Molecular states in carbon nanotube double quantum dots

Gräber, M.R.; Coish, W. A.; Hoffmann, Christian; Weiß, Markus; Furer, J.; Oberholzer, S.; Loss, Daniel; Schönenberger, Christian

doi:10.1103/physrevb.74.075427

Cited by 87 publications

(117 citation statements)

References 17 publications

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“…In the range V g1 > 1.5 V, hexagonal patterns are clearly evident. Current along all hexagon boundaries is finite, indicating that the system is in a strongly coupled regime, and the two dots interact by quantum-mechanical tunnel coupling, analogous to coupling by covalent bonding in a two-atom molecule [27][28][29].…”

Section: Electrical Propertiesmentioning

confidence: 99%

Fabrication of quantum-dot devices in graphene

Moriyama

Morita

Watanabe³

et al. 2010

Science and Technology of Advanced Materials

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We describe our recent experimental results on the fabrication of quantum-dot devices in a graphene-based two-dimensional system. Graphene samples were prepared by micromechanical cleavage of graphite crystals on a SiO 2 /Si substrate. We performed micro-Raman spectroscopy measurements to determine the number of layers of graphene flakes during the device fabrication process. By applying a nanofabrication process to the identified graphene flakes, we prepared a double-quantum-dot device structure comprising two lateral quantum dots coupled in series. Measurements of low-temperature electrical transport show the device to be a series-coupled double-dot system with varied interdot tunnel coupling, the strength of which changes continuously and non-monotonically as a function of gate voltage.

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Section: Electrical Propertiesmentioning

confidence: 99%

Fabrication of quantum-dot devices in graphene

Moriyama

Morita

Watanabe³

et al. 2010

Science and Technology of Advanced Materials

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“…The predictions can be directly verified with our experiments. The tunnel coupling can be deduced from the stability diagram [25], yielding t ∼ 40 µeV, and the estimate for C ef f ≈ 0.46 fF therefore has no free parameters. This result is in excellent agreement with the experimental data of Fig.…”

mentioning

confidence: 99%

Measuring the Complex Admittance of a Carbon Nanotube Double Quantum Dot

Chorley¹,

Wabnig²,

Penfold-Fitch³

et al. 2012

Phys. Rev. Lett.

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We investigate radio-frequency (rf) reflectometry in a tunable carbon nanotube double quantum dot coupled to a resonant circuit. By measuring the in-phase and quadrature components of the reflected rf signal, we are able to determine the complex admittance of the double quantum dot as a function of the energies of the single-electron states. The measurements are found to be in good agreement with a theoretical model of the device in the incoherent limit. Besides being of fundamental interest, our results present an important step forward towards non-invasive charge and spin state readout in carbon nanotube quantum dots. PACS numbers: 73.63.Fg, 73.63.Kv, 73.23.Hk, 03.67.Lx An important requirement in any quantum information processing scheme is fast manipulation and readout of the quantum system in which the quantum information is encoded. This requires an understanding of the response of the quantum system at finite frequencies which, in the case of an electronic device, involves an understanding of its complex admittance [1,2]. Of particular interest in the context of quantum information processing are double quantum dots which are widely used to define charge and spin qubits [3]. However, while double quantum dots have been investigated in detail over the last decade, experiments to measure and analyze their complex admittance have not yet been performed and this topic has only recently been addressed theoretically [4]. The admittance of quantum dots at finite frequencies is non-trivial as exemplified by recent experiments on single quantum dots [5,6]. The physics is even richer for double quantum dots as internal charge dynamics, i.e. charge transfer between the quantum dots, has to be taken into account. However, the dependence of the admittance on the internal charge dynamics also provides a route towards charge and spin state readout [7].In this work we present a detailed experimental study of the complex admittance of a carbon nanotube double quantum dot which is measured using rf reflectometry techniques. The measurements are compared with a theoretical model of the device where we use a density matrix approach to calculate the double quantum dot admittance. The good quantitative agreement between the experimental and theoretical results allows us to determine the effective conductance and susceptance of the double dot as a function of the energies of the single-electron states. Our measurements thus present a first quantitative analysis of the complex admittance of a double quantum dot. The demonstrated technique also provides the basis for a simple and fast detection scheme for charge and spin state readout in carbon nanotubes -a material with considerable potential for spin-based quantum information processing [8-13] -without the need for a separate charge detector [14].The device we consider is a carbon nanotube grown by chemical vapour deposition on degenerately doped Si ter- minated by 300 nm SiO 2 , see Fig. 1(a). The nanotube is contacted by Au source and drain electrodes which form the outer ...

