~ 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

OutlineUniversity of Durham

Good things for quantum computing

Scalability (optical lattices)

Low decoherence(large detuning)

Far-red Far-blue

3D CO2 single-site addressable

Switchable interactions

State-selective single-atom transport

Collisional gates

Experiment

Magic Rydberg lattice

or

(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. BlochControlled collisions for multi-particle entanglement of optically trapped Atoms, Nature, 425, 937 (2003)

University of Durham

Photon scattering rate for a trap frequency of 1 MHz

1000 s-1 at 790 nm!

Nd:YAG

CO2

0.002s-1

Rb5p6p7p

5p

6p

5s

7p

Far redFar blue

0

osc

U Far redFar blue: less power

Low decoherence

x ~ 100 kHz

C. S. Adams et al. J. Phys. B. 36, 1933 (2003).

University of Durham Far infrared: 3D CO2 lattice

~ 12 m

atan

1. 11.8 m lattice constant: single-atom addressable.

2. Similar trap depths for most atoms (molecules).

P = 80 W

w0=50 m

Saddle

y ~ 75 kHz

Single-atom conveyor

8.4 m

2

0

41

10U

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

Single-atom cooling anddetection

Fluorescencedetection

Problem:

Optical pumping and heating

• Solid angle 1/100• Detect 100 photons (1 ms)• Heating 2 mK

0

1Raman 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).

87Rb

University of Durham

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

87Rb

University of Durham

2P3/2

2P1/2

2S1/2

I = 3/21

0

2P3/2

2P1/2

2S1/2

I = 3/21

0

2P3/2

2P1/2

2S1/2

I = 3/21

0

State-selective transport

Left circular 421.1 nm selects 0 Right circular 421.4 nm selects 1

University of Durham

6p 2P

5s 2S1/2

Spin-dependent lattice O. Mandel et al., Nature, 425, 937 (2003).

Separate trapping and transport: 104 times less photon scattering during gate operation!

Collisional gates

0 0

Collisional phase shift

0 1 1 1

0 0 0 1 1 0

1 0

1 1

move

1 0

move

University of Durham

Magnetically insensitive storage

mF = 2

mF = 1

mF = 2

mF = 1

F = 2

F = 1

Raman selection pulse + 790.0 nm move beam

0 0

2P3/2

2P1/2

2S1/2

I = 3/21

0

University of Durham

0 detection 1 detection

2. Computation

1. Initialisation

3. Read-out

Scalable neutral atom quantum computer

University of Durham

Detection is not state specific but transport is!

University of Durham

Lifetime 6.5 s pressure limited

CO2 trap experiment

Solder seal windows

1. Hard solder: melting point 309 oC2. Tested to 275 oC.3. Reusable.4. 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

University of Durham

Pyramid MOT10-9 Torr

Science MOT10-11 Torr

Cold atom beam

Large diameter

laser beam

3D chamberUniversity of Durham

An optical lattice with single lattice site optical control for quantum engineeringR Scheunemann, F S Cataliotti, T W Hänsch and M Weitz, J. Opt. B 2, 645 (2000).

Loading deep CO2 lattices

CO2

CO2+Nd:YAG

University of Durham

CO2Nd:YAG

1D lattice

BEC at one site: - reservoir for extracting single atoms

1. State-selective (site-specific) transport:blue detuning: low scattering

high trap frequencyfaster gates

magnetically insensitive storage.

1. Collisional interactions: slow (not ‘switchable’) motional decoherence.

Disadvantages: CO2 laser

University of Durham

Advantages: single-site addressable

3D CO2 trap collisional gates

G.M. Lankhuijzen and L.D. Noordam, PRL 74, 355 (1995).

n Vdd(kHz) (s) (x 2kHz)

15 50 2.5 50

20 160 10 16

25 400 20 8

30 800 30 5

40 2600 50 3

43

0

21dd 4

nr

ddV

3

1

n

2dd 10V

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) 10.6 1.06

n 25 16

I (Wcm-2) 5x105 5x104

(s) 0.01 10

Ionisation rate

R. M. Potvliege

University of Durham Rydberg gates

~ 10 m

30n40n 3

dd 10V

Low decoherenceUniversity of Durham

Photon scattering rate for a trap frequency of 1 MHz

‘Blue’‘Red’

2

0

41

10~

U

- U0

0

Far redFar blue

1000 s-1 at 790 nm!

Nd:YAG

CO2

0.002s-1

Rb5p6p7p

5p

6p

5s

7p

0

U0

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

Rydion

Magic Rydberg lattice488 nm 514 nm

Long coherence

But 428 nm loose single-site addressable!

2P3/2

2P1/2

2S1/2

I = 3/21

0

428 nm428 nm

421 nm

6p 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. BlochControlled collisions for multi-particle entanglement of optically trapped Atoms, Nature, 425, 937 (2003)

A. Kay, CSA and J. Pachos, preprint

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!

Optical lattices: scalability

Low decoherence

Far-red Far-blue

3D CO2 single-site addressable

Switchable interactions

State-selective single-atom conveyor

Collisional gates

Experiment

Magic Rydberg lattice

ConclusionsUniversity of Durham

Scalable up to 103 qubits

Spatially discriminated parallel read-out

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