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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

g-factor anisotropy and fit parameters.(a) Due to an anisotropic g-tensor electron and nuclear spins have different quantization axes, Beff and Bext, respectively. This leads to a linear contribution of the transverse Overhauser field to the electronic Zeeman splitting, oscillating with the Larmor frequencies of the nuclear spins. (b,c) Fit parameters extracted for different in-plane magnetic field directions θ. The quadrupolar contribution to nuclear broadening δBα=ħδωQ,α/γα, expressed in terms of an equivalent linewidth for the three isotopes using equation (1), vanishes at 45° along the [100] direction. At the same angle, the sin(2θ) dependence of the coupling g⊥ with the transverse hyperfine field reaches a maximum.
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f4: g-factor anisotropy and fit parameters.(a) Due to an anisotropic g-tensor electron and nuclear spins have different quantization axes, Beff and Bext, respectively. This leads to a linear contribution of the transverse Overhauser field to the electronic Zeeman splitting, oscillating with the Larmor frequencies of the nuclear spins. (b,c) Fit parameters extracted for different in-plane magnetic field directions θ. The quadrupolar contribution to nuclear broadening δBα=ħδωQ,α/γα, expressed in terms of an equivalent linewidth for the three isotopes using equation (1), vanishes at 45° along the [100] direction. At the same angle, the sin(2θ) dependence of the coupling g⊥ with the transverse hyperfine field reaches a maximum.

Mentions: To further investigate the origin of these oscillations, we aligned Bext along the [100]-axis and varied its magnitude in Fig. 3. With decreasing Bext, the frequency of the modulation decreases, until at 100 mT only a very fast decay of the echo amplitude followed by a revival at ≈13 μs occurs. This envelope modulation can be explained by an electronic g-factor anisotropy, arising from an asymmetric confinement of the electron in the 2DEG and spin–orbit coupling303132. The main axes of the g-tensor are expected to be the [110] and crystal axis, consistent with the absence of a fast echo modulation with B along these directions. For other field directions, the quantization axis of the electron differs from the external field around which the nuclear spins precess. A linear coupling with the transverse nuclear magnetic field thus appears in the effective magnetic field determining the electronic Zeeman splitting (Fig. 4a; Supplementary Fig. 1; Supplementary Note 3):


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)

g-factor anisotropy and fit parameters.(a) Due to an anisotropic g-tensor electron and nuclear spins have different quantization axes, Beff and Bext, respectively. This leads to a linear contribution of the transverse Overhauser field to the electronic Zeeman splitting, oscillating with the Larmor frequencies of the nuclear spins. (b,c) Fit parameters extracted for different in-plane magnetic field directions θ. The quadrupolar contribution to nuclear broadening δBα=ħδωQ,α/γα, expressed in terms of an equivalent linewidth for the three isotopes using equation (1), vanishes at 45° along the [100] direction. At the same angle, the sin(2θ) dependence of the coupling g⊥ with the transverse hyperfine field reaches a maximum.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: g-factor anisotropy and fit parameters.(a) Due to an anisotropic g-tensor electron and nuclear spins have different quantization axes, Beff and Bext, respectively. This leads to a linear contribution of the transverse Overhauser field to the electronic Zeeman splitting, oscillating with the Larmor frequencies of the nuclear spins. (b,c) Fit parameters extracted for different in-plane magnetic field directions θ. The quadrupolar contribution to nuclear broadening δBα=ħδωQ,α/γα, expressed in terms of an equivalent linewidth for the three isotopes using equation (1), vanishes at 45° along the [100] direction. At the same angle, the sin(2θ) dependence of the coupling g⊥ with the transverse hyperfine field reaches a maximum.
Mentions: To further investigate the origin of these oscillations, we aligned Bext along the [100]-axis and varied its magnitude in Fig. 3. With decreasing Bext, the frequency of the modulation decreases, until at 100 mT only a very fast decay of the echo amplitude followed by a revival at ≈13 μs occurs. This envelope modulation can be explained by an electronic g-factor anisotropy, arising from an asymmetric confinement of the electron in the 2DEG and spin–orbit coupling303132. The main axes of the g-tensor are expected to be the [110] and crystal axis, consistent with the absence of a fast echo modulation with B along these directions. For other field directions, the quantization axis of the electron differs from the external field around which the nuclear spins precess. A linear coupling with the transverse nuclear magnetic field thus appears in the effective magnetic field determining the electronic Zeeman splitting (Fig. 4a; Supplementary Fig. 1; Supplementary Note 3):

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