Charge Relaxation in a Single-Electron<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>Si</mml:mi><mml:mo>/</mml:mo><mml:mi>SiGe</mml:mi></mml:math>Double Quantum Dot

Wang, Ke; Payette, C.; Dovzhenko, Yuliya; Deelman, Peter W.; Petta, J. R.

doi:10.1103/physrevlett.111.046801

Cited by 82 publications

(71 citation statements)

References 31 publications

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“…Further reducing V LB1 strengthens From the slope of a left dot charge transition we extract a right plunger to left plunger capacitance ratio of 24%, which is considerably smaller than the 55% coupling measured in a dual-gate architecture. 30 The ability to tune the tunnel coupling between two dots is an important requirement for spin-based quantum dot qubits. 31 First, it demonstrates control of the confinement potential on short length scales.…”

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confidence: 99%

A reconfigurable gate architecture for Si/SiGe quantum dots

Zajac

Hazard

et al. 2015

Applied Physics Letters

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165

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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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confidence: 99%

A reconfigurable gate architecture for Si/SiGe quantum dots

Zajac

Hazard

et al. 2015

Applied Physics Letters

Self Cite

165

169

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“…7 This massive mobility increase opens up the possibility to fabricate and improve upon Si/SiGe nano-devices such as quantum wires 8,9 and quantum dots. [10][11][12][13] When patterning nano-structures, a balance must be attained between high mobility, usually achieved in channels buried deep underneath the surface (∼ 500 nm), and a sharp confinement potential, which is sharper the shallower the channel is. Sharp confinement allows for fabrication of smaller and better defined nano-structures.…”

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Scattering mechanisms in shallow undoped Si/SiGe quantum wells

et al. 2015

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We report the magneto-transport study and scattering mechanism analysis of a series of increasingly shallow Si/SiGe quantum wells with depth ranging from ∼ 100 nm to ∼ 10 nm away from the heterostructure surface. The peak mobility increases with depth, suggesting that charge centers near the oxide/semiconductor interface are the dominant scattering source. The power-law exponent of the electron mobility versus density curve, μ ∝ nα, is extracted as a function of the depth of the Si quantum well. At intermediate densities, the power-law dependence is characterized by α ∼ 2.3. At the highest achievable densities in the quantum wells buried at intermediate depth, an exponent α ∼ 5 is observed. We propose and show by simulations that this increase in the mobility dependence on the density can be explained by a non-equilibrium model where trapped electrons smooth out the potential landscape seen by the two-dimensional electron gas.

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“…the discussion given in Ref. 43, where, in addition, further details on the numerical evaluation of the hierarchy of equations of motion (19) can be found). Note that the latter statement is strictly speaking only true in the strong coupling limit, U Γ K,mn .…”

Section: B Hierarchical Master Equation Approachmentioning

confidence: 99%

“…Moreover, their populations can reliably and non-invasively be read out using single-electron transistors or quantum point contacts [4,19,20]. As a result strongly nonequilibrium physics is accessible in the quantum dot context.…”

Section: Introductionmentioning

confidence: 99%

“…However, unlike conventional atoms, quantum dots can easily be addressed by complex lead structures which provide both electron exchange (leading for example to transport through the dot) and the manipulation of each dot by electromagnetic fields [16][17][18][19]. Moreover, their populations can reliably and non-invasively be read out using single-electron transistors or quantum point contacts [4,19,20].…”

Section: Introductionmentioning

confidence: 99%

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Formation of nonequilibrium steady states in interacting double quantum dots: When coherences dominate the charge distribution

Härtle

Millis

2014

Phys. Rev. B

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We theoretically investigate the full time evolution of a nonequilibrium double quantum dot structure from initial conditions corresponding to different product states (no entanglement between dot and lead) to a nonequilibrium steady state. and an interaction-induced renormalization of energy levels. We find that when the system carries a single electron on average the formation of the steady state is strongly influenced by the coherence between the dots. The latter can be sizeable and indeed larger in the presence of a bias voltage than it is in equilibrium. Moreover, the interdot coherence is shown to lead to a pronounced difference in the population of the dots.

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Charge Relaxation in a Single-ElectronSi/SiGeDouble Quantum Dot

Cited by 82 publications

References 31 publications

A reconfigurable gate architecture for Si/SiGe quantum dots

A reconfigurable gate architecture for Si/SiGe quantum dots

Scattering mechanisms in shallow undoped Si/SiGe quantum wells

Formation of nonequilibrium steady states in interacting double quantum dots: When coherences dominate the charge distribution

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