A reconfigurable gate architecture for Si/SiGe quantum dots

Abstract

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...

Reduced Sensitivity to Charge Noise in Semiconductor Spin Qubits via Symmetric Operation

“…The device used here and in all subsequent figures differs from the device used in Fig. 2 by the addition of a screening gate [30] and the use of enriched 28 Si (800 ppm 29 Si) [13].…”

“…Some devices in our study differ from Ref. [13] by the addition of a metal screening gate which prevents charge accumulation under gate leads [30]. A proximal dot charge sensor formed by the M and Z gates enables single-shot readout of the qubit state [13].…”

Fabrication of quantum dots in undoped Si/Si0.8Ge0.2 heterostructures using a single metal-gate layer

“…Device designs, dot operation, and qubit manipulation have all been reported using this enhancement-mode architecture [7][8][9][10] .…”

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

“…The dots have average charging energies E c ¼ 6.9 6 0.7 meV, average orbital energies E orb ¼ 3.0 6 0.5 meV, and valley splittings in the range of 35-70 leV. 9,25 In comparison with superconducting qubit cQED devices, which generally support Q > 50 000, 26 hybrid QD-cQED systems generally have Q ¼ 1000-3000. [15][16][17]19 To coherently couple QD qubits to cavity photons, higher quality factors are needed.…”