Measurement of the Spin Relaxation Time of Single Electrons in a Silicon Metal-Oxide-Semiconductor-Based Quantum Dot

Xiao, Ming; House, Matthew; Jiang, Hong-Wen

doi:10.1103/physrevlett.104.096801

Cited by 126 publications

(103 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.

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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“…This weak dependence is qualitatively consistent with spin relaxation via a spin-orbit interaction 32 and two-phonon processes 33 , but may also reflect relaxation through Coulomb coupling with electrons in the gates 34 . Additional work remains to illuminate the relaxation mechanism in detail, but we note that recent experiments in silicon and Si/SiO 2 interfaces have observed a clear power-law dependence only at high magnetic fields (several tesla) 21,23,35 . Based on the split-off band in bulk germanium (0.29 eV, compared to 0.38 eV in InAs (ref.…”

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confidence: 99%

“…The prospect of achieving long coherence times in group IV materials with few nuclear spins has stimulated many proposals 13,14 and intensive experimental efforts [15][16][17][18][19] , and crucially depends on the development of high-quality host materials. Recent advances regarding single quantum dots have been achieved using Zeeman splitting for readout with a finite magnetic field [19][20][21][22][23] . Coupled quantum-dot devices 13,[15][16][17][18]24 in a nuclear spin-free system are more desirable for flexible quantum manipulation 25 but more challenging, and characterization of the spin lifetime has yet to be completed.…”

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confidence: 99%

Hole spin relaxation in Ge–Si core–shell nanowire qubits

et al. 2011

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Controlling decoherence is the biggest challenge in efforts to develop quantum information hardware [1][2][3] . Single electron spins in gallium arsenide are a leading candidate among implementations of solid-state quantum bits, but their strong coupling to nuclear spins produces high decoherence rates [4][5][6] . Group IV semiconductors, on the other hand, have relatively low nuclear spin densities, making them an attractive platform for spin quantum bits. However, device fabrication remains a challenge, particularly with respect to the control of materials and interfaces 7 . Here, we demonstrate state preparation, pulsed gate control and charge-sensing spin readout of hole spins confined in a Ge-Si core-shell nanowire. With fast gating, we measure T 1 spin relaxation times of up to 0.6 ms in coupled quantum dots at zero magnetic field. Relaxation time increases as the magnetic field is reduced, which is consistent with a spin-orbit mechanism that is usually masked by hyperfine contributions.Since the proposal of Loss and DiVincenzo's 1 , the promise of quantum dots for solid-state quantum computation has been underscored by the successful initialization, manipulation and readout of electron spins in GaAs systems 5,[8][9][10] . The electronic wavefunctions in these systems typically overlap with a large number of nuclear spins that are difficult to control and in most cases thermally randomized. The resulting intrinsic spin decoherence rates 4-6 have been successfully reduced by spin-echo techniques 6,11 , but require complex gate sequences that complicate multi-qubit operations 12 . The prospect of achieving long coherence times in group IV materials with few nuclear spins has stimulated many proposals 13,14 and intensive experimental efforts [15][16][17][18][19] , and crucially depends on the development of high-quality host materials. Recent advances regarding single quantum dots have been achieved using Zeeman splitting for readout with a finite magnetic field [19][20][21][22][23] . Coupled quantum-dot devices 13,[15][16][17][18]24 in a nuclear spin-free system are more desirable for flexible quantum manipulation 25 but more challenging, and characterization of the spin lifetime has yet to be completed.Semiconductor nanowires form a favourable platform for quantum devices because of the ability to precisely control their diameter, composition, morphology and electronic properties during synthesis 26 . The prototypical Ge-Si nanowire heterostructure has revealed diverse phenomena at the nanoscale and enabled numerous applications in nanoelectronics. The epitaxial growth of silicon around a single-crystal germanium core (Fig. 1, inset) and the associated valence band offset provide a natural radial confinement of holes that, due to the large sub-band spacing, behave onedimensionally at low temperature 27 . Although the topmost valence band has been predicted to be twofold degenerate and of lighthole character under idealized approximations 28 , it is generally expected that mixing between heavy and light hole...

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“…In GaAs devices, spin-flip times range from ∼200 µs for a two-electron dot [16], to ∼0.85 ms (at 8 T [17]) and > 1 s (at 1 T and 120 mK [18]) for single electron dots. Recent experiments report spin-flip times in single electron dots in Si [19][20][21][22] ranging from 40 ms (at 2 T [19]) to 6 s (at 1 T [20]), at low temperatures. The tunnel coupling for the same Si double dot studied here was found to be 10 ns (25 ns) in the elastic (inelastic) tunneling regime [13].…”

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confidence: 99%