Ramsey interference with single photons

TL;DR

This paper demonstrates a Ramsey interferometer using single photons, creating and manipulating energy superposition states for quantum information processing and communication.

Contribution

It introduces a novel method to realize a high-visibility Ramsey interferometer with single photons, enabling frequency-encoded photonic qubits.

Findings

Successfully generated energy superposition states of single photons

Implemented arbitrary projective measurements on photon states

Achieved high-visibility Ramsey interference with single photons

Abstract

Interferometry using discrete energy levels in nuclear, atomic or molecular systems is the foundation for a wide range of physical phenomena and enables powerful techniques such as nuclear magnetic resonance, electron spin resonance, Ramsey-based spectroscopy and laser/maser technology. It also plays a unique role in quantum information processing as qubits are realized as energy superposition states of single quantum systems. Here, we demonstrate quantum interference of different energy states of single quanta of light in full analogy to energy levels of atoms or nuclear spins and implement a Ramsey interferometer with single photons. We experimentally generate energy superposition states of a single photon and manipulate them with unitary transformations to realize arbitrary projective measurements, which allows for the realization a high-visibility single-photon Ramsey interferometer. Our approach opens the path for frequency-encoded photonic qubits in quantum information processing and quantum communication.