Electro-Optic Frequency Beamsplitters and Tritters for High-Fidelity Photonic Quantum Information Processing

We report experimental realization of high-fidelity photonic quantum gates for frequency-encoded qubits and qutrits based on electro-optic modulation and Fourier-transform pulse shaping. Our frequency version of the Hadamard gate offers near-unity fidelity ($0.99998\pm 0.00003$), requires only a single microwave drive tone for near-ideal performance, functions across the entire C-band (1530-1570 nm), and can operate concurrently on multiple qubits spaced as tightly as four frequency modes apart, with no observable degradation in the fidelity. For qutrits we implement a $3\times 3$ extension of the Hadamard gate: the balanced tritter. This tritter—the first ever demonstrated for frequency modes—attains fidelity $0.9989\pm 0.0004$. These gates represent important building blocks toward scalable, high-fidelity quantum information processing based on frequency encoding.