Quantum-optical state engineering up to the two-photon level

TL;DR

This paper presents a scheme for engineering arbitrary quantum states of traveling light up to two photons, using conditional measurements on entangled photon pairs to remotely prepare desired superpositions.

Contribution

It introduces a novel experimental method to generate arbitrary superpositions of zero, one, and two-photon states in traveling light fields.

Findings

Successfully prepared arbitrary superpositions up to two photons

Verified the scheme experimentally with high fidelity

Demonstrated control over amplitudes and phases of superpositions

Abstract

We propose and experimentally verify a scheme to engineer arbitrary states of traveling light field up to the two-photon level. The desired state is remotely prepared in the signal channel of spontaneous parametric down-conversion by means of conditional measurements on the idler channel. The measurement consists of bringing the idler field into interference with two ancilla coherent states, followed by two single-photon detectors, which, in coincidence, herald the preparation event. By varying the amplitudes and phases of the ancillae, we can prepare any arbitrary superposition of zero- one- and two-photon states.