We address theoretically adiabatic regime of charge transport for a model of two tunnel-coupled quantum dots connected in series. The energy levels of the two dots are harmonically modulated by an external potential with a constant phase shift between the two. Motivated by recent experiments with surface-acoustic-wave excitation, we consider two situations: (a) pure pumping in the absence of external voltage (also at finite temperature), and (b) adiabatic modulation of the current driven by large external bias. In both cases we derive results consistent with published experimental data. For the case (b) we explicitly derive the adiabatic limit of Tien-Gordon formula for photon-assisted tunneling and compare it to the outcome of simple conductance modulation. A tutorial for adiabatic pumping current calculations with the Green function formalism is included.
We present a spectroscopic study of excitation dynamics in self assembled CdTe/ZnTe quantum dots. Insight into details of kinetics is obtained from the time resolved micro-photoluminescence, single photon correlation and subpicosecond excitation correlation measurements done on single quantum dots. It is shown that the pulsed excitation in energy above the energy gap of the barrier material results in separate capture of electrons and holes. The capture of carriers of different charge take place at different delay from excitation.
We report the computer-automated tuning of gate-defined semiconductor double quantum dots in GaAs heterostructures. We benchmark the algorithm by creating three double quantum dots inside a linear array of four quantum dots. The algorithm sets the correct gate voltages for all the gates to tune the double quantum dots into the single-electron regime. The algorithm only requires (1) prior knowledge of the gate design and (2) the pinch-off value of the single gate $T$ that is shared by all the quantum dots. This work significantly alleviates the user effort required to tune multiple quantum dot …
We present Coulomb blockade measurements in a graphene double dot system. The coupling of the dots to the leads and between the dots can be tuned by graphene in-plane gates. The coupling is a non-monotonic function of the gate voltage. Using a purely capacitive model, we extract all relevant energy scales of the double dot system.
A classical hydrodynamic approach is used to calculate the magnetoplasma excitations of two vertically coupled electron dots. The electrons are confined by different parabolic potentials in which case Kohn's theorem is no longer valid. The equilibrium density profiles of the electrons in both dots are calculated as function of the interdot distance. We find that for unequal confinements of the two dots the electron density in one of the dots becomes ring-like. The electron densities are then used to obtain the magnetoplasma frequencies. The oscillator strengths are calculated, and we find that…
We present low temperature transport measurements on double quantum dots in InAs nanowires grown by metal-organic vapor phase epitaxy. Two dots in series are created by lithographically defined top-gates with a procedure involving no extra insulating layer. We demonstrate the full tunability from strong to weak coupling between the dots. The quantum mechanical nature of the coupling leads to the formation of a molecular state extending over both dots. The excitation spectra of the individual dots are observable by their signatures in the nonlinear transport.
We study the spectrum and magnetic properties of double quantum dots in the lowest Landau level for different values of the hopping and Zeeman parameters by means of exact diagonalization techniques in systems of N=6 and N=7 electrons and filling factor close to 2. We compare our results with those obtained in double quantum layers and single quantum dots. The Kohn theorem is also discussed.
The authors report that anisotropic confining potentials in laterally-coupled semiconductor quantum dots (QDs) have large impacts in optical transitions and energies of inter-shell collective electronic excitations. The observed anisotropies are revealed by inelastic light scattering as a function of the in-plane direction of light polarization and can be finely controlled by modifying the geometrical shape of the QDs. These experiments show that the tuning of the QD confinement potential offers a powerful method to manipulate electronic states and far-infrared inter-shell optical transitions …
Tunneling excitations of electrons in dry-etched modulation-doped AlGaAs/GaAs coupled quantum dots (QDs) are probed by resonant inelastic light scattering. A sequence of intra- and intershell excitations are found at energies determined by the interplay between the QD confinement energy $\hbar ω_0$ and the tunneling gap $Δ_{SAS}$, the splitting between the symmetric and anti-symmetric delocalized single particle molecular states. The narrow line-widths displayed by electronic excitations in these nanostructures indicate promising venues for the spectroscopic investigation of entanglement of el…
Pauli exclusion principle can lead to a supression of transport through double quantum dots, even if both quantum dots are connected by a resonant driving ac field. In this work, we study how this effect, known as spin blockade, can be removed by means of the influence of the driving field on the contacts to the leads.
