Steady state dynamics of quantum frequency combs in microring resonators

Abstract: Optical frequency combs are utilized in a wide range of optical applications, including atomic clocks, interferometers, and various sensing technologies. They are often generated via four-wave mixing (FWM) in chip-integrated microring resonators, a method that requires low optical input power due to the high quality factor of the resonator, making it highly efficient. While the classical properties of optical frequency combs are well-established, this work investigates the quantum-mechanical characteristics of the individual comb modes. We derive simple equations describing the squeezing, second-order correlation and joint spectral intensity (JSI) between the generated signal and idler modes. Even with the resonator's detuning limiting the generation of signal- and idler pairs with significant photon numbers, many still exhibit substantial squeezing and entanglement. It is demonstrated that the design and dispersion characteristics of the ring resonator significantly impact the quantum features of the modes. Depending on the design, it is possible to enhance either the particle or mode entanglement of specific signal- and idler pairs. Thus, our findings enable the optimization for utilizing quantum frequency combs in various applications, including quantum sensing, computing and communication.