An entangled LED driven quantum relay over 1km

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An entangled LED driven quantum relay over 1km Christiana Varnava

Dzurnak 1, M. Lucamarini 1, A. J. Bennett 1,M. B. Ward 1, R. V.

Shields 1 1Toshiba Research Europe Ltd, Cambridge, UK 2Engineering

1 An entangled LED driven quantum relay over 1km Christiana Varnava 1,2 R. Mark Stevenson 1, J. Nilsson 1, J. Skiba Szymanska 1, B. Dzurnak 1, M. Lucamarini 1, A. J. Bennett 1,M. B. Ward 1, R. V. Penty 2,I. Farrer 3, D. A. Ritchie 3, and A. J. Shields 1 1Toshiba Research Europe Ltd, Cambridge, UK 2Engineering Department, University of Cambridge, UK 3Cavendish Laboratory, University of Cambridge, UK

2 Overview Introduction Entangled LED (ELED) Design A quantum relay over 1km of optical fibre Results

Secure quantum networks Quantum networks with

trust single photons trusted node Site A quantum

internet) Quantum relays[1] are untrusted and can

entangled pair source EPR UT Site A Bell state

B quantum information is teleported to another

3 Secure quantum networks Quantum networks with classical receive and send nodes require additional trust single photons trusted node Site A quantum channel Site B classical channel (e.g. internet) Quantum relays[1] are untrusted and can guarantee quantum network security On demand entangled pair source EPR UT Site A Bell state measurement reveals no quantum information BSM Site B quantum information is teleported to another network user BSM dependent unitary transformation [1] Jacobs, Phys. Rev. A 66, (2002)

Photonic quantum teleportation platforms Parametric Down Conversion [1,2] driving laser(s) specialist technology Poissonian emission statistics no pair Quantum Dot Entangled LEDs [3 5] Derived from

4 Photonic quantum teleportation platforms Parametric Down Conversion [1,2] driving laser(s) specialist technology Poissonian emission statistics no pair Quantum Dot Entangled LEDs [3 5] Derived from widespread technology IC with multiple sources non linear crystal(s) electrical operation multiple pairs single entangled photon pair Laser driven, as all reported photonic teleportation single entangled photon pairs Electrically driven semiconductor technology offers integration and practical scalability Accidental coincidences (errors) can be very Sub Poissonian emission prevents multipair emission, limits errors for large large, especially without heralding (e.g. 68% [1]) systems Less developed entangled technology Scalable implementations benefit from sub-poissonian, electrically-operated light sources [1] Bouwmeester et al., Nature 390, 575 (1997), Ma et al., Nature 489, 269 (2012), [3] Benson et al., PRL 84, 2513 (2000), [4] Stevenson et al., Nature 439, 179 (2006), [5] Salter et al., Nature 465, 594 (2010)

5 Entangled photon pairs from the ELED LED p i n structure Biexciton cascade from a quantum dot 1 exciton (X) & 1 biexciton (B) photon single photon emission = ( RL + LR )/ 2 quantum dot (15 x 5 nm) electrons holes p-gaas i-gaas InAs QD i-gaas n-gaas C.L. Salter et al, Nature 465, 594 (2010).

6 E LED Design Multiple devices on chip Individually bonded No apertures Small capacitance Allows for pulsed operation Sub Poissonian emission top contact bond ball (Au) 20 μm InAs QDs DBRs EL of quantum dot inside ordinary LED

7 Quantum Relay over 1km of Optical Fibre Quantum Relay allows users on a network to communicate securely without trusting network nodes. input qubits Sender BSM Receiver PC1 laser Laser τ 1 B BS PBS τ 2 τ 3 X ELED D1 PC2 D2 E-LED B X entangled photons D3 output qubits D4 PBS PC3 >1 km fibre PC: Polarisation Controller, BS: Beamsplitter, PBS: Polarising Beamsplitter, SSPD: Superconducting Single Photon Detector, BSM: Bell State Measurement

8 Experimental Details First pulsed teleportation experiment with ELED time-resolved EL of (B) emission qubit encoding: laser pulses tuned to dot wavelength & frequency Beamsplitter ELED photon Photon pair measurement Laser photon polarization encoded BB84 quantum states: D, A, H and V randomized sequence of teleported qubits was recorded V D H A

Poissonian characteristic Advantage over the photon number

9 Results 3 photon intensity τ 1 τ 2 τ 3 B X Laser ELED highly pulsed character Dip in coincidences at τ 2 =τ 3 : sub Poissonian characteristic Advantage over the photon number splitting attack Bell parameter 2.59±0.01 > 2 Entanglement fidelity estimated ~0.94

Results (2): Relay fidelity measured calculated Average relay fidelity fav up to 0.900±0.028 Individual basis fidelities 0.957± 0.042 (H) 0.951±0.0475 (V) 0.845± 0.064 (D) 0.847±0.

10 Results (2): Relay fidelity measured calculated Average relay fidelity fav up to 0.900±0.028 Individual basis fidelities 0.957± (H) 0.951± (V) 0.845± (D) 0.847±0.063 (A) [Dark blue area: no data] two photon interference between simultaneously detected photons is required for teleporting superposition states Limited by coherence time of photons

11 Results (3): Relay fidelity Sender and Receiver have shared information in excess of any information held by an eavesdropper QBER = 1 f av ~ 0.1 [f av =0.90] f av threshold for 4 state error correction[1] : 0.80 Well exceeded Threshold for efficient 4 state BB84 protocol[2]: 0.89 Secure key fraction: 0.11 bits per detected photon [1] H. F. Chau, Phys. Rev. A 66, (R) (2002) [2]H. K. Lo, H. F. Chau, and M. Ardehali, J. Cryptology 18, 133 (2005) 11

12 Conclusions Entangled LEDs are a practical quantum source with fundamental advantages First time entanglement has been distributed by a Q.D. source over a distance more than a few meters Average teleportation fidelity F exceeds classical limit and threshold for BB84 error correction protocols Quantum teleportation and quantum relays can be used to extend quantum networks beyond dedicated links ELED and teleportation performance sufficient for preliminary applications Preprint: Varnava et al., arxiv: (2015)

Heterogeneous teleportation with laser and quantum light sources

Heterogeneous teleportation with laser and quantum light sources R. M. Stevenson 1 *, J. Nilsson 1, A. J. Bennett 1, J. Skiba-Szymanska 1, I. Farrer 2, D. A. Ritchie 2, A. J. Shields 1 * 1 Toshiba Research