Perfect Qubit Transfer No Longer Needs A Laser Pulse

A fundamental limit of 4/e^2 ≈ 0.54 previously capped the excited-state occupation of the receiving qubit in quantum networks, regardless of distance or the strength of connections between qubits. Now, researchers have demonstrated a way to bypass this constraint without relying on an external laser, a technique previously proposed by Cirac et al. The team achieved this by engineering the dispersion relation of the waveguide itself, providing the necessary phase shift at each frequency to time-reverse the propagating pulse. This passive method, utilizing only linear and standard photonic engineering, “suggests new opportunities of photonic design in quantum optics,” and highlights engineered pulse propagation as a powerful tool in waveguide quantum electrodynamics.

Waveguide Chirality Limits Ideal Quantum State Transfer

Engineered waveguide dispersions now allow for perfect quantum state transfer across any distance, circumventing a previously unavoidable limitation on excited-state occupation in ideal systems. This achievement stems from manipulating the temporal pulse shape of photons, ensuring they align with the absorption requirements of the receiving qubit without the need for an external laser pulse.