We studied experimentally the dynamics of the exchange interaction between two antiparallel electron spins in a so-called metastable double quantum dot where coupling to the electron reservoirs can be ignored. We demonstrate that the level of control of such a double dot is higher than in conventional double dots. In particular, it allows to couple coherently two electron spins in an efficient manner following a scheme initially proposed by Loss and DiVincenzo. The present study demonstrates that metastable quantum dots are a possible route to increase the number of coherently coupled quantum …
A dynamical nuclear polarization scheme is studied in gated double dots. We demonstrate that a small polarization ($\sim 0.5%$) is sufficient to enhance the singlet decay time by two orders of magnitude. This enhancement is attributed to an equilibration process between the nuclear reservoirs in the two dots accompanied by reduced fluctuations in the Overhauser fields, that are mediated by the electron-nuclear spin hyperfine interaction.
We study transport through double quantum dots coupled to normal and superconducting leads, where the Andreev reflection plays a key role in determining characteristic transport properties. We shall discuss two typical cases, i.e. double dots with serial or parallel geometry. For the parallel geometry, the interference of electrons via multiple paths is induced, so that the transmission probability has Fano-type dip structures which are symmetric with respect to the Fermi energy. We also investigate the Aharonov-Bohm(AB) effect for the parallel geometry. In some particular situations, we find …
We analytically investigate the non-equilibrium pumping for a double quantum dots system on the basis of the quantum master equation (QME), where the double quantum dots are connected to two external leads by the spin coupling. Each of leads has two tunable parameters, temperature and chemical potential. Using QME formalism, we obtain an analytical expression of the Berry-like phase for eigenstate of the QME in the parameter space. We show that the Berry-like curvature is non zero in the whole region in the parameter space. We also show that the Berry-like curvature vanishes in the case of sin…
We have investigated nucleation of merons in double quantum dots when a lateral distortion with a reflection symmetry is present in the confinement potential. We find that merons can nucleate both inside and at the edge of the dots. In addition to these merons, our results show that electron density modulations can be also present inside the dots. An edge meron appears to have approximately a half integer winding number.
We report electronic transport on silicon double and triple dots created with the optimized number of two gates. Using silicon nitride spacers two dots in series are created below two top gates overlapping a silicon nanowire. Coupling between dots is controlled by gate voltages. A third dot is created either by combined action of gate voltages or local doping depending on the spacers length. The main characteristics of the triple dot stability diagram are quantitatively fitted.
We quantify the contributions of hyperfine and spin-orbit mediated singlet-triplet mixing in weakly coupled InAs quantum dots by electron transport spectroscopy in the Pauli spin blockade regime. In contrast to double dots in GaAs, the spin-orbit coupling is found to be more than two orders of magnitudes larger than the hyperfine mixing energy. It is already effective at magnetic fields of a few mT, where deviations from hyperfine mixing are observed.
We examine the full counting statistics of electron transport through double quantum dots coupled in series, with particular attention being paid to the unique features originating from level renormalization. It is clearly illustrated that the energy renormalization gives rise to a dynamic charge blockade mechanism, which eventually results in super-Poissonian noise. Coupling of the double dots to an external heat bath leads to dephasing and relaxation mechanisms, which are demonstrated to suppress the noise in a unique way.
A single electron transistor (SET) consisting of parallel double quantum dots fabricated in a GaAs/Al$_{x}$Ga$_{1-x}$As heterostructure crystal is demonstrated to serve as an extremely high sensitive detector of submillimeter waves (SMMW). One of the double dots is ionized by SMMW via Kohn-mode plasma excitation, which affects the SET conductance through the other quantum dot yielding the photoresponse. Noise equivalent power of the detector for wavelengths about 0.6 mm is estimated to reach the order of $10^{-17}$ W/$\sqrt{Hz}$ at 70 mK.
We study ground states and excited states in semiconductor quantum dots containing 1 to 12 electrons. For the first time, it is possible to identify the quantum numbers of the states in the excitation spectra and make a direct comparison to exact calculations. A magnetic field induces transitions between excited states and ground state. These transitions are discussed in terms of crossings between single-particle states, singlet-triplet transitions, spin polarization, and Hund's rule. Our impurity-free quantum dots allow for atomic physics experiments in magnetic field regimes not accessible f…
We study fluctuations of conductance of two connected in series dots in the Coulomb blockade regime. The pattern of the fluctuations turns out to be extremely sensitive to a magnetic field. These conductance fluctuations also provide information about the mesoscopic fluctuations of charge of a partially-opened single quantum dot, which are hard to measure directly.
