Tunable Interdot Coupling Research Articles

Tunable interdot coupling in few-electron bilayer graphene double quantum dots

We present a highly controllable double quantum dot device based on bilayer graphene. Using a device architecture of interdigitated gate fingers, we can control the interdot tunnel coupling between 1 and 4 GHz and the mutual capacitive coupling between 0.2 and 0.6 meV, independent of the charge occupation of the quantum dots. The charging energy and, hence, the dot size remain nearly unchanged. The tuning range of the tunnel coupling covers the operating regime of typical silicon and GaAs spin qubit devices.

Double quantum dot-like transport in controllably doped graphene nanoribbon

In this Letter, we demonstrate coupled double-quantum dot (DQD)-like transport in an ∼30 nm-wide controllably doped graphene nanoribbon (GNR). Controlled doping is introduced from hydrogen silsesquioxane by changing its electron exposure dose. The proximity effect, which brings in additional dose accumulation, is utilized to introduce two charge puddles with stronger p-doping at the two ends of the moderately p-doped GNR, which act as two quantum dots. By electrostatically isolating these two charge puddles with simplified overlapping dual gates, DQD-like transport features are measured in the doped GNR at a temperature of 5 K. Moreover, the transition from strongly to weakly coupled DQDs is observed due to electrically tunable inter-dot coupling.

Double-layer-gate architecture for few-hole GaAs quantum dots

We report the fabrication of single and double hole quantum dots using a double-layer-gate design on an undoped accumulation mode /GaAs heterostructure. Electrical transport measurements of a single quantum dot show varying addition energies and clear excited states. In addition, the two-level-gate architecture can also be configured into a double quantum dot with tunable inter-dot coupling.

Electronic Excited States in Bilayer Graphene Double Quantum Dots

We report tunneling spectroscopy experiments on a bilayer graphene double quantum dot device that can be tuned by all-graphene lateral gates. The diameter of the two quantum dots are around 50 nm and the constrictions acting as tunneling barriers are 30 nm in width. The double quantum dot features additional energies on the order of 20 meV. Charge stability diagrams allow us to study the tunable interdot coupling energy as well as the spectrum of the electronic excited states on a number of individual triple points over a large energy range. The obtained constant level spacing of 1.75 meV over a wide energy range is in good agreement with the expected single-particle energy spacing in bilayer graphene quantum dots. Finally, we investigate the evolution of the electronic excited states in a parallel magnetic field.

Transport properties of two laterally coupled vertical quantum dots in series with tunable interdot coupling

We describe the electronic properties of a double dot for which the lateral coupling between the two vertical dots can be controlled in situ with a center gate voltage (Vc) and the current flows through the two dots in series. When Vc is large and positive, the two dots merge. As Vc is made less positive, two dots are formed whose coupling is reduced. We measure charging diagrams for positive and negative source-drain voltages in the weak coupling regime and observe current rectification due to the Pauli spin blockade when the hyperfine interaction between the electrons and the nuclei is suppressed.

Electron States in Parallel Double Quantum Dots with a Tunable Inter-Dot Coupling

We study the electron states on lateral double quantum dots coupled in parallel. The charge stability diagrams are given in terms of the gate voltages of both dots. We discover that the two electron states translate from separated states to coupled states continuously by increasing the inter-dot coupling strength. Our results demonstrate that the parallel-quantum-dot tunability bodes well for future quantum computing applications.

Tunable double dots and Kondo enhanced Andreev transport in InAs nanowires

The effect of Kondo correlations on the subgap structure of a quantum dot contacted by superconducting leads is investigated experimentally in indium-arsenide nanowires. When the zero-bias Kondo effect is suppressed by the superconducting pairing of the electrons a profound enhancement of the first-order Andreev reflection is observed. Devices with local gate control allow individual tuning of multiple quantum dots along the wire, a double dot with tunable interdot coupling is demonstrated.

The Transport Transition Due to Decoupling of the Electron Trajectory in Double-Coupled Open Quantum-Dot

In this paper, we present the results of studies of electron interference in such a quantum-dot molecule, consisting of two split-gate quantum dots with tunable interdot coupling strength. The low-temperature magnetoresistance of this structure shows reproducible fluctuations, which provide information on the characteristic electron trajectories involved in interference. With decreasing inter-dot coupling, we find a marked reduction in the high-frequency components of these fluctuations, and we suggest that this behavior results from an associated reduction of the typical area for coherent electron interference. Since this variation is induced by the change in the inter-dot coupling alone, we suggest that it reflects the influence of the coupling on molecular-like trajectories which coherently span the coupled dot system, without infulence of Coulomb blockade effect because of an open dot system in our case.