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

arXiv:1904.06179 · New Journal of Physics

Heralded amplification of nonlocality via entanglement swapping

Yoshiaki Tsujimoto, Chenglong You, Kentaro Wakui, Mikio Fujiwara, Kazuhiro Hayasaka, Shigehito Miki, Hirotaka Terai, Masahide Sasaki, Jonathan P. Dowling, Masahiro Takeoka

Published Dec 13, 2019• 16 citations
arXivHTMLPDF

Abstract

Abstract To observe the loophole-free violation of the Clauser–Horne–Shimony–Holt (CHSH) inequality between distant two parties, i.e. the CHSH value S > 2 , the main limitation of distance stems from the loss in the transmission channel. The entanglement swapping relay (ESR) is a simple way to amplify the signal and enables us to evade the impact of the transmission loss. Here, we experimentally test the heralded nonlocality amplifier protocol based on the ESR. We observe that the obtained probability distribution is in excellent agreement with those expected by the numerical simulation with experimental parameters which are precisely characterized in a separate measurement. Moreover, we experimentally estimate the nonlocality of the heralded state after the transmission of 10 dB loss just before final detection. The estimated CHSH value is S = 2.113 > 2 , which indicates that our final state possesses nonlocality even with transmission loss and various experimental imperfections. Our result clarifies an important benchmark of the ESR protocol, and paves the way towards the long-distance realization of the loophole-free CHSH-violation as well as device-independent quantum key distribution.

DOI
10.1088/1367-2630/ab61da

Related papers

An Optimal Strategy to Recover Nonlocality of Polarization-Entangled State from a SPDC Source via Entanglement Swapping Relay

Yoshiaki Tsujimoto, Masahiro Takeoka, Chenglong You +7 more

To realize the practical implementation of device-independent quantum key distribution (DIQKD), the main difficulty is that its security is solely based on the detection loophole-free violation of the Clauser-Horne-Shimony-Holt (CHSH) inequality i.e. the CHSH value S > 2 [1]. To circumvent the inevitable losses in the transmission channels which create the detection loophole, several probabilistic methods to recover the nonlicality have been proposed. Here, we theoretically and experimentally investigate the optimal strategy for the method utilizing linear optical entanglement swapping relay (ESR) with photon pairs from spontaneous parametric-down conversion (SPDC) sources [2,3]. In the previous methods, it is common to employ the ESR node in Bob's system as shown in Fig. 1(a) (Hereafter, we call this configuration the local-heralding (LH).). We employ another configuration: The middle-heralding (MH) shown in Fig. 1(b), where the ESR node is placed in the middle of Alice and Bob similar to the measurement device independent QKD. We numerically compare S of the above two schemes by using the numerical simulation based on the characteristic-function approach [3]. The results are shown in Fig. 1(c). We see that the larger values of S are expected in the MH scheme when the dark count probabilities (ν) of the detectors are considered. In experiment, we perform the Bell-test experiment using the ESR with SPDC sources. We employ the MH scheme, and measure S changing the transmission losses. The experimental parameters (the average photon numbers and measurement angles) are chosen such that S is maximized under the condition of the experimental imperfections (mode-mismatch, dark count and so on) and the assumption of the unit local detection efficiencies (η = 1). While the overall detection efficiencies of our system (η ~ 15 %) are not the range of directly observing the violation of the CHSH inequality, S obtained by the experiment well agree with the numerical simulation with experimental parameters. When the overall transmission loss is set to be 10 dB, which corresponds to the transmittance of a 50 km-optical fiber, we observe Sexp= 1.478, while Sth= 1.487 is expected by the numerical simulation. This result means that our numerical simulation can rigorously model the experiment. This allows us to estimate the nonlocality of the quantum state just before the local detection losses by the numerical simulation. The CHSH value is estimated to be Sexpη=1= 2.104 > 2, which indicates that the quantum state with experimental imperfections possesses the potential to violate the CHSH inequality.

Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)•Jun 1, 2019•0 citations

Less entanglement exhibiting more nonlocality with noisy measurements

Gaoyan Zhu, Daniel Dilley, Kunkun Wang +3 more

Abstract The Clauser–Horne–Shimony–Holt (CHSH) inequality test is widely used as a mean of invalidating the local deterministic theories. Most attempts to experimentally test nonlocality have presumed unphysical idealizations that do not hold in real experiments, namely, noiseless measurements. We demonstrate an experimental violation of the CHSH inequality that is free of idealization and rules out local models with high confidence. We show that the CHSH inequality can always be violated for any nonzero noise parameter of the measurement. Intriguingly, less entanglement exhibits more nonlocality in the CHSH test with noisy measurements. Furthermore, we theoretically propose and experimentally demonstrate how the CHSH test with noisy measurements can be used to detect weak entanglement on two-qubit states. Our results offer a deeper insight into the relation between entanglement and nonlocality.

npj Quantum Information•Dec 6, 2021•4 citations

A complete characterization of the heralded noiseless amplification of photons

Natalia Bruno, Valerio Pini, Anthony Martin +1 more

Heralded noiseless amplification of photons has recently been shown to provide a means to overcome losses in complex quantum communication tasks. In particular, to overcome transmission losses that could allow for the violation of a Bell inequality free from the detection loophole, for device independent quantum key distribution (DI-QKD). Several implementations of a heralded photon amplifier have been proposed and the first proof of principle experiments realized. Here we present the first full characterization of such a device to test its functional limits and potential for DI-QKD. This device is tested at telecom wavelengths and is shown to be capable of overcoming losses corresponding to a transmission through 20 km of single mode telecom fibre. We demonstrate heralded photon amplifier with a gain >100 and a heralding probability >83%, required by DI-QKD protocols that use the Clauser–Horne–Shimony–Holt inequality. The heralded photon amplifier clearly represents a key technology for the realization of DI-QKD in the real world and over typical network distances.

arXiv:1306.3425•New Journal of Physics•Sep 2, 2013•18 citations

Bell nonlocality and fully entangled fraction measured in an entanglement-swapping device without quantum state tomography

Karol Bartkiewicz, Karel Lemr, Antonín Černoch +1 more

We propose and experimentally implement an efficient procedure based on entanglement swapping to determine the Bell nonlocality measure of Horodecki et al. [Phys. Lett. A 200, 340 (1995)] and the fully entangled fraction of Bennett et al. [Phys. Rev. A 54, 3824 (1996)] of an arbitrary two-qubit polarization-encoded state. The nonlocality measure corresponds to the amount of the violation of the Clauser-Horne-Shimony-Holt (CHSH) optimized over all measurement settings. By using simultaneously two copies of a given state, we measure directly only six parameters. This is an experimental determination of these quantities without quantum state tomography or continuous monitoring of all measurement bases in the usual CHSH inequality tests. We analyze how well the measured degrees of Bell nonlocality and other entanglement witnesses (including the fully entangled fraction and a nonlinear entropic witness) of an arbitrary two-qubit state can estimate its entanglement. In particular, we measure these witnesses and estimate the negativity of various two-qubit Werner states. Our approach could especially be useful for quantum communication protocols based on entanglement swapping.

arXiv:1609.09653•Physical Review A•Mar 13, 2017•39 citations

Heralded amplification of path entangled quantum states

F Monteiro, E. Verbanis, Valentina Caprara Vivoli +4 more

Abstract Device-independent quantum key distribution (DI-QKD) represents one of the most fascinating challenges in quantum communication, exploiting concepts of fundamental physics, namely Bell tests of nonlocality, to ensure the security of a communication link. This requires the loophole-free violation of a Bell inequality, which is intrinsically difficult due to losses in fibre optic transmission channels. Heralded photon amplification (HPA) is a teleportation-based protocol that has been proposed as a means to overcome transmission loss for DI-QKD. Here we demonstrate HPA for path entangled states and characterise the entanglement before and after loss by exploiting a recently developed displacement-based detection scheme. We demonstrate that by exploiting HPA we are able to reliably maintain high fidelity entangled states over loss-equivalent distances of more than 50 km.

