Entanglement is the key resource in quantum information processing,and an entanglement witness(EW)is designed to detect whether a quantum system has any entanglement.However,prior knowledge of the target states should...Entanglement is the key resource in quantum information processing,and an entanglement witness(EW)is designed to detect whether a quantum system has any entanglement.However,prior knowledge of the target states should be known first to design a suitable EW,which weakens this method.Nevertheless,a recent theory shows that it is possible to design a universal entanglement witness(UEW)to detect negative-partial-transpose(NPT)entanglement in unknown bipartite states with measurement-device-independent(MDI)characteristic.The outcome of a UEW can also be upgraded to be an entanglement measure.In this study,we experimentally design and realize an MDI UEW for two-qubit entangled states.All of the tested states are well-detected without any prior knowledge.We also show that it is able to quantify entanglement by comparing it with concurrence estimated through state tomography.The relation between them is also revealed.The entire experimental framework ensures that the UEW is MDI.展开更多
Bohr’s principle of complementarity has a long history and it is an important topic in quantum theory,among which the famous example is the duality relation.The relation between visibilityC and distinguishability D,C...Bohr’s principle of complementarity has a long history and it is an important topic in quantum theory,among which the famous example is the duality relation.The relation between visibilityC and distinguishability D,C2+D2≤1,has long been recognized as the only representative of the duality relation.However,recent researches have shown that this inequality is not good enough because it is not tight for multipath interferometers.Meanwhile,a tight bound for the multipath interferometer has been put forward.Here we design and experimentally implement a three-path interferometer coupling with path indicator states.The wave property of photons is characterized by l1-norm coherence measure,and the particle property is based on distinguishability of the indicator states.The new duality relation of the three-path interferometer is demonstrated in our experiment,which bounds the union of a right triangle and a part of elliptical area inside the quadrant of a unit circle.Data analysis confirms that the new bound is tight for photons in three-path interferometers.展开更多
The peaks of exciton and biexciton from the single quantum dot(QD)micro-photoluminescence spectra are identified by observing the intensity of those peaks in relation to increasing excitation power.In order to further...The peaks of exciton and biexciton from the single quantum dot(QD)micro-photoluminescence spectra are identified by observing the intensity of those peaks in relation to increasing excitation power.In order to further verify the properties of the exciton and biexciton,we perform auto-and cross correlation measurements.Using the former,we confirm the antibunching property of the signal light emitted from the single QD.Using cross correlation measurement,we verify that the exciton and biexciton emissions originate from the same QD and they are strongly correlated with each other.Lastly,we analyze the behavior of the cross correlation function in both the cases of saturated and unsaturated excitation of the QD.展开更多
We investigate the violation of two types of Leggett-Garg(LG)inequalities in self-assembled quantum dots under the stationarity assumption.By comparing the two types of LG inequalities,we find the better one that is e...We investigate the violation of two types of Leggett-Garg(LG)inequalities in self-assembled quantum dots under the stationarity assumption.By comparing the two types of LG inequalities,we find the better one that is easier to be tested in an experiment.In addition,we show that the fine-structure splitting,background noise and temperature of quantum dots greatly affect the violation of LG inequalities.展开更多
In the original time-domain Bell's inequalities(Leggett-Garg-type inequalities),the physical objective is measured at three time points.When more time points are chosen,several methods can be used to extend these ...In the original time-domain Bell's inequalities(Leggett-Garg-type inequalities),the physical objective is measured at three time points.When more time points are chosen,several methods can be used to extend these inequalities.We experimentally demonstrate the violation of these extended inequalities using single photons from a self-assembled quantum dot.In general,for each extension,the quantity by which the quantum-mechanics value exceeds the classical limit becomes larger as the number of measurement time points increases.This quantity has a maximum value for the extensions that have the same number of measurement time points.Furthermore,we evaluate the noise tolerance for these extensions with a quantity that is related to the number of standard deviations by which the experimental result surpasses the classical limit.展开更多
基金the National Key Research and Development Program of China(Grant No.2016YFA0302700)the National Natural Science Foundation of China(Grant Nos.11674304,11822408,11774335,61490711,11474267,11821404,and 91321313)+3 种基金the Youth Innovation Promotion Association of Chinese Academy of Sciences(Grant No.2017492)the Foundation for Scientific Instrument and Equipment Development of Chinese Academy of Sciences(Grant No.YJKYYQ20170032)the Key Research Program of Frontier Sciences of the Chinese Academy of Sciences(Grant No.QYZDY-SSW-SLH003)the Fundamental Research Funds for the Central Universities,China(Grant No.WK2470000026)。
