Discrimination Of Quantum States Base On Linear Optics

The coin fells to the ground,not front or verso.Throw a dice,one side will upward.In people's experience,no matter how it changes in the world,there is an established rule to follow,as Einstein said:god won't roll the dice.However,with the development of science technology and industrial technology,human can observe more and more things,and a lot of phenomena violate people's daily experience,such as black body spectrum,the structure of atomic and nuclear,electrodynamics phenomena of moving objects,and so on.In order to explain the physics phenomenon and problems well,quantum theory is presented.Quantum information is an important branch of quantum theory.From the view of science,it is the new-rising subject combined the quantum theory with classic information.With the study of science in recent years,the mysteries of quantum theory and classic information have been opened.Quantum information contains two parts.One is quantum computation,which mainly researches quantum computer and quantum algorithms which suited to quantum computer.The other is quantum communication,which mainly includes quantum cryptography,quantum teleportation,long distance quantum communications technology,and so on.These researches are base on the preparation and manipulation of quantum states,so a lot of studies on the fields have been discussed by scientists all over the world.Except entanglement resource,information carriers also are needed in realizing quantum computation and quantum communication,there are all kinds of physical systems.The common physical systems are:cavity quantum electrodynamics,superconducting system,ion trap,optical system,nuclear magnetic resonance,and so on.Because the optical system has its unique advantages,such as high operability,strong anti-jamming ability,transmitting easy,and so on,the optical system has attracted lots of scientists to study among all kinds of the quantum systems,and it has obtained considerable development.However,there are some drawbacks in this system.It is very hard to make photons interact with each other.To overcome the shortcomings,the application of cross-Kerr nonlinearity was presented after many years,which can solve this problem well.In general,a large Kerr nonlinearity at the single-photon level in the nature is practically impossible.While,recently some authors have reported that their experimental demonstrations can make nonlinearities of magnitude up to 10-2 by using multi-level atomic electromagnetically induced transparencies technique.In this article,we mainly introduce Greenberger-Home-Zeilinger state analyzer using hyper-entanglement in optical elements,and with the help of quantum communication bus(qubus)and weak cross-Kerr nonlinearity,we present a scheme to implement nearly deterministic Bell-state measurement.Our achievements as follows:(1)Complete Greenberger-Home-Zeilingerstate analyzer using hyper-entanglementIn this paper,we design a scheme that a polarization GHZ state can be completely and deterministically distinguished by adopting linear momentum degree of freedom as the ancillary qubits or change of roles between the momentum and polarization degrees of freedom.Two ways for distinguishing three-photon GHZ state can be finished in just one quantum circuit.(2)Nearly deterministic Bell-state measurement using quantum communication busWe present a scheme to implement Bell-state measurement for two photons by using robust continuous variable coherent modes,called as quantum communication bus(qubus)and weak cross-Kerr nonlinearity.Remarkably,the success probability is close to unity,and our scheme doesn't require any ancillary entanglement resource.The method of state measurement can be generalized to the case of an arbitrary number of photons and is likely to yield versatile applications for quantum computation and quantum communication.