Observation of the single-electron regime in a highly tunable silicon quantum dot

Lim, Wee Han; Zwanenburg, Floris A.; Huebl, Hans; Möttönen, Mikko; Chan, KW; Morello, Andrea; Dzurak, A. S.

doi:10.1063/1.3272858

Cited by 100 publications

(116 citation statements)

References 17 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.

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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“…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.

178

193

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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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“…A controlled oxidation process is performed after the metallization of each layer to create a thin insulating oxide around the gates, which electrically isolates them from subsequent gate layers. 18,19 Given the symmetry of the design, the upper and lower transport channels are interchangeable. In what follows, we utilize the lower channel to form a charge sensor quantum dot that is sensitive to the electron occupancy of the quantum dots formed in the upper channel.…”

mentioning

confidence: 99%

A reconfigurable gate architecture for Si/SiGe quantum dots

Zajac

Hazard

et al. 2015

Applied Physics Letters

167

169

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We demonstrate a reconfigurable quantum dot gate architecture that incorporates two interchangeable transport channels. One channel is used to form quantum dots and the other is used for charge sensing. The quantum dot transport channel can support either a single or a double quantum dot. We demonstrate few-electron occupation in a single quantum dot and extract charging energies as large as 6.6 meV. Magnetospectroscopy is used to measure valley splittings in the range of 35-70 µeV. By energizing two additional gates we form a few-electron double quantum dot and demonstrate tunable tunnel coupling at the (1,0) to (0,1) interdot charge transition.PACS numbers: 73.21. La, 85.35.Gv Quantum dots have considerable potential for the realization of spin-based quantum devices. 1,2 Extremely long spin coherence times 3-5 and the ability to utilize existing fabrication processes make silicon an attractive host material for quantum dot qubits. 6-8 Existing depletion mode designs use gate electrode patterns that are much larger than the spatial extent of the resulting electron wavefunctions. 9 As a result, it is difficult to precisely control the electronic confinement potential. Successful scaling to a larger number of quantum dots will require fine control of the confinement potential on 20 nm length scales. Accumulation mode designs, 10,11 where electrons are accumulated under small positively biased gates (instead of depleted using large "stadium" gate designs 12 ) allow control of the confinement potential on a much smaller length scale and merit further development.In this letter we present a reconfigurable accumulation mode device architecture that utilizes three overlapping aluminum gate layers. The device architecture has two parallel (and interchangeable) transport channels. One of the channels is used to create single and double quantum dots, while the other channel is used to define a charge sensor quantum dot. 13 The natural length scale of this gate architecture is comparable to the resulting dot size, allowing a higher degree of control compared to depletion mode devices. 12 Direct local accumulation also reduces capacitive cross-coupling, simplifying the formation of double quantum dots and tuning of the relevant tunnel rates. The architecture demonstrated here provides a straightforward method for scaling to a larger series array of N quantum dots, with the required number of gate electrodes in each channel growing linearly as 2N +1.The device is fabricated on an undoped Si/SiGe heterostructure with the growth profile shown in Fig. 1(a). A SiGe relaxed buffer substrate is grown on a Si wafer by linearly varying the Ge concentration from 0 to 30% over 3 µm. The surface of this virtual substrate is then polished before growing an additional 225 nm thick Si 0.7 Ge 0.3 layer, followed by an 8 nm Si quantum well a) Department of Physics, Harvard University, Cambridge, MA 02138, USA (QW), a 50 nm Si 0.7 Ge 0.3 spacer and a 2 nm protective Si cap. The Si QW is uniaxially strained by the Si/Si 0.7 Ge 0.3 lattice...

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Observation of the single-electron regime in a highly tunable silicon quantum dot

Cited by 100 publications

References 17 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

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

A reconfigurable gate architecture for Si/SiGe quantum dots

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