Coherent quantum oscillations and echo measurements of a Si charge qubit

Shi, Zhan; Simmons, C. B.; Ward, Daniel R.; Prance, Jonathan; Mohr, Robert; Koh, Teck Seng; Gamble, John King; Wu, Xian; Savage, D. E.; Lagally, M. G.; Friesen, Mark; Coppersmith, S. N.; Eriksson, M. A.

doi:10.1103/physrevb.88.075416

Cited by 104 publications

(106 citation statements)

References 21 publications

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“…4 we fit T 2 * using the experimentally determined dJ/d«, the measured E tot , and constant values δ« rms = 6.4 ± 0.1 μeV and δh rms = 4.2 ± 0.1 neV. The fit is good, and the values of δ« rms and δh rms agree well with previous reports of charge noise and fluctuations in the nuclear field in similar devices and materials (14,29,30,(32)(33)(34). Fig.…”

Section: Significancesupporting

confidence: 73%

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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178

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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Section: Significancesupporting

confidence: 73%

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

178

193

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“…While, truly single qubit operations in silicon have been reported in the past few Si is significantly broader because of the random distribution of the three stable isotopes, while that of 28 Si has sharp doublet features, corresponding to the hyperfine splittings due to the 31 P nuclear spins. [71] Prospective Articles years, [93][94][95][96] it was only this year that the isotope engineering of silicon was proven essential, even for single qubits in silicon. [97,98] For a single qubit, such as a single donor, a single quantum dot or a single double-quantum dot, a variety of foreign materials and structures, including gate insulators, metal contacts, and SETs for readouts should be placed nearby.…”

Section: Single-spin Qubits In Siliconmentioning

confidence: 99%

Isotope engineering of silicon and diamond for quantum computing and sensing applications

2014

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Some of the stable isotopes of silicon and carbon have zero nuclear spin, whereas many of the other elements that constitute semiconductors consist entirely of stable isotopes that have nuclear spins. Silicon and diamond crystals composed of nuclear-spin-free stable isotopes ( 28 Si, 30 Si, or 12 C) are considered to be ideal host matrixes to place spin quantum bits (qubits) for quantum-computing and -sensing applications, because their coherent properties are not disrupted thanks to the absence of host nuclear spins. The present paper describes the state-of-theart and future perspective of silicon and diamond isotope engineering for development of quantum information-processing devices.

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“…A fault tolerant quantum computer may require as many as 10 8 simultaneously tuned qubits [18], yet typical strain-graded heterostructures have qubit-affecting inhomogeneities on the length scale of a single qubit [19]. Three types of wafer inhomogeneities have been studied in detail: variation of lateral strain, mosaic structure, and disorder on Si/SiGe interfaces.…”

Section: Introductionmentioning

confidence: 99%

“…Quantum dot qubits in silicon can be formed in several different ways by harnessing a combination of spin and/or charge states: successful realizations have demonstrated the single-spin qubit [3][4][5][6], the singlet-triplet qubit [7,8], the charge qubit [9][10][11], the exchange-only qubit [12], and the hybrid quantum dot qubit [13,14]. While metal-oxide-semiconductor devices can confine electrons at the Si-oxide interface independent of the Si strain state, Si/SiGe heterostructures only confine electrons in the Si quantum well if that well is under tensile strain, a state that is typically achieved by epitaxial growth on relaxed SiGe [15].…”

Section: Introductionmentioning

confidence: 99%

Characterization of a gate-defined double quantum dot in a Si/SiGe nanomembrane

Knapp

Mohr

et al. 2016

Nanotechnology

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Abstract. We report the fabrication and characterization of a gate-defined double quantum dot formed in a Si/SiGe nanomembrane. In the past, all gatedefined quantum dots in Si/SiGe heterostructures were formed on top of straingraded virtual substrates. The strain grading process necessarily introduces misfit dislocations into a heterostructure, and these defects introduce lateral strain inhomogeneities, mosaic tilt, and threading dislocations. The use of a SiGe nanomembrane as the virtual substrate enables the strain relaxation to be entirely elastic, eliminating the need for misfit dislocations. However, in this approach the formation of the heterostructure is more complicated, involving two separate epitaxial growth procedures separated by a wet-transfer process that results in a buried non-epitaxial interface 625 nm from the quantum dot. We demonstrate that in spite of this buried interface in close proximity to the device, a double quantum dot can be formed that is controllable enough to enable tuning of the inter-dot tunnel coupling, the identification of spin states, and the measurement of a singlet-to-triplet transition as a function of an applied magnetic field.

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Coherent quantum oscillations and echo measurements of a Si charge qubit

Cited by 104 publications

References 21 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

Isotope engineering of silicon and diamond for quantum computing and sensing applications

Characterization of a gate-defined double quantum dot in a Si/SiGe nanomembrane

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