Quantum cryptography with highly entangled photons from semiconductor quantum dots

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.

Entanglement-based quantum key distribution with a blinking-free quantum dot operated at a temperature up to 20 K

“…The infrastructure is identical to the one used in a previous QKD experiment. 16 After an initial synchronization and polarization correction routine, the key generation is performed overnight for a total duration of about 8 h. The observed QBER, shown in Fig. 3(b), was evaluated periodically for 10% of the key bits (which were then discarded) and has an average value of 8.42%.…”

“…The biexciton-exciton (XX-X) spontaneous decay cascade in epitaxially grown semiconductor quantum dots (QDs) has been demonstrated to be a viable alternative to SPDC sources due to the sub-Poissonian entangled photon pair emission statistics. 13 In particular, GaAs QDs obtained by the Al droplet etching technique 14 are capable of emitting polarization-entangled photon pairs with a fidelity to the jϕ þ i Bell state beyond 0.98, 15,16 owing to an intrinsically low exciton fine structure splitting (FSS), 17 a low exciton lifetime of about 230 ps, and a near-zero multiphoton emission probability even at maximum brightness. 18 This allowed the demonstration of entanglement-based QKD with a QBER as low as 1.9%.…”

“…18 This allowed the demonstration of entanglement-based QKD with a QBER as low as 1.9%. 16,19 Independent of the QD materials used, the best performances in terms of entanglement fidelity and biexciton state-preparation efficiency have been obtained by operating the QD sources at temperatures below 10 K and using the resonant two-photonexcitation (TPE) condition. 20,21 One of the drawbacks of the very low working temperatures is that they are difficult to achieve in satellites, where strong payload restrictions have to be met.…”

“…This resonant TPE scheme is the same as used in previous experiments. 15,16,18 Figure 1(b) shows the microphotoluminescence spectra of a QD when adjusting E P at the working point V P;0 ¼ 0.3 V, used for the further measurements, and then sweeping V P from 0 to 1.5 V. The inset shows the corresponding diode current. In the voltage range of about 0.15 to 0.35 V, the QD is in its charge neutral configuration, and only the biexciton (XX) and the exciton (X) transition lines are visible.…”

Quantum violation of local causality in urban network with hybrid photonic technologies

“…At the basis of many of these quantum communication protocols is the phenomenon of Bell nonlocality [9][10][11], arguably the most radical departure between classical and quantum descriptions of nature. Besides its profound foundational implications, generating nonlocal correlations has become of crucial importance for a variety of quantum technologies, ranging from distributed computing [12], quantum cryptography [13][14][15][16][17][18][19] and quantum key distribution [20,21] to randomness generation [22][23][24] and selftesting [25,26].…”