No free lunch: the tradeoff between heralding rate and efficiency in microresonator-based heralded single photon sources

TL;DR

This paper investigates the tradeoff between heralding rate and efficiency in microresonator-based single photon sources, revealing that optimizing for one often degrades the other due to photon loss effects.

Contribution

It derives coupling conditions to optimize heralding rate and coincidence counts, highlighting the impact on heralding efficiency in microresonator photon sources.

Findings

Critical coupling does not maximize heralding rate.

Optimal coupling conditions depend on desired tradeoff.

Enhancing heralding rate can significantly reduce efficiency.

Abstract

Generation of heralded single photons has recently been demonstrated using spontaneous four-wave mixing in integrated microresonators. While the results of coincidence measurements on the generated photon pairs from these systems show promise for their utility in heralding applications, such measurements do not reveal all of the effects of photon losses within the resonator. These effects, which include a significant degradation of the heralding efficiency, depend strongly on the relative strengths of the coupling of the ring modes to loss modes and channel modes. We show that the common choice of critical coupling does not optimize the rate of successfully heralded photons, and derive the coupling condition needed to do so, as well as the condition needed to maximize the rate of coincidence counts. Optimizing these rates has a considerable negative effect on the heralding efficiency.