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Quantum mechanically, the four quantum dots (the dotted square boxes) between two qubit dots of the neighboring cells form a coherent QCA.
Source publication
Without resorting to spin-spin coupling, we propose a scalable spin quantum computing scheme assisted with a semiconductor multiple-quantum-dot structure. The techniques of single electron transitions and the nanostructure of quantum-dot cellular automata (QCA) are used to generate charge entangled states of two electrons, which are then converted...
Contexts in source publication
Context 1
... and ∆ a tunneling coupling. Based on the above architecture, one can find that the two double-dot pairs (e.g., C i -D i and A j -B j in Fig. 3) between the qubit dots of two neighboring cells form a QCA. QCA was originally proposed as a transistorless alternative to digital circuit devices at nanoscale 17,18 . Recently, semiconductor QCA has been fabricated from GaAs/AlGaAs heterostructures 22 and from buried dopants 23 as well. Due to the Coulomb repulsion, when a QCA is ...
Context 2
... is the charge-to-spin conversion of two-electron entanglement states. We shall use the QCA structure to generate a charge entangled state via single electron transitions and then convert it into a spin en- tangled state using single-spin rotations only. Explicitly, consider a pair of neighboring unit cells, e.g. the ith and the jth cells (see Fig. 3). The initial state of the two excess electrons is given ...
Similar publications
A thorough simulation study is carried out on thermal and quantum delocalization effects on the feasibility of a quantum-dot cellular automata (QCA) cell. The occupation correlation of two electrons is modeled with a simple four-site array of harmonic quantum dots (QD). QD sizes range from 20 nm to 40 nm with site separations from 20 nm to 100 nm,...
Taking the excess electron spin in a unit cell of semiconductor multiple quantum-dot structure as a qubit, we can implement scalable quantum computation without resorting to spin-spin interactions. The technique of single electron tunnelings and the structure of quantum-dot cellular automata (QCA) are used to create a charge entangled state of two...
Citations
... The electron qubit may be implemented in several ways 13 : as a charge qubit [14][15][16][17][18][19] , a spin qubit 20,21 or encoded in electronic Schrödinger cat states 22,23 . The solidstate qubit based on electron spin in electrostatic quantum dots is the easiest to implement and is one of a few promising candidates for quantum computing 24 . ...
We examine spin-dependent displacement of a single electron, resulting in separation and relocation of the electron wavefunction components, and thus charge parts, corresponding to opposite spins. This separation is induced by a pulse of an electric field which generates varying Rashba type spin-orbit coupling. This mechanism is next implemented in a nanodevice based on a gated quantum dot defined within a quantum nanowire. The electric field pulse is generated by ultrafast changes of voltages, of the order of several hundred mV, applied to nearby gates. The device is modeled realistically with appropriate material parameters and voltages applied to the gates, yielding an accurate confinement potential and Rashba coupling. At the end, we propose a spin-to-charge conversion device, which with an additional charge detector will allow for electron spin state measurement.
... These features make quantum dots particularly useful in the study of mesoscopic physics, as well as the potential applications for nanotechnology and quantum information processing. Quantum dots are also promising candidates for realizations of scalable quantum computer, implemented with the electron charge and/or spin qubits, even with Majorana fermions [1][2][3][4][5][6][7][8]. ...
We investigate the dynamics of charge--states coherence in a degenerate double--dot Aharonov--Bohm interferometer with finite interdot Coulomb interactions. The quantum coherence of the charge states is found to be sensitive to the transport setup configurations, involving both the single--electron impurity channels and the Coulomb--assisted ones. We numerically demonstrate the emergence of a complete coherence between the two charge states, with the relative phase being continuously controllable through the magnetic flux. Remarkably, a fully coherent charge qubit arises at the double--dots electron pair tunneling resonance condition, where the chemical potential of one electrode is tuned at the center between a single--electron impurity channel and the related Coulomb--assisted channel. This pure quantum state of charge qubit could be \emph{experimentally located} at the current--voltage characteristic turnover position, where differential conductance sign changes. We further elaborate the underlying mechanism for both the real--time and the stationary charge--states coherences in the double--dot systems of study.
... However, the energy involved in the debate of the magnetic structure is rather small as compared to the energies in ∼eV range in this study. Collinear calculations with antiferromagnetic spin configurations and fixed volume reasonably reproduced experimentally observed unit cell parameters [49,50], magnetic structure [51][52][53][54], bandgaps [55], and the bulk moduli [49,56], as reported in the previous publication [45]. For the bulk calculations, the cell distortion induced by the anti-ferromagnetic spin configuration is very small and the energy difference is about 0.14 meV per 22 atom cell between with and without allowing lattice distortion, which is quite small compared to the energies discussed in eV range. ...
