CQT QUANTUMOO QUANTUM GR GR GR OUP OU

Introduction to QKD CQT QUANTUM O • Quantum Cryptography = Quantum Key Distribution –

Prepare and Send CQT QUANTUM O • Need for Random Numbers • Different Photons,

CQT QUANTUM O Entanglement based QKD GR • Ekert 1991 (E 91) – Let’s

CQT QUANTUM O Entanglement based QKD GR • Pairsource: BBO, lean & compact –

Detection of Photons CQT QUANTUM O • Detection: Polarization analyzer l/2 22. 5° PBS

Setup Ilja Gerhardt CQT QUANTUM O GR OUP M. Peloso et al. , New

Problems in Daylight CQT QUANTUM O • Destruction of detectors • Non-linearity of the

CQT QUANTUM O Expected Rates at daylight GR OUP Ilja Gerhardt M. Peloso et

CQT Sun & Solutions QUANTUM O GR OUP 6. 7 nm -12 d. B

CQT Setup QUANTUM O GR OUP Alice Bob Ilja Gerhardt M. Peloso et al.

CQT QUANTUM O Measured rates at daylight GR OUP • Sync possible at daylight

Experimental results total detection rate at receiver (kcps) CQT QUANTUM O GR OUP total

Conclusions • CQT QUANTUM O GR OUP • Entanglement based QKD in daylight, 4

CQT QUANTUM O Thanks for your attention http: //qolah. org Ilja Gerhardt GR OUP

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CQT QUANTUMOO QUANTUM GR GR GR OUP OU P Entanglement-based Free Space Quantum Cryptography in Full Daylight Ilja Gerhardt, Matthew P. Peloso, Caleb Ho, Ilja Gerhardt Antía Lamas-Linares and Christian Kurtsiefer

Introduction to QKD CQT QUANTUM O • Quantum Cryptography = Quantum Key Distribution – Have a Random Number at two locations One-time pad for encryption • 1980 ies: Prepare and Send – Bennet Brassard, BB 84 – Send single Photons, non-cloning theorem • 1990 ies: Entanglement Based… why? Ilja Gerhardt GR OUP

Prepare and Send CQT QUANTUM O • Need for Random Numbers • Different Photons, different Colors? – Dimensionality of Hilbert space needs to be known for security Ilja Gerhardt GR OUP

CQT QUANTUM O Entanglement based QKD GR • Ekert 1991 (E 91) – Let’s measure two qubits of an entangled entity – Perfect (Anti)correlation – Bell’s inequality violated = eavesdropper knowledge can be eliminated via PA • Photons for convenience… • Freespace: Ad-hoc set-up Ilja Gerhardt OUP

CQT QUANTUM O Entanglement based QKD GR • Pairsource: BBO, lean & compact – Strong temporally correlated – Broader than dimmed lasers 10’’ Ilja Gerhardt 19’’ OUP

Detection of Photons CQT QUANTUM O • Detection: Polarization analyzer l/2 22. 5° PBS 50: 50 APD, +45° V PBS H Ilja Gerhardt GR OUP -45° J. G. Rarity et al. , J. Mod. Opt. 41, 2345 (19

Setup Ilja Gerhardt CQT QUANTUM O GR OUP M. Peloso et al. , New J. Phys. 11 045007 (2

Problems in Daylight CQT QUANTUM O • Destruction of detectors • Non-linearity of the detector GR OUP – Saturation • Accidental clicks – Confused with real coincidence events (QBER) • Fluctuations of ~30 d. B (day/night) M. Peloso et al. , New J. Phys. 11 045007 (2 Ilja Gerhardt

CQT QUANTUM O Expected Rates at daylight GR OUP Ilja Gerhardt M. Peloso et al. , New J. Phys. 11 045007 (2

CQT Sun & Solutions QUANTUM O GR OUP 6. 7 nm -12 d. B - 3 -4 d. B 100µrad FOV=10 cm Dt=1 ns Ilja Gerhardt M. Peloso et al. , New J. Phys. 11 045007 (2

CQT Setup QUANTUM O GR OUP Alice Bob Ilja Gerhardt M. Peloso et al. , New J. Phys. 11 045007 (2

CQT QUANTUM O Measured rates at daylight GR OUP • Sync possible at daylight Ilja Gerhardt M. Peloso et al. , New J. Phys. 11 045007 (2

Experimental results total detection rate at receiver (kcps) CQT QUANTUM O GR OUP total 'local' detector rate at source (kcps) coincidences (cps) raw key rate (s-1) accidental coincidence rate ra (cps) Ilja Gerhardt key rate after error correction (s-1) QBER (%) M. Peloso et al. , New J. Phys. 11 045007 (2

Conclusions • CQT QUANTUM O GR OUP • Entanglement based QKD in daylight, 4 days run without interruption Synchronization works at ambient conditions Noise Suppression • Brighter Sources… 70 pairs/(s m. W MHz) • – Spectral – Temporal – Spatial Ilja Gerhardt M. Peloso et al. , New J. Phys. 11 045007 (2

CQT QUANTUM O Thanks for your attention http: //qolah. org Ilja Gerhardt GR OUP