Generation of non-classical light in a photon-number superposition

TL;DR

This paper demonstrates on-demand generation of quantum superpositions of zero, one, and two photons using a single artificial atom, enabling advanced control over photon-number states for quantum technologies.

Contribution

It introduces a method to produce controlled superpositions of multiple photon-number states with high precision using pulsed coherent control.

Findings

Generated superpositions of vacuum, one, and two photons.

Achieved two-photon terms exceeding one-photon components.

Enabled phase super-resolving interferometry.

Abstract

The ability to generate light in a pure quantum state is essential for advances in optical quantum technologies. However, obtaining quantum states with control in the photon-number has remained elusive. Optical light fields with zero and one photon can be produced by single atoms, but so far it has been limited to generating incoherent mixtures, or coherent superpositions with a very small one-photon term. Here, we report on the on-demand generation of quantum superpositions of zero, one, and even two photons, via pulsed coherent control of a single artificial atom. Driving the system up to full atomic inversion leads to the generation of quantum superpositions of vacuum and one photon, with their relative populations controlled by the driving laser intensity. A stronger driving of the system, with $2\pi$-pulses, results in a coherent superposition of vacuum, one and two photons, with the two-photon term exceeding the one-photon component, a state allowing phase super-resolving interferometry. Our results open new paths for optical quantum technologies with access to the photon-number degree-of-freedom.