... However, the energy involved in the debate of the magnetic structure is rather small as compared to the energies in ∼eV range in this study. Collinear calculations with antiferromagnetic spin configurations and fixed volume reasonably reproduced experimentally observed unit cell parameters [49,50], magnetic structure [51][52][53][54], bandgaps [55], and the bulk moduli [49,56], as reported in the previous publication [45]. For the bulk calculations, the cell distortion induced by the anti-ferromagnetic spin configuration is very small and the energy difference is about 0.14 meV per 22 atom cell between with and without allowing lattice distortion, which is quite small compared to the energies discussed in eV range. ...
... Thus, (111) and (110) surfaces were considered in the slab models (figures 1(b) and (c)). Experimentally observed cell parameters [49,50] were used to construct the slab models. The computational supercell dimensions in the slab plane are 7.202 Å × 10.185 Å and 7.202 Å × 7.202 Å for (110) and (111) (110) and (111) of Gd 2 Zr 2 O 7 respectively, with the γ = 90°for the (110) and 120°for (111) surfaces, respectively. ...
Defect formation energies of point defects of two pyrochlores Gd2Ti2O7 and Gd2Zr2O7 as a function of crystal size were calculated. Density functional theory with plane-wave basis sets and the projector-augmented wave method were used in the calculations. The results show that the defect formation energies of the two pyrochlores diverge as the size decreases to the nanometer range. For Gd2Ti2O7 pyrochlore, the defect formation energy is higher at nanometers with respect to that of the bulk, while it is lower for Gd2Zr2O7. The lowest defect formation energy for Gd2Zr2O7 is found at 15?20 ?. The different behaviors of the defect formation energies as a function of crystal size are caused by different structural adjustments around the defects as the size decreases. For both pyrochlore compositions at large sizes, the defect structures are similar to those of the bulk. As the size decreases, for Gd2Ti2O7, additional structure distortions appear at the surfaces, which cause the defect formation energy to increase. For Gd2Zr2O7, additional oxygen Frenkel pair defects are introduced, which reduce the defect formation energy. As the size further decreases, increased structure distortions occur at the surfaces, which cause the defect formation energy to increase. Based on a hypothesis that correlates the energetics of defect formation and radiation response for complex oxides, the calculated results suggest that at nanometer range Gd2Ti2O7 pyrochlore is expected to have a lower radiation tolerance, and those of Gd2Zr2O7 pyrochlore to have a higher radiation tolerance. The highest radiation tolerance for Gd2Zr2O7 pyrochlore is expected to be found at ~2 nanometers.
... The small AHE signal for H-2 can be explained by the incorporation of interstitial H at the surface, which led to less formation of ferromagnetic Co-H-Co complexes and limited M to low values. In addition, the superparamagnetic contributions by ferromagnetic clusters (without a percolation process) cannot induce a large AHE, as observed in figure 3(c) [31]. ...
The electrical transport characteristics and anomalous Hall effect (AHE) were investigated for a hydrogen-injected Co-doped ZnO thin film. Based on the measurements of resistivity and the Hall effect between 5 K and 300 K, the existence of Co-H-Co complexes was observed to introduce the AHE and enable the AHE to persist up to room temperature. The observed H-induced AHE originates from the asymmetric scattering of carrier hopping between the localized states driven by ferromagnetic Co-H-Co complexes, and a theoretical study using first-principle calculations supports the experimental results well. This large ferromagnetic response of charge carriers by the hydrogen-induced AHE on semiconducting oxides will stimulate the further investigation of room-temperature spintronic applications.
... It has been shown in [5,6,7,8] that, by manipulating spin degrees of freedom, we are able to perform universal quantum computation (UQC) with movable electrons. The key idea is that we encode qubits in the electron spins, but make measurement [5,6] or make entanglement [7,8] by means of the electron charges. ...
... It has been shown in [5,6,7,8] that, by manipulating spin degrees of freedom, we are able to perform universal quantum computation (UQC) with movable electrons. The key idea is that we encode qubits in the electron spins, but make measurement [5,6] or make entanglement [7,8] by means of the electron charges. As spin and charge (i.e., orbit) degrees of freedom commute, a measurement on the charge of an electron does not affect the spin of the electron. ...
... As spin and charge (i.e., orbit) degrees of freedom commute, a measurement on the charge of an electron does not affect the spin of the electron. With these ideas, we could use the movable (or say, free) electrons to entangle the spin states of different electrons [5,6,7,8,9], to analyze the multipartite entanglement [5,9], and to purify the existing entanglement [10]. ...
