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

Transcription

1 Multi-user quantum key distribution with a semi-conductor source of entangled photon pairs C. Autebert1, J. Trapateau2, A. Orieux2, A. Lemaître3, C. Gomez-Carbonell3, E. Diamanti2, I. Zaquine2, and S. Ducci1 arxiv: Laboratoire MPQ, Université Paris Diderot, Sorbonne Paris Cité, CNRS-UMR 7162, Paris 2 LTCI, CNRS, Télécom ParisTech, Université Paris-Saclay, Paris 3 Centre de Nanosciences et de Nanotechnologies, CNRS/Université Paris Sud, UMR 9001, Marcoussis 01/22

2 Outline I/ QKD, why BBM92 II/ Practical integrated sources for QKD: AlGaAs source of entangled photon pairs at Telecom wavelength III/ Optimising the use of quantum ressources: Multi-user entanglement distribution with DWDM techniques IV/ Set-up & Experimental results V/ Perspectives 02/22

3 I/ Quantum Key Distribution BB84 QKD with single photons: non-commutation of σz and σx H/V H V + 1 t7 0 t6 1 t5 1 t4 0 t3 1 t2 1 t1 +/ attenuated laser diodes (cheap single photons) single-photon detectors (expensive...) limited distance (losses/noise) lots of hardware-related attacks C.H. Bennett & G. Brassard, Proc. IEEE Comp., Syst. & Signal Process. 175, 8 (1984). 03/22

4 I/ Quantum Key Distribution BBM92 QKD with photon pairs: entanglement (& non-locality) H/V H/V quantum server +/ t1 Ψ AB t2 t3 Ψ AB = t3 HV VH 2 = t2 t1 +/ entangled photon sources (expensive) single-photon detectors (expensive...) increased distance (less sensitive to losses/noise) towards device-independent security C.H. Bennett, G. Brassard & N.D. Mermin, Phys. Rev. Lett. 68, (1992). 04/22

5 II/ Practical integrated sources for QKD wide deployment of QKD need for cheap, easy-to-operate systems 1 transistor standard Telecom/computing components mass-manufacturing possibilities room temperature operation alignment-free operation... integrated photonics platforms: silicon (CMOS) III-V semiconductors: InP, AlGaAs... dielectric crystals (LiNbO3, KTP...) glass 109 transistors E. Diamanti, H.-K. Lo, B. Qi & Z. Yuan, arxiv: , Review (2016). A. Orieux & E. Diamanti, arxiv: , to appear in J. Opt. Topical Review (2016). 05/22

6 II/ AlGaAs source Huge χ(2) for spontanteous parametric down-conversion (SPDC) n(algaas) dχ(2)(algaas) 100 pm/v VS VS n(ppln) 2.2 dχ(2)(ppln) 20 pm/v ωa ωp L ωb E ħωa SPDC efficiency: ηspdc L.(dχ(2))2 ħωb ηspdc(algaas) 25 ηspdc(ppln) mm-long VS cm-long vaveguides ħωp 06/22

7 II/ AlGaAs source SPDC, different phase-matching techniques energy conservation: ωa + ωb = ωp (with ωa ωb) Δ[ħω] = 0 phase-matching (momentum conservation): Δ[ħk] = Δ[ħnω/c] = 0 n(ωa)ωa + n(ωb)ωb = n(ωp)ωp n(½ωp) = n(ωp) n 0 ½ωp ωp ω 07/22

8 II/ AlGaAs source SPDC, different phase-matching techniques phase-matching (momentum conservation): Δ[ħk] = Δ[ħnω/c] = 0 quasi-pm: n(½ωp)ωp = n(ωp)ωp 2πc/ΛQPM periodic poling of AlGaAs (still technologically challenging) z ΛQPM 08/22

9 II/ AlGaAs source SPDC, different phase-matching techniques phase-matching (momentum conservation): Δ[ħk] = Δ[ħnω/c] = 0 quasi-pm: n(½ωp)ωp = n(ωp)ωp 2πc/ΛQPM periodic poling of AlGaAs (still technologically challenging) z ΛQPM birefringent PM: nte(½ωp) = ntm(ωp) insertion of Al-Oxyde layers (fragile material) TE n z TM 0 TE TM ½ωp ωp ω 08/22

10 II/ AlGaAs source SPDC, modal phase-matching technique energy conservation: ωa + ωb = ωp (with ωa ωb) phase-matching (modal, type II): nte00(ωa)ωa + ntm00(ωb)ωb = ntebragg(ωp)ωp ntm00(ωa)ωa + nte00(ωb)ωb = ntebragg(ωp)ωp n TE00 TM00 TEBragg (1) (2) transverse modes: TEBragg TE00 TM V TE H z 0 ωa ωb ½ωp ωp TM00 ω F. Boitier et al., Phys. Rev. Lett. 112, (2014). C. Autebert et al., Optica 3, (2016). core layer Bragg mirrors 09/22

11 II/ AlGaAs source Direct bandgap semi-conductor electrical injection of the Bragg mode laser diode & non-linear crystal with the same waveguide no need for an external pump laser transverse modes: TEBragg TE00 TM00 F. Boitier et al., Phys. Rev. Lett. 112, (2014). 10/22

