1. ~ 12  m Neutral atom quantum computing in optical lattices: far red or far blue? C. S. Adams University of Durham 17 November 2004 University of Durham

2. Outline University of Durham Good things for quantum computing Scalability (optical lattices) Low decoherence (large detuning) Far-red Far-blue 3D CO 2 single-site addressable Switchable interactions State-selective single-atom transport Collisional gates Experiment Magic Rydberg lattice or

3. (i)Neutral atoms in optical lattices. Single-qubit addressable. - Patterned loading - Pointer Switchable interactions. - Cavity QED - Collisions - Rydberg Scaling to 2(3)D. Low decoherence. University of Durham 1.Ions. Single-qubit addressable. Switchable interactions. Scaling to 2(3)D. Low decoherence. Architecture for a large-scale ion-trap quantum computer, D. Kielpinski, C. Monroe, D.J. Wineland Nature, 417, 709 (2002). Quantum computing: atoms or ions? 2. Neutral atoms: (i) Optical lattices (optical microtraps); (ii) Atom chips. O. Mandel, M. Greiner, A. Widera, T. Rom, T. W. Hänsch, and I. Bloch Controlled collisions for multi-particle entanglement of optically trapped Atoms, Nature, 425, 937 (2003)

4. University of Durham Photon scattering rate for a trap frequency of 1 MHz 1000 s -1 at 790 nm! Nd:YAG CO 2 0.002s -1 Rb 5p6p7p 5p 6p 5s 7p Far redFar blue Far red Far blue: less power Low decoherence

5. x ~ 100 kHz C. S. Adams et al. J. Phys. B. 36, 1933 (2003). University of Durham Far infrared: 3D CO 2 lattice ~ 12  m  atan   1.11.8  m lattice constant: single-atom addressable. 2.Similar trap depths for most atoms (molecules). P = 80 W w 0 =50  m Saddle y ~ 75 kHz

6. Single-atom conveyor 8.4  m Photon scattering rate ‘Blue’ ‘Red’ Single-atom tweezer Diener et al. Phys. Rev. Lett. 36, 1933 (2003). University of Durham Wavelength Range Near-infra-red Spin-dependent lattice

7. Single-atom cooling and detection Fluorescence detection Problem: Optical pumping and heating Solid angle 1/100 Detect 100 photons (1 ms) Heating 2 mK Raman sideband cooling Repumper C. Monroe, D.M. Meekhof, B.E. King, S.R. Jefferts, W.M. Itano, D.J. Wineland, and P. Gould, Resolved-sideband Raman cooling of a bound atom to the 3D zero-point energy, Phys. Rev. Lett. 75, 4011 (1995). 87 Rb University of Durham

8. Single-atom addressability Stimulated Raman transitions. Single-atom cooling and detection. Single-site addressable. Single-qubit rotations. State-selective single atom transport. ? ~ 12  m ~ 5  m 87 Rb University of Durham 2 P 3/2 2 P 1/2 2 S 1/2 I = 3/2

9. 2 P 3/2 2 P 1/2 2 S 1/2 I = 3/2 2 P 3/2 2 P 1/2 2 S 1/2 I = 3/2 State-selective transport Left circular 421.1 nm selectsRight circular 421.4 nm selects University of Durham 6p 2P6p 2P 5s 2 S 1/2 Spin-dependent lattice O. Mandel et al., Nature, 425, 937 (2003). Separate trapping and transport: 10 4 times less photon scattering during gate operation!

10. Collisional gates Collisional phase shift move  move University of Durham

11. Magnetically insensitive storage m F =  2 m F =  1 m F =  2 m F =  1 F = 2 F = 1 Raman selection pulse + 790.0 nm move beam     2 P 3/2 2 P 1/2 2 S 1/2 I = 3/2 University of Durham

12. detection 2. Computation 1. Initialisation 3. Read-out Scalable neutral atom quantum computer University of Durham Detection is not state specific but transport is!

