Feasibility study of frequency-encoded photonic qubits over a free-space channel

Abstract: Frequency-bin quantum encoding shows great promise for quantum communication given its high-dimensional scaling, compatibility with photonic integrated circuits and synergy with classical optical communication technology. However, to date all demonstrations have been performed over single-mode and static channels, while the transmission over fluctuating and turbulent channels has not been addressed. We propose and demonstrate a novel approach that leverages field-widened interferometers to decode frequency-bins transmitted over free-space channels without any adaptive optics or modal filtering. Moreover, we investigate the phase stability requirements so that frequency-bin encoding could be feasible for satellite to ground quantum links. Our passive approach expands the versatility of frequency-bin encoding, paving the way towards long-range and fluctuating channels.