Adaptively measuring the temporal shape of ultrashort single photons for higher-dimensional quantum information processing

TL;DR

This paper introduces an adaptive method to accurately reconstruct the complex spectro-temporal profile of ultrashort single photons, enabling higher-dimensional quantum information encoding and processing.

Contribution

It presents a novel adaptive scheme combining ultrafast control and quantum optics to map and reconstruct the mode structure of fragile quantum states.

Findings

Successfully reconstructs arbitrary amplitude and phase profiles of single photons.

Demonstrates encoding of qubits and qudits in multiple spectro-temporal modes.

Potential to increase quantum information capacity using broadband ultrashort photons.

Abstract

A photon is the single excitation of a particular spatiotemporal mode of the electromagnetic field. A precise knowledge of the mode structure is therefore essential for its processing and detection, as well as for applying generic quantum light states to novel technologies. Here we demonstrate an adaptive scheme for reconstructing the arbitrary amplitude and phase spectro-temporal profile of an ultrashort single-photon pulse. The method combines techniques from the fields of ultrafast coherent control and quantum optics to map the mode of a fragile quantum state onto that of an intense coherent field. In addition, we show that the possibility of generating and detecting quantum states in multiple spectro-temporal modes may serve as a basis for encoding qubits (and qudits) into single, broadband, ultrashort, photons. Providing access to a much larger Hilbert space, this scheme may boost the capacity of current quantum information protocols.