A deterministic and efficient source of frequency-polarization hyper-encoded photonic qubits

TL;DR

This paper demonstrates a deterministic, high-purity, and high-indistinguishability source of frequency-polarization hyper-encoded photonic qubits using a semiconductor quantum dot, advancing quantum information processing capabilities.

Contribution

The authors present a novel deterministic method for generating frequency-polarization hyper-encoded photonic qubits with high fidelity and indistinguishability, overcoming probabilistic limitations of previous sources.

Findings

Generation rate of 4 MHz with 28% probability at first lens

Photon purity exceeds 98% and indistinguishability exceeds 91%

Fidelity to target state is 94% with concurrence of 77%

Abstract

The frequency or color of photons is an attractive degree of freedom to encode and distribute the quantum information over long distances. However, the generation of frequency-encoded photonic qubits has so far relied on probabilistic non-linear single-photon sources and inefficient gates. Here, we demonstrate the deterministic generation of photonic qubits hyper-encoded in frequency and polarization based on a semiconductor quantum dot in a cavity. We exploit the double dipole structure of a neutral exciton and demonstrate the generation of any quantum superposition in amplitude and phase, controlled by the polarization of the pump laser pulse. The source generates frequency-polarization single-photon qubits at a rate of 4 MHz corresponding to a generation probability at the first lens of 28 $\pm$ 2%, with a photon number purity > 98%. The photons show an indistinguishability > 91% for each dipole and 88% for a balanced quantum superposition of both. The density matrix of the hyper-encoded photonic state is measured by time-resolved polarization tomography, evidencing a fidelity to the target state of 94 $\pm$ 8% and concurrence of 77 $\pm$ 2%, here limited by frequency overlap in our device. Our approach brings the advantages of quantum dot sources to the field of quantum information processing based on frequency encoding.