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“…Evidence of molecular states forming in double quantum dots due to a strong inter-dot tunnel-coupling has also been found in a variety of systems (Schmidt et al 1997, Schedelbeck et al 1997, Blick et al 1998, Brodsky et al 2000, Bayer et al 2001, Ota et al 2005, Hüttel et al 2005, Fasth et al 2005, Mason et al 2004, Biercuk et al 2005, Graeber et al 2006. For example, molecular states have been observed in many-electron gated quantum dots in linear transport (Blick et al 1998) (solid lines of Figure 5(b)) and transport through excited states (Hüttel et al 2005) (dashed lines in Figure 5(b)).…”

Section: Molecular States In Double Dotsmentioning

confidence: 80%

“…For example, molecular states have been observed in many-electron gated quantum dots in linear transport (Blick et al 1998) (solid lines of Figure 5(b)) and transport through excited states (Hüttel et al 2005) (dashed lines in Figure 5(b)). In addition, molecular states have been observed in vertical-lateral gated double quantum dots (Hatano et al 2005), gated dots formed in quantum wires (Fasth et al 2005) and gated carbon-nanotube double dots (Mason et al 2004, Biercuk et al 2005, Graeber et al 2006. A large interdot tunnel coupling is essential for generating a large exchange interaction J, and is therefore very important for the implementation of fast two-qubit gates in the Loss-DiVincenzo proposal.…”

Section: Molecular States In Double Dotsmentioning

confidence: 99%

“…When the double dot is occupied by only N = 0, 1 electrons and is coupled weakly to leads, an explicit expression can be found for the current passing through a sequentially-coupled double dot, as shown in Figure 5(a) (Ziegler et al 2000, Graeber et al 2006. It is straightforward to diagonalize H C + H T in the subspace of N = 1 electrons on the quantum dot.…”

Section: Molecular States In Double Dotsmentioning

confidence: 99%

See 1 more Smart Citation

Quantum Computing with Spins in Solids

Coish

Loss

2007

Handbook of Magnetism and Advanced Magnetic Materials

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The ability to perform high-precision one-and two-qubit operations is sufficient for universal quantum computation. For the Loss-DiVincenzo proposal to use single electron spins confined to quantum dots as qubits, it is therefore sufficient to analyze only single-and coupled double-dot structures, since the strong Heisenberg exchange coupling between spins in this proposal falls off exponentially with distance and long-ranged dipolar coupling mechanisms can be made significantly weaker. This scalability of the Loss-DiVincenzo design is both a practical necessity for eventual applications of multi-qubit quantum computing and a great conceptual advantage, making analysis of the relevant components relatively transparent and systematic. We review the Loss-DiVincenzo proposal for quantum-dot-confined electron spin qubits, and survey the current state of experiment and theory regarding the relevant single-and double-quantum dots, with a brief look at some related alternative schemes for quantum computing.

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Molecular states in carbon nanotube double quantum dots

Cited by 87 publications

References 17 publications

Fabrication of quantum-dot devices in graphene

Fabrication of quantum-dot devices in graphene

Measuring the Complex Admittance of a Carbon Nanotube Double Quantum Dot

Quantum Computing with Spins in Solids

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