Generation And Characterization Of Metalens-based Quantum Sources

Light source is an important tool in our daily life and work.Our civilization develops with the revolution of light sources.The birth of quantum source provides a new direction of research in light source,which will possibly promote the next industrial revolution.The most important concept in quantum source is quantum entanglement.Quantum entanglement,core of quantum theories,plays an extremely important role in quantum communication and quantum computation.There have been explorations of fundamental physics of quantum entanglement since the discovery of this fabulous phenomenon.Although for now,the answer to this question still remains unclear,quantum entanglement indeed accelerates the development of quantum physics both in research and applications.Based on the development of quantum entanglement theories,some novol technologies,such as quantum teleportation,quantum radar and universal quantum computer,are moving towards practical use.Photon system is naturally an excellent carrier of quantum source for its advantages like fast propagation speed,nice coherence and multi freedoms.To satisfy the demands of these fields,development of quantum sources with higher channel capacity and noise-resistant ability becomes a new focus issue in research,which requires to improve the dimension and particle number of quantum sources.Besides,integration of quantum sources is another important trend.Researchers have developed integrated photonic quantum chips,which contributes to the development of integration of quantum sources.In this article,we choose photons as the carriers of quantum entanglement.We design and fabricate phase-encoded metalenses and for the first time introduce metalens-array into high-dimensional and multiphoton quantum sources.Based on this metalens-array-BBO device,we generate high-dimensional quantum entanglements and 4-photon and 6-photon quantum states.The properties of the quantum source,such as correlations,entanglement,purity and brightness,are illustrated by quantum state tomography(QST)and Hong-Ou-Mandel interference.Experimental results show that all the entangled states based on the device have fidelities over 95% and the indistinguishability of 4-photon quantum source is over 85%.The above results show the success of the first trial in this crossing field.Metalens-based quantum sources provide a brand new way and platform for integrated photonic quantum sources.After generation of quantum states,we further explore the characterization of quantum states.Here we introduce weak measurement and weak value.By calculating the relationship between the joint weak value and the quantum density matrix,we could directly measure a specific element in the density matrix,avoiding a full QST process.Another project in this direction is the precision advantage of weak measurement with imperfect detectors by using weak value amplification(WVA).The experimental results demonstrate the great performance of weak measurement in characterization of quantum systems.In this article,we innovatively introduce metalens into high-dimensional and multiphoton quantum source.We successfully generate and characterize the highdimensional and multiphoton quantum states and prove the phase-encoding ability of metalens.Our results show the superiority and potential of metalens in highdimensional and multiphoton quantum source,which provides a new direction and reliable platform for integrated quantum device.Further more,we explore the project of direct measurement of high-dimensional entangled states based on weak value measurement.Our theory is applicable to any high-dimensional entangled states.Finally,we demonstrate the the precision advantage and noise-resistant ability of weak measurement with imperfect detectors by using weak value amplification compared to classical measurement.