Electron spin qubits in silicon, whether in quantum dots or in donor atoms, have long been considered attractive qubits for the implementation of a quantum computer due to the semiconductor vacuum character of silicon and its compatibility with the microelectronics industry. While donor electron spins in silicon provide extremely long coherence times and access to the nuclear spin via the hyperfine interaction, quantum dots have the complementary advantages of fast electrical operations, tunability and scalability. Here we present an approach to a novel hybrid double quantum dot by coupling a donor to a lithographically patterned artificial atom. Using gate-based rf reflectometry, we probe the charge stability of this double quantum dot system and the variation of quantum capacitance at the interdot charge transition. Using microwave spectroscopy, we find a tunnel coupling of 2.7 GHz and characterise the charge dynamics, which reveals a charge T2* of 200 ps and a relaxation time T1 of 100 ns. Additionally, we demonstrate spin blockade at the inderdot transition, opening up the possibility to operate this coupled system as a singlet-triplet qubit or to transfer a coherent spin state between the quantum dot and the donor electron and nucleus.
Transport measurements at cryogenic temperatures through a few electron top gated quantum dot fabricated in a silicon/silicon-germanium heterostructure are reported. Variations in gate voltage induce a transition from an isolated dot toward a dot strongly coupled to the leads. In addition to Coulomb blockade, when the dot is strongly coupled to the leads, we observe the appearance of a zero bias conductance peak due to the Kondo effect. The Kondo peak splits in a magnetic field, and the splitting scales linearly with the applied field. We also observe a transition from pure Coulomb blockade to…
We prepare a triple quantum dot with a separate contact lead to each dot to study Pauli spin blockade in the tunnel-coupled three dots in a row. We measure the tunneling current flowing between the center dot and either the left or right dot with the left and right leads as a common source and the center lead as a drain. In the biased stability diagram, we establish Pauli spin blockade in the respective neighboring dots, with features similarly obtained in double quantum dot systems. We further realize Pauli spin blockade with two different conditions by tuning the inter-dot coupling gates: st…
We study the conductance spectrum of graphene quantum dots, both single and multiple cases. The single electron tunneling phenomenon is investigated and the periodicity, amplitude and line shape of the Coulomb blockade oscillations at low temperatures are obtained. Further, we discuss the transport behavior when multiple dots are assembled in array and find a phase transition of conductance spectra from individual Coulomb blockade to collective Coulomb blockade.
We present measurements of resonant tunneling through discrete energy levels of a silicon double quantum dot formed in a thin silicon-on-insulator layer. In the absence of piezoelectric phonon coupling, spontaneous phonon emission with deformation-potential coupling accounts for inelastic tunneling through the ground states of the two dots. Such transport measurements enable us to observe a Pauli spin blockade due to effective two-electron spin-triplet correlations, evident in a distinct bias-polarity dependence of resonant tunneling through the ground states. The blockade is lifted by the exc…
We present a theory of zero-bias anomalies and dephasing rates for a Coulomb-blockaded quantum dot, driven out of equilibrium by coupling to voltage biased source and drain leads. We interpret our results in terms of the statistics of voltage fluctuations in the system.
We report on the valley blockade and the multielectron Kondo effect generated by an impurity atom in a silicon nano field effect device. According to the spin-valley nature of tunnelling processes, and consistently with those allowed by the valley blockade regime, the manifestation of Kondo effect obeys to the periodicity 4 of the electron filling sequence typical of silicon emerging at occupation N=1, 2, 3. The spin-valley Kondo effect emerges under different kinds of screening depending on the electron filling. By exploiting the valley blockade regime, valley index conservation in the Kondo …
We present measurements on spin blockade in a laterally integrated quantum dot. The dot is tuned into the regime of strong Coulomb blockade, confining ~ 50 electrons. At certain electronic states we find an additional mechanism suppressing electron transport. This we identify as spin blockade at zero bias, possibly accompanied by a change in orbital momentum in subsequent dot ground states. We support this by probing the bias, magnetic field and temperature dependence of the transport spectrum. Weak violation of the blockade is modelled by detailed calculations of non-linear transport taking i…
We investigate current fluctuations in a three-terminal quantum dot in the sequential tunneling regime. Dynamical spin blockade can be induced when the spin-degeneracy of the dot states is lifted by a magnetic field. This results in super-Poissonian shot noise and positive zero-frequency cross-correlations. Our proposed setup can be realized with semiconductor quantum dots.
