Quantum entanglement and quantum nonlocality of N-photon entangled states ｜ψNm） m Cm [cos γ｜N - m） 1 ｜m）2 ＋ e^iθm sinγ｜m）1｜N- m）2] and their superpositions are studied. We point out that the relative ph...Quantum entanglement and quantum nonlocality of N-photon entangled states ｜ψNm） m Cm [cos γ｜N - m） 1 ｜m）2 ＋ e^iθm sinγ｜m）1｜N- m）2] and their superpositions are studied. We point out that the relative phase θm affects the quantum nonlocality but not the quantum entanglement for the state ｜ψNm）. We show that quantum nonlocality can be controlled and manipulated by adjusting the state parameters of ｜ψNm）, superposition coefficients, and the azimuthal angles of the Bell operator. We also show that the violation of the Bell inequality can reach its maximal value under certain conditions. It is found that quantum superpositions based on ｜ψNm） can increase the amount of entanglement, and give more ways to reach the maximal violation of the Bell inequality.展开更多
We investigate the violation factor of the original Bell-Mermin inequality. Until now, we have used an assumption that the results of measurement are . In this case, the maximum violation factor is as follows: and . T...We investigate the violation factor of the original Bell-Mermin inequality. Until now, we have used an assumption that the results of measurement are . In this case, the maximum violation factor is as follows: and . The quantum predictions by n-partite Greenberger-Horne-Zeilinger state violate the Bell-Mermin inequality by an amount that grows exponentially with n. Recently, a new measurement theory is proposed [K. Nagata and T. Nakamura, International Journal of Theoretical Physics, 49, 162 (2010)]. The values of measurement outcome are . Here we use the new measurement theory. We consider a multipartite GHZ state. We use the original Bell-Mermin inequality. It turns out that the original Bell-Mermin inequality is satisfied irrespective of the number of particles. In this case, the maximum violation factor is as follows: and . Thus the original Bell-Mermin inequality is satisfied by the new measurement theory. We propose the following conjecture: All the two-orthogonal-settings experimental correlation functions admit local realistic theories irrespective of a state if we use the new measurement theory.展开更多
Richard Feynman once said, “I think it is safe to say that no one understands Quantum Mechanics”. The well-known article on the Einstein-Podolsky-Rosen (EPR) paradox brought forth further doubts on the interpretatio...Richard Feynman once said, “I think it is safe to say that no one understands Quantum Mechanics”. The well-known article on the Einstein-Podolsky-Rosen (EPR) paradox brought forth further doubts on the interpretation of quantum theory. Einstein’s doubt on quantum theory is a doubleedged sword: experimental verification of quantum theory would contradict the hypothesis that speed of light is finite. It has been almost a century since the creation of quantum theory and special relativity, and the relevant doubts brought forward remain unresolved. We posit that the existence of discontinuity points and quantum wormholes would imply superluminal phenomenon or infinite speed of light, which provides for an important supplement to the invariance principle of the speed of light and superluminal phenomena. This can potentially resolve the inconsistency between special relativity and quantum theory.展开更多
We directly introduce a Bell-type inequality for four-qubit systems. Using the inequality we investigate quantum nonlocality of a generic family of states ｜Gabcd〉[Phys. Rev. A 65 052112（2002）] and several canonica...We directly introduce a Bell-type inequality for four-qubit systems. Using the inequality we investigate quantum nonlocality of a generic family of states ｜Gabcd〉[Phys. Rev. A 65 052112（2002）] and several canonical four-qubit entangled states. It has been demonstrated that the inequality is maximally violated by the so called ＂four-qubit the maximally entangled state ｜Gm〉＂ and it is also violated by four-qubit W state and a special family of states ｜Gab00〉. Moreover, a useful entanglement-nonlocality relationship for the family of states ｜Gab00〉is derived. Finally, we present a scheme of preparation of the state ｜Gm〉with linear optics and cross-Kerr nonlinearities.展开更多
Entanglement, the Einstein-Podolsky Rosen （EPR） paradox and Bell＇s failure of local-hidden- variable （LHV） theories are three historically famous forms of ＂quantum nonlocality＂. We give experimental criteria fo...Entanglement, the Einstein-Podolsky Rosen （EPR） paradox and Bell＇s failure of local-hidden- variable （LHV） theories are three historically famous forms of ＂quantum nonlocality＂. We give experimental criteria for these three forms of nonlocality in multi-particle systems, with the aim of better understanding the transition from microscopic to macroscopic nonlocality. We examine the nonlocality of N separated spin J systems. First, we obtain multipartite Bell inequalities that address the correlation between spin values measured at each site, and then we review spin squeezing inequal- ities that address the degree of reduction in the variance of collective spins. The latter have been particularly useful as a tool for investigating entanglement in Bose Einstein eondensates （BEC）. We present solutions for two topical quantum states： multi-qubit Greenberger-Horne Zeilinger （GHZ） states, and the ground state of a two-well BEC.展开更多
Effects of photon addition on the quantum nonlocality of squeezed entangled coherent states for Bell-inequality tests are studied theoretically. By utilizing the method of photon-parity measurement, it is found that p...Effects of photon addition on the quantum nonlocality of squeezed entangled coherent states for Bell-inequality tests are studied theoretically. By utilizing the method of photon-parity measurement, it is found that photon addition can always increase the degrees of Bell violations within a certain parameter range. A possible scheme for generating photon-added squeezed entangled coherent states is proposed.展开更多
We propose a scheme of entangling two photons from two separated sources.Our proposal which is inspired by the time-bin entanglement developed recently,provides a novel alternative for revealing contradiction between ...We propose a scheme of entangling two photons from two separated sources.Our proposal which is inspired by the time-bin entanglement developed recently,provides a novel alternative for revealing contradiction between quantum nonlocality and local realism based on two independent single photon sources.展开更多
文摘Quantum entanglement and quantum nonlocality of N-photon entangled states ｜ψNm） m Cm [cos γ｜N - m） 1 ｜m）2 ＋ e^iθm sinγ｜m）1｜N- m）2] and their superpositions are studied. We point out that the relative phase θm affects the quantum nonlocality but not the quantum entanglement for the state ｜ψNm）. We show that quantum nonlocality can be controlled and manipulated by adjusting the state parameters of ｜ψNm）, superposition coefficients, and the azimuthal angles of the Bell operator. We also show that the violation of the Bell inequality can reach its maximal value under certain conditions. It is found that quantum superpositions based on ｜ψNm） can increase the amount of entanglement, and give more ways to reach the maximal violation of the Bell inequality.
