Quantum optical coherence: From linear to nonlinear interferometers

TL;DR

This paper introduces a classification scheme for interferometers based on the number of nonlinear elements, supported by theoretical analysis and experimental validation of coherence measurements in different configurations.

Contribution

It presents a novel classification framework for interferometers involving nonlinear elements and demonstrates its effectiveness through theory and experiments.

Findings

The classification scheme accurately describes different interferometer types.

Experimental results align well with theoretical predictions.

The setup enables switching between different nonlinear configurations easily.

Abstract

Interferometers provide a highly sensitive means to investigate and exploit the coherence properties of light in metrology applications. However, interferometers come in various forms and exploit different properties of the optical states within. In this paper, we introduce a classification scheme that characterizes any interferometer based on the number of involved nonlinear elements by studying their influence on single-photon and photon-pair states. Several examples of specific interferometers from these more general classes are discussed, and the theory describing the expected first-order and second-order coherence measurements for single-photon and single-photon-pair input states is summarized and compared. These theoretical predictions are then tested in an innovative experimental setup that is easily able to switch between implementing an interferometer consisting of only one or two nonlinear elements. The resulting singles and coincidence rates are measured in both configurations and the results are seen to fit well with the presented theory. The measured results of coherence are tied back to the presented classification scheme, revealing that our experimental design can be useful in gaining insight into the properties of the various interferometeric setups containing different degrees of nonlinearity.