On the quantum statistics of Brillouin scatterings

A. Pieczonková, Jan Peřina

A. Pieczonková

Evan A. Cryer-Jenkins, Georg Enzian, Lars Freisem +5 more

Brillouin–Mandelstam scattering is one of the most accessible nonlinear optical phenomena and has been widely studied since its theoretical discovery one hundred years ago. The scattering mechanism is a three-wave-mixing process between two optical fields and one acoustic field and has found a broad range of applications spanning microscopy to ultra-narrow-linewidth lasers. Building on the success of utilizing this nonlinearity at a classical level, a rich avenue is now being opened to explore Brillouin scattering within the paradigm of quantum optics. Here, we take a key step in this direction by employing quantum optical techniques yet to be utilized for Brillouin scattering to characterize the second-order coherence of Stokes scattering across the Brillouin lasing threshold. We use a silica microsphere resonator and single-photon counters to observe the expected transition from bunched statistics of thermal light below the lasing threshold to Poissonian statistics of coherent light above the threshold. Notably, at powers approaching the lasing threshold, we also observe super-thermal statistics, which arise due to instability and a “flickering” in and out of lasing as the pump field is transiently depleted. The statistics observed across the transition, including the “flickering,” are a result of the full nonlinear three-wave-mixing process and cannot be captured by a linearized model. These measurements are in good agreement with numerical solutions of the three-wave Langevin equations and are well demarcated by analytical expressions for the instability and the lasing thresholds. These results demonstrate that applying second-order-coherence and photon-counting measurements to Brillouin scattering provides new methods to advance our understanding of Brillouin scattering itself and progress toward quantum-state preparation and characterization of acoustic modes.

Zheshen Zhang, Xuan Quyen Dinh, Paul L. Voss

The spectra and optical quantum state of guided acoustic wave Brillouin scattering in optical fibers are measured. Spectra from 0.95 to 2 GHz are obtained with amplitude resolution as sensitive as 0.01 shot noise unit. Quantum homodyne tomography measurements confirm the thermal quantum statistics of guided acoustic wave Brillouin scattering, which is useful knowledge in the context of experimental continuous-variable quantum key distribution.

Detlef Dürr, Martin Kolb, T. Moser +1 more

Mateo Restrepo, Ángela M. Guzmán, William T. Rhodes +1 more

We analyze the quantum statistical properties of light scattered by an acousto-optic modulator. From the perspective of quantum mechanics, the acousto-optic effect arises from a nonlinear interaction between three bosonic fields: the laser light, the Brillouin-scattered light, and an acoustic wave. The Hamiltonian coincides with that of sum-frequency generation, where the sum-frequency mode is known to exhibit sub-Poissonian statistics. We calculate the free temporal evolution of the Fano factor for Brillouin backscattered light and determine that sub-Poissonian statistics are obtained when faint laser light is scattered by a counter-propagating coherent acoustic wave with low average phonon number. The use of sub-Poissonian light would lead to an increase of the security for quantum key distribution.