We report the distribution of a cryptographic key, secure from photon number splitting attacks, over 35 km of optical fiber using single photons from an InAs quantum dot emitting ∼ 1.3 µm in a pillar microcavity. Using below GaAs-bandgap optical excitation, we demonstrate suppression of multiphoton emission to 10% of the Poissonian level without detector dark count subtraction. The source is incorporated into a phase encoded interferometric scheme implementing the BB84 protocol for key distribution over standard telecommunication optical fiber. We show a transmission distance advantage over that possible with (length-optimized) uniform intensity weak coherent pulses at 1310 nm in the same system. The majority of experimental realizations demonstrating quantum key distribution (QKD) have relied on encoding information onto weak coherent pulses (WCPs).1,2,3 Due to the Poissonian nature of laser light, there is a finite probability of generating two or more photons per pulse from such a source. This opens up a security threat where an eavesdropper, Eve, can take advantage of these extra photons by performing a photon number splitting (PNS) attack.4 To compensate for this security loophole, the transmitter, Alice, has to attenuate the signal by an amount that increases with distance, which reduces the transmission rate and ultimately limits the maximum secure transmission distance to the authorized recipient, Bob.5 Decoy-pulse techniques have been developed to help mitigate the risks associated with multiphoton pulse emission, 6,7 and PNS secure key distribution distances are now starting to exceed those achieved with uniform pulse intensities.
8A single quantum emitter will exhibit "anti-bunching" of the photon emission times, 9 such that a regulated stream of single photons with zero probability of emitting more than one photon in any given excitation pulse can be expected. Applying an efficient single quantum emitter in a cryptographic system would outperform all other methods developed to date. Several experiments using single photons with wavelengths compatible with silicon technology have already been used for QKD. These include using a stream of single-photon pulses generated by a single nitrogen-vacancy color center in a diamond 10 and emission from a quantum dot.11 Telecom wavelength QKD has been achieved by using pairs of photons produced via spontaneous parametric down conversion.
12,13In this letter we demonstrate QKD using an opticallyexcited, triggered single-photon source (SPS) emitting at a telecom wavelength. Our source, which shows a ten-fold reduction in multi-photon emission compared to a laser, has been used to distribute keys secure from the PNS attack over 35 km along standard optical fiber. By applying a security analysis for imperfect devices (GLLP),
14we demonstrate a transmission distance advantage compared to the same system configuration incorporating uniform intensity pulses from a laser source at the same wavelength.We have previously demonstrated that a low density of telecom waveleng...
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