Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Optics Express

Franson interferometer for characterizing highly non-degenerate correlated biphoton sources

Adam Fallon, E. J. Katz, Ian R. Nemitz, John Lekki

Published Feb 13, 2025• 3 citations
Publisher

Abstract

We report the demonstration of a Franson interferometer for a highly non-degenerate time-energy entangled biphoton source. A Franson interferometer realizes a Bell test for time-energy entanglement and can thus be used to verify entanglement distribution in quantum networks and security in quantum key distribution. The highly non-degenerate source has signal and idler photons at 810 nm and 1550 nm, respectively, making this source a potential interconnect between free-space and fiber optic quantum networks. We observe a single channel visibility of V =0.992(6) with an average visibility over the four output channels of V =0.984(3). These visibilities overcome the visibility threshold necessary in closing the postselection loophole in the Franson interferometer Bell test.

DOI
10.1364/oe.537588

Related papers

Bell inequality experiment for a high brightness time-energy entangled source

Ian R. Nemitz, Jonathan R. Dietz, Evan J. Katz +4 more

A periodically poled MgO – doped LiNbO3 (MgO:LN) non-degenerate photon pair source is utilized for spontaneous parametric down-conversion of 532 nm photons into time-energy entangled pairs of 794 and 1614 nm photons. The entangled photons are separated using previously detailed sorting optics, such that each wavelength is independently directed through one of two modified Mach-Zehnder interferometers – also known as a Franson interferometer – after which they are fiber-optically guided to high-efficiency photon detectors. Output from the detectors is sent to a high resolution time tagger, where coincidences between the entangled photons are recorded. By varying the length of the long path in one Mach-Zehnder interferometer, it is possible to observe high visibility sinusoidal fringes in the measured coincidence rates (while no variation is seen in single photon detection rates). These fringes – due to interference between the photon probability amplitudes – are indicative of a violation of the Bell inequality, and confirm inconsistencies with local hidden variable theory for the correlations of the time-energy entangled photon pairs.

Nonlinear Frequency Generation and Conversion: Materials and Devices•Mar 4, 2019•0 citations

Experimental Demonstration of Conjugate-Franson Interferometry

Changchen Chen, Jeffrey H. Shapiro, Franco N. C. Wong

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.

arXiv:2104.15084•Physical Review Letters•Aug 27, 2021•11 citations

Experimental demonstration of quantum correlations over more than 10 km

Wolfgang Tittel, Jurgen Brendel, B. Gisin +3 more

Energy and time entangled photons at a wavelength of 1310 nm are produced by parametric down-conversion in a ${\mathrm{KNbO}}_{3}$ crystal and are sent into all-fiber interferometers using a telecommunications fiber network. The two interferometers of this Franson-type test of the Bell inequality are located 10.9 km apart from one another. Two-photon fringe visibilities of up to 81.6% are obtained. These strong nonlocal correlations support the nonlocal predictions of quantum mechanics and provide evidence that entanglement between photons can be maintained over long distances.

arXiv:quant-ph/9707042•Physical Review A•May 1, 1998•237 citations

Cougate-Franson interferometry for testing nonlocality of time-energy entangled biphotons

Changchen Chen, Jeffrey H. Shapiro, Franco N. C. Wong

We report the first experimental demonstration of a conjugate-Franson interferometer, i.e., a nonlocal interferometer that can certify time-energy entanglement. Our measured 96% visibility tightly bounds the temporal correlation of biphotons generated by spontaneous parametric down-conversion.

Conference on Lasers and Electro-Optics•Jan 1, 2021•0 citations

Cross time-bin photonic entanglement for quantum key distribution

Anthony Martin, Florian Kaiser, A. Vernier +3 more

We report a fully fibered source emitting cross time-bin-entangled photons at 1540 nm from type-II spontaneous parametric down-conversion. Compared to standard time-bin-entanglement realizations, the preparation interferometer requires no phase stabilization, simplifying its implementation in quantum key distribution experiments. Bell-type tests of such a cross time-bin state are performed in the Franson configuration and lead to two-photon interference raw visibilities greater than 95$%$, which are only limited by the dark counts in the detectors and imperfections in the analysis system. Just by trusting the randomness of the beam splitters, the correlations generated by the source can be proved of nonclassical origin even in a passive implementation. The obtained results confirm the suitability of this source for time-bin-based quantum key distribution.

arXiv:1207.6586•Physical Review A•Feb 4, 2013•52 citations

Security of high-dimensional quantum key distribution protocols using Franson interferometers

