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Multi-user quantum key distribution with a semi-conductor source of entangled photon pairs

Claire Autebert, Julien Trapateau, Adeline Orieux, Aristide Lemaître, Carmen Gómez, Eleni Diamanti, Isabelle Zaquine, S. Ducci

Published Jul 1, 2016• 0 citations
OpenAlex

Abstract

Quantum cryptography with entangled photon pairs can be more powerful than protocols based onsingle photons or weak coherent pulses: they can tolerate higher losses and thus allow thedistribution of quantum secret keys (QKD) over longer distances [1], they also provide a waytowards device-independent quantum cryptography [2]. However, in order to enable a wide use ofentangled photon pairs in future quantum telecommunication systems, further developments areneeded to demonstrate performant sources that can be easily fabricated and integrated into Telecomfiber networks.Here we present a source consisting of an aluminium gallium arsenide waveguide generatingphoton pairs in the Telecom band by type II spontaneous parametric down-conversion [3]. Such adevice has already been proven to work under electrical pumping [4]. Thanks to the very smallbirefringence of the guided modes, the pairs are directly generated in a polarization-entangled Bellstate, without the need for any post-compensation. Moreover, as the photons are emitted over alarge bandwidth (about 100 nm) with a joint spectrum that exhibits frequency anticorrelation, thesame source can be used to simultaneously distribute keys among multiple pairs of users by usingstandard Telecom wavelength demultiplexers [5]. Here, we experimentally show the distribution ofquantum secret keys with the BBM92 QKD protocol [6] between four different pairs of users with acommercial 100 GHz demultiplexer (0.8 nm channel width and spacing). Under CW pumpingconditions, using free-running InGaAs single-photon detectors, we achieve a secret key rate of 0.21bits/s and a qubit error rate (QBER) of 6.9% over 50 km of standard optical fiber.Our results, obtained with a robust and simple experimental set-up, open the way towards theimplementation of practical device-independent quantum communication protocols.

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Quantum Key distribution (QKD) enables two parties, Alice and Bob, to share a sequence of random bit whose secrecy is guaranteed by the fondations of quantum physics. The natural counterpart of this genuine inviolability lies in moderate key generation rates and achievable distances, due to severe exper- imental constraints, such as photon generation probabilities, detector's inefficiencies, detector's dark counts, and losses in fiber distribution channels. As well as improving these exper- imental resources since the last couple of years, several strate- gies are developed for increasing this bit rate. One promising way consists in exploiting the spectral correlations of time- energy entangled photons, enabling higher information con- tent per paired photon. Our idea is to combine the maturity of QKD schemes with high performance standard telecom com- ponents to propose a practical scheme allowing the distribu- tion of secret bits over 200 km at unprecedented rates.