arXiv:1612.01802•Quantum Science and Technology•May 31, 2017•29 citations

Interplay of quantum resources in nonlocality tests

Hai-Hao Dong, Yuwei Zhu, Su-Yi Cheng +8 more

Nonlocality, evidenced by the violation of Bell inequalities, not only signifies entanglement but also highlights measurement incompatibility in quantum systems. Utilizing the tilted Clauser-Horne-Shimony-Holt (CHSH) Bell inequality, our high-efficiency optical setup achieves a loophole-free violation of 2.0132 . This result provides a device-independent lower bound on entanglement, quantified as the entanglement of formation at 0.0159 . Moreover, by tuning the parameters of the tilted CHSH inequality, we enhance the estimation of measurement incompatibility, which is quantified by an effective overlap of 4.3883 × 10 − 5 . To explore the intricate interplay among nonlocality, entanglement, and measurement incompatibility, we generate mixed states, allowing for flexible modulation of entanglement via fast switching among the four Bell states using Pockels cells, achieving a fidelity above 99.10 % . Intriguingly, our results reveal a counterintuitive relationship where increasing incompatibility initially boosts nonlocality but eventually leads to its reduction. Typically, maximal nonlocality does not coincide with maximal incompatibility. This experimental study sheds light on the optimal management of quantum resources for Bell-inequality-based quantum information processing.

