Fully Arbitrary Control of Frequency-Bin Qubits

TL;DR

This paper demonstrates the first fully arbitrary and high-fidelity control of frequency-bin qubits using a quantum frequency processor, enabling precise quantum state manipulations for scalable quantum communication.

Contribution

It introduces a method for complete arbitrary control of frequency-bin qubits with near-unity fidelity, validated through experimental rotations and Bayesian tomography.

Findings

Achieved near-unity mode-transformation fidelity for all fundamental rotations.

Successfully rotated a single frequency-bin qubit to 41 points on the Bloch sphere.

Confirmed state fidelities greater than 0.98 for all tested cases.

Abstract

Accurate control of two-level systems is a longstanding problem in quantum mechanics. One such quantum system is the frequency-bin qubit: a single photon existing in superposition of two discrete frequency modes. %and a potential building block for scalable, fiber-compatible quantum information processing. In this work, we demonstrate fully arbitrary control of frequency-bin qubits in a quantum frequency processor for the first time. We numerically establish optimal settings for multiple configurations of electro-optic phase modulators and pulse shapers, experimentally confirming near-unity mode-transformation fidelity for all fundamental rotations. Performance at the single-photon level is validated through the rotation of a single frequency-bin qubit to 41 points spread over the entire Bloch sphere, as well as tracking of the state path followed by the output of a tunable frequency beamsplitter, with Bayesian tomography confirming state fidelities $\mathcal{F}_\rho>0.98$ for all cases. Such high-fidelity transformations expand the practical potential of frequency encoding in quantum communications, offering exceptional precision and low noise in general qubit manipulation.