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Quantum 2.0 Conference and Exhibition

Generation of four-photon GHZ states on a laser written integrated platform

Giacomo Corrielli, Mathias Pont, Andreas Fyrillas, Iris Agresti, Gonzalo Carvacho, Nicolas Maring, Pierre-Emmanuel Emeriau, Francesco Ceccarelli, Riccardo Albiero, Paulo Henrique Dias Ferreira, Niccolò Somaschi, Jean Sénellart, Martina Morassi, Aristide Lemaître, Isabelle Sagnes, P. Senellart, Fabio Sciarrino, Marco Liscidini, Nadia Belabas, Roberto Osellame

Published Jan 1, 2023• 1 citation
Publisher

Abstract

We present a laser-written glass photonic circuit that, in synergy with a quantum dot based single photon source, generates a four-photon Greenberger-Horne-Zeilinger entangled state at the rate of 0.5 Hz with 86.0 ± 0.4% fidelity.
DOI
10.1364/quantum.2023.qm4a.7

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•Apr 11, 2017•0 citations
We present an experiment where a reconfigurable photonic processor fabricated in glass by femtosecond laser micromachining is used for the generation of four-photons GHZ entangled states, with high efficiency and fidelity. The chip is used in synergy with a bright and quasi-deterministic source of single photons based on semiconductor quantum dot. The very efficient interfacing of these two platforms is ensured by the excellent connectivity between glass photonic circuits and standard optical fibers. In addition, in order to benchmark the quality of the generated states, this processor is used to implement a quantum secret sharing protocol on chip.
Mutually entangled multi-photon states are at the heart of all-optical quantum technologies. While impressive progresses have been reported in the generation of such quantum light states using free space apparatus, high-fidelity high-rate on-chip entanglement generation is crucial for future scalability. In this work, we use a bright quantum-dot based single-photon source to demonstrate the high fidelity generation of 4-photon Greenberg-Horne-Zeilinger (GHZ) states with a low-loss reconfigurable glass photonic circuit. We reconstruct the density matrix of the generated states using full quantum-state tomography reaching an experimental fidelity to the target ∣GHZ4⟩|{\text{GHZ}_4}\rangle∣GHZ4​⟩ of FGHZ4(86.0±0.4) %\mathcal{F}_{\text{GHZ}_4} (86.0\pm0.4)\,\%FGHZ4​​(86.0±0.4)%, and a purity of PGHZ4=(76.3±0.6) %\mathcal{P}_{\text{GHZ}_4}=(76.3\pm0.6)\,\%PGHZ4​​=(76.3±0.6)%. The entanglement of the generated states is certified with a semi device-independent approach through the violation of a Bell-like inequality by more than 39 standard deviations. Finally, we carry out a four-partite quantum secret sharing protocol on-chip where a regulator shares with three interlocutors a sifted key with up to 1978 bits, achieving a qubit-error rate of 10.87 %10.87\,\%10.87%. These results establish that the quantum-dot technology combined with glass photonic circuitry for entanglement generation on chip offers a viable path for intermediate scale quantum computation and communication.
Abstract Mutually entangled multi-photon states are at the heart of all-optical quantum technologies. While impressive progresses have been reported in the generation of such quantum light states using free space apparatus, high-fidelity high-rate on-chip entanglement generation is crucial for future scalability. In this work, we use a bright quantum-dot based single-photon source to demonstrate the high fidelity generation of 4-photon Greenberg-Horne-Zeilinger (GHZ) states with a low-loss reconfigurable glass photonic circuit. We reconstruct the density matrix of the generated states using full quantum-state tomography reaching an experimental fidelity to the target state of FGHZ4=(86.0±0.4) %{{{{\mathcal{F}}}}}_{{{{{\rm{GHZ}}}}}_{4}}=(86.0\pm 0.4)\, \%FGHZ4​​=(86.0±0.4)% F GHZ 4 = ( 86.0 ± 0.4 ) % , and a purity of PGHZ4=(76.3±0.6) %{{{{\mathcal{P}}}}}_{{{{{\rm{GHZ}}}}}_{4}}=(76.3\pm 0.6)\, \%PGHZ4​​=(76.3±0.6)% P GHZ 4 = ( 76.3 ± 0.6 ) % . The entanglement of the generated states is certified with a semi device-independent approach through the violation of a Bell-like inequality by more than 39 standard deviations. Finally, we carry out a four-partite quantum secret sharing protocol on-chip where a regulator shares with three interlocutors a sifted key with up to 1978 bits, achieving a qubit-error rate of 10.87%. These results establish that the quantum-dot technology combined with glass photonic circuitry offers a viable path for entanglement generation and distribution.
The ability to generate states of light with specific quantum correlations is very important in quantum communication and computation. While this ability has been realized in bulk optics, most approaches implemented so far are not suitable for the integrated photonic circuits that are expected to revolutionize quantum photonics in the near future. This work shows that, by using the path-encoding representation, one can generate entangled Greenberger-Horne-Zeilinger states in an integrated device. This approach is scalable and compatible with several platforms, from laser-written devices to silicon photonics.
Multipartite entangled states are an essential building block for advanced quantum networking applications. Realizing such tasks in practice puts stringent requirements on the characteristics of the states in terms of fidelity and generation rate, along with a desired compatibility with telecommunication network deployment. Here, we demonstrate a photonic platform design capable of producing high-fidelity Greenberger-Horne-Zeilinger (GHZ) states, at telecom wavelength and in a compact and scalable configuration. Our source relies on spontaneous parametric down-conversion in a layered Sagnac interferometer, which only requires a single nonlinear crystal. This enables the generation of highly indistinguishable photon pairs, followed by entanglement fusion to create four-qubit polarization-entangled GHZ states with fidelity up to (94.73±0.21)% with respect to the ideal state, at a rate of 1.7 Hz. We provide a complete characterization of our source and highlight its suitability for practical quantum network applications.
We study the generation of Greenberger-Horne-Zeilinger (GHZ) states of three path-encoded photons. Inspired by the seminal work of Bouwmeester et al. [1] on polarization-entangled GHZ states, we find a corresponding path representation for the photon states of an optical circuit, identify the elements required for the state generation, and propose a possible implementation of our strategy. Besides the practical advantage of employing an integrated system that can be fabricated with proven lithographic techniques, our example suggests that it is possible to enhance the generation efficiency by using microring resonators.