Charge Sensing and Controllable Tunnel Coupling in a Si/SiGe Double Quantum Dot

Simmons, C. B.; Thalakulam, Madhu; Rosemeyer, B. M.; Bael, B. J. Van; Sackmann, Eric K.; Savage, D. E.; Lagally, M. G.; Joynt, Robert; Friesen, Mark; Coppersmith, S. N.; Eriksson, M. A.

doi:10.1021/nl9014974

Cited by 95 publications

(93 citation statements)

References 44 publications

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“…Transport characteristics of such systems strongly depend on the internal parameters, in particular, on the ratio between inter-dot Coulomb repulsion U ′ and the hopping between the dots t, provided that U > U ′ , |t|. The ratio can be tuned experimentally for example by changing the height of the barrier between the dots [57]. When the inter-dot Coulomb correlations are relatively strong, U ′ /|t| > 1, the electrons in the ground state of the chain will be mostly occupying the outermost dots.…”

Section: Numerical Resultsmentioning

confidence: 99%

The tunnel magnetoresistance in chains of quantum dots weakly coupled to external leads

Weymann

2009

J. Phys.: Condens. Matter

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Abstract. We analyze numerically the spin-dependent transport through coherent chains of three coupled quantum dots weakly connected to external magnetic leads. In particular, using the diagrammatic technique on the Keldysh contour, we calculate the conductance, shot noise and tunnel magnetoresistance (TMR) in the sequential and cotunneling regimes. We show that transport characteristics greatly depend on the strength of the interdot Coulomb correlations, which determines the spacial distribution of electron wave function in the chain. When the correlations are relatively strong, depending on the transport regime, we find both negative TMR as well as TMR enhanced above the Julliere value, accompanied with negative differential conductance (NDC) and super-Poissonian shot noise. This nontrivial behavior of tunnel magnetoresistance is associated with selection rules that govern tunneling processes and various high-spin states of the chain that are relevant for transport. For weak interdot correlations, on the other hand, the TMR is always positive and not larger than the Julliere TMR, although super-Poissonian shot noise and NDC can still be observed.

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Section: Numerical Resultsmentioning

confidence: 99%

The tunnel magnetoresistance in chains of quantum dots weakly coupled to external leads

Weymann

2009

J. Phys.: Condens. Matter

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“…[33][34][35] For V MB1 = 285 mV, 2t c < k B T e and the transition is thermally broadened. For V MB1 = 360 and 385 mV values of t c = 5 µeV and 15 µeV are extracted by fitting the data to Eq.…”

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confidence: 99%

“…21.La, 85.40.-e, 85. 35.Gv Quantum dots have considerable potential for the realization of spin-based quantum devices. 1,2 Extremely long spin coherence times [3][4][5] and the ability to utilize existing fabrication processes make silicon an attractive host material for quantum dot qubits.…”

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confidence: 99%

A reconfigurable gate architecture for Si/SiGe quantum dots

Zajac

Hazard

et al. 2015

Applied Physics Letters

159

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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“…25) in an elaborate procedure. This method requires a small tunnel coupling to guarantee that the line shapes are determined by thermal broadening.…”

Section: Introductionmentioning

confidence: 99%

Determination of energy scales in few-electron double quantum dots

Taubert

Schuh

Wegscheider

et al. 2011

Review of Scientific Instruments

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The capacitive couplings between gate-defined quantum dots and their gates vary considerably as a function of applied gate voltages. The conversion between gate voltages and the relevant energy scales is usually performed in a regime of rather symmetric dot-lead tunnel couplings strong enough to allow direct transport measurements. Unfortunately, this standard procedure fails for weak and possibly asymmetric tunnel couplings, often the case in realistic devices. We have developed methods to determine the gate voltage to energy conversion accurately in the different regimes of dot-lead tunnel couplings and demonstrate strong variations of the conversion factors. Our concepts can easily be extended to triple quantum dots or even larger arrays.

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Charge Sensing and Controllable Tunnel Coupling in a Si/SiGe Double Quantum Dot

Cited by 95 publications

References 44 publications

The tunnel magnetoresistance in chains of quantum dots weakly coupled to external leads

The tunnel magnetoresistance in chains of quantum dots weakly coupled to external leads

A reconfigurable gate architecture for Si/SiGe quantum dots

Determination of energy scales in few-electron double quantum dots

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