- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Universal Multipartite D-Level Entanglement Witnesses for Realistic Measurement Settings
摘要： Entanglement is an essential resource in quantum information science [1] and its presence in any quantum system can be experimentally detected through entanglement witness operators [2]. In particular, measuring a negative expectation value of a witness with high statistical confidence provides a necessary and sufficient condition to confirm the generation of a genuine multipartite [3] and/or d-level entangled state [4]. In recent years, the experimental generation of complex quantum states has intensified the need for witnesses that are capable of detecting such systems and are experimentally optimal at the same time. This means that the witness should require the least measurement effort (in terms of number and complexity of the measurement settings), include only projections on single qudits, while at the same time possessing a high noise tolerance (Fig. 1a). However, “experimentally-friendly” witnesses capable of accomplishing these tasks have not been derived yet. Here, we provide a universal method to construct experimentally-optimal witnesses capable of detecting entanglement in any arbitrarily-complex quantum state that can be customized towards experimental restrictions and/or accessible measurement settings [5]. As an example, using our technique and exploiting the stabilizer formalism [6,7], we derive an entanglement witness for N-partite d-level cluster states that consists of only two measurement settings. We apply our method to experimentally measure the expectation value of a witness for a four-partite three-level optical cluster states [8]. Through projection measurements in an optical time/frequency photon system [9-10], we measured a witness expectation value -0.28±0.04<0 (Fig.1b), thus confirming the realization of genuine four-partite cluster state entanglement. Finally, we used the derived witness to investigate the white noise tolerance of multipartite d-level cluster states and demonstrate that this increases with the number of level. Our approach is completely universal and can be applied to any complex quantum state.
关键词： entanglement witnesses,multipartite d-level entanglement,entanglement,measurement settings,quantum information
更新于2025-09-12 10:27:22
-
Witnessing bipartite entanglement sequentially by multiple observers
摘要： We investigate sharing of bipartite entanglement in a scenario where half of an entangled pair is possessed and projectively measured by one observer, called Alice, while the other half is subjected to measurements performed sequentially, independently, and unsharply, by multiple observers, called Bobs. We ?nd that there is a limit on the number of observers in this entanglement distribution scenario. In particular, for a two-qubit maximally entangled initial shared state, no more than 12 Bobs can detect entanglement with a single Alice for arbitrary, possibly unequal, sharpness parameters of the measurements by the Bobs. The number of Bobs remains unaltered for a ?nite range of near-maximal pure initial entanglement, a feature that also occurs in the case of equal sharpness parameters at the Bobs. Furthermore, we show that for nonmaximally entangled shared pure states, the number of Bobs decreases with the amount of initial entanglement, providing a coarse-grained but operational measure of entanglement.
关键词： sequential measurements,entanglement,unsharp measurements,entanglement witnesses,quantum correlation
更新于2025-09-09 09:28:46
-
Practical measurement-device-independent entanglement quantification
摘要： The robust estimation of entanglement is key to the validation of implementations of quantum systems. On the one hand, the evaluation of standard entanglement measures, either using quantum tomography or using quantitative entanglement witnesses, requires perfect implementation of measurements. On the other hand, measurement-device-independent entanglement witnesses (MDIEWs) can certify entanglement of all entangled states using untrusted measurement devices. We show that MDIEWs can be used as well to quantify entanglement according to standard entanglement measures, and we present a practical method to derive such witnesses using experimental data only.
关键词： quantum systems,quantum tomography,measurement-device-independent,entanglement witnesses,entanglement quantification
更新于2025-09-09 09:28:46