Fringe visibility and which-way information in Young's double slit experiments with light scattered from single atoms

TL;DR

This paper analyzes recent experiments with single atoms in Young's double slit setup, exploring how which-way information affects interference visibility and illustrating quantum complementarity.

Contribution

It generalizes and compares recent experiments with single atoms, highlighting different methods of recording which-way information in quantum interference.

Findings

Interference visibility decreases with obtainable which-way information.

Different experimental methods record which-way data in single-atom double slit setups.

The analysis emphasizes the complementarity principle in quantum mechanics.

Abstract

Young's double slit experiment has often been used to illustrate the concept of complementarity in quantum mechanics. If information can in principle be obtained about the path of the photon, then the visibility of the interference fringes is reduced or even destroyed. This Gedanken experiment discussed by Bohr and Einstein can be realized when the slit is replaced by individual atoms sensitive to the transferred recoil momentum of a photon which "passes through the slit". Early pioneering experiments were done with trapped ions and atom pairs created via photo-dissociation. Recently, it became possible to perform interference experiments with single neutral atoms cooled to the absolute ground state of a harmonic oscillator potential. The slits are now single atoms representing a two-level system, and the excitation in the harmonic oscillator potential is the which-way marker. In this note, we analyze and generalize two recent experiments performed with single atoms and emphasize the different ways they record which-way information.