13. University of Durham Lifetime 6.5 s pressure limited CO 2 trap experiment

14. Solder seal windows 1.Hard solder: melting point 309 o C 2.Tested to 275 o C. 3.Reusable. 4.Flexibility: high optical quality, any substrate, any coating. 5.ZnSe saving  £750 per window! 1 st baking cycle at 2.3 Nm 2 nd baking cycle at 2.5 Nm Ultimate pressure of pumping station S. G. Cox et al. Rev. Sci. Instrum. 74, 1311 (2003); K. J. Weatherill et. al. in preparation University of Durham

15. Pyramid MOT 10 -9 Torr Science MOT 10 -11 Torr Cold atom beam Large diameter laser beam 3D chamber University of Durham

16. An optical lattice with single lattice site optical control for quantum engineering R Scheunemann, F S Cataliotti, T W Hänsch and M Weitz, J. Opt. B 2, 645 (2000). Loading deep CO 2 lattices CO 2 CO 2 +Nd:YAG University of Durham CO 2 Nd:YAG 1D lattice BEC at one site: - reservoir for extracting single atoms

17. 1.State-selective (site-specific) transport: blue detuning: low scattering high trap frequency faster gates magnetically insensitive storage. 1.Collisional interactions: slow (not ‘switchable’) motional decoherence. Disadvantages: CO 2 laser University of Durham Advantages: single-site addressable 3D CO 2 trap collisional gates

18. G.M. Lankhuijzen and L.D. Noordam, PRL 74, 355 (1995). nV dd (kHz)  (  s)  (x 2  kHz) 15502.550 201601016 25400208 30800305 402600503 D. Jaksch, J.I. Cirac, P. Zoller, S.L. Rolston, R. Cote, M.D. Lukin, Fast quantum gates for neutral atoms, Phys. Rev. Lett. 85, 2208 (2000). 780 nm 483 nm (  m) 10.61.06 n2516 I (Wcm -2 )5x10 5 5x10 4  (  s) 0.0110 Ionisation rate R. M. Potvliege University of Durham Rydberg gates ~ 10  m

19. Low decoherence University of Durham Photon scattering rate for a trap frequency of 1 MHz ‘Blue’ ‘Red’ - U 0 0 Far redFar blue 1000 s -1 at 790 nm! Nd:YAG CO 2 0.002s -1 Rb 5p6p7p 5p 6p 5s 7p 0 U0U0

20. 428 nm 13d More blue! University of Durham Davidson, Lee, Adams, Kasevich, and S. Chu, PRL. 74, 1311 (1995). 4 s Ramsey fringes! Rb model potential calculation R.M. Potvliege and C.S. Adams, preprint 13d 10d 5s 10d 428 nm Magic Rydberg lattice 488 nm514 nm Long coherence But 428 nm loose single-site addressable!

21. 2 P 3/2 2 P 1/2 2 S 1/2 I = 3/2 428 nm 421 nm 6p 2P6p 2P University of Durham One quantum computer with a pointer Global addressing of a cluster state 2  pulse on a free bound transition O. Mandel, M. Greiner, A. Widera, T. Rom, T. W. Hänsch, and I. Bloch Controlled collisions for multi-particle entanglement of optically trapped Atoms, Nature, 425, 937 (2003) A. Kay, CSA and J. Pachos, preprint

22. University of Durham 428 nm lattice proposal R.M. Potvliege and C.S. Adams, preprint 1.Rb-87 BEC Mott Insulator 2.Local addressing with a ‘pointer’? 3.Patterned loading 4.Rydberg gates + state selective transport to perform read-out 125 mW in 50  m 100 kHz @ 428 nm S. Peil et al. PRA 67, 051603 (2003). Accordion lattice 780 nm loads every 5th site of 428 nm lattice £75k!

23. Optical lattices: scalability Low decoherence Far-red Far-blue 3D CO 2 single-site addressable Switchable interactions State-selective single-atom conveyor Collisional gates Experiment Magic Rydberg lattice Conclusions University of Durham Scalable up to 10 3 qubits Spatially discriminated parallel read-out

24. Acknowledgements Collaborators: Robert Potvliege (Rydberg theory) Graduate students: Paul Griffin Kevin Weatherill Matt Pritchard Research assistants: Simon Cox (up to 08/04) Collaborators: Erling Riis (Strathclyde) Ifan Hughes, Simon Cornish Technical support: Robert Wylie (Strathclyde) Financial support: EPSRC http://massey.dur.ac.uk/ University of Durham