Integrated photonic quantum gates for polarization qubits

TLDR

Integrated photonic devices promise new possibilities for quantum mechanics tests and applications, yet handling polarization‑encoded qubits remains lacking, and the growing demand for integrated photonics underscores this gap. The authors aim to demonstrate a high‑fidelity photonic controlled‑NOT gate for polarization‑encoded qubits on a glass chip. The gate is realized by femtosecond‑laser‑written partially polarizing beam splitters integrated on a glass chip, allowing full device accessibility for quantum process tomography. The integrated CNOT gate is demonstrated, exhibiting high‑fidelity truth‑table performance, the ability to generate and convert entanglement, and is fully characterized via quantum process tomography.

Abstract

The ability to manipulate quantum states of light by integrated devices may open new perspectives both for fundamental tests of quantum mechanics and for novel technological applications. However, the technology for handling polarization-encoded qubits, the most commonly adopted approach, is still missing in quantum optical circuits. Here we demonstrate the first integrated photonic controlled-NOT (CNOT) gate for polarization-encoded qubits. This result has been enabled by the integration, based on femtosecond laser waveguide writing, of partially polarizing beam splitters on a glass chip. We characterize the logical truth table of the quantum gate demonstrating its high fidelity to the expected one. In addition, we show the ability of this gate to transform separable states into entangled ones and vice versa. Finally, the full accessibility of our device is exploited to carry out a complete characterization of the CNOT gate through a quantum process tomography. As quantum information processing continues to develop apace, the need for integrated photonic devices becomes ever greater for both fundamental measurements and technological applications. To this end, Crespiet al.demonstrate a high-fidelity photonic controlled-NOT gate on a glass chip.