Enhancement-mode double-top-gated metal-oxide-semiconductor nanostructures with tunable lateral geometry

Nordberg, Eric P; Eyck, Gregory A. Ten; Stalford, Harold; Muller, Richard P.; Young, Ralph W.; Eng, Kevin; Tracy, Lisa A; Childs, Kenton D.; Wendt, Joel R.; Grubbs, Robert K.; Stevens, Jeffrey; Lilly, Michael; Eriksson, M. A.; Carroll, Malcolm S.

doi:10.1103/physrevb.80.115331

Cited by 60 publications

(28 citation statements)

References 46 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.

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172

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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.

Self Cite

172

193

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“…In addition, focused ion beam techniques beyond sub-nanometer scale [5]–[9] have gained an important role as silicon based nano-domain engineering [10], [11], [12] has become one of the most important tool in materials research, low dimensional system electronics, semiconductor manufacturing and nanotechnology overall. Recent experimental investigations of quantum information processing via single electron devices in gate defined quantum dots [13], [14] confirm silicon based spin quantum-information processor as a promising candidate for future quantum computer architectures [15]. In that context series of investigations of electrically [16], [17], [18] and optically [19] induced ion kinetics in solid state quantum systems reveal that focusing of coherent ions through oriented crystal, may enhance precise confinement and manipulation of individual spins in quantum information processing [20], [21].…”

Section: Introductionmentioning

confidence: 99%

Quantum Entanglement and Spin Control in Silicon Nanocrystal

Berec

2012

PLoS ONE

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Selective coherence control and electrically mediated exchange coupling of single electron spin between triplet and singlet states using numerically derived optimal control of proton pulses is demonstrated. We obtained spatial confinement below size of the Bohr radius for proton spin chain FWHM. Precise manipulation of individual spins and polarization of electron spin states are analyzed via proton induced emission and controlled population of energy shells in pure 29Si nanocrystal. Entangled quantum states of channeled proton trajectories are mapped in transverse and angular phase space of 29Si axial channel alignment in order to avoid transversal excitations. Proton density and proton energy as impact parameter functions are characterized in single particle density matrix via discretization of diagonal and nearest off-diagonal elements. We combined high field and low densities (1 MeV/92 nm) to create inseparable quantum state by superimposing the hyperpolarizationed proton spin chain with electron spin of 29Si. Quantum discretization of density of states (DOS) was performed by the Monte Carlo simulation method using numerical solutions of proton equations of motion. Distribution of gaussian coherent states is obtained by continuous modulation of individual spin phase and amplitude. Obtained results allow precise engineering and faithful mapping of spin states. This would provide the effective quantum key distribution (QKD) and transmission of quantum information over remote distances between quantum memory centers for scalable quantum communication network. Furthermore, obtained results give insights in application of channeled protons subatomic microscopy as a complete versatile scanning-probe system capable of both quantum engineering of charged particle states and characterization of quantum states below diffraction limit linear and in-depth resolution.PACS numbers: 03.65.Ud, 03.67.Bg, 61.85.+p, 67.30.hj

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“…One-qubit and two-qubit manipulations have been demonstrated in the GaAs quantum-dot systems. 9,[23][24][25][26] In silicon quantum-dot systems, despite difficulties such as the fabrication-induced disorder 27 and the valley degree of freedom, [28][29][30][31] high tunability has been reported 32,33 as a milestone toward coherent control of the qubit.…”

Section: Introductionmentioning

confidence: 99%

Quantum theory of the charge-stability diagram of semiconductor double-quantum-dot systems

2011

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We complete our recently introduced theoretical framework treating the double-quantum-dot system with a generalized form of Hubbard model. The effects of all quantum parameters involved in our model on the charge-stability diagram are discussed in detail. A general formulation of the microscopic theory is presented and, truncating at one orbital per site, we study the implication of different choices of the model confinement potential on the Hubbard parameters as well as the charge-stability diagram. We calculate the charge-stability diagram keeping three orbitals per site and find that the effect of additional higher-lying orbitals on the subspace with lowest-energy orbitals only can be regarded as a small renormalization of Hubbard parameters, thereby justifying our practice of keeping only the lowest orbital in all other calculations. The role of the harmonic-oscillator frequency in the implementation of the Gaussian model potential is discussed, and the effect of an external magnetic field is identified to be similar to choosing a more localized electron wave function in microscopic calculations. The full matrix form of the Hamiltonian, including all possible exchange terms and several peculiar charge-stability diagrams due to unphysical parameters, is presented in the Appendices, thus emphasizing the critical importance of a reliable microscopic model in obtaining the system parameters defining the Hamiltonian.

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Enhancement-mode double-top-gated metal-oxide-semiconductor nanostructures with tunable lateral geometry

Cited by 60 publications

References 46 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

Quantum Entanglement and Spin Control in Silicon Nanocrystal

Quantum theory of the charge-stability diagram of semiconductor double-quantum-dot systems

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