Controlling hole spins in quantum dots and wells

Chesi, Stefano; Wang, Xiaoya Judy; Coish, W. A.

doi:10.1140/epjp/i2014-14086-2

Cited by 11 publications

(9 citation statements)

References 130 publications

(256 reference statements)

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“…(12) with the spin operators given in Eqs. (14), (15), (16). If the electronic state is well-described by an s-like band, the isotropic contact interaction dominates, giving the well-known result for an electron spin in a quantum dot, 6,7…”

Section: B Summary Of Key Resultsmentioning

confidence: 99%

First-principles hyperfine tensors for electrons and holes in GaAs and silicon

2020

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Understanding (and controlling) hyperfine interactions in semiconductor nanostructures is important for fundamental studies of material properties as well as for quantum information processing with electron, hole, and nuclear-spin states. Through a combination of first-principles densityfunctional theory (DFT) and k · p theory, we have calculated hyperfine tensors for electrons and holes in GaAs and crystalline silicon. Accounting for relativistic effects near the nuclear core, we find contact hyperfine interactions for electrons in GaAs that are consistent with Knight-shift measurements performed on GaAs quantum wells and are roughly consistent with prior estimates extrapolated from measurements on InSb. We find that a combination of DFT and k · p theory (DFT+k · p) is necessary to accurately determine the contact hyperfine interaction for electrons at a conduction-band minimum in silicon that is consistent with bulk Knight-shift measurements. For hole spins in GaAs, the overall magnitude of the hyperfine couplings we find from DFT is consistent with previous theory based on free-atom properties, and with heavy-hole Overhauser shifts measured in GaAs (and InGaAs) quantum dots. In addition, we theoretically predict that the heavy-hole hyperfine coupling to the As nuclear spins is stronger and almost purely Ising, while the (weaker) coupling to the Ga nuclear spins has significant non-Ising corrections. In the case of hole spins in silicon, we find (surprisingly) that the strength of the hyperfine interaction in the valence band is comparable to that in the conduction band and that the hyperfine tensors are highly anisotropic (Ising) in the heavy-hole subspace. These results suggest that the hyperfine coupling cannot be ruled out as a limiting mechanism for coherence (T * 2 ) times recently measured for heavy holes in silicon quantum dots. arXiv:2001.05963v2 [cond-mat.mes-hall]

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Section: B Summary Of Key Resultsmentioning

confidence: 99%

First-principles hyperfine tensors for electrons and holes in GaAs and silicon

2020

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“…When developing spin-qubit technology, a fundamental question arises: What defines the coupling of a single isolated spin to the external magnetic field? While this has been well studied for electrons [2,16], the complexity of hole-spin states makes this a nontrivial question [17][18][19][20][21][22]. Holes occupy the valence band, which originates from l = 1 atomic p orbitals, with an effective spin of S = 3 2 and a strong intrinsic spin-orbit coupling.…”

Section: Introductionmentioning

confidence: 99%

Electrical control of the g tensor of the first hole in a silicon MOS quantum dot

et al. 2021

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Single holes confined in semiconductor quantum dots are a promising platform for spin-qubit technology, due to the electrical tunability of the g factor of holes. However, the underlying mechanisms that enable electric spin control remain unclear due to the complexity of hole-spin states. Here, we study the underlying hole-spin physics of the first hole in a silicon planar metal-oxide-semiconductor (MOS) quantum dot. We show that nonuniform electrode-induced strain produces nanometer-scale variations in the heavy-hole-light-hole (HH-LH) splitting. Importantly, we find that this nonuniform strain causes the HH-LH splitting to vary by up to 50% across the active region of the quantum dot. We show that local electric fields can be used to displace the hole relative to the nonuniform strain profile, allowing a mechanism for electric modulation of the hole g tensor. Using this mechanism, we demonstrate tuning of the hole g factor by up to 500%. In addition, we observe a potential sweet spot where dg (110) /dV = 0, offering a configuration to suppress spin decoherence caused by electrical noise. These results open a path towards a technology involving engineering of nonuniform strains to optimize spin-based devices.

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“…Anisotropic hyperfine couplings between a central qubit spin and environmental spins are important for nitrogen-vacancy centers in diamond, [26][27][28] electrons bound to phosphorus donor impurities in silicon, 29,30 electrons in graphene or carbon nanotubes, 31,32 and especially for hole spins in III-V semiconductors or silicon. [33][34][35][36][37] Heavy-hole spins can indeed approach the extreme-anisotropic limit of a pure Ising-like coupling to nuclear spins. 33 Finally, singlettriplet (S-T 0 ) qubits, describing two electrons in a double quantum dot, are described by precisely the same anisotropic decoherence model 38 as a heavy-hole spin qubit (see Fig.…”

Section: Introductionmentioning

confidence: 99%

“…37 Measurements of a coherent-population-trapping dip 39,40 have suggested long hole-spin coherence times, 100 ns. These measurements have been supported by timedomain studies for single-hole spin echoes 41,42 and modelocking or spin-echo measurements for ensembles.…”

Section: Introductionmentioning

confidence: 99%

Maximizing the purity of a qubit evolving in an anisotropic environment

2015

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We provide a general method to calculate and maximize the purity of a qubit interacting with an anisotropic non-Markovian environment. Counter to intuition, we find that the purity is often maximized by preparing and storing the qubit in a superposition of non-interacting eigenstates. For a model relevant to decoherence of a heavy-hole spin qubit in a quantum dot or for a singlettriplet qubit for two electrons in a double quantum dot, we show that preparation of the qubit in its non-interacting ground state can actually be the worst choice to maximize purity. We further give analytical results for spin-echo envelope modulations of arbitrary spin components of a hole spin in a quantum dot, going beyond a standard secular approximation. We account for general dynamics in the presence of a pure-dephasing process and identify a crossover timescale at which it is again advantageous to initialize the qubit in the non-interacting ground state. Finally, we consider a general two-axis dynamical decoupling sequence and determine initial conditions that maximize purity, minimizing leakage to the environment.

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Controlling hole spins in quantum dots and wells

Cited by 11 publications

References 130 publications

First-principles hyperfine tensors for electrons and holes in GaAs and silicon

First-principles hyperfine tensors for electrons and holes in GaAs and silicon

Electrical control of the g tensor of the first hole in a silicon MOS quantum dot

Maximizing the purity of a qubit evolving in an anisotropic environment

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