文摘We investigate the violation factor of the original Bell-Mermin inequality. Until now, we have used an assumption that the results of measurement are . In this case, the maximum violation factor is as follows: and . The quantum predictions by n-partite Greenberger-Horne-Zeilinger state violate the Bell-Mermin inequality by an amount that grows exponentially with n. Recently, a new measurement theory is proposed [K. Nagata and T. Nakamura, International Journal of Theoretical Physics, 49, 162 (2010)]. The values of measurement outcome are . Here we use the new measurement theory. We consider a multipartite GHZ state. We use the original Bell-Mermin inequality. It turns out that the original Bell-Mermin inequality is satisfied irrespective of the number of particles. In this case, the maximum violation factor is as follows: and . Thus the original Bell-Mermin inequality is satisfied by the new measurement theory. We propose the following conjecture: All the two-orthogonal-settings experimental correlation functions admit local realistic theories irrespective of a state if we use the new measurement theory.
文摘Richard Feynman once said, “I think it is safe to say that no one understands Quantum Mechanics”. The well-known article on the Einstein-Podolsky-Rosen (EPR) paradox brought forth further doubts on the interpretation of quantum theory. Einstein’s doubt on quantum theory is a doubleedged sword: experimental verification of quantum theory would contradict the hypothesis that speed of light is finite. It has been almost a century since the creation of quantum theory and special relativity, and the relevant doubts brought forward remain unresolved. We posit that the existence of discontinuity points and quantum wormholes would imply superluminal phenomenon or infinite speed of light, which provides for an important supplement to the invariance principle of the speed of light and superluminal phenomena. This can potentially resolve the inconsistency between special relativity and quantum theory.
基金supported by the National Natural Science Foundation of China(Grant Nos.11475054 and 11371005)Hebei Natural Science Foundation of China(Grant Nos.A2012205013 and A2014205060)+1 种基金the Fundamental Research Funds for the Central Universities of Ministry of Education of China(Grant Nos.3142014068 and 3142014125)Langfang Key Technology Research and Development Program of China(Grant No.2014011002)
文摘We directly introduce a Bell-type inequality for four-qubit systems. Using the inequality we investigate quantum nonlocality of a generic family of states ｜Gabcd〉[Phys. Rev. A 65 052112（2002）] and several canonical four-qubit entangled states. It has been demonstrated that the inequality is maximally violated by the so called ＂four-qubit the maximally entangled state ｜Gm〉＂ and it is also violated by four-qubit W state and a special family of states ｜Gab00〉. Moreover, a useful entanglement-nonlocality relationship for the family of states ｜Gab00〉is derived. Finally, we present a scheme of preparation of the state ｜Gm〉with linear optics and cross-Kerr nonlinearities.
文摘Entanglement, the Einstein-Podolsky Rosen （EPR） paradox and Bell＇s failure of local-hidden- variable （LHV） theories are three historically famous forms of ＂quantum nonlocality＂. We give experimental criteria for these three forms of nonlocality in multi-particle systems, with the aim of better understanding the transition from microscopic to macroscopic nonlocality. We examine the nonlocality of N separated spin J systems. First, we obtain multipartite Bell inequalities that address the correlation between spin values measured at each site, and then we review spin squeezing inequal- ities that address the degree of reduction in the variance of collective spins. The latter have been particularly useful as a tool for investigating entanglement in Bose Einstein eondensates （BEC）. We present solutions for two topical quantum states： multi-qubit Greenberger-Horne Zeilinger （GHZ） states, and the ground state of a two-well BEC.
基金Project supported by the National Natural Science Foundation of China (Grant No. 11074087)the Natural Science Foundation of Hubei Province, China (Grant No. 2010CDA075)the Natural Science Foundation of Wuhan City, China (GrantNo. 201150530149)
文摘Effects of photon addition on the quantum nonlocality of squeezed entangled coherent states for Bell-inequality tests are studied theoretically. By utilizing the method of photon-parity measurement, it is found that photon addition can always increase the degrees of Bell violations within a certain parameter range. A possible scheme for generating photon-added squeezed entangled coherent states is proposed.
文摘We propose a scheme of entangling two photons from two separated sources.Our proposal which is inspired by the time-bin entanglement developed recently,provides a novel alternative for revealing contradiction between quantum nonlocality and local realism based on two independent single photon sources.
