Experimental bilocality violation without shared reference frames

Abstract

Non-classical correlations arising in complex quantum networks are attracting growing interest, both from a fundamental perspective and for potential applications in information processing. In particular, in an entanglement swapping scenario a new kind of correlations arise, the so-called nonbilocal correlations that are incompatible with local realism augmented with the assumption that the sources of states used in the experiment are independent. In practice, however, bilocality tests impose strict constraints on the experimental setup and in particular to presence of shared reference frames between the parties. Here, we experimentally address this point showing that false positive nonbilocal quantum correlations can be observed even though the sources of states are independent. To overcome this problem, we propose and demonstrate a new scheme for the violation of bilocality that does not require shared reference frames and thus constitute an important building block for future investigations of quantum correlations in complex networks.

Experimental demonstration of non-bilocality with truly independent sources and strict locality constraints

“…One might argue that a correlation was established between the two cw lasers prior to the occurrence of the two SFWM processes [2,4]. Previous experimental tests against bilocal hidden variable models in a quantum network failed both the space-like separation and independent source requirements [3][4][5]. Here we present in this Letter an experimental study to reject bilocal hidden variable models with both locality and independent source loopholes closed.…”

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Entanglement swapping entangles two particles that have never interacted [1], which implicitly assumes that each particle carries an independent local hidden variable, i.e., the presence of bilocality [2]. Previous experimental studies of bilocal hidden variable models did not fulfil the central requirement that the assumed two local hidden variable models must be mutually independent [3][4][5]. By harnessing the laser phase randomization [6] rising from the spontaneous emission to the stimulated emission to ensure the independence between entangled photon-pairs created at separate sources and separating relevant events spacelike to satisfy the nosignaling condition, for the first time, we simultaneously close the loopholes of independent source, locality and measurement independence in an entanglement swapping experiment in a network.

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Maximal qubit violation of n-locality inequalities in a star-shaped quantum network

“…This implies that recent experiments violating the bilocality inequality [27,28] have to rely on assumptions about the measurement device and being thus device-dependent in clear opposition to the general aim of Bellʼs theorem. Finally, as pointed out in [31], when shared reference frames are added in the scenario, some particular situations may require that no internal communication is ensured between B A and B C , i.e. the presence of the local measurements scenario.…”

Self-error-rejecting quantum state transmission of entangled photons for faithful quantum communication without calibrated reference frames

“…Moreover, even for a noiseless channel with ideal photon transmission, the misalignment of reference frames between the communicating parties will directly affect their measure- * The first two authors contributed equally to this work. † Corresponding author: fgdeng@bnu.edu.cn ments relative to each other [28][29][30], thus it decreases the entanglement available for post-processing quantum information tasks [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. For instance, in the polarization encoding, the horizontal and vertical polarization states constitute a basis for encoding a qubit [23,24], which can be denoted as |0 → |H and |1 → |V .…”