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

rr

Wire-guide apparatus at CCM

Loading the guide

Mirror MOT1 108 atoms 70 K

1.5 mm220 m

CompressedMagnetic trap

2 107 atoms 510 K

Magnetic trap2 107 atoms 80 K

1 mm 3 106 atoms

59 K

3 105 atoms

10 K

Evaporating to low temperature

2 104 atoms

0.3 KBEC

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 nK350 nK

270 nK

Tc=380 nK

thermal cloud

BEC

Below 380nK 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 too EM fieldso gravityo other feeble forces

metal slab

height

dissipation

resistivity of metal

fluctuating field outside

spin flips (and heating)

Johnson noiseHugely increases the spin flip rate

Henkel, Pötting and Wilkens Appl. Phys B 69,379 (1999)

11 s

Spin flip rate near a surface

skin depth

fast decay due topresence of surface modes

1

10

100

10 20 30 40 50 60 70 80 90 100

Height (um)

Lif

etim

e (s

)

1.8 MHz flip

560 kHz flip

TheoryPRA 70 013811 (2004)

S. Scheel

Spin flip lifetime above metal wire

Expt. PRL 91 080401 (2003)M. Jones

life

tim

e (s

)

skin depth (m)1

atom height = 50 m, say

10 100 10001

10

100

Atom/surface “impedance matching”

And what material has~ 50 m skin depth?

gold, aluminium, copper,…

skin depth ~ atom height

perfect conductor insulator

Ways to improve the traps near a surface:(i) Keep the metal thin

(ii) Use insulating surface

the subjectof part II

~200 G at surface

2) Videotape atom chip

Period ~100 m

Equivalent alternating currents

N S N S N

Alternating magnetization

N S N S N

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

800nK320nK

<150nKmomentum distributions

Evaporate to make BEC

C. Sinclair et al. PRA (2005)

200 nK cloud, 45 m from surface

double image

SN

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

SiO2 top layer

Si {111} pyramid

70.5o

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

condensatephase coherent state

Take a condensate in a smooth trap

number state

Mott insulator

corrugated trap

Gradually corrugate the trap

laser lightoptical fibre

BECMott 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 arrowspin-up represents 1

spin down represents 0 this atom represents0 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

opti

cal fibre

0.9999 bragg stack

dielectric coated micro-mirror 0.9999

cavity length

reflection

finesse = 5 200

74 pm

390 nm

100 m

No atoms

One atom

• “strong coupling”g

g2/

this allows coherent atom-photon coupling

F = 2

F = 35S

5Pe.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

N S N S NQGATES

FASTNET

AtomChips

€ PPARC

Royal Society

EPSRC

£

Money

1D gas and Mott insulator Anne Curtis Isabel Llorente-Garcia Benoit Darquié

Wire chips & interferometry Stefan Eriksson Rob Sewell Daniel Sahagun-Sanchez Jos Dingian

Theory Stefan Scheel Duncan O’Dell

Michael Kraft Zak Moktadir Carsten GollaschFabrication

Single atom production and detectionGabriel Dutier Jonathan AshmoreMichael Trupke Jon Goldwin