamental importance in quantum science and technology, the experimental certification of nonclassicality is still a challenging task, especially in realistic scenarios where losses and noise imbue the system. Here, we present the first experimental implementation of the recently introduced phase-space inequalities for nonclassicality certification, which conceptually unite phase-space representations with correlation conditions. We demonstrate the practicality and sensitivity of this approach by studying nonclassicality of a family of noisy and lossy quantum states of light. To this end, we experimentally generate single-photon-added thermal states with various thermal mean photon numbers and detect them at different loss levels. Based on the reconstructed Wigner and Husimi Q functions, the inequality conditions detect nonclassicality despite the fact that the involved distributions are nonnegative, which includes cases of high losses (93%) and cases where other established methods do not reveal nonclassicality. We show the advantages of the implemented approach and discuss possible extensions that assure a wide applicability for quantum science and technologies.
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Affiliation(s)
- Nicola Biagi
- Istituto Nazionale di Ottica (CNR-INO), L.go E. Fermi 6, 50125 Florence, Italy
- LENS and Department of Physics & Astronomy, University of Firenze, 50019 Sesto Fiorentino, Florence, Italy
| | - Martin Bohmann
- Institute for Quantum Optics and Quantum Information-IQOQI Vienna, Austrian Academy of Sciences, Boltzmanngasse 3, 1090 Vienna, Austria
- Vienna Center for Quantum Science and Technology (VCQ), Vienna, Austria
| | - Elizabeth Agudelo
- Institute for Quantum Optics and Quantum Information-IQOQI Vienna, Austrian Academy of Sciences, Boltzmanngasse 3, 1090 Vienna, Austria
| | - Marco Bellini
- Istituto Nazionale di Ottica (CNR-INO), L.go E. Fermi 6, 50125 Florence, Italy
- LENS and Department of Physics & Astronomy, University of Firenze, 50019 Sesto Fiorentino, Florence, Italy
| | - Alessandro Zavatta
- Istituto Nazionale di Ottica (CNR-INO), L.go E. Fermi 6, 50125 Florence, Italy
- LENS and Department of Physics & Astronomy, University of Firenze, 50019 Sesto Fiorentino, Florence, Italy
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Biagi N, Costanzo LS, Bellini M, Zavatta A. Entangling Macroscopic Light States by Delocalized Photon Addition. Phys Rev Lett 2020; 124:033604. [PMID: 32031852 DOI: 10.1103/physrevlett.124.033604] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2019] [Indexed: 06/10/2023]
Abstract
We present a scheme, based on the delocalized heralded addition of a single photon, to entangle two or more distinct field modes, each containing arbitrary light states. A high degree of entanglement can in principle endure light states of macroscopic intensities and is expected to be particularly robust against losses. We experimentally establish and measure significant entanglement between two identical weak laser pulses containing up to 60 photons each.
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Affiliation(s)
- Nicola Biagi
- Istituto Nazionale di Ottica (CNR-INO), L.go E. Fermi 6, 50125 Florence, Italy and LENS and Department of Physics & Astronomy, University of Firenze, 50019 Sesto Fiorentino, Florence, Italy
| | - Luca S Costanzo
- Istituto Nazionale di Ottica (CNR-INO), L.go E. Fermi 6, 50125 Florence, Italy and LENS and Department of Physics & Astronomy, University of Firenze, 50019 Sesto Fiorentino, Florence, Italy
| | - Marco Bellini
- Istituto Nazionale di Ottica (CNR-INO), L.go E. Fermi 6, 50125 Florence, Italy and LENS and Department of Physics & Astronomy, University of Firenze, 50019 Sesto Fiorentino, Florence, Italy
| | - Alessandro Zavatta
- Istituto Nazionale di Ottica (CNR-INO), L.go E. Fermi 6, 50125 Florence, Italy and LENS and Department of Physics & Astronomy, University of Firenze, 50019 Sesto Fiorentino, Florence, Italy
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Costanzo LS, Coelho AS, Biagi N, Fiurášek J, Bellini M, Zavatta A. Measurement-Induced Strong Kerr Nonlinearity for Weak Quantum States of Light. Phys Rev Lett 2017; 119:013601. [PMID: 28731763 DOI: 10.1103/physrevlett.119.013601] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/27/2017] [Indexed: 06/07/2023]
Abstract
Strong nonlinearity at the single photon level represents a crucial enabling tool for optical quantum technologies. Here we report on experimental implementation of a strong Kerr nonlinearity by measurement-induced quantum operations on weak quantum states of light. Our scheme coherently combines two sequences of single photon addition and subtraction to induce a nonlinear phase shift at the single photon level. We probe the induced nonlinearity with weak coherent states and characterize the output non-Gaussian states with quantum state tomography. The strong nonlinearity is clearly witnessed as a change of sign of specific off-diagonal density matrix elements in the Fock basis.
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Affiliation(s)
- Luca S Costanzo
- Istituto Nazionale di Ottica (INO-CNR), Largo E. Fermi 6, 50125 Florence, Italy
- LENS and Department of Physics, University of Firenze, 50019 Sesto Fiorentino, Florence, Italy
| | - Antonio S Coelho
- Departamento de Engenharia Mecânica, Universidade Federal do Piauí, 64049-550 Teresina, Piauí, Brazil
| | - Nicola Biagi
- Istituto Nazionale di Ottica (INO-CNR), Largo E. Fermi 6, 50125 Florence, Italy
- LENS and Department of Physics, University of Firenze, 50019 Sesto Fiorentino, Florence, Italy
| | - Jaromír Fiurášek
- Department of Optics, Palacký University, 17. listopadu 1192/12, CZ-771 46 Olomouc, Czech Republic
| | - Marco Bellini
- Istituto Nazionale di Ottica (INO-CNR), Largo E. Fermi 6, 50125 Florence, Italy
- LENS and Department of Physics, University of Firenze, 50019 Sesto Fiorentino, Florence, Italy
| | - Alessandro Zavatta
- Istituto Nazionale di Ottica (INO-CNR), Largo E. Fermi 6, 50125 Florence, Italy
- LENS and Department of Physics, University of Firenze, 50019 Sesto Fiorentino, Florence, Italy
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