We study the evolution of a quantum state of a double quantum dot system interacting with the electromagnetic environment and with the lattice modes, in the presence of a coupling between the two dots. We propose a unified approach to the simulation of the system evolution under joint impact of the two reservoirs. We discuss the sub- and superradiant radiative decay of the system, the phonon-induced decay of entanglement between the dots, and the transfer of excitation between them.
We study two double dot systems, one with dots in parallel and one with dots in series, and argue they admit an exact solution via the Bethe ansatz. In the case of parallel dots we exploit the exact solution to extract the behavior of the linear response conductance. The linear response conductance of the parallel dot system possesses multiple Kondo effects, including a Kondo effect enhanced by a nonpertubative antiferromagnetic RKKY interaction, has conductance zeros in the mixed valence regime, and obeys a non-trivial form of the Friedel sum rule.
We investigate spin-polarized transport phenomena through double quantum dots coupled to ferromagnetic leads in series. By means of the slave-boson mean-field approximation, we calculate the conductance in the Kondo regime for two different configurations of the leads: spin-polarization of two ferromagnetic leads is parallel or anti-parallel. It is found that transport shows some remarkable properties depending on the tunneling strength between two dots. These properties are explained in terms of the Kondo resonances in the local density of states.
We propose and analyze a new scheme of realizing both spin filtering and spin pumping by using ac-driven double quantum dots in the Coulomb blockade regime. By calculating the current through the system we demonstrate that the spin polarization of the current can be controlled by tuning the parameters (amplitude and frequency) of the ac field. We also discuss spin relaxation and decoherence effects in the pumped current.
We theoretically investigate the magnitude and range of the photon-mediated interaction between two quantum dots embedded in a photonic crystal waveguide, including fabrication disorder both in the crystal and in the dot positioning. We find that disorder-induced light localization has a drastic effect on the excitation transfer rate - as compared to an ideal structure - and that this rate varies widely among different disorder configurations. Nevertheless, we also find that significant rates of 50 micro-eV at a range of 10 micro-meters can be achieved in realistic systems.
We study electron transport through double quantum dots in series. The tunnel coupling of the discrete dot levels to external leads causes a shift of their energy. This energy renormalization affects the transport characteristics even in the limit of weak dot-lead coupling, when sequential transport dominates. We propose an experimental setup which reveals the renormalization effects in either the current-voltage characteristics or in the stability diagram.
Semiconductor quantum dots are converging towards the demanding requirements of photonic quantum technologies. Among different systems, quantum dots with dimensions exceeding the free-exciton Bohr radius are appealing because of their high oscillator strengths. While this property has received much attention in the context of cavity quantum electrodynamics, little is known about the degree of indistinguishability of single photons consecutively emitted by such dots and on the proper excitation schemes to achieve high indistinguishability. A prominent example is represented by GaAs quantum dots…
The coherent time evolution of electrons in double quantum dots induced by fast bias-voltage switches is studied theoretically. As it was shown experimentally, such driven double quantum dots are potential devices for controlled manipulation of charge qubits. By numerically solving a quantum master equation we obtain the energy- and time-resolved electron transfer through the device which resembles the measured data. The observed oscillations are found to depend on the level offset of the two dots during the manipulation and, most surprisingly, also the on initialization stage. By means of an …
We study the occupation of two electrostatically-coupled single-level quantum dots with spinless electrons as a function of gate voltage. While the total occupation of the double-dot system varies monotonically with gate voltage, we predict that the competition between tunneling and Coulomb interaction can give rise to a nonmonotonic filling of the individual quantum dots. This non-monotonicity is a signature of the correlated nature of the many-body wavefunction in the reduced Hilbert space of the dots. We identify two mechanisms for this nonmonotonic behavior, which are associated with chang…
We have investigated the magnetoplasmon excitations in arrays of circular and noncircular quantum dots within the Thomas-Fermi-Dirac-von Weizsäcker approximation. Deviations from the ideal collective excitations of isolated parabolically confined electrons arise from local perturbations of the confining potential as well as interdot Coulomb interactions. The latter are unimportant unless the interdot separations are of the order of the size of the dots. Local perturbations such as radial anharmonicity and noncircular symmetry lead to clear signatures of the violation of the generalized Kohn th…
We investigate quantum photovoltaic effect in double quantum dots by applying nonequilibrium quantum master equation. The drastic suppression of the photovoltaic current is observed near the open circuit voltage, which leads to the large filling factor. We find that there always exists an optimal inter-dot tunneling that significantly enhances the photovoltaic current. The maximal output power will also be obtained around the optimal inter-dot tunneling. Moreover, the open circuit voltage approximately behaves as the product of the eigen-level gap and the Carnot efficiency. These results sugge…
We study the sub-gap spectrum and the transport properties of a double quantum dot coupled to metallic and superconducting leads. The coupling of both quantum dots to the superconducting lead induces a non-local pairing in both quantum dots by the Andreev reflection processes. Additionally, we obtain two channels of Cooper pair tunneling into a superconducting lead. In such a system, the direct tunneling process (by one of two dots) or the crossed tunneling process (by both quantum dots at the same time) is possible. We consider the dependence of the Andreev transmittance on an inter-dot tunne…
The control of Kerr nonlinearity with electric fields in an asymmetric double quantum-dot systems coupling with tunneling is investigated theoretically. It is found that,by proper tuning of two light beams and tunneling via a bias voltage, the Kerr nonlinearity can be enhanced and varied within a wide scale.
