Quantum mechanical complementarity probed in a closed-loop Aharonov-Bohm interferometer

TL;DR

This study investigates quantum complementarity in a closed-loop Aharonov-Bohm interferometer, demonstrating that dephasing occurs only when path information is obtainable, emphasizing the fundamental role of information acquisition over back-action.

Contribution

It reveals that dephasing in a ring interferometer depends on the availability of path information, challenging the idea that strong environment interaction alone causes decoherence.

Findings

Interference suppression occurs only when path information can be obtained.

Dephasing is not solely due to environment coupling, but linked to information accessibility.

Strong coupling does not necessarily lead to dephasing without path information.

Abstract

According to Bohr's complementarity principle, a particle possesses wave-like properties only when the different paths the particle may take are indistinguishable. In a canonical example of a two-path interferometer with a which-path detector, observation of interference and obtaining which-path information are mutually exclusive. Such duality has been demonstrated in optics with a pair of correlated photons and in solid-state devices with phase-coherent electrons. In the latter case, which-path information was provided by a charge detector embedded near one path of a two-path electron interferometer. Note that suppression of interference can always be understood either as obtaining path information or as unavoidable back action by the detector. The present study reports on dephasing of an Aharonov-Bohm (AB) ring interferometer via a coupled charge detector adjacent to the ring. In contrast to the two-path interferometer, charge detection in the ring does not always provide path information. Indeed, we found that the interference was suppressed only when path information could be acquired, even if only in principle. This demonstrates that dephasing does not always take place by coupling the `environment' to the interfering particle: path information of the particle must be available too. Moreover, this is valid regardless of the strength of environment-interferometer coupling, which refutes the general notion of the effect of strong interaction with the environment. In other words, it verifies that an acquisition of which-path information is more fundamental than the back-action in understanding quantum mechanical complementarity.