Delayed-choice test of complementarity with single photons

TL;DR

This paper experimentally tests quantum complementarity using single photons from a diamond color center in a delayed-choice Mach-Zehnder interferometer, confirming the fundamental relation between interference visibility and which-path information.

Contribution

It demonstrates a delayed-choice experiment with single photons from a solid-state source, verifying the complementarity relation in a relativistically separated setup.

Findings

Measured interference visibility and distinguishability obey the complementarity relation V^2 + D^2 ≤ 1.

Confirmed the quantum principle of complementarity in a delayed-choice configuration.

Used single photons from a diamond N-V center in a Mach-Zehnder interferometer.

Abstract

We report an experimental test of complementarity using clock-triggered single-photon pulses emitted by an individual N-V color center in a diamond nanocrystal. The single photons are sent into a Mach-Zehnder interferometer with an output beamsplitter of adjustable reflection coefficient R. In addition, the choice of introducing or removing this beamsplitter is random and relativistically space-like separated from the entering of the photon inside the interferometer, as required for the Wheeler's delayed-choice regime. Each set value of R allows us to observe interference with visibility V and to obtain incomplete which-path information characterized by the distinguishability D. The measured values of V and D are found to obey the complementarity relation V^2 + D^2 =< 1.