We present low temperature charge sensing measurements of nanoscale phosphorus-implanted double-dots in silicon. The implanted phosphorus forms two 50 nm diameter islands with source and drain leads, which are separated from each other by undoped silicon tunnel barriers. Occupancy of the dots is controlled by surface gates and monitored using an aluminium single electron transistor which is capacitively coupled to the dots. We observe a charge stability diagram consistent with the designed many-electron double-dot system and this agrees well with capacitance modelling of the structure. We disc…
We analyze the zero temperature conductance of a parallel T-shaped double quantum dot system. We present an analytical expression for the conductance of the system in terms of the total number of electrons in both quantum dots. Our results confirm that the system's conductance is strongly influenced by the dot which is not directly connected to the leads. We discuss our results in connection with similar results reported in the literature.
We apply an elementary measurement scheme to calculate the electronic triplet-singlet transition mediated by hyperfine interaction in a double quantum dot. We show how the local character of the hyperfine interaction and the nuclear back-action process (flip-flop) are crucial to cancel destructive interferences of the triplet-singlet transition probability. It is precisely this cancellation which differentiates the hyperfine interaction from an anisotropic magnetic field which mixes the triplet and the singlet eigenstates.
We calculate the stationary current through two double quantum dots which are interacting via a common phonon environment. Numerical and analytical solutions of a master equation in the stationary limit show that the current can be increased as well as decreased due to a dissipation mediated interaction. This effect is closely related to collective, spontaneous emission of phonons (Dicke super- and subradiance effect), and the generation of a `cross-coherence' with entanglement of charges in singlet or triplet states between the dots. Furthermore, we discuss an inelastic `current switch' mecha…
Exchange-coupled singlet-triplet spin qubits in two gate-defined double quantum dots are considered theoretically. Using charge density operators to describe the double-dot orbital states, we calculate the Coulomb couplings between the qubits, and identify optimal bias points for single- and two-qubit operations, as well as convenient idle positions. The same intuitive formulation is used to derive dephasing rates of these qubits due to the fluctuating charge environment, thereby providing the main considerations for a quantum computation architecture that is within current experimental capabi…
We consider the photon-assisted tunneling (PAT) and the Landau-Zener-Stueckelberg (LZS) interference for double quantum dots induced electrostatically along a semiconducting carbon nanotube. An atomistic tight-binding approach and the time-dependent configuration interaction method are employed for description of the systems of a few confined electrons and holes. We reproduce the patterns of the LZS interference recently observed for the quantum double dots describing transport across hole-localized states. Moreover, we indicate that for charge configurations for which the ground-state is Paul…
We present a study of the electronic structure of two laterally coupled gaussian quantum dots filled with two particles. The exact diagonalization method has been used in order to inspect the spatial correlations and examine the particular spin singlet-triplet configurations for different coupling degrees between quantum dots. The outcome of our research shows this structure to have highly modifiable properties promoting it as an interesting quantum device, showing the possible use of this states as a quantum bit gate.
