| Wave-particle duality is an essential property of quantum systems.It has brought a long-term discussion in the history of quantum theory.Local realism theory holds that ”wave” and ”particle” are inherent properties of photons,and each photon exhibits only one property.This theory cannot explain the correlation between the experiment setting and the property the photon shows.Therefore,local realism theory assumes that photons acquire the experiment sets in advance and choose to display specific properties correspondingly.To test the above assumption,Wheeler proposed to delay the measurement choice until the photon has passed through the first beam splitter in the Mach-Zehnder interferometer(MZI).Experiments implemented in various systems show that wave and particle are not predefined properties but different phenomena under different perspectives.Quantum delayed-choice(QDC)experiments employ quantum states(qubit)instead of classical random bits to control the state of the MZI.Within the control of quantum states,MZI will be in the superposition of open and closed,which means we can observe the quantum superposition of wave and particle properties.Thus in one experimental setting,we can observe two complementary phenomena simultaneously.QDC experiments need to satisfy two conditions: 1.Locality condition: The state of the control qubit is determined after the photon enters the MZI.2.Quantum condition: MZI should be in the superposition state of open and closed.However,quantum control gates require local interactions.It imposes high requirements on the locality condition.To meet the quantum condition,it's necessary to precisely control the relative phase between wave and particle states and thus prove the coherence.Previous QDC experiments didn't satisfy the above requirements at the same time.This work aims to realize a quantum delayed-choice experiment satisfying the above conditions in multiphoton systems.First,we study the wave and particle properties of photon S in the MZI.1.To satisfy the first condition,we utilize entangled photon pair C,A instead of a single qubit to control the MZI.Photon C directly controls the state of photon S via a Control-Hadamard gate.Photon A is transmitted to another lab 141 m away and measured on a random polarization base.With precise time synchronization and fast polarization modulation,the above two events are spacelike separated.Since photon C does not contain any information about the experimental setting without measuring photon A,our research strictly satisfies the Einstein locality condition.This work fulfills the locality loophole with the non-local correlation between photons C and A.2.To verifying the second one,we record the coincidence counts of photon S,C and A,and project photon S on the superposition state of wave and particle.By adjusting the relative phase between wave and particle states,we observed the interference of them.Compared with the mixed state of wave and particle in Wheeler's delayed-choice experiment,quantum superposition is sensitive to the phase in the entangled photon pair C,A.For the first time,we observed the quantum superposition state of wave and particle in a QDC experiment without locality loophole,which provides new insights for the study of wave-particle duality.Based on the above non-local QDC experiment,this research further tests the hypothesis of wave-particle objectivity of photons.With a cascaded HOM interferometer,we do Bell state measurement on photons C and A,generate the entangled state of photon S and the entangled photons C and A(so-called entangled-entanglement),and thus controlled the wave-particle duality of photon S with entangled states.We measured the correlation function of the entangled two parts.The results violated the CHSH inequality and exceeded the classical limit by six standard deviations,indicating the non-classical correlation.Different from delayed-choice experiments before,photon C is in the mixed state with our configuration,and there is no definite ”open” or ”closed”state of MZI.Therefore,it's impossible to strictly define ”wave” or ”particle” properties,which directly shows that wave-particle objectivity is invalid. |
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