Wave Packet Echo in Optical Lattice and Decoherence Time

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Wave Packet Echo in Optical Lattice and
Decoherence Time

• Chao Zhuang
• U(t)
• Aug. 15, 2006
• CQISC2006

University of Toronto
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Aephraim Steinberg Matthew Partlow Samansa
Maneshi Jalani Kanem
Department of Physics, Center for Quantum
Information and Quantum Control, Institute for
Optical Sciences University of Toronto
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Outline

• Pulse echo
• Two level system
• Life time T1, T2, T2
• How it works in What system
• Wave packet echo in optical lattice
• Setup and Measurement
• Optimize echo pulse
• Decoherence and coherence control

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Something General
T1 longitudinal lifetime De-population
T2 transverse homogeneous lifetime De-coherence
T2 transverse inhomogeneous lifetime De-phase
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Pulse echo How it works
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Pulse echo Timeline
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Pulse echo Why its important

• Inhomogeneous decay due to dephasing can be
  reversed!
• (De)coherence time due to homogeneous decay can
  be measured directly.
• Coherence time decides how long quantum
  information can be stored in a quantum system.

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Pulse echo What system

• Spin Echo
• Nuclear Magnetic Resonance
• E. L. Hahn, Phys. Rev. 80, 580 (1950)
• Photon Echo
• Optical Resonance
• N. A. Kurnit, I. D. Abella, and S. R. Hartmann,
  Phys. Rev. Lett. 13, 567 (1964)
• Wave Packet Echo
• F. B. J. Buchkremer, R. Dumke, H. Levsen, G.
  Birkl, and W. Ertmer, Phys. Rev. Lett. 85, 3121
  (2000)

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Optical Lattice
Wave Packet
Optical lattices are periodic potentials formed
by the ac Stark shift (light shift) seen by atoms
when they interact with a set of interfering
laser beams.
I. H. Deutsch and P. S. Jessen, Phys. Rev. A 57,
1972(1998).
Motional atoms in optical lattice
Motional wave packets in optical lattice
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Experimental Setup Vertical Optical Lattice
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Measuring State Population
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Measuring Coherence Oscillations in the Lattice
dephasing due to lattice depth inhomogeneities
T2
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Anatomy of an Echo
original oscillation
oscillation from echo pulse
the echo itself
Dephasing due to primarily lattice inhomogeneities
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Echo in the Lattice (using lattice shifts and
delays as coupling pulses)
max. 13
t
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Preliminary data on Coherence time in 1D and 3D
Lattice

• Decoherence due to
• transverse motion of atoms

inter-well tunneling,
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2D Fourier Spectroscopy
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Initial Results
drive freq. Hz
observed oscillation freq. Hz
driven monochromatically with 10 cycles
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What if we try bang-bang?
(Repeat pulses before the bath gets amnesia
trade-off since each pulse is imperfect.)
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bang-bang pulse sequences...Some coherence out
to gt 3 ms now...
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Summary

• Optimisation of certain class of echo pulses
• Preliminary work on 3D lattice
• Preliminary work on characterization of
  frequency
• response of the system due to Quasi-monochromatic
  excitation
• Observation of higher-order Echoes
• Future work
• Characterize homogeneous and inhomogeneous
• broadening through 2D FT spectroscopy
• Design adiabatic pulses for inversion of
  states
• Study decoherence due to tunneling