Single charge sensing and transport in double quantum dots fabricated from commercially grown Si/SiGe heterostructures

We report magnetotransport measurements of a SiGe heterostructure containing a 20 nm p-Ge quantum well with a mobility of 800 000 cm2 V−1 s−1. By dry etching arrays of wires with widths between 1.0 μm and 3.0 μm, we were able to measure the lateral depletion thickness, built-in potential, and the phase coherence length of the quantum well. Fourier analysis does not show any Rashba related spin-splitting despite clearly defined Shubnikov-de Haas oscillations being observed up to a filling factor of ν = 22. Exchange-enhanced spin-splitting is observed for filling factors below ν = 9. An analysis of boundary scattering effects indicates lateral depletion of the hole gas by 0.5 ± 0.1 μm from the etched germanium surface. The built-in potential is found to be 0.25 ± 0.04 V, presenting an energy barrier for lateral transport greater than the hole confinement energy. A large phase coherence length of 3.5 ± 0.5 μm is obtained in these wires at 1.7 K.

mentioning

confidence: 99%

Magnetotransport in p-type Ge quantum well narrow wire arrays

Newton

Llandro

Mansell

et al. 2015

“…23,24 A 3 lm thick linearly graded Si 1Àx Ge x relaxed buffer substrate is grown on top of a Si wafer (resistivity >5000 X cm). The buffer is chemically and mechanically polished before the growth of a 170-375 nm thick Si 0:7 Ge 0:3 layer, an 8 nm thick Si quantum well (QW), a 50-60 nm thick Si 0:7 Ge 0:3 spacer, and a 2-4 nm thick Si cap.…”

mentioning

confidence: 99%

Circuit quantum electrodynamics architecture for gate-defined quantum dots in silicon

Cady

Zajac

et al. 2017

Self Cite

We demonstrate a hybrid device architecture where the charge states in a double quantum dot (DQD) formed in a Si/SiGe heterostructure are read out using an on-chip superconducting microwave cavity. A quality factor Q = 5,400 is achieved by selectively etching away regions of the quantum well and by reducing photon losses through low-pass filtering of the gate bias lines. Homodyne measurements of the cavity transmission reveal DQD charge stability diagrams and a charge-cavity coupling rate g c /2π = 23 MHz. These measurements indicate that electrons trapped in a Si DQD can be effectively coupled to microwave photons, potentially enabling coherent electron-photon interactions in silicon.

“…7,9,10 However, at present the realization of stable QDs in a two-dimensional electron gas (2DEG) at a modulation-doped Si/SiGe heterostructure is still challenging due to the problem of charge noise which cause sudden changes to the QD states. 11,12 To realize stable qubit operation it is necessary to characterize and reduce the charge noise in quantum point contacts (QPCs) which form tunnel junctions with the QD.…”

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confidence: 99%

Characterization and suppression of low-frequency noise in Si/SiGe quantum point contacts and quantum dots

Takeda

Obata

Fukuoka

et al. 2013

We report on the effects of a global top gate on low-frequency noise in Schottky gate-defined quantum point contacts (QPCs) and quantum dots (QDs) in a modulation-doped Si/SiGe heterostructure. For a relatively large top gate voltage, the QPC current shows frequent switching with 1/f 2 Lorentzian type charge noise. As the top gate voltage is decreased, the QPC pinch-off voltage becomes less negative, and the 1/f 2 noise becomes rapidly suppressed in a homogeneous background 1/f noise. We apply this top-gating technique to double QDs to stabilize the charge state for the electron number down to zero.Coherent control of single electron spin in solids aiming towards the realization of fundamental devices for quantum computation has been performed extensively in GaAs 1-6 and more recently in Si 7,8 as well. Si quantum dots (QDs) are one of the most promising candidates for implementing scalable spin quantum bit (qubit) systems because of the long coherence time due to weak spinorbit and hyperfine interactions. Recent experiments on Si QDs have shown the relaxation time T 1 and the dephasing time T * 2 much longer than those observed for GaAs QDs. 7,9,10 However, at present the realization of stable QDs in a two-dimensional electron gas (2DEG) at a modulation-doped Si/SiGe heterostructure is still challenging due to the problem of charge noise which cause sudden changes to the QD states. 11,12 To realize stable qubit operation it is necessary to characterize and reduce the charge noise in quantum point contacts (QPCs) which form tunnel junctions with the QD.Charge noise in gate-defined QPCs has been studied in detail for modulation-doped GaAs/AlGaAs heterostructures using techniques of asymmetrically biasing gates 13 , bias-cooling 14 , top gate biasing 15 and combinations of them. In Ref. 13 they observed charge noise caused by thermally activated trapping and detrapping by charge traps in local potential minima formed near the QPC channel when Schottky gates were occasionally biased to align the energy level of the charge trap and Fermi level of the QPC channel. On the other hand, in Ref. 14,15 , the charge noise is attributed to the electron tunneling between the surface and the 2DEG via charge traps in between. They observed strong charge noise reduction by application of bias-cooling or top gate technique which makes the operation voltage of the surface Schottky gate less negative. Then the tunnel rate of electrons from the