12 II/ AlGaAs source Direct polarization Bell state generation over a large bandwidth ωp TE00 TM00 TE00 30 nm H,ωA V,ωB TM00 λp (nm) ωp or λa,b (nm) λa,b (nm) λa,b (nm) 8 nm λp = intensity (a.u.) ΨA,B = V,ωA H,ωB HV + eiφ VH 2 very small birefringence no need for walk-off compensation nor interferometric schemes F. Boitier et al., Phys. Rev. Lett. 112, (2014). 11/22

13 III/ Ressource optimisation DWDM Dense Wavelength Division Multiplexing (DWDM) 0.8 nm (100 GHz) 73 laser diodes 1 long-distance SMF fiber 73 channels DEMUX MUX Internet server ITU 100 GHz grid nm nm nm nm nm nm 73 homes neighbourhood Internet access a single fiber deployed for many users 12/22

14 III/ Multi-user entanglement distribution Dense Wavelength Division Multiplexing (DWDM) 0.8 nm (100 GHz) 1 entanglement source 36 channel pairs Ψ DEMUX quantum Internet server ITU 100 GHz grid nm nm nm nm nm nm Bob 3 Bob 2 Bob 1 Alice 1 Alice 2 Alice 3 72 clients 36 pairs of clients 72 SMF fibers distribution of entangled photon pairs between symmetric channels around the degeneracy wavelength a single source for many pairs of users J. Trapateau et al., J. Appl. Phys. 118, (2015). 13/22

15 III/ Multi-user entanglement distribution nm nm nm DWDM & large-band frequency anti-correlation λp = nm ωb TE00 JSI(A,B) (narrow-linewidth pumping) ωb = ωp ωa TM00 λa nm 15 nm 25 λb intensity (a.u.) nm ωa 16 pairs of channels/users available over the 30-nm bandwidth of the entangled pairs 14/22

16 III/ Multi-user entanglement distribution DWDM & large-band frequency anti-correlation ωb JSI(A,B) (narrow-linewidth pumping) ITU 100 GHz grid: nm nm nm nm nm nm nm nm nm ωb = ωp ωa ωa 4 pairs of channels/users in our experiment (8+1 channels DWDM) 15/22

17 IV/ Multi-user BBM92-QKD experiment quantum server AlGaAs waveguide holographic mask 63x B29 B28 DWDM B26 A24 10x SMF collimator CW Ti:sa laser Peltier cooler nm A22 A21 long-pass filter fiber links Alice 23 polarization controller Bob 27 APD time coincidence counter APD λ/2 PBS polarization controller PBS λ/2 16/22

18 IV/ Multi-user BBM92-QKD experiment BBM92 protocol: H/V H/V quantum server HV VH Ψ AB = = t1 2 +/ t2 Ψ AB t3 t1 t2 t3 +/ ❶ local basis choices & coincidence measurements Rraw ❷ basis reconcilliation (sifting) Rsift = ½Rraw t1 ❶ t2 t3 t4 t5 t6 t7 t8 AB AB AB AB AB AB AB AB ❷ C.H. Bennett, G. Brassard & N.D. Mermin, Phys. Rev. Lett. 68, (1992). X.F. Ma, C.-H.F. Fung & H.-K. Lo, Phys. Rev. A 76, (2007). 17/22

19 IV/ Multi-user BBM92-QKD experiment BBM92 protocol: H/V H/V quantum server HV VH Ψ AB = = t1 +/ t2 Ψ AB t3 t1 t2 t3 +/ ❶ local basis choices & coincidence measurements Rraw ❷ basis reconcilliation (sifting) Rsift = ½Rraw ❸ error estimation (QBER) & correction e & f(e) ❹ secret key extraction Rkey Rsift( 1 f(e)h2(e) H2(e) ) with H2(x) = x.log2(x) (1 x).log2(1 x) t1 ❶ t2 t3 t4 t5 t6 t7 t8 AB AB AB AB AB AB AB AB ❷ ❸ ❹ C.H. Bennett, G. Brassard & N.D. Mermin, Phys. Rev. Lett. 68, (1992). X.F. Ma, C.-H.F. Fung & H.-K. Lo, Phys. Rev. A 76, (2007). 17/22

20 IV/ Multi-user BBM92-QKD experiment Coincidence histograms for A23 B27 over 50 km: Cfalse Rsift = Cmin Cmax + Cmin τhisto Cfalse Rfalse = Cmax Cfalse τhisto V= Cmax Cmin Cmax + Cmin e = ½(1 V) E. Waks, A. Zeevi & Y. Yamamoto, Phys. Rev. A 65, (2002). 18/22

21 IV/ Multi-user BBM92-QKD experiment BBM92-QKD results VS distance: set-up parameters: - collection efficiency: ηcol = 5% - fiber losses: α = 0.22 db/km - detection efficiency: ηdet = 20% - spurious count probability: d = 4.4x polarization error (PMD): b = 6% 19/22

22 IV/ Multi-user BBM92-QKD experiment There is room for improvement (higher rates & longer distance): - AR coating & laser-diode-to-smf packaging collection efficiency 4 - superconducting detectors detection efficiency 4 no dark counts - no use of PM fibers polarization error 3% realistic improved parameters: - collection efficiency: ηcol 21% - fiber losses: α 0.22 db/km - detection efficiency: ηdet 87% - spurious count probability: d 2x polarization error (PMD): b 2.5% 20/22

23 V/ Perspectives Electrical pumping & chip-to-fiber packaging fully integrated source Use of 40-channel DWDM & active switches 20 pairs of users per source + quantum repeaters + cheaper single-photon detectors + (measurement-)device-independence practical QKD fiber network 21/22

24 question time arxiv: /22