Modes of photons play essential roles in interference. Using the fiber-based nonlinear interferometry that separates the nonlinear gain control from dispersion engineering, we show a new approach of modifying the mode structure of quantum state.
The success of many protocols in optical quantum information processing relies on the availability of photon states with a well-defined spatial and temporal mode, but the latter is often difficult to engineer. The authors present a new approach based on nonlinear interferometry that separates the nonlinear gain control from the dispersion engineering, resulting in photon pairs simultaneously possessing the advantages of high purity, high collection efficiency, high brightness, and flexibility in wavelength and bandwidth selection.
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 four-wave 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.
Two-mode squeezing is central to entangled-photon generation and nonlinear interferometry, yet standard perturbative low-gain treatments and Gaussian formalisms can obscure the interference of photon-number amplitudes, especially in nonlinear interferometers and at high gain. Here we derive a closed-form Fock-basis expression for the action of the two-mode squeezing operator on arbitrary number states, enabling the direct analysis of nonlinear interferometers in the photon-number basis at arbitrary squeezing strength. Within this framework, we provide intuitive physical interpretations of several known quantum-interference effects and identify a new multi-photon interference phenomenon in a four-crystal geometry that could readily be observed in laboratories. Our work provides a compact analytic toolkit and explicit design rules for engineering multi-photon interference, with applications in quantum sensing, precision metrology, and quantum state generation.