Quantum Noise Control in Nonlinear Multimode Fibers through Active Input Shaping

Multimode fibers exhibit complex behavior in both linear and nonlinear regimes. In the linear regime, random mode mixing leads to speckle patterns at the output, which can be controlled and shaped arbitrarily through a combination of computational inverse design techniques and spatial modulation of the input beam (1). In the nonlinear regime this system hosts various novel intensity phenomena, including modal thermalization, spatiotemporal mode locking, and self-cleaning of femtosecond pulses (2). While nonlinearity plays a significant role in shaping quantum noise in few-mode systems, its effects on quantum noise in multimode nonlinear systems remain largely unexplored, with no prior attempts to control output noise similarly to intensity. Our findings here demonstrate that both noise and intensity can be controlled in these systems through active input control. We demonstrate successful noise suppression of up to 20 dB at a selected pixel without compromising intensity. Furthermore, we exploit nonlinearity-induced modal correlations to create multipixel states with noise suppression of up to 12 dB compared to a linearly attenuated state. This study presents the first demonstration of noise control achieved through active input shaping in nonlinear multimode fibers, opening new avenues for generating and manipulating quantum states in these systems.

1. Caravaca-Aguirre, A. M., et al., Optics express 21.10 (2013): 12881-12887.

2. Wright, L. G., et al., Nature photonics 9.5 (2015): 306-310.