We study conductance through a quantum dot under Coulomb blockade conditions in the presence of an external periodic perturbation. The stationary state is determined by the balance between the heating of the dot electrons by the perturbation and cooling by electron exchange with the cold contacts. We show that Coulomb blockade peak can have a peculiar shape if heating is affected by dynamic localization, which can be an experimental signature of this effect.
We study the mechanism of nuclear spin relaxation in quantum dots due to the electron exchange with 2D gas. We show that the nuclear spin relaxation rate is dramatically affected by the Coulomb blockade and can be controlled by gate voltage. In the case of strong spin-orbit coupling the relaxation rate is maximal in the Coulomb blockade valleys whereas for the weak spin-orbit coupling the maximum of the nuclear spin relaxation rate is near the Coulomb blockade peaks.
We extend the theory of Coulomb blockade oscillations to quantum dots which are deformed by the confining potential. We show that shape deformations can generate sequences of conductance resonances which carry the same internal wavefunction. This fact may cause strong correlations of neighboring conductance peaks. We demonstrate the relevance of our results for the interpretation of recent experiments on semiconductor quantum dots.
We present an experimental study of the fluctuations of Coulomb blockade peak positions of a quantum dot. The dot is defined by patterning the two-dimensional electron gas of a silicon MOSFET structure using stacked gates. This permits variation of the number of electrons on the quantum dot without significant shape distortion. The ratio of charging energy to single particle energy is considerably larger than in comparable GaAs/AlGaAs quantum dots. The statistical distribution of the conductance peak spacings in the Coulomb blockade regime was found to be unimodal and does not follow the Wigne…
Double quantum dots are convenient solid-state platforms to encode quantum information. Two-electron spin states can be conveniently detected and manipulated using strong quantum selection rules based on the Pauli exclusion principle, leading to the well-know Pauli spin blockade of electron transport for triplet states. Coherent spin states would be optimally preserved in an environment free of nuclear spins, which is achievable in silicon by isotopic purification. Here we report on a deliberately engineered, gate-defined silicon metal-oxide-semiconductor double quantum dot system. The electro…
We present Coulomb Blockade measurements of two few-electron quantum dots in series which are configured such that the electrochemical potential of one of the two dots is aligned with spin-selective leads. The charge transfer through the system requires co-tunneling through the second dot which is $not$ in resonance with the leads. The observed amplitude modulation of the resulting current is found to reflect spin blockade events occurring through either of the two dots. We also confirm that charge redistribution events occurring in the off-resonance dot are detected indirectly via changes in …
The total spin of correlated electrons in a quantum dot changes with magnetic field and this effect is generally linked to the change in the total angular momentum from one magic number to another, which can be understood in terms of an `electron molecule' picture for strong fields. Here we propose to exploit this fact to realize a spin blockade, i.e., electrons are prohibited to tunnel at specific values of the magnetic field. The spin-blockade regions have been obtained by calculating both the ground and excited states. In double dots the spin-blockade condition is found to be less stringent…
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 study conductance through a quantum dot under Coulomb blockade conditions in the presence of an external periodic perturbation. The stationary state is determined by the balance between the heating of the dot electrons by the perturbation and cooling. We analyze two cooling mechanisms: electron exchange with the cold contacts and emission of phonons. Together with the usual linear Ohmic heating of the dot electrons we consider possible effects of dynamic localization. The combination of the abovementioned factors may result in a drastic change of the shape of the Coulomb blockade peak with …
Influence of forced mechanical vibrations of a suspended single-electron transistor on electron tunneling through the quantum dot limited by the Coulomb blockade is investigated. It is shown that mechanical oscillations of the quantum dot lead to the Coulomb blockade breakdown, shown in sharp resonant peaks in the transistor conductance dependence on the excitation frequency at values corresponding to the mechanical oscillations eigen modes. Physical mechanism of the observed effect is considered. It is presumably connected with oscillations of the mutual electrical capacitances between the qu…
We study the addition energy spectra of phosphorene quantum dots focusing on the role of dot size, edges passivation, number of layers and dielectric constant of the substrate where the dots are deposited. We show that for sufficiently low dielectric constants ($\varepsilon_{sub} < 4$), Coulomb blockade can be observed in dot sizes larger than 10 nm, for both passivated and unpassivated edges. For higher dielectric constants (up to $\varepsilon_{sub} = 30$), Coulomb blockade demands smaller dot sizes, but this depends whether the edges are passivated or not. This dramatic role played by the su…
We show that randomness of the electron wave functions in a quantum dot contributes to the fluctuations of the positions of the conductance peaks. This contribution grows with the conductance of the junctions connecting the dot to the leads. It becomes comparable with the fluctuations coming from the randomness of the single particle spectrum in the dot while the Coulomb blockade peaks are still well-defined. In addition, the fluctuations of the peak spacings are correlated with the fluctuations of the conductance peak heights.