We investigate the possibility to have electron-pairs in decoherence-free subspace (DFS), by means of the quantum-dot cellular automata (QCA) and single-spin rotations, to carry out a high-fidelity and deterministic universal quantum computation. We show that our QCA device with electrons tunneling in two dimensions is very suitable for DFS encoding, and argue that our design favors a scalable quantum computation robust to collective dephasing errors. Keywords: Decoherence-free subspace (DFS), Quantum-dot cellular automata (QCA), Universal quantum computation (UQC) Communicated by: to be filled by the Editorial Spin degrees of freedom of electrons in quantum dots have been considered as good candidates to encode qubits over past years, due to their long decoherence time and full controllability. Of particular interest is the recent achievements of ultrafast manipulation of electron spin in conduction band of the quantum dot [1, 2] and coherent tunneling of electrons between neighboring quantum dots [3, 4]. These technical progresses have led to more and more concerns on movable electron based quantum gates.
... Some progress on decoherence entanglement dynamics in cavity optical systems has been reported based on exact master equations [11, 12, 13] . Further applications to the decoherence dynamics of electron charge and spin entanglement in terms of the quantum dots [32, 33] are expected. The full non-equilibrium electron dynamics and the real time monitoring of spin polarization processes in quantum dots are future topics. ...
In this article, we report the recent progress on decoherence dynamics of electrons in quantum dot quantum computing systems
using the exact master equation we derived recently based on the Feynman–Vernon influence functional approach. The exact master
equation is valid for general nanostructure systems coupled to multi-reservoirs with arbitrary spectral densities, temperatures
and biases. We take the double quantum dot charge qubit system as a specific example, and discuss in details the decoherence
dynamics of the charge qubit under coherence controls. The decoherence dynamics risen from the entanglement between the system
and the environment is mainly non-Markovian. We further discuss the decoherence of the double-dot charge qubit induced by
quantum point contact (QPC) measurement where the master equation is re-derived using the Keldysh non-equilibrium Green function
technique due to the non-linear coupling between the charge qubit and the QPC. The non-Markovian decoherence dynamics in the
measurement processes is extensively discussed as well.
... It has been shown in [5,6,7,8] that, by manipulating spin degrees of freedom, we are able to perform universal quantum computation (UQC) with movable electrons. The key idea is that we encode qubits in the electron spins, but make measurement [5,6] or make entanglement [7,8] by means of the electron charges. ...
... It has been shown in [5,6,7,8] that, by manipulating spin degrees of freedom, we are able to perform universal quantum computation (UQC) with movable electrons. The key idea is that we encode qubits in the electron spins, but make measurement [5,6] or make entanglement [7,8] by means of the electron charges. As spin and charge (i.e., orbit) degrees of freedom commute, a measurement on the charge of an electron does not affect the spin of the electron. ...
... As spin and charge (i.e., orbit) degrees of freedom commute, a measurement on the charge of an electron does not affect the spin of the electron. With these ideas, we could use the movable (or say, free) electrons to entangle the spin states of different electrons [5,6,7,8,9], to analyze the multipartite entanglement [5,9], and to purify the existing entanglement [10]. ...
We investigate the possibility to have electron-pairs in dephasing-free subspace (DFS), by means of the quantum-dot cellular automata (QCA) and single-spin rotations, to carry out a high-fidelity and deterministic universal quantum computation. We show that our QCA device with electrons tunneling two dimensionally is very suitable for DFS encoding, and argue that our design favors a scalable quantum computation robust to collective dephasing errors. Comment: 10 pages, 3 figures
We examine spin-dependent displacement of a single electron, resulting in separation and relocation of the electron wave-function components, and thus charge parts, corresponding to opposite spins. This separation is induced by a pulse of an electric field which generates varying Rashba type spin-orbit coupling. This mechanism is next implemented in a nanodevice based on a gated quantum dot defined within a quantum nanowire. The electric-field pulse is generated by ultrafast changes of voltages, of the order of several hundred mV, applied to nearby gates. The device is modeled realistically with appropriate material parameters and voltages applied to the gates, yielding an accurate confinement potential and Rashba coupling. At the end, we propose a spin-to-charge conversion device, which with an additional charge detector will allow for electron-spin state measurement.
In terms of the exact quantum master equation solution for open electronic systems, the coherent dynamics of two charge states described by two parallel quantum dots with one fully polarized electron on either dot is investigated in the presence of spin-orbit interaction. We demonstrate that the double dot system can stay in a dynamically decoherence free space. The coherence between two double dot charge states can be precisely manipulated through a spin-orbit coupling. The effects of the temperature, the finite bandwidth of lead, and the energy deviations during the coherence manipulation are also explored.
We propose a scheme for a large-scale cluster state preparation of single-charged semiconductor quantum dots utilizing Faraday
rotation. Without interaction between quantum dots, the exciton induced Faraday rotation could distribute the spatially separate
quantum dots into a quantum network assisted by cavity QED. We obtain the corresponding parameters from the numerical simulation
based on the input-output process for the required Faraday rotation and some discussion is made in view of experimental feasibility.
