Quantum-Dot Spin-State Preparation with Near-Unity Fidelity

1
Quantum-Dot Spin-State Preparation with
Near-Unity Fidelity

• M. Atatüre, J. Dreiser, A. Badolato, A. Högele,
• K. Karrai, A. Imamoglou
• Science 312, 551 (2006)

30.01.07
2
Overview

• Optical controlling of spin in quantum-dots at 4
  K
• High fidelity spin state preparation due to Pauli
  blockade
• Self-assembled InAs/GaAs QD

3
Four-Level System for B0
EF
EF
g (s) Spontaneous spin-flip Raman scattering

• (s-)
• Laser absorbtion

EF
EF
x Hyperfine induced spin-flip
4
Four-Level System for Bgt0
EF
EF
g (s) Spontaneous spin-flip Raman scattering

• (s-)
• Laser absorbtion

EF
EF
x Hyperfine induced spin-flip
5
Four-Level System for Bgt0 with Repump Laser
EF
EF
g (s)
g (s-)

• (s)
• Laser absorbtion

• (s-)
• Laser absorbtion

EF
EF
x Hyperfine induced spin-flip
6
How It Works
Blocked!
EF
7
Results Laser Absorption
Repump Laser detuned by 6 GHz (Zeeman splitting)
Absorbtion suppressed due to Pauli blockade
Absorbtion due to cotunneling
Linewidth of the transition X-
8
Results High Fidelity
Theoretical model
Repump Laser
Experimental data
Exponential fit
9
Conclusions and Outlook

• High-fidelity spin preparation (99.8 )
• Spin cooling down to 20 mK (T4 K)
• Works for both spins
• Prepare arbitrary superpostition of spin states
• Tune g by changing the magnetic field orientation
  with respect to the confinement axis

EF
EF
g