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Zhongguo kexue. Wulixue Lixue Tianwenxue

Experimental preparation and nonlocality of the high-pure four-photon Greenberger-Horne-Zeilinger states

HuaiXin LU, Lianzhen Cao, JiaQiang ZHAO, XiaoQin WANG

Published Aug 1, 2013• 1 citation
Publisher

Abstract

Using the spontaneous parametric down conversion and post-selection method, we experimentally prepare the four-photon Greenberger-Horne-Zeilinger (GHZ) states with a high fidelity about 83.1%. Then, an efficiently method to improve the contrast ratio of the four-photon state is reported by theoretical analysis and experiment optimization. Based on the state, we study the local realism of this state and achieve 28 standard deviations, confirm the existence of genuine four-particle entanglement. Our work has important significance for experimental preparation and studying nonlocality of the high-fidelity multiple-photon entanglement states.

DOI
10.1360/132012-1028

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Using the spontaneous parametric down conversion and post-selection method, we experimentally prepare the four-photon Greenberger-Horne-Zeilinger (GHZ) states with a high fidelity about 83.1%. Then, an efficiently method to improve the contrast ratio of the four-photon state is reported by theoretical analysis and experiment optimization. Based on the state, we study the local realism of this state and achieve 28 standard deviations, confirm the existence of genuine four-particle entanglement. Our work has important significance for experimental preparation and studying nonlocality of the high-fidelity multiple-photon entanglement states.
We report the first experimental violation of local realism by four-photon Greenberger-Horne-Zeilinger (GHZ) entanglement. In the experiment, the nonstatistical GHZ conflicts between quantum mechanics and local realism are confirmed, within the experimental accuracy, by four specific measurements of polarization correlations between four photons. In addition, our experimental results also demonstrate a strong violation of Mermin-Ardehali-Belinskii-Klyshko inequality by 76 standard deviations. Such a violation can only be attributed to genuine four-photon entanglement.
Using spontaneous parametric down conversion and optimizing the scheme of experiment, we prepared the generalized Greenberger-Horne-Zeilinger (GGHZ) states. With over-complement quantum tomography, we achieve the density matrix and calculate the fidelity of the state as 85%±1%. Then, based on the state, we measure the expectation value of Bell-Mermin operator. In the experiment we obtained accordant result with theoretical calculation. It is show that the nonlocality of quantum states is directly related to the degree of tripartite entanglement. And the results also testify our scheme of GGHZ states and measure method of nonlocality.
Using spontaneous parametric down conversion and optimizing the scheme of experiment,we prepared the generalized Greenberger-Horne-Zeilinger(GGHZ) states.With over-complement quantum tomography,we achieve the density matrix and calculate the fidelity of the state as 85%±1%.Then,based on the state,we measure the expectation value of Bell-Mermin operator.In the experiment we obtained accordant result with theoretical calculation.It is show that the nonlocality of quantum states is directly related to the degree of tripartite entanglement.And the results also testify our scheme of GGHZ states and measure method of nonlocality.
High-quality entangled photon pairs generated via spontaneous parametric down-conversion have made great contributions to the modern quantum information science and the fundamental tests of quantum mechanics. However, the quality of the entangled states decreases sharply when moving from biphoton to multiphoton experiments, mainly due to the lack of interactions between photons. Here, for the first time, we generate a four-photon Greenberger-Horne-Zeilinger state with a fidelity of 98%, which is even comparable to the best fidelity of biphoton entangled states. Thus, it enables us to demonstrate an ultrahigh-fidelity entanglement swapping-the key ingredient in various quantum information tasks. Our results push the fidelity of multiphoton entanglement generation to a new level and would be useful in some demanding tasks, e.g., we successfully demonstrate the genuine multipartite nonlocality of the observed state in the nonsignaling scenario by violating a novel Hardy-like inequality, which requires very high state-fidelity.
Nonlocality is the defining feature of quantum entanglement. Entangled states with multiple particles are of crucial importance in fundamental tests of quantum physics as well as in many quantum information tasks. One of the archetypal multipartite quantum states, Greenberger-Horne-Zeilinger (GHZ) state, allows one to observe the striking conflict of quantum physics to local realism in the so-called all-versus-nothing way. This is profoundly different from Bell's theorem for two particles, which relies on statistical predictions. Here, we demonstrate an integrated photonic chip capable of generating and manipulating the four-photon GHZ state. We perform a complete characterization of the four-photon GHZ state using quantum state tomography and obtain a state fidelity of 0.729±0.006. We further use the all-versus-nothing test and the Mermin inequalities to witness the quantum nonlocality of GHZ entanglement. Our work paves the way to perform fundamental tests of quantum physics with complex integrated quantum devices.
Quantum information science has leaped forward with the exploration of high-dimensional quantum systems, offering greater potential than traditional qubits in quantum communication and quantum computing. To advance the field of high-dimensional quantum technology, a significant effort is underway to progressively enhance the entanglement dimension between two particles. An alternative effective strategy involves not only increasing the dimensionality but also expanding the number of particles that are entangled. We present an experimental study demonstrating multi-partite quantum non-locality beyond qubit constraints, thus moving into the realm of strongly entangled high-dimensional multi-particle quantum systems. In the experiment, quantum states were encoded in the path degree of freedom (DoF) and controlled via polarization, enabling efficient operations in a two-dimensional plane to prepare three- and four-particle Greenberger-Horne-Zeilinger (GHZ) states in three-level systems. Our experimental results reveal ways in which high-dimensional systems can surpass qubits in terms of violating local-hidden-variable theories. Our realization of multiple complex and high-quality entanglement technologies is an important primary step for more complex quantum computing and communication protocols. Experimental demonstrations of genuine high-dimensional multipartite quantum nonlocality have been lacking so far. Here, the authors fill this gap using entangled photons, surpassing qubit-based limits and paving the way for device-independent quantum information processing in more complex systems.