We investigate the influence of thermal energy on the current flow and electron spin states in double quantum dots in series. The quadruplet Pauli spin blockade, which is caused by the quadruplet and doublet states, occurs at low temperatures affecting the transport properties. As the temperature increases, the quadruplet Pauli spin blockade occurs as a result of the thermal energy, even in regions where it does not occur at low temperatures. This is because the triplet state is formed in one dot as a result of the gradual change of the Fermi distribution function of the electrodes with increa…
It is demonstrated that parallel weakly coupled quantum dots exhibit non-equilibrium blockade regimes caused by a full occupation in the spin triplet state, in analogy to the Pauli spin blockade in serially weakly coupled quantum dots. Charge tends to accumulate in the two-electron triplet for bias voltages that support transitions between the singlet and three-electron states.
We report the observation of Coulomb blockade in a quantum dot contacted by two quantum point contacts each with a single fully-transmitting mode, a system previously thought to be well described without invoking Coulomb interactions. At temperatures below 50 mK we observe a periodic oscillation in the conductance of the dot with gate voltage that corresponds to a residual quantization of charge. From the temperature and magnetic field dependence, we infer the oscillations are Mesoscopic Coulomb Blockade, a type of Coulomb blockade caused by electron interference in an otherwise open system.
Double quantum dot systems in the spin blockade regime exhibit leakage currents that have been attributed to the Hyperfine interaction. We model weakly coupled double-dot transport using a rate equation approach which accounts for Hyperfine flip-flop transitions. The rate equations allow us to obtain self-consistently the time evolution for electronic charge occupations and for the nuclei polarizations in each dot. We analyze the current in the spin blockade region as a function of magnetic field and observe hysteretic behavior for fields corresponding to the crossing between triplet and singl…
We analyze coherent spin phenomena in triple quantum dots in triangular configuration under crossed DC and AC magnetic fields. In particular, we discuss the interplay between Aharonov-Bohm current oscillations, coherent electron trapping and spin blockade under electron spin resonance conditions. We demonstrate that, for certain field frequencies, AC magnetic fields induce an antiresonant behavior in the current, allowing for both removal and restoration of entangled spin blockaded states by tuning the AC field frequency. Our theoretical predictions indicate how to manipulate spin qubits in a …
By using bosonization method and unitary transformation, we give a general relation between the dimensionless tunneling conductance and the fractional Coulomb blockade conductance peak splitting which is valid both for weak and strong transmission between two quantum dots, and show that the tunneling conductance has a linear temperature dependence in the low energy and low temperature limit.
Spins in gate-defined silicon quantum dots are promising candidates for implementing large-scale quantum computing. To read the spin state of these qubits, the mechanism that has provided the highest fidelity is spin-to-charge conversion via singlet-triplet spin blockade, which can be detected in-situ using gate-based dispersive sensing. In systems with a complex energy spectrum, like silicon quantum dots, accurately identifying when singlet-triplet blockade occurs is hence of major importance for scalable qubit readout. In this work, we present a description of spin blockade physics in a tunn…
Electronic transport through a two-path triple-quantum-dot system with two source leads and one drain is studied. By separating the conductance of the two double dot paths, we are able to observe double dot and triple dot physics in transport and study the interaction between the paths. We observe channel blockade as a result of inter-channel Coulomb interaction. The experimental results are understood with the help of a theoretical model which calculates the parameters of the system, the stability regions of each state and the full dynamical transport in the triple dot resonances.
Coulomb blockade resonances are measured in a GaAs quantum dot in which both shape deformations and interactions are small. The parametric evolution of the Coulomb blockade peaks shows a pronounced pair correlation in both position and amplitude, which is interpreted as spin pairing. As a consequence, the nearest-neighbor distribution of peak spacings can be well approximated by a smeared bimodal Wigner surmise, provided that interactions which go beyond the constant interaction model are taken into account.
