Rutger M T Thijssen Van der Waals Zeeman Instituut voor Experimentele Natuurkunde Abstract In Amsterdam We have recently produced the first twodimensional lattice of magnetic microtraps for ultracold atoms based on patterned magnetic films 1 Ultracold rubidium atoms are transferred to ID: 273268
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Slide1
Coherent excitation of Rydberg atoms on an atom chip
Rutger M. T. ThijssenVan der Waals - Zeeman Instituut voor Experimentele NatuurkundeSlide2
Abstract
In Amsterdam We have recently produced the first two-dimensional lattice of magnetic microtraps for ultracold atoms based on patterned magnetic films [1]. Ultracold rubidium atoms are transferred to hundreds of individual microtraps, each cloud hovering 10 micrometers above the chip surface and separated by ~20 micrometers. We are currently investigating highly excited Rydberg states of the atoms, used to mediate long-range interactions between neighbouring microtraps. This could allow entanglement of mesoscopic ensembles of atoms and paves the road toward quantum information processing with neutral atoms. We have built a dedicated laser system using 780 nm and 480 nm narrow-band diode lasers stabilised to a two-photon electromagnetically induced transparency resonance in a Rubidium vapour cell. We can excite Rydberg states from n=19 up to n~100. We have used this system to excite and image Rydberg atoms in ultracold rubidium gas confined in a surface magneto-optical trap. We are now studying the influence of the nearby (magnetic and conducting) chip surface on the Rydberg excited atoms.
[1] S. Whitlock, R. Gerritsma, T. Fernholz and R. J. C. Spreeuw, New J. Phys. 11 023021 (2009) Slide3
Quantum Information Processing
QubitsCoherenceSwitchable interactionsScalabilitySlide4
MAGCHIPSSlide5
MAGCHIPS
Permanent magnetic lattice atom chip
Gold-coated for laser cooling
500 populated magnetic microtraps
Prospective qubits
87
Rb,
T
~
m
K
10
µ
m
22
µ
m
Magnetised
film
“Atom chip”(room temperature)Slide6
Neutral atoms: intrinsically weak interaction with environmentExquisite control & manipulation
ScalabilityStable qubits
Quantum information on MAGCHIPSSlide7
Neutral atoms: intrinsically weak interaction with environmentExquisite control & manipulation
ScalabilityStable qubits
Quantum information on MAGCHIPS
Intrinsically weak interaction with environment
Good: long coherence times (~sec.)
Challenge: quantum information requires interaction: we have to work to add an interaction between qubits (i.e. traps)Slide8
Rydberg atoms
Hydrogen-like atomHigh principal (n) quantum numberLarge dipole-dipole interaction between Rydberg atoms
Dipole blockadeSlide9
Rydberg Excitation
Toptica DL-100 diode laser (30mW)
Toptica TA-SHG 110 frequency doubled diode laser, tunable from 488-479nm (n=18-ionization threshold) (300mW)
|
n
d
|5s
|5p
780nm (infrared)
480nm (blue)
|
n
s
Slide10
Electromagnetically Induced Transparency
|nd
|5s
|5p
Ω
p
δω
p
γ
12
Detuning (
δω
p
)Slide11
Electromagnetically Induced Transparency
|
nd
|5s
|5p
Ω
c
Ω
p
δω
p
γ
12
Detuning (
δω
p
)Slide12
Electromagnetically Induced Transparency – dressed states
|a+
780nm (infrared)
|a
0
(5s)
|a
-
Rediagonalise interaction Hamiltonian
Interference between |a+
and |a-
dressed states: reduced probe absorption on two-photon resonance
|5s
|5p
|
n
d
Ω
c
Ω
p
Autler – Townes splitting + Fano interferenceSlide13
+
EIT – interfering pathways
|5s
|5p
|
n
d
Ω
c
Ω
p
|5s
|5p
|
n
d
Ω
p
|5s
|5p
|
n
d
(
Ω
c
)
2
Ω
p
Fano interferenceSlide14
EIT – frequency stabilisation in a vapour cell
Coupling laser detuning (MHz)
vapour cell EIT, |39d
dichroic mirror
dichroic mirror
Rubidium vapour cell
fast photodiode
780 nm diode laser
480 nm diode laserSlide15
EIT Imaging
optical fiberSlide16
EIT Imaging
optical fiberSlide17
Position (px)
Detuning (MHz)
Optical density
EIT Imaging
Blue laser frequency locked to vapour cell EIT
Red laser scanned over resonanceSlide18
Surface effects
Near-field blackbody radiation from chip
“mirror” effect: Rydberg atom interacting with itself
Photoelectric effect on surface: adsorbed Rb, Au
Patch potentials
Crystal defects in FePt
Adsorbed Rb ionsSlide19
Summary
MAGCHIPS experiment Rydberg / EIT for interactions between qubitsBuilt laser systemBuilt frequency locking setup for probe and coupling laserImaged Rydberg / EIT in surface magneto-optical trap Investigating effects of surface on Rydberg levels
Build a quantum computer…Slide20
Summary
MAGCHIPS experiment Rydberg / EIT for interactions between qubitsBuilt laser systemBuilt frequency locking setup for probe and coupling laserImaged Rydberg / EIT in surface magneto-optical trap Investigating effects of surface on Rydberg levels
Build a quantum computer…Slide21
THANK YOU
Questions?
Rutger M. T. Thijssen
rmeijert@science.uva.nlSlide22Slide23
2-photon gates
Zoller Mesoscopic Rydberg gates using EIT
Rydberg
interaction
|0> |1>
|0> |1>
Focused
lasers
Ensemble A
Ensemble B
Microwave/Raman
6.8 GHzSlide24Slide25
Rydberg Atoms
One highly excited electron (n=20-100)Rydberg formula:Size ~ n^2Lifetime ~ n^3Polarisability ~n^7Van der Waals interaction ~ n^11Dipole blockade shifts nearby Rydberg levels