Optical Orientation of Nuclear Spins in an Individual Quantum Dot

Electron spins trapped in solid-state systems can
exhibit strong hyperfine interactions with a nuclear
spin reservoir, which is normally fluctuating and
randomly oriented. As this represents a fundamental
decoherence mechanism for the electron spin, several
theoretical scenarios to suppress this effect in
semiconductor quantum dots (QDs) have been proposed.
However, implementing these proposals requires a
deeper understanding of the properties of the QD
nuclear spin ensemble and of the possibilities to
manipulate the nuclear spins. The present work
describes an experimental assessment of these topics.
Optical preparation and detection of the spin and
energy of QD electrons was used to manipulate and
measure the average nuclear spin polarization (NSP)
in an individual QD. Studying NSP as a function of
external paramters such as magnetic fields, QD charge
and of time revealed the nonlinear character of
electron-nuclear spin coupling and led to the
identification of the dominant spin-relaxation
mechanisms for QD nuclei. Ultimately, further
understanding of the subtle interactions that govern
the QD nuclear spin system could enable us to improve
the spin coherence time of QD electrons.

Autorentext

P.M. studied Physics from 1998 to 2004 both at ETH Zürich and ENSParis. After obtaining his Diploma he worked as a ResearchAssistant at JILA (Univerity of Colorado). From 2005 to 2008 hegraduated with the present work under the supervision of Prof. A.Imamoglu (ETH Zürich). P.M. is currently a postdoctoral ResearchScholar at Harvard University.

Klappentext

Electron spins trapped in solid-state systems can exhibit strong hyperfine interactions with a nuclear spin reservoir, which is normally fluctuating and randomly oriented. As this represents a fundamental decoherence mechanism for the electron spin, several theoretical scenarios to suppress this effect in semiconductor quantum dots (QDs) have been proposed. However, implementing these proposals requires a deeper understanding of the properties of the QD nuclear spin ensemble and of the possibilities to manipulate the nuclear spins. The present work describes an experimental assessment of these topics. Optical preparation and detection of the spin and energy of QD electrons was used to manipulate and measure the average nuclear spin polarization (NSP) in an individual QD. Studying NSP as a function of external paramters such as magnetic fields, QD charge and of time revealed the nonlinear character of electron-nuclear spin coupling and led to the identification of the dominant spin-relaxation mechanisms for QD nuclei. Ultimately, further understanding of the subtle interactions that govern the QD nuclear spin system could enable us to improve the spin coherence time of QD electrons.