arXiv:2408.10489•Physical Review Research•Jun 5, 2025•1 citation
Abstract To observe the loophole-free violation of the Clauser–Horne–Shimony–Holt (CHSH) inequality between distant two parties, i.e. the CHSH value S > 2 , the main limitation of distance stems from the loss in the transmission channel. The entanglement swapping relay (ESR) is a simple way to amplify the signal and enables us to evade the impact of the transmission loss. Here, we experimentally test the heralded nonlocality amplifier protocol based on the ESR. We observe that the obtained probability distribution is in excellent agreement with those expected by the numerical simulation with experimental parameters which are precisely characterized in a separate measurement. Moreover, we experimentally estimate the nonlocality of the heralded state after the transmission of 10 dB loss just before final detection. The estimated CHSH value is S = 2.113 > 2 , which indicates that our final state possesses nonlocality even with transmission loss and various experimental imperfections. Our result clarifies an important benchmark of the ESR protocol, and paves the way towards the long-distance realization of the loophole-free CHSH-violation as well as device-independent quantum key distribution.
To realize the practical implementation of device-independent quantum key distribution (DIQKD), the main difficulty is that its security is solely based on the detection loophole-free violation of the Clauser-Horne-Shimony-Holt (CHSH) inequality i.e. the CHSH value S > 2 [1]. To circumvent the inevitable losses in the transmission channels which create the detection loophole, several probabilistic methods to recover the nonlicality have been proposed. Here, we theoretically and experimentally investigate the optimal strategy for the method utilizing linear optical entanglement swapping relay (ESR) with photon pairs from spontaneous parametric-down conversion (SPDC) sources [2,3]. In the previous methods, it is common to employ the ESR node in Bob's system as shown in Fig. 1(a) (Hereafter, we call this configuration the local-heralding (LH).). We employ another configuration: The middle-heralding (MH) shown in Fig. 1(b), where the ESR node is placed in the middle of Alice and Bob similar to the measurement device independent QKD. We numerically compare S of the above two schemes by using the numerical simulation based on the characteristic-function approach [3]. The results are shown in Fig. 1(c). We see that the larger values of S are expected in the MH scheme when the dark count probabilities (ν) of the detectors are considered. In experiment, we perform the Bell-test experiment using the ESR with SPDC sources. We employ the MH scheme, and measure S changing the transmission losses. The experimental parameters (the average photon numbers and measurement angles) are chosen such that S is maximized under the condition of the experimental imperfections (mode-mismatch, dark count and so on) and the assumption of the unit local detection efficiencies (η = 1). While the overall detection efficiencies of our system (η ~ 15 %) are not the range of directly observing the violation of the CHSH inequality, S obtained by the experiment well agree with the numerical simulation with experimental parameters. When the overall transmission loss is set to be 10 dB, which corresponds to the transmittance of a 50 km-optical fiber, we observe Sexp= 1.478, while Sth= 1.487 is expected by the numerical simulation. This result means that our numerical simulation can rigorously model the experiment. This allows us to estimate the nonlocality of the quantum state just before the local detection losses by the numerical simulation. The CHSH value is estimated to be Sexpη=1= 2.104 > 2, which indicates that the quantum state with experimental imperfections possesses the potential to violate the CHSH inequality.
Abstract The Clauser–Horne–Shimony–Holt (CHSH) inequality test is widely used as a mean of invalidating the local deterministic theories. Most attempts to experimentally test nonlocality have presumed unphysical idealizations that do not hold in real experiments, namely, noiseless measurements. We demonstrate an experimental violation of the CHSH inequality that is free of idealization and rules out local models with high confidence. We show that the CHSH inequality can always be violated for any nonzero noise parameter of the measurement. Intriguingly, less entanglement exhibits more nonlocality in the CHSH test with noisy measurements. Furthermore, we theoretically propose and experimentally demonstrate how the CHSH test with noisy measurements can be used to detect weak entanglement on two-qubit states. Our results offer a deeper insight into the relation between entanglement and nonlocality.
Heralded noiseless amplification of photons has recently been shown to provide a means to overcome losses in complex quantum communication tasks. In particular, to overcome transmission losses that could allow for the violation of a Bell inequality free from the detection loophole, for device independent quantum key distribution (DI-QKD). Several implementations of a heralded photon amplifier have been proposed and the first proof of principle experiments realized. Here we present the first full characterization of such a device to test its functional limits and potential for DI-QKD. This device is tested at telecom wavelengths and is shown to be capable of overcoming losses corresponding to a transmission through 20 km of single mode telecom fibre. We demonstrate heralded photon amplifier with a gain >100 and a heralding probability >83%, required by DI-QKD protocols that use the Clauser–Horne–Shimony–Holt inequality. The heralded photon amplifier clearly represents a key technology for the realization of DI-QKD in the real world and over typical network distances.
We propose and experimentally implement an efficient procedure based on entanglement swapping to determine the Bell nonlocality measure of Horodecki et al. [Phys. Lett. A 200, 340 (1995)] and the fully entangled fraction of Bennett et al. [Phys. Rev. A 54, 3824 (1996)] of an arbitrary two-qubit polarization-encoded state. The nonlocality measure corresponds to the amount of the violation of the Clauser-Horne-Shimony-Holt (CHSH) optimized over all measurement settings. By using simultaneously two copies of a given state, we measure directly only six parameters. This is an experimental determination of these quantities without quantum state tomography or continuous monitoring of all measurement bases in the usual CHSH inequality tests. We analyze how well the measured degrees of Bell nonlocality and other entanglement witnesses (including the fully entangled fraction and a nonlinear entropic witness) of an arbitrary two-qubit state can estimate its entanglement. In particular, we measure these witnesses and estimate the negativity of various two-qubit Werner states. Our approach could especially be useful for quantum communication protocols based on entanglement swapping.
Abstract Device-independent quantum key distribution (DI-QKD) represents one of the most fascinating challenges in quantum communication, exploiting concepts of fundamental physics, namely Bell tests of nonlocality, to ensure the security of a communication link. This requires the loophole-free violation of a Bell inequality, which is intrinsically difficult due to losses in fibre optic transmission channels. Heralded photon amplification (HPA) is a teleportation-based protocol that has been proposed as a means to overcome transmission loss for DI-QKD. Here we demonstrate HPA for path entangled states and characterise the entanglement before and after loss by exploiting a recently developed displacement-based detection scheme. We demonstrate that by exploiting HPA we are able to reliably maintain high fidelity entangled states over loss-equivalent distances of more than 50 km.
Nonlocality, evidenced by the violation of Bell inequalities, not only signifies entanglement but also highlights measurement incompatibility in quantum systems. Utilizing the tilted Clauser-Horne-Shimony-Holt (CHSH) Bell inequality, our high-efficiency optical setup achieves a loophole-free violation of 2.0132 . This result provides a device-independent lower bound on entanglement, quantified as the entanglement of formation at 0.0159 . Moreover, by tuning the parameters of the tilted CHSH inequality, we enhance the estimation of measurement incompatibility, which is quantified by an effective overlap of 4.3883 × 10 − 5 . To explore the intricate interplay among nonlocality, entanglement, and measurement incompatibility, we generate mixed states, allowing for flexible modulation of entanglement via fast switching among the four Bell states using Pockels cells, achieving a fidelity above 99.10 % . Intriguingly, our results reveal a counterintuitive relationship where increasing incompatibility initially boosts nonlocality but eventually leads to its reduction. Typically, maximal nonlocality does not coincide with maximal incompatibility. This experimental study sheds light on the optimal management of quantum resources for Bell-inequality-based quantum information processing.