Generation of spectrally uncorrelated biphotons via fiber nonlinear quantum interference

Spectrally uncorrelated biphotons are the essential resources for achieving various quantum information processing protocols.We theoretically investigate the generation of spectrally uncorrelated biphotons emitted by spontaneous fourwave mixing from a fiber nonlinear interferometer which consists of an N-stage nonlinear gain fiber and an(N-1)-stage dispersion modulation fiber.The output biphoton states of nonlinear interference are the coherent superposition of various biphoton states born in each nonlinear fiber,and thus the interference fringe will reshape the biphoton joint spectra.As a result,resorting to Taylor expansion to first order for phase mismatching,we theoretically verify that the orientation of phase matching contours will rotate in a specific way with only varying the length of dispersion modulation fiber.The rotation in orientation of phase matching contours may result in spectrally uncorrelated biphotons and even arbitrary correlation biphotons.Further,we choose micro/nanofiber as the nonlinear gain fiber and single-mode communication fiber as dispersion modulation fiber to numerically simulate the generation of spectrally uncorrelated biphotons from spontaneous fourwave mixing.Here,due to significant frequency detuning(hundreds of THz),Raman background noise can be considerably suppressed,even at room temperature,and photons with largely tunable wavelengths can be achieved,indicating a practicability in many quantum fields.A photon mode purity of 97.2%will be theoretically attained without weakening the heralding nature of biphoton sources.We think that this fiber nonlinear interference with the flexibly engineered quantum state can be an excellent practical source for quantum information processing.

Engineering the spectral profile of photon pairs by using multi-stage nonlinear interferometers

Using the quantum interference of photon pairs in N-stage nonlinear interferometers(NLIs),the contour of the joint spectral function can be modified into an islands pattern.We perform two series of experiments.One is that all of the nonlinear fibers in pulse pumped NLIs are identical;the other is that the lengths of N pieces of nonlinear fibers are different.We not only demonstrate how the pattern of spectral function changes with the stage number N,but also characterize how the relative intensity of island peaks varies with N.The results well agree with theoretical predictions,revealing that the NLI with lengths of N pieces of nonlinear fibers following binomial distribution can provide a better active filtering function.Our investigation shows that the active filtering effect of multi-stage NLI is a useful tool for efficiently engineering the factorable two-photon state—a desirable resource for quantum information processing.

Semiparametric theory based MIMO model and performance analysis

In this article, a new approach for modeling multiinput multi-output （MIMO） systems with unknown nonlinear interference is introduced. The semiparametric theory based MIMO model is established, and Kernel estimation is applied to combat the nonlinear interference. Furthermore, we derive MIMO capacity for these systems and explore the asymptotic properties of the new channel matrix via theoretical analysis. The simulation results show that the semiparametric theory based modeling and kernel estimation are valid to combat this kind of interference.