Многомодовые перепутанные состояния в связанных оптических параметрических взаимодействиях и их применения в телепортации (1103849), страница 5

Просмтор этого файла доступен только зарегистрированным пользователям. Но у нас супер быстрая регистрация: достаточно только электронной почты!

Текст из файла (страница 5)

SayginThe main goal of this thesis is to elaborate the quantum properties ofmultifrequency fields, spatial single-mode and multimode, generated in coupledparametric wave interactions and their applications for teleportation of entangledquantum states. The coupled parametric processes under consideration aretwo five-frequency interactions. One of the coupled interactions comprises twoparametric down-conversion processes accompanied by an up-conversion process.It involves the fields of two pumping waves with multiple frequencies:ωp = ω1 + ω2 ,2ωp = ω2 + ω3,ω1 + ωp = ω3 ,(1)The other coupled interaction occures in the field of a single pumping wave andconsists of the process of parametric down-conversion accompanied by two upconversion processes:ωp = ω1 + ω2 ,ω1 + ωp = ω3 ,ω2 + ωp = ω4 .(2)These interactions can be realized in aperiodic nonlinear photonic crystals(ANPC) having fulfilled the quasi-phase matching conditions for all the threewave processes.It has been shown that the resulting three-mode field, formed in (1), is inthree-mode entangled state.

The analysis of the two-mode entanglement suggeststhat the presence of the up-conversion process may significantly decrease the noiseinfluence of one parametric down-conversion process, involved in (1), on the otherprocess. The optimal parameters for the noise influence decrease have been found.The entanglement analysis, carried out for (2), has proved that modes withfrequencies ω1 , ω2 (low-frequency modes) and modes with frequencies ω3, ω4(high-frequency modes) exhibit two-mode entanglement. It has been shown by theanalysis of block entanglement, which was fulfilled with the help of the symplecticeigenvalues criterion, that the low-frequency and high-frequency mode bunches areentangled.The investigation of spatial multimode fields was conducted for twoconfigurations of quantum imaging schemes: the scheme with near located object,when the input image is directly projected on the ANPC, and the scheme withfar located object, where the spatial spectrum of the initial image is put to theinput face of the ANPC.

For both configurations the signal-to-noise ration of22generated images is calculated and studied. The analysis has shown that thesignal-to-noise ratio, normalized to its input value (for initial image), tends to1/4 for all generated images, as the interaction length for coupled interaction (2)increases. In order to reveal the entanglement properties of generated images thestatistics of difference of photon numbers for various pairs of images has beeninvestigated. It has been determined that the output images with low-frequencycarriers and images with high-frequency carriers are entangled.Entangled states play important role in quantum communication.

In the workschemes for teleportation of entangled spatial single-mode states and entangledimages using auxiliary quantum states obtained in interaction (2) are proposedand thoroughly analyzed. In order to qualify the performance of these schemes thetwo quantities were considered: fidelity and noise contribution that degrades theentanglement of the initial state. For the image teleportation scheme the qualityof teleportation strongly depends on the relation of the widths of the spatialspectra of the images to be teleported and the four-frequency auxiliary fields. Thequality of transfer of entangled states, both single-mode and images, depends onthe amount of entanglement initial states possess: the more entangled states tobe teleported, the more entangled auxiluary states should be in order to achievethe same fidelity.The influence of the pixel size of the detectors on the quality of teleportationhas been analysed in detail.

It has been shown that the increase of the pixel sizeresults in decrease of quantum noise contribution which, in turn, leads to theincrease in the quality of teleportation.Practical significance:• The entanglement of up-converted modes (spatial single-mode andmultimode) in (2) offers the possibility to obtain ultra-violet entangledstates, when the traditional methods can not be applied, due to the pumpingfrequency value falls into the absorption band.• The two-frequency entanglement, formed in two pairs of frequencies (2),can be exploited for teleportation of two-frequency entangled states, bothsingle-mode and multimode.• Implementation of coupled parametric interactions, having place in a singlecrystal, offers a compact way to obtain multimode entangled states.The results of the thesis are published in 8 scientific papers and presented at19 conferences.23.

Характеристики

Список файлов диссертации