Atom chips: A vision for neutral atom QIP E.A. Hinds Imperial College, 11 July 2006 Imperial College London

Videotape atom chip Atom guiding with microscopic wires Outline Towards QIP MOT on a chip

Principle of the magnetic guide for atoms Energy B 1) Metallic atom chips Energy r r

Wire-guide apparatus at CCM

Loading the guide Mirror MOT atoms 70  K 1.5 mm 220  m Compressed Magnetic trap atoms 510  K Magnetic trap atoms 80  K

1 mm atoms 59  K atoms 10  K Evaporating to low temperature atoms 0.3  K BEC 2  m  60  m

Below 380 nK the atoms all jump into the ground state ……Bose-Einstein condensate The atoms behave collectively as a single quantum wave ATOM LASER Switch off the axial trap ……. ….matter wave propagates along magnetic guide

560 nK 380 nK 350 nK 270 nK T c =380 nK thermal cloud BEC Below 380  nK the cloud Bose condenses the atoms are now ready to be used….

23 mm 3.5 microns of gold Au sputtered on a Si wafer, patterned by ion beam milling 67  m atom interferometer on a chip spectacular sensitivity to o EM fields o gravity o other feeble forces

metal slab height dissipation resistivity of metal fluctuating field outside spin flips (and heating) Johnson noise Hugely increases the spin flip rate Henkel, Pötting and Wilkens Appl. Phys B 69,379 (1999) Spin flip rate near a surface skin depth fast decay due to presence of surface modes

1.8 MHz flip 560 kHz flip Theory PRA (2004) S. Scheel Spin flip lifetime above metal wire Expt. PRL (2003) M. Jones

lifetime (s) skin depth (  m) 1 atom height = 50  m, say Atom/surface “impedance matching” And what material has ~ 50  m skin depth? gold, aluminium, copper,… skin depth ~ atom height perfect conductorinsulator Ways to improve the traps near a surface: (i) Keep the metal thin (ii) Use insulating surface the subject of part II

~200 G at surface 2) Videotape atom chip Period ~100  m Equivalent alternating currents NSNSN Alternating magnetization NSNSN Add a bias field to make an array of field zeros where atoms are trapped

Loading a videotape microtrap NSNS wire videotape still more bias -- ++ collect atoms in mirror MOT bias field transfer to wire trap more bias off keep bias atoms now in microtrap 800nK 320nK <150nK momentum distributions Evaporate to make BEC C. Sinclair et al. PRA (2005)

200 nK cloud, 45  m from surface double image S N imaging light 6 kHz × 11 Hz 10  K cloud, 45  m from surface ~1000 atoms Imaging the cloud the BEC is ready for experiments…..and applications

e.g. oscillations viewed directly in the waveguide Centre of mass oscillation at trap frequency f Length oscillation at frequency √(12/5) f

pyramid MOT Helicity flips on each reflection 3) Pyramid MOT on a chip

{100} Si wafer SiO 2 top layer Si {111} pyramid 70.5 o This can prepare an integrated array of many small clouds or single atoms (in progress) integrated pyramid MOTs

What’s coming now? 2. entangling one atom with one photon 3. controlled entanglement of 2 atoms 1. making an atom qubit register and QIP is in the works: e.g integrated: atom interferometers clocks gyroscopes.....etc.

1. making a quantum register smooth trap condensate phase coherent state Take a condensate in a smooth trap number state Mott insulator corrugated trap Gradually corrugate the trap

laser light optical fibre BEC Mott insulator …………we are doing it on a videotape chip The atom string can be a quantum information register

…………a quantum information register of atoms each atom stores a bit of quantum information …….the direction of the arrow spin-up represents 1 spin down represents 0 this atom represents 0 and 1 both together controlled collisions can do calculations …….this leaves each atom entangled with its neighbour

90  m concave mirrors etched in silicon after coating with gold, we see focal spots under a microscope 2. entangling an atom with a photon

……… high finesse optical cavity optical fibre bragg stack dielectric coated micro-mirror cavity length reflection finesse = pm 390 nm 100  m No atoms One atom “strong coupling” g  g 2 / 

this allows coherent atom-photon coupling F = 2 F = 3 5S 5P e.g. photon pistol F = 2 F = 3 Coherent exchange of quantum information between atom and photon optical interface to atom quantum memory this idea leads to

atoms can be entangled through a shared cavity photon an alternative quantum logic gate 3. entangling two atoms in an optical microcavity

Summary Microscopic atom waveguides, motors, interferometers etc. are starting to make new quantum instruments We can make circuits of quantum gas floating above wires and permanent magnets on atom chips It will soon be possible to prepare atom arrays on chips. Single atoms will be moved in controlled ways. They will be coupled to each other and to light cavities. Quantum computing with neutral atoms will take a bit longer. The present The near future

Many people work on these experiments NSNSN QGATES FASTNET AtomChips € PPARC Royal Society EPSRC £ Money 1D gas and Mott insulator Anne CurtisIsabel Llorente-Garcia Benoit Darqui é Wire chips & interferometry Stefan ErikssonRob SewellDaniel Sahagun-SanchezJos Dingian Theory Stefan ScheelDuncan O’Dell Michael KraftZak MoktadirCarsten Gollasch Fabrication Single atom production and detection Gabriel DutierJonathan AshmoreMichael TrupkeJon Goldwin