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Quantum cryptography with entangled photon pairs can be more powerful than protocols based onsingle photons or weak coherent pulses: they can tolerate higher losses and thus allow thedistribution of quantum secret keys (QKD) over longer distances [1], they also provide a waytowards device-independent quantum cryptography [2]. However, in order to enable a wide use ofentangled photon pairs in future quantum telecommunication systems, further developments areneeded to demonstrate performant sources that can be easily fabricated and integrated into Telecomfiber networks.Here we present a source consisting of an aluminium gallium arsenide waveguide generatingphoton pairs in the Telecom band by type II spontaneous parametric down-conversion [3]. Such adevice has already been proven to work under electrical pumping [4]. Thanks to the very smallbirefringence of the guided modes, the pairs are directly generated in a polarization-entangled Bellstate, without the need for any post-compensation. Moreover, as the photons are emitted over alarge bandwidth (about 100 nm) with a joint spectrum that exhibits frequency anticorrelation, thesame source can be used to simultaneously distribute keys among multiple pairs of users by usingstandard Telecom wavelength demultiplexers [5]. Here, we experimentally show the distribution ofquantum secret keys with the BBM92 QKD protocol [6] between four different pairs of users with acommercial 100 GHz demultiplexer (0.8 nm channel width and spacing). Under CW pumpingconditions, using free-running InGaAs single-photon detectors, we achieve a secret key rate of 0.21bits/s and a qubit error rate (QBER) of 6.9% over 50 km of standard optical fiber.Our results, obtained with a robust and simple experimental set-up, open the way towards theimplementation of practical device-independent quantum communication protocols.
In view of real world applications of quantum information technologies, the combination of miniature quantum resources with existing fibre networks is a crucial issue. Among such resources, on-chip entangled photon sources play a central role for applications spanning quantum communications, computing and metrology. Here, we use a semiconductor source of entangled photons operating at room temperature in conjunction with standard telecom components to demonstrate multi-user quantum key distribution, a core protocol for securing communications in quantum networks. The source consists of an AlGaAs chip emitting polarization entangled photon pairs over a large bandwidth in the main telecom band around 1550 nm without the use of any off-chip compensation or interferometric scheme; the photon pairs are directly launched into a dense wavelength division multiplexer (DWDM) and secret keys are distributed between several pairs of users communicating through different channels. We achieve a visibility measured after the DWDM of 87% and show long-distance key distribution using a 50-km standard telecom fibre link between two network users. These results illustrate a promising route to practical, resource-efficient implementations adapted to quantum network infrastructures.
The scalability of quantum communication networks requires compact, fiber-integrated, easy-to-deploy, and efficient wavelength-division-multiplexed (WDM) sources for multi-user secure key distribution. Here, we demonstrate such a multi-channel source of polarization-entangled photon pairs in the low-loss telecom C-band based on type-0 spontaneous parametric downconversion in a fiber-coupled Zn-indiffused MgO-doped periodically poled lithium-niobate (MgO:PPLN) ridge waveguide in the Sagnac configuration. The source can be easily tuned to generate the |Φ+⟩ or |Φ−⟩ Bell state in 14 channel pairs of the International Telecommunication Union dense WDM (100-GHz spacing) grid around 1550-nm with a raw fidelity of ≳89%, with a maximum value of ≳94%. The raw concurrence is ≳0.8 for both Bell states in all channel pairs, and the observed S-parameter (>2.56 ± 0.04 in all 14-channel pairs) shows a strong violation of CHSH-Bell’s inequality. The source’s suitability for long-distance entanglement transmission is also demonstrated by the successful transfer of entangled photons up to 100 km while maintaining fidelity >85% and quantum bit error rate <9%. The effect of polarization mode dispersion on entanglement distribution among remote users is also studied in detail. All these performance metrics are measured using conventional room-temperature semiconductor-based single-photon avalanche detectors, and these are the best reported with these detectors. Our highly flexible source can support up to ∼40 user pairs to communicate simultaneously, and it can be easily deployed into the current metro-area fiber-optic telecom infrastructure to form a complete WDM-based quantum communication network.
Abstract In view of real-world applications of quantum information technologies, the combination of miniature quantum resources with existing fibre networks is a crucial issue. Among such resources, on-chip entangled photon sources play a central role for applications spanning quantum communications, computing and metrology. Here, we use a semiconductor source of entangled photons operating at room temperature in conjunction with standard telecom components to demonstrate multi-user quantum key distribution, a core protocol for securing communications in quantum networks. The source consists of an AlGaAs chip-emitting polarisation entangled photon pairs over a large bandwidth in the main telecom band around 1550 nm without the use of any off-chip compensation or interferometric scheme; the photon pairs are directly launched into a dense wavelength division multiplexer (DWDM) and secret keys are distributed between several pairs of users communicating through different channels. We achieve a visibility measured after the DWDM of 87% and show long-distance key distribution using a 50-km standard telecom fibre link between two network users. These results illustrate a promising route to practical, resource-efficient implementations adapted to quantum network infrastructures.
We experimentally demonstrate multi-user distribution of polarization entanglement using commercial telecom wavelength division demultiplexers. The entangled photon pairs are generated from a broadband source based on spontaneous parametric down conversion in a periodically poled lithium niobate crystal using a double path setup employing a Michelson interferometer and active phase stabilisation. We test and compare demultiplexers based on various technologies and analyze the effect of their characteristics, such as losses and polarization dependence, on the quality of the distributed entanglement for three channel pairs of each demultiplexer. In all cases, we obtain a Bell inequality violation, whose value depends on the demultiplexer features. This demonstrates that entanglement can be distributed to at least three user pairs of a network from a single source. Additionally, we verify for the best demultiplexer that the violation is maintained when the pairs are distributed over a total channel attenuation corresponding to 20 km of optical fiber. These techniques are therefore suitable for resource-efficient practical implementations of entanglement-based quantum key distribution and other quantum communication network applications.
We demonstrate the distribution of polarization-entangled photons for the purpose of quantum key distribution (QKD) along active telecom fibers. Entangled photon pairs of 810 nm wavelength generated by a Sagnac interferometer source were coupled into standard telecom single mode fibers. The fibers were either dark or carrying a standardized 1550 nm ethernet signals (1000BASE-ZX) with a nominal speed of 1 GBps from regular media converter devices, without any requirements on the optical power or spectrum transmitted. Our system demonstrates a QKD network covering 6 km in distance with a central service provider for classical and quantum data.
Quantum Key distribution (QKD) enables two parties, Alice and Bob, to share a sequence of random bit whose secrecy is guaranteed by the fondations of quantum physics. The natural counterpart of this genuine inviolability lies in moderate key generation rates and achievable distances, due to severe exper- imental constraints, such as photon generation probabilities, detector's inefficiencies, detector's dark counts, and losses in fiber distribution channels. As well as improving these exper- imental resources since the last couple of years, several strate- gies are developed for increasing this bit rate. One promising way consists in exploiting the spectral correlations of time- energy entangled photons, enabling higher information con- tent per paired photon. Our idea is to combine the maturity of QKD schemes with high performance standard telecom com- ponents to propose a practical scheme allowing the distribu- tion of secret bits over 200 km at unprecedented rates.