Integrated optical waveplates for arbitrary operations on polarization-encoded single-qubits

TL;DR

This paper introduces integrated optical waveplates fabricated by femtosecond laser pulses, enabling arbitrary single-qubit polarization operations on-chip, and demonstrates their application in quantum state tomography of entangled photons.

Contribution

It presents the first integrated waveguide-based waveplates capable of arbitrary single-qubit polarization rotations, expanding the toolkit for on-chip quantum photonics.

Findings

Successfully fabricated and tested integrated waveplates for polarization control.

Demonstrated quantum state tomography of entangled photons using the new waveplates.

Enabled full manipulation of polarization-encoded qubits on-chip.

Abstract

Integrated photonic technologies applied to quantum optics have recently enabled a wealth of breakthrough experiments in several quantum information areas. Path encoding was initially used to demonstrate operations on single or multiple qubits. However, a polarization encoding approach is often simpler and more effective. Two-qubits integrated logic gates as well as complex interferometric structures have been successfully demonstrated exploiting polarization encoding in femtosecond-laser-written photonic circuits. Still, integrated devices performing single-qubit rotations are missing. Here we demonstrate waveguide-based waveplates, fabricated by femtosecond laser pulses, capable to effectively produce arbitrary single-qubit operations in the polarization encoding. By exploiting these novel components we fabricate and test a compact device for the quantum state tomography of two polarization-entangled photons. The integrated optical waveplates complete the toolbox required for a full manipulation of polarization-encoded qubits on-chip, disclosing new scenarios for integrated quantum computation, sensing and simulation, and possibly finding application also in standard photonic devices.