文摘Entanglement is the key resource in quantum information processing,and an entanglement witness(EW)is designed to detect whether a quantum system has any entanglement.However,prior knowledge of the target states should be known first to design a suitable EW,which weakens this method.Nevertheless,a recent theory shows that it is possible to design a universal entanglement witness(UEW)to detect negative-partial-transpose(NPT)entanglement in unknown bipartite states with measurement-device-independent(MDI)characteristic.The outcome of a UEW can also be upgraded to be an entanglement measure.In this study,we experimentally design and realize an MDI UEW for two-qubit entangled states.All of the tested states are well-detected without any prior knowledge.We also show that it is able to quantify entanglement by comparing it with concurrence estimated through state tomography.The relation between them is also revealed.The entire experimental framework ensures that the UEW is MDI.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2016YFA0302700 and 2017YFA0304100)the National Natural Science Foundation of China(Grant Nos.11822408,11674304,11774335,61490711,11474267,11821404,11325419,11904356,and 91321313)+5 种基金the Youth Innovation Promotion Association,Chinese Academy of Sciences(Grant No.2017492)the Foundation for Scientific Instrument and Equipment Development,Chinese Academy of Sciences(Grant No.YJKYYQ20170032)the Key Research Program of Frontier Sciences,Chinese Academy of Sciences(Grant No.QYZDY-SSW-SLH003),the Fundamental Research Funds for the Central Universities,China(Grant Nos.WK2470000026 and WK2030000008)Science Foundation of Chinese Academy of Sciences(Grant No.ZDRW-XH-2019-1),Anhui Initiative in Quantum Information Technologies,China(Grant Nos.AHY020100,AHYPT003,and AHY060300)the National Postdoctoral Program for Innovative Talents of China(Grant No.BX20180293)the China Postdoctoral Science Foundation(Grant No.2018M640587).
文摘Bohr’s principle of complementarity has a long history and it is an important topic in quantum theory,among which the famous example is the duality relation.The relation between visibilityC and distinguishability D,C2+D2≤1,has long been recognized as the only representative of the duality relation.However,recent researches have shown that this inequality is not good enough because it is not tight for multipath interferometers.Meanwhile,a tight bound for the multipath interferometer has been put forward.Here we design and experimentally implement a three-path interferometer coupling with path indicator states.The wave property of photons is characterized by l1-norm coherence measure,and the particle property is based on distinguishability of the indicator states.The new duality relation of the three-path interferometer is demonstrated in our experiment,which bounds the union of a right triangle and a part of elliptical area inside the quadrant of a unit circle.Data analysis confirms that the new bound is tight for photons in three-path interferometers.
基金Supported by the National Basic Research Program of China,and the National Natural Science Foundation of China under Grant Nos 60921091,10874162 and 10734060.
文摘The peaks of exciton and biexciton from the single quantum dot(QD)micro-photoluminescence spectra are identified by observing the intensity of those peaks in relation to increasing excitation power.In order to further verify the properties of the exciton and biexciton,we perform auto-and cross correlation measurements.Using the former,we confirm the antibunching property of the signal light emitted from the single QD.Using cross correlation measurement,we verify that the exciton and biexciton emissions originate from the same QD and they are strongly correlated with each other.Lastly,we analyze the behavior of the cross correlation function in both the cases of saturated and unsaturated excitation of the QD.
基金Supported by the National Basic Research Program of China,and the National Natural Science Foundation of China under Grant Nos 60921091,11274289.
文摘We investigate the violation of two types of Leggett-Garg(LG)inequalities in self-assembled quantum dots under the stationarity assumption.By comparing the two types of LG inequalities,we find the better one that is easier to be tested in an experiment.In addition,we show that the fine-structure splitting,background noise and temperature of quantum dots greatly affect the violation of LG inequalities.
基金by the National Basic Research Program of Chinathe National Natural Science Foundation of China under Grant Nos 60921091,10874162 and 10734060。
文摘In the original time-domain Bell's inequalities(Leggett-Garg-type inequalities),the physical objective is measured at three time points.When more time points are chosen,several methods can be used to extend these inequalities.We experimentally demonstrate the violation of these extended inequalities using single photons from a self-assembled quantum dot.In general,for each extension,the quantity by which the quantum-mechanics value exceeds the classical limit becomes larger as the number of measurement time points increases.This quantity has a maximum value for the extensions that have the same number of measurement time points.Furthermore,we evaluate the noise tolerance for these extensions with a quantity that is related to the number of standard deviations by which the experimental result surpasses the classical limit.
