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Quadrupolar and anisotropy effects on dephasing in two-electron spin qubits in GaAs.

Botzem T, McNeil RP, Mol JM, Schuh D, Bougeard D, Bluhm H - Nat Commun (2016)

Bottom Line: Interesting effects arise from the quadrupolar interaction of nuclear spins with electric field gradients, which have been shown to suppress diffusive nuclear spin dynamics and might thus enhance electron spin coherence.However, this effect disappears for appropriate field directions.Furthermore, we observe an additional modulation of coherence attributed to an anisotropic electronic g-tensor.

View Article: PubMed Central - PubMed

Affiliation: JARA-Institute for Quantum Information, RWTH Aachen University, D-52074 Aachen, Germany.

ABSTRACT
Understanding the decoherence of electron spins in semiconductors due to their interaction with nuclear spins is of fundamental interest as they realize the central spin model and of practical importance for using them as qubits. Interesting effects arise from the quadrupolar interaction of nuclear spins with electric field gradients, which have been shown to suppress diffusive nuclear spin dynamics and might thus enhance electron spin coherence. Here we show experimentally that for gate-defined GaAs quantum dots, quadrupolar broadening of the nuclear Larmor precession reduces electron spin coherence by causing faster decorrelation of transverse nuclear fields. However, this effect disappears for appropriate field directions. Furthermore, we observe an additional modulation of coherence attributed to an anisotropic electronic g-tensor. These results complete our understanding of dephasing in gated quantum dots and point to mitigation strategies. They may also help to unravel unexplained behaviour in self-assembled quantum dots and III-V nanowires.

No MeSH data available.


Related in: MedlinePlus

Device layout and quadrupole broadening.(a) Gates used for pulsed qubit control are depicted in blue; the energy of the conduction band edge ECB is shown on the left. (b) Nuclear spins 3/2 with magnetic moment μ in the proximity of the quantum dot experience quadrupolar coupling with electric field gradients Vx′x′ induced by crystal distortion due to the electric field of the triangular quantum well. (c) While the centre transition, with splitting ω0, stays unchanged, the satellite transitions, distorted by the electron's own charge, exhibit a quadrupolar shift by ωQ. (d) The resulting frequency distribution F(ω) consists of two Gaussians with different variances, one showing an excess quadrupolar broadening of δωQ. (e) Echo amplitude for magnetic fields along the [110] axis, showing oscillations with the relative Larmor frequencies of the three nuclear spins. A semi-classical model (solid line) is used to fit the data (dots, offset for clarity).
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f1: Device layout and quadrupole broadening.(a) Gates used for pulsed qubit control are depicted in blue; the energy of the conduction band edge ECB is shown on the left. (b) Nuclear spins 3/2 with magnetic moment μ in the proximity of the quantum dot experience quadrupolar coupling with electric field gradients Vx′x′ induced by crystal distortion due to the electric field of the triangular quantum well. (c) While the centre transition, with splitting ω0, stays unchanged, the satellite transitions, distorted by the electron's own charge, exhibit a quadrupolar shift by ωQ. (d) The resulting frequency distribution F(ω) consists of two Gaussians with different variances, one showing an excess quadrupolar broadening of δωQ. (e) Echo amplitude for magnetic fields along the [110] axis, showing oscillations with the relative Larmor frequencies of the three nuclear spins. A semi-classical model (solid line) is used to fit the data (dots, offset for clarity).

Mentions: The qubit studied here is a two-electron spin qubit124, using the mz=0 subspace of the spin singlet S and spin triplet T0 of two-electron spins. These electrons are confined in a GaAs double quantum dot formed by electrostatic gating (Fig. 1a) of a two-dimensional electron gas (2DEG). The effects explored in this work apply equally to single electron spins.


Quadrupolar and anisotropy effects on dephasing in two-electron spin qubits in GaAs.

Botzem T, McNeil RP, Mol JM, Schuh D, Bougeard D, Bluhm H - Nat Commun (2016)

Device layout and quadrupole broadening.(a) Gates used for pulsed qubit control are depicted in blue; the energy of the conduction band edge ECB is shown on the left. (b) Nuclear spins 3/2 with magnetic moment μ in the proximity of the quantum dot experience quadrupolar coupling with electric field gradients Vx′x′ induced by crystal distortion due to the electric field of the triangular quantum well. (c) While the centre transition, with splitting ω0, stays unchanged, the satellite transitions, distorted by the electron's own charge, exhibit a quadrupolar shift by ωQ. (d) The resulting frequency distribution F(ω) consists of two Gaussians with different variances, one showing an excess quadrupolar broadening of δωQ. (e) Echo amplitude for magnetic fields along the [110] axis, showing oscillations with the relative Larmor frequencies of the three nuclear spins. A semi-classical model (solid line) is used to fit the data (dots, offset for clarity).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4835533&req=5

f1: Device layout and quadrupole broadening.(a) Gates used for pulsed qubit control are depicted in blue; the energy of the conduction band edge ECB is shown on the left. (b) Nuclear spins 3/2 with magnetic moment μ in the proximity of the quantum dot experience quadrupolar coupling with electric field gradients Vx′x′ induced by crystal distortion due to the electric field of the triangular quantum well. (c) While the centre transition, with splitting ω0, stays unchanged, the satellite transitions, distorted by the electron's own charge, exhibit a quadrupolar shift by ωQ. (d) The resulting frequency distribution F(ω) consists of two Gaussians with different variances, one showing an excess quadrupolar broadening of δωQ. (e) Echo amplitude for magnetic fields along the [110] axis, showing oscillations with the relative Larmor frequencies of the three nuclear spins. A semi-classical model (solid line) is used to fit the data (dots, offset for clarity).
Mentions: The qubit studied here is a two-electron spin qubit124, using the mz=0 subspace of the spin singlet S and spin triplet T0 of two-electron spins. These electrons are confined in a GaAs double quantum dot formed by electrostatic gating (Fig. 1a) of a two-dimensional electron gas (2DEG). The effects explored in this work apply equally to single electron spins.

Bottom Line: Interesting effects arise from the quadrupolar interaction of nuclear spins with electric field gradients, which have been shown to suppress diffusive nuclear spin dynamics and might thus enhance electron spin coherence.However, this effect disappears for appropriate field directions.Furthermore, we observe an additional modulation of coherence attributed to an anisotropic electronic g-tensor.

View Article: PubMed Central - PubMed

Affiliation: JARA-Institute for Quantum Information, RWTH Aachen University, D-52074 Aachen, Germany.

ABSTRACT
Understanding the decoherence of electron spins in semiconductors due to their interaction with nuclear spins is of fundamental interest as they realize the central spin model and of practical importance for using them as qubits. Interesting effects arise from the quadrupolar interaction of nuclear spins with electric field gradients, which have been shown to suppress diffusive nuclear spin dynamics and might thus enhance electron spin coherence. Here we show experimentally that for gate-defined GaAs quantum dots, quadrupolar broadening of the nuclear Larmor precession reduces electron spin coherence by causing faster decorrelation of transverse nuclear fields. However, this effect disappears for appropriate field directions. Furthermore, we observe an additional modulation of coherence attributed to an anisotropic electronic g-tensor. These results complete our understanding of dephasing in gated quantum dots and point to mitigation strategies. They may also help to unravel unexplained behaviour in self-assembled quantum dots and III-V nanowires.

No MeSH data available.


Related in: MedlinePlus