"Quantum cryptography with highly entangled photons from semiconductor quantum dots."

19.04.2021

New Paper from the Walther-Group out in ScienceAdvances!

Abstract

Semiconductor quantum dots are capable of emitting polarization entangled photon pairs with ultralow multipair emission probability even at maximum brightness. Using a quantum dot source with a fidelity as high as 0.987(8), we implement here quantum key distribution with an average quantum bit error rate as low as 1.9% over a time span of 13 hours. For a proof of principle, the key generation is performed with the BBM92 protocol between two buildings, connected by a 350-m-long fiber, resulting in an average raw (secure) key rate of 135 bits/s (86 bits/s) for a pumping rate of 80 MHz, without resorting to time- or frequency-filtering techniques. Our work demonstrates the viability of quantum dots as light sources for entanglement-based quantum key distribution and quantum networks. By increasing the excitation rate and embedding the dots in state-of-the-art photonic structures, key generation rates in the gigabits per second range are in principle at reach.

read more

Full-state tomography of the entangled photon pair.
Fig. 2 Full-state tomography of the entangled photon pair. Two-qubit polarization state after transport of the X photons through a 700-m-long fiber. Density matrix with a concurrence of 0.95(2) before (A) and after (B) polarization correction, resulting in a fidelity of 0.987(8).