BEC research in Durham

Magnetic Field (G)157 159 161 163 165

a / a

0

0

2500

5000

7500

10000

145 160 175

-4000

0

4000

Cornish et al, PRL 85, 1795 (2000)

BEC with Tunable Interactions1. 85Rb BEC Experiment 2. Rb-Cs Mixtures

Thomas et al,J. Opt. B 5, S107 (2003)

Cs FeshbachResonance

133 Cs87 Rb

Staff: Simon Cornish, CSAStudents: Margaret Harris

Malcolm ParksPatrick Tierney

Finance: Royal SocietyEPSRC GR/S78339/01

Parker et al. PRL 90, 220401 (2003).Parker et al. PRL 92, 160403 (2004).

3. Theory: vortices,solitons, sound

Staff: Nick Proukakis, CSAStudents: Nick Parker

Eleni Sakallari (-07/04)Andrew Martin

Finance: EPSRC GR/S78339/01

~ 12 µm

Neutral atom quantum computing in optical lattices: far red or far blue?

C. S. Adams

University of Durham

MESUMA 04

Dresden 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 inteactions

State-selective single-atom transport

Collisional gates

Experiment

Magic Rydberg lattice

or

2. Neutral atoms in optical lattice.

Single-qubit addressable.- Patterned loading- Cavity QED- Microtraps

Switchable interactions.- Rydberg

Scaling to 2(3)D.

Low decoherence.

~ 12 µm

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

University of Durham

1. Ions. (ENS, Caltech, MPQ, Sussex)

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?

3D CO2 lattice 10 x 10 x 10 sites

8.4 µm

Low decoherenceUniversity of Durham

Photon scattering rate for a trap frequency of 1 MHz

25 s-1 at 790 nm!

Nd:YAG

CO20.002s-1

Rb5p6p7p

5p

6p

5s

7p

Far redFar blue

λν 0

osc

U∝

λπη 02 a

∝Lamb-DickeBlue: less power

νx ~ 100 kHz

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

University of Durham Far infrared: 3D CO2 lattice

~ 12 µm

θ = atan(2)

θ

1. 11.8 µm lattice constant: single-atom addressable.2. Similar trap depths for most atoms (molecules).

P = 80 W

w0=50 µm

Saddle

νy ~ 75 kHz

Single-atom conveyor

8.4 µm

2

0

41

10−<U

ωh

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

Problems:

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-site addressable.

Single-qubit rotations.

State-selective single atom transport.

Single-atom cooling and detection.

~ 12 µm

~ 5 µm

87Rb

University of Durham

2P3/2

2P1/2

2S1/2

I = 3/210

2P3/2

2P1/2

2S1/2

I = 3/210

2P3/2

2P1/2

2S1/2

I = 3/210

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

Collisional gates

0 0

Collisionalphase shift

0 1 1 1

0 0 0 1 1 0

1 0

1 1

move

1 0

π/2 π/2

π/2 π/2

π/2π/2

π/2 π/2

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 π/2 π/2

π π

π π

π/2 π/2

0 02P3/2

2P1/2

2S1/2

I = 3/210

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

Largediameter

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 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, Phys. Rev. Lett. 74, 355 (1995).

350260040

53080030

82040025

161016020

502.55015

Γ (x 2π kHz)τ (µs)Vdd(kHz)n

43

0

21dd 4

nrddV ∝=

πε 31n

∝τ

Γ> 100ddV

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

100.01τ (µs)

5x1045x105I (Wcm-2)

1625n

1.0610.6λ (µm)

Ionisation rate

R. M. Potvliege, private communication

University of Durham Rydberg gates

~ 10 µm

Low decoherenceUniversity of Durham

Photon scattering rate for a trap frequency of 1 MHz

25 s-1 at 790 nm!

Nd:YAG

CO2

0.0002 s-1 at 450 nm!

0.002s-1

Rb5p6p7p

5p

6p

5s

7p

Far redFar blue

‘Blue’‘Red’

2

0

41

10~ −

Uωh0

- U0

0

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 ττ >

Magic Rydberg lattice488 nm 514 nm

Long coherence

University of Durham 428 nm lattice proposal

R.M. Potvliege and C.S. Adams, preprint

2P3/2

2P1/2

2S1/2

I = 3/210

0 detection 1 detection

1. Doubled 856 nm: 3 orthogonal beam pairs.phase stable

2. Mott insulator

3. Local addressing with a ‘pointer’

4. Transfer to expandable lattice + state selective transport to perform read-out

T. Calarco et al. quant-ph/0403197

428 nm428 nm

421 nm

6p 2P

125 mW in 50 µm

100 kHz

Optical lattices: scalability

Low decoherenceFar-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 GriffinKevin WeatherillMatt Pritchard

Research assistants: Simon Cox (up to 08/04)

Collaborators: Erling Riis (Strathclyde)Ifan Hughes, Simon Cornish

Technical support: Robert Wylie (Strathclyde)

Financial support: Previously EPSRC

http://massey.dur.ac.uk/

University of Durham