Fully tunable hyperfine interactions of hole spin qubits in Si and Ge quantum dots

Bosco, Stefano; Loss, Daniel

doi:10.48550/arxiv.2106.13744

Cited by 3 publications

(7 citation statements)

References 49 publications

(125 reference statements)

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“…These effects may be more or less critical depending on the actual design of the quantum dots. They are not only relevant for the manipulation and readout of spin qubits [41,42,65], but raise new opportunities and challenges, such as the detection of the fingerprints of correlations in the dynamics of quantum dots and quantum dot arrays, or when piling up additional electrons in one-dimensional channels [81].…”

Section: Discussionmentioning

confidence: 99%

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Two-body Wigner molecularization in asymmetric quantum dot spin qubits

Abadillo-Uriel,

Martinez,

Filippone

et al. 2021

Preprint

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Coulomb interactions strongly influence the spectrum and the wave functions of few electrons or holes confined in a quantum dot. In particular, when the confinement potential is not too strong, the Coulomb repulsion triggers the formation of a correlated state, the Wigner molecule, where the particles tend to split apart. We show that the anisotropy of the confinement potential strongly enhances the molecularization process and affects the performances of quantum-dot systems used as spin qubits. Relying on analytical and numerical solutions of the two-particle problem -both in a simplified single-band approximation and in realistic setups -we highlight the exponential suppression of the singlet-triplet gap with increasing anisotropy. We compare the molecularization effects in different semiconductor materials and discuss how they specifically hamper Pauli spin blockade readout and reduce the exchange interactions in two-qubit gates.

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Section: Discussionmentioning

confidence: 99%

“…Interestingly, some architectures, such as dots confined along a one-dimensional (nanowire) channel [5,[37][38][39], can produce very anisotropic qubits. This anisotropy may be leveraged to enhance the qubit performances by, e.g., increasing the Rabi frequencies (as proposed in hole spin qubits [40][41][42]).…”

Section: Introductionmentioning

confidence: 99%

Two-body Wigner molecularization in asymmetric quantum dot spin qubits

Abadillo-Uriel,

Martinez,

Filippone

et al. 2021

Preprint

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“…2(a), only shown for low electric field, correspond to Eq. (25). In analogy, we show the low-field approximation for the overlap amplitude between the HH and LH wave functions in Fig.…”

Section: And For the Matrix Elements Of Kmentioning

confidence: 97%

“…These working points are ideal for qubit manipulation because they maximize the speed of operation, while reducing drastically the effect of charge noise [55,56]. However, the qubit is not protected against other sources of noise such as random fluctuations of l y or hyperfine noise, that could still be addressed by appropriately designing the QD [25,53]. A detailed analysis of these noise sources in Ge NWs is of interest but is beyond the scope of the present work.…”

Section: A Qubit Operationmentioning

confidence: 99%

“…The physics of hole spins in semiconductors such as germanium (Ge) and silicon (Si) has attracted much attention lately because it naturally enables stronger SOI than in electron systems [6][7][8][9][10][11][12]. Another great advantage of hole spins is their tunable response to the hyperfine interactions [13][14][15][16][17][18], a major decoherence channel in spin qubits [19][20][21][22][23][24], which can be made far weaker than in electron QDs [25,26]. Furthermore in Si and Ge, the hyperfine interactions can also be minimized by isotopically purifying the material [27,28].…”

Section: Introductionmentioning

confidence: 99%

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Hole Spin Qubits in Ge Nanowire Quantum Dots: Interplay of Orbital Magnetic Field, Strain, and Growth Direction

Adelsberger,

Benito,

Bosco

et al. 2021

Preprint

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Hole spin qubits in quasi one-dimensional structures are a promising platform for quantum information processing because of the strong spin-orbit interaction (SOI). We present analytical results and discuss device designs that optimize the SOI in Ge semiconductors. We show that at the magnetic field values at which qubits are operated, orbital effects of magnetic fields can strongly affect the response of the spin qubit. We study one-dimensional hole systems in Ge under the influence of electric and magnetic fields applied perpendicularly to the device. In our theoretical description, we include these effects exactly. The orbital effects lead to a strong renormalization of the g-factor.We find a sweet-spot of the nanowire (NW) g-factor where charge noise is strongly suppressed and present an effective low-energy model that captures the dependence of the SOI on the electromagnetic fields. Moreover, we compare properties of NWs with square and circular cross-sections with ones of gate-defined one-dimensional channels in two-dimensional Ge heterostructures. Interestingly, the effective model predicts a flat band ground state for fine-tuned electric and magnetic fields. By considering a quantum dot (QD) harmonically confined by gates, we demonstrate that the NW g-factor sweet spot is retained in the QD. Our calculations reveal that this sweet spot can be designed to coincide with the maximum of the SOI, yielding highly coherent qubits with large Rabi frequencies. We also study the effective g-factor of NWs grown along different high symmetry axes and find that our model derived for isotropic semiconductors is valid for the most relevant growth directions of non-isotropic Ge NWs. Moreover, a NW grown along one of the three main crystallographic axes shows the largest SOI. Our results show that the isotropic approximation is not justified in Ge in all cases.

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Squeezed hole spin qubits in Ge quantum dots with ultrafast gates at low power

et al. 2021

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Hole spin qubits in planar Ge heterostructures are one of the frontrunner platforms for scalable quantum computers. In these systems, the spin-orbit interactions permit efficient all-electric qubit control. We propose a minimal design modification of planar devices that enhances these interactions by orders of magnitude and enables low power ultrafast qubit operations in the GHz range. Our approach is based on an asymmetric potential that strongly squeezes the quantum dot in one direction. This confinement-induced spin-orbit interaction does not rely on microscopic details of the device such as growth direction or strain and could be turned on and off on demand in state-of-the-art qubits.

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Fully tunable hyperfine interactions of hole spin qubits in Si and Ge quantum dots

Cited by 3 publications

References 49 publications

Two-body Wigner molecularization in asymmetric quantum dot spin qubits

Two-body Wigner molecularization in asymmetric quantum dot spin qubits

Hole Spin Qubits in Ge Nanowire Quantum Dots: Interplay of Orbital Magnetic Field, Strain, and Growth Direction

Squeezed hole spin qubits in Ge quantum dots with ultrafast gates at low power

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