We study spin correlation in a double quantum dot containing a few electrons in each dot (around 10). Clear current rectification with negative differential conductance is observed in the cotunneling regime, which is well explained by a Pauli spin blockade. The current feature is discussed in connection with exchange singlet-triplet splitting based on two simple models, one of which takes coherent interdot coupling and the other incoherent interdot coupling into account.
We consider statistical correlations between the heights of conductance peaks corresponding to two different levels in a Coulomb-blockaded quantum dot. Correlations exist for two peaks at the same magnetic field if the field does not fully break time-reversal symmetry as well as for peaks at different values of a magnetic field that fully breaks time-reversal symmetry. Our results are also relevant to Coulomb-blockade conductance peak height statistics in the presence of weak spin-orbit coupling in a chaotic quantum dot.
We investigate the two-terminal nonlinear conductance of a Coulomb-blockaded quantum dot attached to chiral edge states. Reversal of the applied magnetic field inverts the system chirality and leads to a different polarization charge. As a result, the current--voltage characteristic is not an even function of the magnetic field. We show that the corresponding magnetic-field asymmetry arises from single-charge effects and vanishes in the limit of high temperature.
We present transport measurements on a lateral double dot produced by combining local anodic oxidation and electron beam lithography. We investigate the tunability of our device and demonstrate, that we can switch between capacitive and tunnel coupling. In the regime of capacitive coupling we observe the phenomenon of spin blockade in a magnetic field and analyze the influence of capacitive interdot coupling on this effect.
Transport measurements are presented on a class of electrostatically defined lateral dots within a high mobility two dimensional electron gas (2DEG). The new design allows Coulomb Blockade(CB) measurements to be performed on a single lateral dot containing 0, 1 to over 50 electrons. The CB measurements are enhanced by the spin polarized injection from and into 2DEG magnetic edge states. This combines the measurement of charge with the measurement of spin through spin blockade spectroscopy. The results of Coulomb and spin blockade spectroscopy for first 45 electrons enable us to construct the a…
Scanning-probe magnetometry is a valuable experimental tool to investigate magnetic phenomena at the micro- and nanoscale. We theoretically analyze the possibility of measuring magnetic fields via the electrical current flowing through quantum dots. We characterize the shot-noise-limited magnetic-field sensitivity of two devices: a single dot in the Coulomb blockade regime, and a double dot in the Pauli blockade regime. Constructing such magnetometers using carbon nanotube quantum dots would benefit from the large, strongly anisotropic and controllable g tensors, the low abundance of nuclear s…
We derive closed expressions for the universal weak localization peak of the average conductance peak heights in Coulomb blockade quantum dots in the crossover from orthogonal to unitary symmetry. The scale for the crossover is independent of the number of channels in each lead, in contrast with the case of open dots. The functional form of the weak localization peak is independent of temperature. We also derive analytically the variance of the conductance peak heights as a function of the crossover parameter.
The current-voltage characteristics through a metallic quantum dot which is well coupled to a metallic lead are measured. It is shown that the I-V curves are composed of two contributions. One is a suppression of the tunneling conductivity at the Fermi level and the second is an oscillating feature which shifts with gate voltage. The results indicate that Zero-Bias-Anomaly and Coulomb Blockade phenomena coexist in an asymmetric strongly coupled quantum dot.
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…
Two strongly coupled quantum dots are theoretically and experimentally investigated. In the conductance measurements of a GaAs based low-dimensional system additional features to the Coulomb blockade have been detected at low temperatures. These regions of finite conductivity are compared with theoretical investigations of a strongly coupled quantum dot system and good agreement of the theoretical and the experimental results has been found.
Transient current spectroscopy is proposed and demonstrated in order to investigate the energy relaxation inside a quantum dot in the Coulomb blockade regime. We employ a fast pulse signal to excite an AlGaAs/GaAs quantum dot to an excited state, and analyze the non-equilibrium transient current as a function of the pulse length. The amplitude and time-constant of the transient current are sensitive to the ground and excited spin states. We find that the spin relaxation time is longer than, at least, a few microsecond.
We discuss a new entangled state that has been observed in the conduction across a quantum dot. At Coulomb blockade, electrons from the contacts correlate strongly to those localized in the dot, due to cotunneling processes. Because of the strong Coulomb repulsion on the dot, its electron number is unchanged w.r.to the dot in isolation, but the total spin is fully or partly compensated. In a dot with N=even at the singlet-triplet crossing, which occurs in large magnetic field, Kondo correlations lead to a total spin S=1/2.
