Pauli spin blockade in undoped Si/SiGe two-electron double quantum dots

Borselli, Matthew; Eng, Kevin; Croke, E. T.; Maune, Brett; Huang, Biqin; Ross, Richard S.; Kiselev, A. A.; Deelman, Peter W.; Alvarado-Rodriguez, Ivan; Schmitz, A.; Sokolich, M.; Holabird, K.S.; Hazard, Thomas; Gyure, Mark F.; Hunter, A. T.

doi:10.1063/1.3623479

Cited by 107 publications

(113 citation statements)

References 18 publications

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“…The double-quantum dot is defined using two layers of electrostatic gates (39)(40)(41)(42)(43)(44). The lower layer of depletion gates is shown in Fig.…”

Section: Methodsmentioning

confidence: 99%

Two-axis control of a singlet–triplet qubit with an integrated micromagnet

Wu¹,

Ward²,

Prance

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

175

193

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The qubit is the fundamental building block of a quantum computer. We fabricate a qubit in a silicon double-quantum dot with an integrated micromagnet in which the qubit basis states are the singlet state and the spin-zero triplet state of two electrons. Because of the micromagnet, the magnetic field difference ΔB between the two sides of the double dot is large enough to enable the achievement of coherent rotation of the qubit's Bloch vector around two different axes of the Bloch sphere. By measuring the decay of the quantum oscillations, the inhomogeneous spin coherence time T 2 * is determined. By measuring T 2 * at many different values of the exchange coupling J and at two different values of ΔB, we provide evidence that the micromagnet does not limit decoherence, with the dominant limits on T 2 * arising from charge noise and from coupling to nuclear spins.semiconductor spin qubit | quantum nanoelectronics F abricating qubits composed of electrons in semiconductor quantum dots is a promising approach for the development of a large-scale quantum computer because of the approach's potential for scalability and for integrability with classical electronics. Much recent progress has been made, and spin manipulation has been demonstrated in systems of two (1-5), three (6, 7), and four (8) quantum dots. A great deal of attention has focused on the singlet-triplet qubit in quantum dots (1, 2, 9-18), which consists of the S z = 0 subspace of two electrons, for which the basis can be chosen to be a singlet and a triplet state. Full two-axis control on the Bloch sphere is achieved by electrical gating in the presence of a magnetic field difference ΔB between the two dots. In previous experiments (2, 9-14), ΔB arises from coupling to nuclear spins in the material, and slow fluctuations in these nuclear fields lead to inhomogeneous decoherence times that, without special nuclear state preparation, typically are shorter than the period of the quantum oscillations. In III-V materials, ΔB is large, so fast oscillation periods of order 10 ns are achievable, but the inhomogeneous dephasing time is also ∼10 ns, so that oscillations from ΔB are overdamped, ending before a complete cycle is observed (2). The fluctuations of the nuclear spin bath can be mitigated to some extent (10), but inhomogeneous dephasing times in III-V materials are short enough that high-fidelity control is still very challenging. Coupling to nuclear spins in silicon is substantially weaker, leading to longer coherence times, but also smaller field differences and hence slower quantum oscillations (14,19).Here, we report the operation of a singlet-triplet qubit in which the magnetic field difference ΔB between the dots is imposed by an external micromagnet (20,21). Because the field from the micromagnet is stable in time, a large ΔB can be imposed without creating inhomogeneous dephasing. We present data demonstrating underdamped quantum oscillations, and, by investigating a variety of voltage configurations and two ΔB configurations, we show that the m...

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“…The double-quantum dot is defined using two layers of electrostatic gates (39)(40)(41)(42)(43)(44). The lower layer of depletion gates is shown in Fig.…”

Section: Methodsmentioning

confidence: 99%

Two-axis control of a singlet–triplet qubit with an integrated micromagnet

Wu¹,

Ward²,

Prance

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

175

193

View full text Add to dashboard Cite

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“…If this is the case, the multivalley system can be reduced to an effective single-valley qubit, a potentially nuclear-spin-free analog to the well-known GaAs counterpart. 50,51 In fact, many recent experiments performed on Si/SiGe quantum dots have no evidence of valley degeneracy, [33][34][35][52][53][54] indicating that the splitting is large enough to justify a single-valley treatment. On the other hand, a recent proposal of valley-defined qubits uses the valley degree of freedom as a tool for gate operations.…”

Section: Introductionmentioning

confidence: 99%

“…31,32 For this reason, silicon-based quantum dots have become the new focus of interest, and recent progress emphasizes their perspectives. [33][34][35][36] Another advantage of silicon 8,29 over GaAs is a larger g factor, which allows spin manipulations in smaller magnetic fields. On the other hand, device fabrication of silicon dots is more challenging, 37 the spin-orbit interactions are weaker, and the dots must be smaller due to a larger effective mass.…”

Section: Introductionmentioning

confidence: 99%

Theory of spin relaxation in two-electron laterally coupled Si/SiGe quantum dots

2012

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Highly accurate numerical results of phonon-induced two-electron spin relaxation in silicon double quantum dots are presented. The relaxation, enabled by spin-orbit coupling and the nuclei of 29 Si (natural or purified abundance), is investigated for experimentally relevant parameters, the interdot coupling, the magnetic field magnitude and orientation, and the detuning. We calculate relaxation rates for zero and finite temperatures (100 mK), concluding that our findings for zero temperature remain qualitatively valid also for 100 mK. We confirm the same anisotropic switch of the axis of prolonged spin lifetime with varying detuning as recently predicted in GaAs. Conditions for possibly hyperfine-dominated relaxation are much more stringent in Si than in GaAs. For experimentally relevant regimes, the spin-orbit coupling, although weak, is the dominant contribution, yielding anisotropic relaxation rates of at least two orders of magnitude lower than in GaAs.

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“…16 As a result, Si spin QC has emerged as an active subfield of modern condensed matter physics. Outstanding experimental progress in Si spin QC has been reported in the last few years in Si quantum dots (QDs), [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] and in donor-based architectures. [36][37][38][39][40][41][42][43][44][45][46][47][48] Theoretical research on Si QDs has also evolved at a brisk pace.…”

Section: Introductionmentioning

confidence: 99%

Coherent electrical rotations of valley states in Si quantum dots using the phase of the valley-orbit coupling

Culcer

2012

Phys. Rev. B

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A gate electric field has a small but non-negligible effect on the phase of the valley-orbit coupling in Si quantum dots. Finite interdot tunneling between valley eigenstates in a double quantum dot is enabled by a small difference in the phase of the valley-orbit coupling between the two dots, and it in turn allows controllable rotations of two-dot valley eigenstates at a level anticrossing. We present a comprehensive analytical discussion of this process, with estimates for realistic structures.

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Pauli spin blockade in undoped Si/SiGe two-electron double quantum dots

Cited by 107 publications

References 18 publications

Two-axis control of a singlet–triplet qubit with an integrated micromagnet

Two-axis control of a singlet–triplet qubit with an integrated micromagnet

Theory of spin relaxation in two-electron laterally coupled Si/SiGe quantum dots

Coherent electrical rotations of valley states in Si quantum dots using the phase of the valley-orbit coupling

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