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~ 12 m m

University of Durham. Neutral atom quantum computing in optical lattices: far red or far blue?. ~ 12 m m. C. S. Adams University of Durham 17 November 2004. University of Durham. Outline. Good things for quantum computing. Scalability (optical lattices). Low decoherence (large detuning).

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~ 12 m m

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  1. University of Durham Neutral atom quantum computing in optical lattices: far red or far blue? ~ 12 mm C. S. AdamsUniversity of Durham17 November 2004

  2. University of Durham Outline Good things for quantum computing Scalability (optical lattices) Low decoherence (large detuning) Far-blue Far-red or 3D CO2 single-site addressable State-selective single-atom transport Collisional gates Experiment Switchable interactions Magic Rydberg lattice

  3. Quantum computing:atoms or ions? University of Durham • 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). 2. Neutral atoms: (i) Optical lattices (optical microtraps); (ii) Atom chips. (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. 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. Low decoherence University of Durham Photon scattering rate for a trap frequency of 1 MHz Far blue Far red 7p 6p 5p 1000 s-1 at 790 nm! Rb 7p 6p 5p CO2 0.002s-1 Nd:YAG 5s Far blue: less power Far red

  5. Far infrared: 3D CO2 lattice University of Durham C. S. Adams et al. J. Phys. B. 36, 1933 (2003). ~ 12 mm P = 80 W q w0=50 mm q = atan(2) • 1. 11.8 mm lattice constant: single-atom addressable. • Similar trap depths for most atoms (molecules). Saddle nx ~ 100 kHz ny ~ 75 kHz

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

  7. Single-atom cooling anddetection University of Durham 87Rb • Problem: • Optical pumping and heating • Solid angle 1/100 • Detect 100 photons (1 ms) • Heating 2 mK Repumper Fluorescence detection Raman sideband cooling 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).

  8. Single-atom addressability University of Durham 87Rb ~ 12 mm 2P3/2 2P1/2 I = 3/2 2S1/2 ~ 5 mm Stimulated Raman transitions. Single-atom cooling and detection. Single-site addressable. Single-qubit rotations. State-selective single atom transport. ?

  9. State-selective transport University of Durham Spin-dependent lattice O. Mandel et al., Nature, 425, 937 (2003). Separate trapping and transport: 104 times less photon scattering during gate operation! 2P3/2 2P3/2 6p2P 2P1/2 2P1/2 I = 3/2 I = 3/2 2S1/2 2S1/2 5s2S1/2 Left circular 421.1 nm selects Right circular 421.4 nm selects

  10. Collisional gates University of Durham p/2 p/2 p/2 p/2 move move Collisional phase shift p/2 p/2 p/2 p/2

  11. Magnetically insensitive storage University of Durham 2P3/2 2P1/2 I = 3/2 Raman selection pulse + 790.0 nm move beam p/2 p/2 2S1/2 p p F = 2 mF= -2 mF= +2 p p F = 1 p/2 p/2 mF= +1 mF= -1

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

  13. CO2 trap experiment University of Durham Lifetime 6.5 s pressure limited

  14. Solder seal windows University of Durham • Hard solder: melting point 309 oC • Tested to 275 oC. • Reusable. • Flexibility: high optical quality, any substrate, any coating. • 5. ZnSe saving - £750 per window! 1st baking cycle at 2.3 Nm 2nd 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

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

  16. Loading deep CO2 lattices University of Durham CO2 Nd:YAG CO2+Nd:YAG 1D lattice CO2 BEC at one site: - reservoir for extracting single atoms 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).

  17. 3D CO2 trap collisional gates University of Durham Advantages: single-site addressable 1. State-selective (site-specific) transport: blue detuning: low scattering high trap frequency faster gates magnetically insensitive storage. Disadvantages: CO2 laser • Collisional interactions: slow (not ‘switchable’) • motional decoherence.

  18. Rydberg gates University of Durham 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). ~ 10 mm 483 nm Ionisation rate 780 nm R. M. Potvliege G.M. Lankhuijzen and L.D. Noordam, PRL 74, 355 (1995).

  19. Low decoherence University of Durham Photon scattering rate for a trap frequency of 1 MHz Far blue Far red 7p 6p 5p 1000 s-1 at 790 nm! Rb 7p 6p 5p CO2 0.002s-1 Nd:YAG 5s U0 0 ‘Blue’ ‘Red’ 0 - U0

  20. More blue! University of Durham Long coherence 13d 10d Magic Rydberg lattice 488 nm 514 nm Rb model potential calculation R.M. Potvliege and C.S. Adams, preprint 10d 428 nm Davidson, Lee, Adams, Kasevich, and S. Chu, PRL. 74, 1311 (1995). 13d 5s 428 nm 4 s Ramsey fringes! But 428 nm loose single-site addressable!

  21. One quantum computer with a pointer University of Durham A. Kay, CSA and J. Pachos, preprint 2P3/2 6p2P 2P1/2 I = 3/2 2S1/2 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) 421 nm Global addressing of a cluster state 428 nm 428 nm 2p pulse on a free bound transition

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

  23. University of Durham Conclusions Optical lattices: scalability Low decoherence Far-blue Far-red 3D CO2 single-site addressable Magic Rydberg lattice State-selective single-atom conveyor Collisional gates Spatially discriminated parallel read-out Scalable up to 103 qubits Experiment Switchable interactions

  24. Acknowledgements University of Durham 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/

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