Three terminal tunnelling experiments on quantum dots in the Coulomb blockade regime allow a quantitative determination of the coupling strength of individual quantum states to the leads. Exploiting this insight we have observed independent fluctuations of the coupling strengths as a function of electron number and magnetic field due to changes in the shape of the wave function in the dot. Such a detailed understanding and control of the dot-lead coupling can be extended to more complex systems such as coupled dots, and is essential for building functional quantum electronic systems.
The fluctuations and the distribution of the conductance peak spacings of a quantum dot in the Coulomb-blockade regime are studied and compared with the predictions of random matrix theory (RMT). The experimental data were obtained in transport measurements performed on a semiconductor quantum dot fabricated in a GaAs-AlGaAs heterostructure. It is found that the fluctuations in the peak spacings are considerably larger than the mean level spacing in the quantum dot. The distribution of the spacings appears Gaussian both for zero and for non-zero magnetic field and deviates strongly from the RM…
We measure transport at finite bias through a double quantum dot formed by top-gates in an InAs nanowire. Pauli spin-bockade is confirmed with several electrons in the dot. This is expected due to the small exchange interactions in InAs and the large singlet-triplet splitting, which can be measured and tuned by a gate voltage.
Spin blockade occurs when an electron is unable to access an energetically favorable path through a quantum dot due to spin conservation, resulting in a blockade of the current through the dot. Spin blockade is the basis of a number of recent advances in spintronics, including the measurement and the manipulation of individual electron spins. We report measurements of the spin blockade regime in a silicon double quantum dot, revealing a complementary phenomenon: lifetime-enhanced transport. We argue that our observations arise because the decay times for electron spins in silicon are long, ena…
Signatures of "mesoscopic Coulomb blockade" are reported for quantum dots with one fully transmitting point-contact lead, T1 = 1, T2 << 1. Unlike Coulomb blockade (CB) in weak-tunneling devices (T1, T2 << 1), one-channel CB is a mesoscopic effect requiring quantum coherence. Several distinctive features of mesoscopic CB are observed, including a reduction in CB upon breaking time-reversal symmetry with a magnetic field, relatively large fluctuations of peak position as a function of magnetic field, and strong temperature dependence on the scale of the quantum level spacing.
We present a theory of electronic properties and the spin blockade phenomena in a gated linear triple quantum dot. Quadruple points where four different charge configurations are on resonance, particularly involving (1,1,1) configuration, are considered. In the symmetric case, the central dot is biased to higher energy and a single electron tunnels through the device when (1,1,1) configuration is resonant with (1,0,1),(2,0,1),(1,0,2) configurations. The electronic properties of a triple quantum dot are described by a Hubbard model containing two orbitals in the two unbiased dots and a single o…
We report Pauli spin blockade in an impurity defined carbon nanotube double quantum dot. We observe a pronounced current suppression for negative source-drain bias voltages which is investigated for both symmetric and asymmetric coupling of the quantum dots to the leads. The measured differential conductance agrees well with a theoretical model of a double quantum dot system in the spin-blockade regime which allows us to estimate the occupation probabilities of the relevant singlet and triplet states. This work shows that effective spin-to-charge conversion in nanotube quantum dots is feasible…
Pauli blockade mechanisms -- whereby carrier transport through quantum dots is blocked due to selection rules even when energetically allowed -- are a direct manifestation of the Pauli exclusion principle, as well as a key mechanism for manipulating and reading out spin qubits. Pauli spin blockade is well established for systems such as GaAs QDs, but is to be further explored for systems with additional degrees of freedom, such as the valley quantum numbers in carbon-based materials or silicon. Here we report experiments on coupled bilayer graphene double quantum dots, in which the spin and va…
We study the effect of the exchange interaction on the Coulomb blockade peak height statistics in chaotic quantum dots. Because exchange reduces the level repulsion in the many body spectrum, it strongly affects the fluctuations of the peak conductance at finite temperature. We find that including exchange substantially improves the description of the experimental data. Moreover, it provides further evidence of the presence of high spin states (S>1) in such systems.
