Evaluation of polarization entanglement generated by pulsed spontaneous parametric down-conversion with multi-pairs using four single-photon detectors for quantum state tomography
- 作者：Akio Yoshizawa ; yoshizawa-akio@aist.go.jp ; Daiji Fukuda ; Hidemi Tsuchida
- 关键词：Quantum state tomography ; Fidelity ; Entanglement ; Spontaneous parametric down-conversion ; Photon-number-resolving single-photon detector ; Threshold single-photon detector
- 刊名：Optics Communications
- 出版年：2012
- 期刊代码：50_00304018
- 类别：ph
- 出版时间：15 July, 2012
- 卷：285
- 期：16
- 页码：3502-3506
- 文件大小：629 K
摘要
Quantum state tomography (QST) is widely used to evaluate entanglement generated by spontaneous parametric down-conversion. Two-fold coincidence counts for 16 different configurations have been measured using single-photon detectors to estimate the fidelity (i.e., the probability overlap between ideal and real states) from the reconstructed density matrix. However, multi-pair emission events degrade the fidelity. Here, we numerically analyze pulse-pumped polarization-entangled photon pairs for single-photon detectors that can or cannot count the number of incident photons to estimate the fidelity given by QST. Threshold single-photon detectors are desirable for QST from a practical point of view. Our analysis suggests that using four threshold single-photon detectors for two-fold coincidence measurements offers almost the same fidelity as that given by four photon-number-resolving single-photon detectors. The fidelity estimated by QST becomes poor and loss independent when two threshold single-photon detectors are used.