We systematically investigate electron transport through double quantum dots with particular emphasis on interference induced via multiple paths of electron propagation. By means of the slave-boson mean-field approximation, we calculate the conductance, the local density of states, the transmission probability in the Kondo regime at zero temperature. It is clarified how the Kondo-assisted transport changes its properties when the system is continuously changed among the serial, parallel and T-shaped double dots. The obtained results for the conductance are explained in terms of the Kondo reson…
We analyse the ground state properties of vertical double quantum dots in the lowest Landau level regime for filling factor ν=2. This analysis follow two lines: on the one hand, we study the dispersion relation of different collective excitations and look for the roton-type minima that signal some type of order within the ground state. On the other hand, we calculate expected values of the antiferremagnetic order operator defined as <S_x^RS_x^L>. We conclude that of the three existing types of ground state at ν=2 the canted and symmetric states show spin order on the plane of the dots. In the …
Simulations of the elastic strain fields for double Ge/Si quantum dots located on the same wetting layer are carried out. The cluster approximation is used for the atomistic model based on the Keating potential. The spatial distributions of the strain energy density and electron potential energy are calculated using clusters containing atoms of 150 coordination spheres. It is shown that the used cluster boundary conditions are close to the periodic boundary conditions.
We report theoretical investigations of indirectly coupled double quantum dots (QD) side connected to an one-dimensional quantum wire. Due to quantum interference controlled by the parameter $k_F L$, with $k_F$ the Fermi wave number of the wire and $L$ the distance between the two QDs, distinctly different Kondo resonances are predicted depending on the range of $k_F L$. A true bound Kondo states is found while an anomalous Kondo resonance gives rise to both reduction and enhancement of conductance.
We study electron tunneling through two small ferromagnetic dots. Quantum charge fluctuations and interdot coupling make each Coulomb peak of the conductance at zero interdot coupling split across. The interdot tunnel coupling is determined by the relative orientation of magnetizations of the two dots, leading to different splitting energies of the Coulomb peaks in parallel and antiparallel magnetization alignments. As a result, a very large tunneling magnetoresistance occurs near the Coulomb peaks, and its sign may be either positive or negative.
We theoretically investigate electron transport through an Aharonov-Bohm interferometer containing laterally coupled double quantum dots. We introduce the indirect coupling parameter $α$, which characterizes the strength of the coupling via the reservoirs between two quantum dots. $|α|=1$ indicates the strongest coupling, where only a single mode contributes to the transport in the system. Two conduction modes exist in a system where $|α|\neq 1$. The interference effects such as the Fano resonance and the Aharonov-Bohm oscillation are suppressed as the absolute value of the parameter $α$ decre…
Charge localization seems unlikely to occur in two vertically coupled symmetric quantum dots even if a small bias voltage breaks the exact isospin-symmetry of the system. However for a three-electron double quantum dot we find a strong localization of charges at certain vertically applied magnetic fields. The charge localization is directly connected to new ground state transitions between eigenstates differing only in parity. The transitions are driven by magnetic field dependent Coulomb correlations between the electrons and give rise to strong isospin blockade signatures in transport throug…
Charge-based quantum computation can be attained through reliable control of single electrons in lead-less quantum systems. Single-charge transitions in electrically-isolated double quantum dots (DQD) realised in phosphorus-doped silicon can be detected via capacitively coupled single-electron tunnelling devices. By means of time-resolved measurements of the detector's conductance, we investigate the dots' occupancy statistics in temperature. We observe a significant reduction of the effective electron temperature in the DQD as compared to the temperature in the detector's leads. This sets pro…
We have employed time-dependent local-spin density functional theory to analyze the multipole spin and charge density excitations in GaAs-AlGaAs quantum dots. The on-plane transferred momentum degree of freedom has been taken into account, and the wave-vector dependence of the excitations is discussed. In agreement with previous experiments, we have found that the energies of these modes do not depend on the transferred wave-vector, although their intensities do. Comparison with a recent resonant Raman scattering experiment [C. Schüller et al, Phys. Rev. Lett {\bf 80}, 2673 (1998)] is made. Th…
Electron transport experiments on two lateral quantum dots coupled in series are reviewed. An introduction to the charge stability diagram is given in terms of the electrochemical potentials of both dots. Resonant tunneling experiments show that the double dot geometry allows for an accurate determination of the intrinsic lifetime of discrete energy states in quantum dots. The evolution of discrete energy levels in magnetic field is studied. The resolution allows to resolve avoided crossings in the spectrum of a quantum dot. With microwave spectroscopy it is possible to probe the transition fr…
We have investigated micro-photoluminescence ($μ$-PL) and excitation ($μ$-PLE) spectra of a single GaAs/AlGaAs quantum dot grown on a GaAs (411)A surface. We observed sharp resonant lines in both $μ$-PL and $μ$-PLE spectra, corresponding to the discrete energy levels of the dot. When the sample was excited at one of the resonant lines, resonant luminescence lines appear not only in Stokes side but also in anti-Stokes side. We discuss the possible origins of the anomalus anti-Stokes luminescence.
