Yao Group @ HKU Physics
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Suppression of collective fluctuations, and generation and detection of entanglement in spin ensembles |
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A bottleneck problem in quantum computing based on III-V
semiconductors is the fast decoherence of electron spin qubits due
to fluctuations of lattice nuclear spins. We found approaches for
suppressing fluctuations of nuclear spin bath and enhancing qubit
coherence time in different quantum dot systems using in situ
feedbacks in dynamical nuclear polarization processes (see
[17] [21] in publication list). One
of the work is collaborated with Duncan Steel’s experimental group
in Univ. of Michigan whose experiments demonstrated the suppression
of electron spin decoherence by 2 orders of magnitude through
optically controlled nuclear field locking effect in self-assembled quantum
dot.
We also discovered a dynamical nuclear polarization scheme for squeezing the nuclear spin bath
of an electron towards many-body singlets which has zero collective
spin fluctuations and large scale entanglement (see [22] in
publication list). We further
generalized this discovery and developed an approach to prepare
multipartite entanglement through irreversible processes of
collective pumping, applicable to various systems including atomic
spin qubits and donor nuclear spin qubits in Kane’s architecture
(see [23] [26] in publication list).
In the latter system, various symmetric and asymmetric Dicke states
can be deterministically prepared.
In a recent work, we bring up the concept of using Fraunhofer
diffraction of Stokes photons for probing the correlations of
internal degrees of freedom of scatters. We exploit this
diffraction phenomenon for two uses in cold atomic ensembles:
(1) detection of spin entanglement from a sharp diffraction
feature; (2) diffraction based quantum metrology with
collectively enhanced sensitivity. See [36].
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