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

Botzem, Tim; McNeil, Robert; Mol, Jan-Michael; Schuh, Dieter; Bougeard, Dominique; Bluhm, Hendrik

doi:10.1038/ncomms11170

Cited by 33 publications

(48 citation statements)

References 35 publications

(74 reference statements)

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“…The influence of transverse Overhauser fluctuations, B i ⊥ , on the CPMG signal decay was simulated using a semiclassical theory [14,34,35] that previously gave good agreement with echo [17,36] and CPMG [6] experiments (see Suppl. Section 6 for details).…”

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confidence: 93%

Spectrum of the Nuclear Environment for GaAs Spin Qubits

et al. 2017

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Using a singlet-triplet spin qubit as a sensitive spectrometer of the GaAs nuclear spin bath, we demonstrate that the spectrum of Overhauser noise agrees with a classical spin diffusion model over six orders of magnitude in frequency, from 1 mHz to 1 kHz, is flat below 10 mHz, and falls as 1/f 2 for frequency f 1 Hz. Increasing the applied magnetic field from 0.1 T to 0.75 T suppresses electronmediated spin diffusion, which decreases spectral content in the 1/f 2 region and lowers the saturation frequency, each by an order of magnitude, consistent with a numerical model. Spectral content at megahertz frequencies is accessed using dynamical decoupling, which shows a crossover from the few-pulse regime ( 16 π-pulses), where transverse Overhauser fluctuations dominate dephasing, to the many-pulse regime ( 32 π-pulses), where longitudinal Overhauser fluctuations with a 1/f spectrum dominate.

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confidence: 93%

Spectrum of the Nuclear Environment for GaAs Spin Qubits

et al. 2017

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“…In a recent experiment, Botzem et al [47] have investigated nuclear spin correlations using a technique based on electron spin-echo measurements in a GaAs DQD, and have interpreted the results in terms of a distribution of quadrupole splittings for the three nuclear species. For a magnetic field either parallel or perpendicular to the axis of the DQD they report a line width δB which is of order 2 mT for the As nuclei, and is of order 0.4 -0.5 mT for the two Ga species.…”

Section: Discussionmentioning

confidence: 99%

Electron spin-flip correlations due to nuclear dynamics in driven GaAs double dots

et al. 2017

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We present experimental data and associated theory for correlations in a series of experiments involving repeated Landau-Zener sweeps through the crossing point of a singlet state and a spin aligned triplet state in a GaAs double quantum dot containing two conduction electrons, which are loaded in the singlet state before each sweep, and the final spin is recorded after each sweep. The experiments reported here measure correlations on time scales from 4 µs to 2 ms. When the magnetic field is aligned in a direction such that spin-orbit coupling cannot cause spin flips, the correlation spectrum has prominent peaks centered at zero frequency and at the differences of the Larmor frequencies of the nuclei, on top of a frequency-independent background. When the spin-orbit field is relevant, there are additional peaks, centered at the frequencies of the individual species. A theoretical model which neglects the effects of high-frequency charge noise correctly predicts the positions of the observed peaks, and gives a reasonably accurate prediction of the size of the frequency-independent background, but gives peak areas that are larger than the observed areas by a factor of two or more. The observed peak widths are roughly consistent with predictions based on nuclear dephasing times of the order of 60 µs. However, there is extra weight at the lowest observed frequencies, which suggests the existence of residual correlations on the scale of 2 ms. We speculate on the source of these discrepancies.

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“…We obtained this result by using γ ext = 700 µeV in Eq. (6) and N = 36589 sites. We computed n = 148 eigenstates of system M+L with energies in the vicinity of S and found quality indicators f γ = 0.008 and f n = 21.16.…”

Section: Tunnel-coupling In Realistic Systemsmentioning

confidence: 99%

“…For a finite number of sites N in the 2D toy-model, this fluctuation can be compensated by an additional external decay parameter γ ext used as regularization factor, which is added to iγ m → i(γ m + γ ext ) as already introduced in Eq. (6). To define a quality indicator for the fluctuation, we use…”

Section: Markov Approximationmentioning

confidence: 99%

Calculation of tunnel couplings in open gate-defined disordered quantum dot systems

et al. 2018

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Quantum computation based on semiconductor electron-spin qubits requires high control of tunnel-couplings, both across quantum dots and between the quantum dot and the reservoir. The tunnel-coupling to the reservoir sets the qubit detection and initialization bandwidth for energyresolved spin-to-charge conversion and is essential to tune single-electron transistors commonly used as charge detectors. Potential disorder and the increasing complexity of the two-dimensional gatedefined quantum computing devices sets high demands on the gate design and the voltage tuning of the tunnel barriers. We present a Green's formalism approach for the calculation of tunnelcouplings between a quantum dot and a reservoir. Our method takes into account in full detail the two-dimensional electrostatic potential of the quantum dot, the tunnel barrier and reservoir. A Markov approximation is only employed far away from the tunnel barrier region where the density of states is sufficiently large. We calculate the tunnel-coupling including potential disorder effects, which become increasingly important for large-scale silicon-based spin-qubit devices. Studying the tunnel-couplings of a single-electron transistor in Si/SiGe as a showcase, we find that charged defects are the dominant source of disorder leading to variations in the tunnel-coupling of four orders of magnitude.arXiv:1805.01728v1 [cond-mat.mes-hall]

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

Cited by 33 publications

References 35 publications

Spectrum of the Nuclear Environment for GaAs Spin Qubits

Spectrum of the Nuclear Environment for GaAs Spin Qubits

Electron spin-flip correlations due to nuclear dynamics in driven GaAs double dots

Calculation of tunnel couplings in open gate-defined disordered quantum dot systems

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