Silicon quantum dots are attractive candidates for the development of scalable, spin-based qubits. Pauli spin blockade in double quantum dots provides an efficient, temperature independent mechanism for qubit readout. Here we report on transport experiments in double gate nanowire transistors issued from a CMOS process on 300 mm silicon-on-insulator wafers. At low temperature the devices behave as two few-electron quantum dots in series. We observe signatures of Pauli spin blockade with a singlet-triplet splitting ranging from 0.3 to 1.3 meV. Magneto-transport measurements show that transition…
We study electronic transport through an Aharonov-Bohm interferometer with single-level quantum dots embedded in the two arms. The full counting statistics in the shot-noise regime is calculated to first order in the tunnel-coupling strength. The interplay of interference and charging energy in the dots leads to a dynamical channel blockade that is tunable by the magnetic flux penetrating the Aharonov-Bohm ring. We find super-Poissonian behavior with diverging second and higher cumulants when the Aharonov-Bohm flux approaches an integer multiple of the flux quantum.
We investigate a silicon single-electron transistor (SET) in a metal-oxide-semiconductor (MOS) structure by applying a magnetic field perpendicular to the sample surface. The quantum dot is defined electrostatically in a point contact channel and by the potential barriers from negatively charged interface traps. The magnetic field dependence of the excitation spectrum is primarily driven by the Zeeman effect. In the two-electron singlet-triplet (ST) transition, electron-electron Coulomb interaction plays a significant role. The evolution of Coulomb blockade peaks with magnetic field B is also …
Spin qubits based on interacting spins in double quantum dots have been successfully demonstrated. Readout of the qubit state involves a conversion of spin to charge information, universally achieved by taking advantage of a spin blockade phenomenon resulting from Pauli's exclusion principle. The archetypal spin blockade transport signature in double quantum dots takes the form of a rectified current. Currently more complex spin qubit circuits including triple quantum dots are being developed. Here we show both experimentally and theoretically (a) that in a linear triple quantum dot circuit, t…
In the present work we theoretically study thermoelectric transport and heat transfer in a junction including a $T$-shaped double quantum dot coupled to nonmagnetic electrodes and supplemented with a third dot in a parallel configuration. We focus on the combined effect of Coulomb interactions and quantum interference occurring in the $T$-shaped portion of the considered triple quantum dot on the thermoelectric electron transport. The transport through the system is studied within the Coulomb blockade regime in the limit of strong intra-dot interactions between electrons beyond the linear resp…
Singlet-triplet spin blockade in a few-electron lateral double quantum dot is investigated using simultaneous transport and charge-sensing measurements. Transport from the (1,1) to the (0,2) electron occupancy states is strongly suppressed relative to the opposite bias [(0,2) to (1,1)]. At large bias, spin blockade ceases as the (0,2) triplet state enters the transport window, giving a direct measure of exchange splitting as a function of magnetic field. A simple model for current and steady-state charge distribution in spin-blockade conditions is developed and found to be in excellent agreeme…
Asymmetry in a three-electron double quantum dot (DQD) allows spin blockade, when spin-3/2 (quadruplet) states and spin-1/2 (doublet) states have different charge configurations. We have observed this DQD spin blockade near the (1,2)-(2,1) charge transition using a pulsed-gate technique and a charge sensor. We then use this spin blockade to detect Landau-Zener-Stückelberg (LZS) interference and coherent oscillations between the spin quadruplet and doublet states. Such studies add to our understandings of coherence and control properties of three-spin states in a double dot, which in turn would…
Hyperfine interaction (HFI) in carbon nanotube and graphene quantum dots is due to the presence of 13C atoms. We theoretically show that in these structures the short-range nature of the HFI gives rise to a coupling between the valley degree of freedom of the electron and the nuclear spin, in addition to the usual electron spin-nuclear spin coupling. We predict that this property of the HFI affects the Pauli blockade transport in carbon-based double quantum dots. In particular, we show that transport is blocked only if both the spin and the valley degeneracies of the quantum dot levels are lif…
We investigate spin states of few electrons in a double quantum dot by coupling them weakly to a magnetic field resilient NbTiN microwave resonator. We observe a reduced resonator transmission if resonator photons and spin singlet states interact. This response vanishes in a magnetic field once the quantum dot ground state changes from a spin singlet into a spin triplet state. Based on this observation, we map the two-electron singlet-triplet crossover by resonant spectroscopy. By measuring the resonator only, we observe Pauli spin blockade known from transport experiments at finite source-dra…
