1. Aiming at Quantum Information Processing on an Atom Chip Caspar Ockeloen

2. Outline Quantum Information with Ultracold Atoms Magnetic lattice atom chip Atom number fluctuations Conclusion

3. Quantum Information Requirements: Scalable Long coherence time Nearest neighbor interactions

4. Ultracold Atoms Clean and isolated Quantum systems Coherence time up to 1 minute! 10 4 – 10 3 – 10 2 – 10 1 – 1 – 10 -1 – 10 -2 – 10 -3 – 10 -4 – 10 -5 – 10 -6 – 10 -7 – – Liquid Helium – Ultracold atoms – Solar surface – Room temperature Kelvin – High T C superconductor

5. Magnetic lattice atom chip 22 µm Magnetic FePt film + External B-field Rubidium atoms (  K) 10-1000 atoms per trap Lattice of ~500 traps Goal: each trap ↔ 1 qubit Magnetic trapping

6. Magnetic lattice atom chip BB Trapping and manipulating atoms Ultra high vacuum + atom chip Lasers + magnetic field trap atoms Cooled to several  K Transfer atoms to microtraps Image atoms with CCD camera CCD p=ħk

7. Absorption Imaging S. Whtilock et al “Two-dimensional array of microtraps with atomic shift register on a chip”, NJP, (2009) CCD Atom chip Absorption image of full lattice

8. Single site manipulation Optically address single sites Transport all atoms across the lattice How to make qubits?

9. Collective excitations Requires small and well defined ensembles of atoms One excitation shared over ensemble Highly entangled state Potentially more robust and faster Excitation rate depends on atom number

10. Classical limit: Shot Noise Atoms are discrete particles Poisson distribution: N ± √N atoms

11. Three-body loss Dominant loss process Three atoms → Molecule + Free atom 3-body interaction: density dependent

12. Three-body loss Effects on atom number distribution Initial distribution 3-body loss Poisson distribution N = 100  N = 10

13. F =0.6 Fluctuations Fano factor: F = 1 ↔ Poisson Three-body loss Mean atom number

14. (a)

15. Fluctuations Sub-Poissonian! S. Whitlock, C. Ockeloen, R.J.C Spreeuw, PRL 104, 120402 (2010)

16. Fluctuations Not limited by technical noise Fluctuations below classical limit Promise for high fidelity operations Ideal starting point for Quantum Information F = 0.5 ± 0.2 for 50 < N < 300

17. Conclusions Magnetic lattice atom chip > 500 atom clouds Optically resolved and addressable Sub-Poissonian atom number fluctuations Promising platform for Quantum Information F = 0.5 ± 0.2

18. Outlook Long range interactions New lattice design –New geometries –5  m spacing –In vacuum imaging Quantum Computer...

19. Thank you S. Whitlock, C. Ockeloen, R.J.C Spreeuw, “ Sub-Poissonian Atom- Number Fluctuations by Three-Body Loss in Mesoscopic Ensembles,” Phys. Rev. Lett. 104, 120402 (2010) S Whitlock, R Gerritsma, T Fernholz and R J C Spreeuw, “Two- dimensional array of microtraps with atomic shift register on a chip,” New J. Phys. 11, 023021 (2009)