Integrated quantum memory for quantum communication

1. Integrated quantum memory for quantum communication • E. Saglamyurek, N. Sinclair, C. La Mela, and W.Tittel • Institute for Quantum Information Science • University of Calgary, Canada M. George, R. Ricken, and W. Sohler Institut für Angewandte Physik University of Paderborn, Germany

2. Quantum memory, dream and reality • Two-pulse photon-echo-based storage of light • - Photon-echo quantum memory (CRIB & AFC) in RE crystals • AFC-based storage of light pulses in Tm:LiNbO3 waveguides • storage of 500 ps pulses • storage of 100 modes • Conclusion Integrated quantum memory for quantum communication WT, M. Afzelius, T. Chanelière, R. Cone, S. Kröll, S.A. Moiseev, and M. Sellars, Las. Phot. Rev. 2010

3. Quantum memory QM • A single-photon gun • A synchronization device for quantum data • - A key ingredient for a quantum repeater |y> 2hv QM ‘click’ EPR EPR BSM QM EPR EPR Lvovsky, Sanders, WT, Nature Photonics (2010); Simon et al., quant-ph (2010)

4. Quantum memory: dream and reality Different storage media and protocols * post selected Hedges et al., HBSM’09; DeRiedmatten et al., Nature (2008), Usmani et al., quant/ph (2010), Reim et al., Nature Photonics (2009), Longdell et al., PRL (2005)

5. Ghom absorption w p-pulse frequency p/2-pulse electric field amplitude v echo-pulse t t1 2t1 u u w=w0 w<w0 w>w0 p-pulse v w<w0 w>w0 dephasing rephasing echo at t=2t Storage of light using two-pulse photo-echoes Kopvil’em & Nagibarov, Fiz. Metall. Metalloved. (1963) Kurnit, Abella & Hartmann, Phys. Rev. Lett. (1964)

6. w v u Photon storage using two-pulse photo-echoes • Time-bin qubit (single photon) input: spontaneous emission adds significant noise • Pecho= Pnoise • rout =Frin+(1-F)rin • F= tr(rinrout) • = (Pecho+Pnoise)/(Pecho+ 2Pnoise) = 2/3 • = Fclassical(max) P(x) P(x) x x Ruggiero et al, PRA (2009); Sanguard, WT et al., quant-ph (2010), Massar &Popescu, PRL (1995)

7. Absorption inhom hom Frequency Rare-earth-ion doped crystals Stress and defects Inhomogeneous broadening • - transitions in the visible and at telecom wavelength • at 4 K: Ghom 50 Hz – 100 kHz, T2 up to 4 ms • Ground state coherence up to 30 s • - Ginhom 0.5 – 500 GHz RE ions have been usedextensively in for classicalstorage and data processing, and are wellsuited for CRIB and AFC-based quantum memory

8. Ghom absorption absorption opt. depth W frequency frequency frequency Photon-echo quantum memory (CRIB) • Preparation of an opticallythick, single absorption line • Controlledreversibleinhomogeneousbroadening (CRIB) • Absorption of light in arbitrary quantum state -> fastdephasing • Reduction of broadening to zero • Phase matching: f(z) = -2kz; EineikzEoute-ikz • Reestablishment of broadening, withreversedsign (interaction with external electric field) fi = Dit Di -> -Di i -> Time reversed evolution of atomic system and reemission of light in backward direction with unity efficiency and fidelity Moiseev et al., PRL (2001); Nilsson et al., Opt. Comm. (2005);Kraus, WT et al., PRA(2006); Alexanderet al.,PRL (2006); Hoseini et al., Nature 2009; Hedges et al., HBSM’09, WT et al., Las. Phot. Revs. (2010).

9. absorption absorption W frequency frequency Photon-echo quantum memory (AFC) • Preparation of an atomic frequency comb • Absorption of light in arbitrary quantum state -> fast dephasing and repetitive rephasing at tn =1/ncomb with 2pDitn= n 2p • Phase matching f(z) = -2kz enables backwards recall • Reversible mapping of optical coherence onto spin coherence allows recall on demand ncomb Ghom -> Reemission of light withunityefficiency and fidelity, very good multi-modestoragecapacities Hesselink et al., PRL (1979); Afzelius et al., PRA (2009); De Riedmatten et al., Nature. (2008); Afzeliuset al., PRL (2010); Usmani et al., quant-ph (2010).

10. Ti:Tm:LiNbO3 waveguides 80 ms 2.4 ms • Thulium • 795 nm zero phonon absorption line, Ghom ~200 kHz @3K • large, polarization and wavelength dependent optical depth (amin~2.2/cm @ 3K & 795.5 nm) • T1(3H4)=80 ms - optical pumping into magnetic ground-state sublevels (T1~sec @ B=150G & T=3K) • LiNbO3: • no inversion symmetry -> Stark shifting of resonance lines • “telecommunication” material, waveguide fabrication well mastered • Waveguide • - large Rabi frequencies • fast switching of large electric fields using closely spaced electrodes • - simplified integration with fibre optic components and into networks N. Sinclair, WT et al., J. Lumin. (2010)

11. The setup Laser AOM pol. mod. PBS t≥500 ps 795.5 nm Detector Tm:LiNbO3waveguide T=3K B=150 G Oscilloscope • - prepare AFC (10 –100 ms long pulse sequence) • wait 0.8 ms – 1 ms • send data to be stored • register transmitted and recalled data P al Width ~1/t time frequency frequency • fibre-to-fibre coupling loss ~15dB

12. Data storage – 20 ns long pulses Frequency comb Transmitted light 0.10 D 0.08 d1 g d0 0.06 opt. power (au) 0.04 Recalled light hinternal≈ 1.25 % 0.02 F=2, d0~1.1, d1~1.6 -> h ~ 1.6 % 0.00 -100 0 100 200 Time (ns)

13. Generation of broadband AFC Spectral width > GHz time

14. Data storage - 550 ps long pulses opt. power (au) echo, hinternal~5% 550 ps

15. Multi-mode storage opt. power (au) Detector response

16. Conclusion • AFC-based light storage in a Tm:LiNbO3 waveguide • Promising for integration • Broadband storage of light • Multi-mode storage • Internal storage efficiency ~5% • Fibre-to-fibre loss 15 dB • Next: • storage of time-bin qubits • storage of single photons & entangled time-bin qubits • explore unique possibilities of rapid electric field switching

17. Thank you Collaborations: Prof. W. Sohler