Elements of the theory of interference and interferometers

A. F. Boden

Dorilian Lopez-Mago, Lukáš Novotný

The interference of entangled photon pairs permits the study of the fundamental properties of quantum mechanics. The process is also finding practical applications in optical imaging. The Michelson interferometer provides an elegant means for characterizing the degree of two-photon entanglement, but the technique has not yet been described and analyzed in detail. Here we provide a full description of the interference of collinear down-converted photons in a Michelson interferometer. We explain the basic elements that characterize the interference pattern and complement the theory with experimental measurements. The two-photon Michelson interferometer can be used in quantum optical coherence tomography for dispersion-free imaging and localization.

Anna V. Paterova, Leonid A. Krivitsky

Nonlinear interferometers with correlated photons hold promise to advance optical characterization and metrology techniques by improving their performance and affordability. These interferometers offer subshot noise phase sensitivity and enable measurements in detection-challenging regions using inexpensive and efficient components. The sensitivity of nonlinear interferometers, defined by the ability to measure small shifts of interference fringes, can be significantly enhanced by using multiple nonlinear elements, or crystal superlattices. However, to date, experiments with more than two nonlinear elements have not been realized, thus hindering the potential of nonlinear interferometers. Here, we build a nonlinear interferometer with up to five nonlinear elements, referred to as superlattices, in a highly stable and versatile configuration. We study the modification of the interference pattern for different configurations of the superlattices and perform a proof-of-concept gas sensing experiment with enhanced sensitivity. Our approach offers a viable path towards broader adoption of nonlinear interferometers with correlated photons for imaging, interferometry, and spectroscopy.

Ángel S. Sanz, Salvador Miret-Artés

M. Ley, R. Loudon

Expressions are derived for the density matrix elements appropriate to single-quantum excitation of the two arms of optical interferometers where an amplifier is inserted into one of the arms. The results are used to calculate mean intensities, correlations and photon number distributions for the outputs of Michelson and Hanbury Brown and Twiss interferometers. It is concluded that the noise output of the amplifier obscures quantum effects in the interferometer responses.

Peter Hawkes, Erwin K. Kasper