Aiming at Quantum Information Processing on an Atom Chip

Aiming at Quantum Information Processing on an Atom Chip

Caspar Ockeloen

OutlineOutline

• Quantum Information with Ultracold Atoms

• Magnetic lattice atom chip

• Atom number fluctuations

• Conclusion

Quantum InformationQuantum Information

Requirements:

• Scalable

• Long coherence time

• Nearest neighbor interactions

Ultracold AtomsUltracold Atoms

• Clean and isolated Quantum systems

• Coherence time up to 1 minute!

104 –103 –102 –101 –

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 TC superconductor

Magnetic lattice atom chipMagnetic 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

Magnetic lattice atom chipMagnetic 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

Absorption ImagingAbsorption Imaging

S. Whtilock et al “Two-dimensional array of microtraps with atomic shift register on a chip”, NJP, (2009)

Atom chip

Absorption image of full lattice

Single site manipulationSingle site manipulation

• Optically address single sites

• Transport all atoms across the lattice

How to make qubits?

Collective excitationsCollective 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

Classical limit: Shot NoiseClassical limit: Shot Noise

• Atoms are discrete particles

• Poisson distribution: N ± √N atoms

Three-body lossThree-body loss

• Dominant loss process

• Three atoms → Molecule + Free atom

• 3-body interaction: density dependent

Three-body lossThree-body loss

Effects on atom number distribution

Initial distribution3-body lossPoisson distribution

Poisson distributionN = 100 N = 10

F =0.6

Fluctuations

Fano factor:F = 1 ↔ Poisson

Three-body lossThree-body loss

Mean atom number

Mean atom numberMean atom number

(a)

FluctuationsFluctuations

Sub-Poissonian!

S. Whitlock, C. Ockeloen, R.J.C Spreeuw, PRL 104, 120402 (2010)

FluctuationsFluctuations

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

ConclusionsConclusions

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

OutlookOutlook

• Long range interactions

• New lattice design – New geometries– 5 m spacing– In vacuum imaging

• Quantum Computer...

Thank youThank 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)