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Register a new userQuantum key distribution using a triggered quantum dot source emitting near 1.3 microns
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Authors
P. M. Intallura
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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 microns 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.
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Deterministic solid-state quantum light sources are key building blocks in photonic quantum technologies. While several proof-of-principle experiments of quantum communication using such sources have been realized, all of them required bulky setups. Here, we evaluate for the first time the performance of a compact and stand-alone fiber-coupled single-photon source emitting in the telecom O-band ($1321,$nm) for its application in quantum key distribution (QKD). For this purpose, we developed a compact 19 rack module including a deterministically fiber-coupled quantum dot single-photon source integrated into a Stirling cryocooler, a pulsed diode laser for driving the quantum dot, and a fiber-based spectral filter. We further employed this compact quantum light source in a QKD testbed designed for polarization coding via the BB84 protocol resulting in $g^{(2)}(0) = 0.10pm0.01$ and a raw key rate of up to $(4.72pm0.13),$kHz using an external laser for excitation. In this setting we investigate the achievable performance expected in full implementations of QKD. Using 2D temporal filtering on receiver side, we evaluate optimal parameter settings for different QKD transmission scenarios taking also finite key size effects into account. Using optimized parameter sets for the temporal acceptance time window, we predict a maximal tolerable loss of $23.19,$dB. Finally, we compare our results to previous QKD systems using quantum dot single-photon sources. Our study represents an important step forward in the development of fiber-based quantum-secured communication networks exploiting sub-Poissonian quantum light sources.
Decoy-state quantum key distribution (QKD) is a standard technique in current quantum cryptographic implementations. Unfortunately, existing experiments have two important drawbacks: the state preparation is assumed to be perfect without errors and the employed security proofs do not fully consider the finite-key effects for general attacks. These two drawbacks mean that existing experiments are not guaranteed to be secure in practice. Here, we perform an experiment that for the first time shows secure QKD with imperfect state preparations over long distances and achieves rigorous finite-key security bounds for decoy-state QKD against coherent attacks in the universally composable framework. We quantify the source flaws experimentally and demonstrate a QKD implementation that is tolerant to channel loss despite the source flaws. Our implementation considers more real-world problems than most previous experiments and our theory can be applied to general QKD systems. These features constitute a step towards secure QKD with imperfect devices.
Global quantum secure communication can be achieved using quantum key distribution (QKD) with orbiting satellites. Established techniques use attenuated lasers as weak coherent pulse (WCP) sources, with so-called decoy-state protocols, to generate the required single-photon-level pulses. While such approaches are elegant, they come at the expense of attainable final key due to inherent multi-photon emission, thereby constraining secure key generation over the high-loss, noisy channels expected for satellite transmissions. In this work we improve on this limitation by using true single-photon pulses generated from a semiconductor quantum dot (QD) embedded in a nanowire, possessing low multi-photon emission ($<10^{-6}$) and an extraction system efficiency of -15 dB (or 3.1%). Despite the limited efficiency, the key generated by the QD source is greater than that generated by a WCP source under identical repetition rate and link conditions representative of a satellite pass. We predict that with realistic improvements of the QD extraction efficiency to -4.0 dB (or 40%), the quantum-dot QKD protocol outperforms WCP-decoy-state QKD by almost an order of magnitude. Consequently, a QD source could allow generation of a secure key in conditions where a WCP source would simply fail, such as in the case of high channel losses. Our demonstration is the first specific use case that shows a clear benefit for QD-based single-photon sources in secure quantum communication, and has the potential to enhance the viability and efficiency of satellite-based QKD networks.
We demonstrate a quantum dot single photon source at 900 nm triggered at 300 MHz by a continuous wave telecommunications wavelength laser followed by an electro-optic modulator. The quantum dot is excited by on-chip-generated second harmonic radiation, resonantly enhanced by a GaAs photonic crystal cavity surrounding the InAs quantum dot. Our result suggests a path toward the realization of telecommunications-wavelength-compatible quantum dot single photon sources with speeds exceeding 1 GHz.
Quantum key distribution---exchanging a random secret key relying on a quantum mechanical resource---is the core feature of secure quantum networks. Entanglement-based protocols offer additional layers of security and scale favorably with quantum repeaters, but the stringent requirements set on the photon source have made their use situational so far. Semiconductor-based quantum emitters are a promising solution in this scenario, ensuring on-demand generation of near-unity-fidelity entangled photons with record-low multi-photon emission, the latter feature countering some of the best eavesdropping attacks. Here we first employ a quantum dot to experimentally demonstrate a modified Ekert quantum key distribution protocol with two quantum channel approaches: both a 250 meter long single mode fiber and in free-space, connecting two buildings within the campus of Sapienza University in Rome. Our field study highlights that quantum-dot entangled-photon sources are ready to go beyond laboratory experiments, thus opening the way to real-life quantum communication.
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