We investigate experimentally and theoretically the resonant emission of single InAs/GaAs quantum dots in a planar microcavity. Due to the presence of at least one residual charge in the quantum dots, the resonant excitation of the neutral exciton is blocked. The influence of the residual doping on the initial quantum dots charge state is analyzed, and the resonant emission quenching is interpreted as a Coulomb blockade effect. The use of an additional non-resonant laser in a specific low power regime leads to the carrier draining in quantum dots and allows an efficient optical gating of the e…
We theoretically investigate the controlled dynamic polarization of lattice nuclear spins in GaAs double quantum dots containing two electrons. Three regimes of long-term dynamics are identified, including the build up of a large difference in the Overhauser fields across the dots, the saturation of the nuclear polarization process associated with formation of so-called "dark states," and the elimination of the difference field. We show that in the case of unequal dots, build up of difference fields generally accompanies the nuclear polarization process, whereas for nearly identical dots, buil…
We investigate the Aharonov-Bohm (AB) effect for the double quantum dots in the Kondo regime using the slave-boson mean-field approximation. In contrast to the non-interacting case, where the AB oscillation generally has the period of 4$π$ when the two-subring structure is formed via the interdot tunneling $t_c$, we find that the AB oscillation has the period of 2$π$ in the Kondo regime. Such effects appear for the double quantum dots close to the T-shaped geometry even in the charge-fluctuation regime. These results follow from the fact that the Kondo resonance is always fixed to the Fermi le…
We report on low temperature measurements in a fully tunable carbon nanotube double quantum dot. A new fabrication technique has been used for the top-gates in order to avoid covering the whole nanotube with an oxide layer as in previous experiments. The top-gates allow us to form single dots, control the coupling between them and we observe four-fold shell filling. We perform inelastic transport spectroscopy via the excited states in the double quantum dot, a necessary step towards the implementation of new microwave-based experiments.
We investigate resonant tunneling through molecular states of coupled double quantum dots embedded in an Aharonov-Bohm (AB) interferometer. The conductance through the system consists of two resonances associated with the bonding and the antibonding quantum states. We predict that the two resonances are composed of a Breit-Wigner resonance and a Fano resonance, those widths and Fano factor depending on the AB phase very sensitively. Further, we point out that the bonding properties, such as the covalent and the ionic bonding, can be identified by the AB oscillations.
We calculate the orbital magnetization of single and double quantum dots coupled both by Coulomb interaction and by electron tunneling. The electronic states of the quantum dots are calculated in a tight-binding model and the magnetization is discussed in relation to the energy spectrum and to the edge and bulk states. We identify effects of chirality of the electronic orbits and of the anti-crossing of the energy levels when the magnetic field is varied. We also consider the effects of detuning the energy spectra of the quantum dots by an external gate potential. We compare our results with t…
Spontaneous nuclear polarization is predicted in double quantum dots in the spin-blocked electron transport regime. The polarization results from an instability of the zero-polarization state when singlet and triplet electron energy levels are brought into resonance by the effective hyperfine field of the nuclei on the electrons. The nuclear spins, once polarized, serve as a cold bath for cooling electrons below the lattice (phonon) temperature. We estimate the relevant time scales and discuss the conditions necessary to observe these phenomena.
We demonstrate double quantum dots fabricated in undoped Si/SiGe heterostructures relying on a double top-gated design. Charge sensing shows that we can reliably deplete these devices to zero charge occupancy. Measurements and simulations confirm that the energetics are determined by the gate-induced electrostatic potentials. Pauli spin blockade has been observed via transport through the double dot in the two electron configuration, a critical step in performing coherent spin manipulations in Si.
We report the experimental realization of double quantum dots in single-walled carbon nanotubes. The device consists of a nanotube with source and drain contact, and three additional top-gate electrodes in between. We show that, by energizing these top-gates, it is possible to locally gate a nanotube, to create a barrier, or to tune the chemical potential of a part of the nanotube. At low temperatures we find (for three different devices) that in certain ranges of top-gate voltages our device acts as a double quantum dot, evidenced by the typical honeycomb charge stability pattern.