Thomas Brougham, Stephen Mark Barnett, Kevin T. McCusker +2 more

Franson interferometers are increasingly being proposed as a means of securing high-dimensional energy–time entanglement-based quantum key distribution (QKD) systems. Heuristic arguments have been proposed that purport to demonstrate the security of these schemes. We show, however, that such systems are vulnerable to attacks that localize the photons to several temporally separate locations. This demonstrates that a single pair of Franson interferometers is not a practical approach to securing high-dimensional energy–time entanglement-based QKD. This observation leads us to investigate the security of modified Franson-based-protocols, where Alice and Bob have two or more Franson interferometers. We show that such setups can improve the sensitivity against attacks that localize the photons to multiple temporal locations. While our results do not constitute a full security proof, they do show that a single pair of Franson interferometers is not secure and that multiple such interferometers could be a promising candidate for experimentally realizable high-dimensional QKD.

arXiv:1305.4541•Journal of Physics B Atomic Molecular and Optical Physics•May 9, 2013•66 citations
We report the demonstration of a Franson interferometer for a highly non-degenerate time-energy entangled biphoton source. A Franson interferometer realizes a Bell test for time-energy entanglement and can thus be used to verify entanglement distribution in quantum networks and security in quantum key distribution. The highly non-degenerate source has signal and idler photons at 810 nm and 1550 nm, respectively, making this source a potential interconnect between free-space and fiber optic quantum networks. We observe a single channel visibility of V =0.992(6) with an average visibility over the four output channels of V =0.984(3). These visibilities overcome the visibility threshold necessary in closing the postselection loophole in the Franson interferometer Bell test.
A periodically poled MgO – doped LiNbO3 (MgO:LN) non-degenerate photon pair source is utilized for spontaneous parametric down-conversion of 532 nm photons into time-energy entangled pairs of 794 and 1614 nm photons. The entangled photons are separated using previously detailed sorting optics, such that each wavelength is independently directed through one of two modified Mach-Zehnder interferometers – also known as a Franson interferometer – after which they are fiber-optically guided to high-efficiency photon detectors. Output from the detectors is sent to a high resolution time tagger, where coincidences between the entangled photons are recorded. By varying the length of the long path in one Mach-Zehnder interferometer, it is possible to observe high visibility sinusoidal fringes in the measured coincidence rates (while no variation is seen in single photon detection rates). These fringes – due to interference between the photon probability amplitudes – are indicative of a violation of the Bell inequality, and confirm inconsistencies with local hidden variable theory for the correlations of the time-energy entangled photon pairs.
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.
Energy and time entangled photons at a wavelength of 1310 nm are produced by parametric down-conversion in a KNbO3{\mathrm{KNbO}}_{3}KNbO3​ crystal and are sent into all-fiber interferometers using a telecommunications fiber network. The two interferometers of this Franson-type test of the Bell inequality are located 10.9 km apart from one another. Two-photon fringe visibilities of up to 81.6% are obtained. These strong nonlocal correlations support the nonlocal predictions of quantum mechanics and provide evidence that entanglement between photons can be maintained over long distances.
We report a fully fibered source emitting cross time-bin-entangled photons at 1540 nm from type-II spontaneous parametric down-conversion. Compared to standard time-bin-entanglement realizations, the preparation interferometer requires no phase stabilization, simplifying its implementation in quantum key distribution experiments. Bell-type tests of such a cross time-bin state are performed in the Franson configuration and lead to two-photon interference raw visibilities greater than 95%, which are only limited by the dark counts in the detectors and imperfections in the analysis system. Just by trusting the randomness of the beam splitters, the correlations generated by the source can be proved of nonclassical origin even in a passive implementation. The obtained results confirm the suitability of this source for time-bin-based quantum key distribution.
Franson interferometers are increasingly being proposed as a means of securing high-dimensional energy–time entanglement-based quantum key distribution (QKD) systems. Heuristic arguments have been proposed that purport to demonstrate the security of these schemes. We show, however, that such systems are vulnerable to attacks that localize the photons to several temporally separate locations. This demonstrates that a single pair of Franson interferometers is not a practical approach to securing high-dimensional energy–time entanglement-based QKD. This observation leads us to investigate the security of modified Franson-based-protocols, where Alice and Bob have two or more Franson interferometers. We show that such setups can improve the sensitivity against attacks that localize the photons to multiple temporal locations. While our results do not constitute a full security proof, they do show that a single pair of Franson interferometers is not secure and that multiple such interferometers could be a promising candidate for experimentally realizable high-dimensional QKD.