It is shown that the universal set of quantum logic gates can be realized using solid-state quantum bits based on coherent electron transport in quantum wires. The elementary quantum bits are realized with a proper design of two quantum wires coupled through a potential barrier. Numerical simulations show that (a) a proper design of the coupling barrier allows one to realize any one-qbit rotation and (b) Coulomb interaction between two qbits of this kind allows the implementation of the CNOT gate. These systems are based on a mature technology and seem to be integrable with conventional electronics.
We address the dynamics of entanglement and quantum discord for two noninteracting qubits initially prepared\ud in a maximally entangled state and then subjected to a classical colored noise, i.e., coupled with an external\ud environment characterized by a noise spectrum of the form 1/f α.More specifically, we address systems in which\ud the Gaussian approximation fails, i.e., mere knowledge of the spectrum is not enough to determine the dynamics\ud of quantum correlations. We thus investigate the dynamics for two different configurations of the environment:\ud in the first case, the noise spectrum is due to the interaction of each qubit with a single bistable fluctuator with\ud an undetermined switching rate, whereas in the second case we consider a collection of classical fluctuators with\ud fixed switching rates. In both cases, we found analytical expressions for the time dependence of entanglement\ud and quantum discord, which may also be extended to a collection of fluctuators with random switching rates.\ud The environmental noise is introduced by means of stochastic time-dependent terms in the Hamiltonian, and this\ud allows us to describe the effects of both separate and common environments. We show that the non-Gaussian\ud character of the noise may lead to significant effects, e.g., environments with the same power spectrum, but\ud different configurations give rise to the opposite behavior for quantum correlations. In particular, depending\ud on the characteristics of the environmental noise considered, both entanglement and discord display either a\ud monotonic decay or the phenomena of sudden death and revivals. Our results show that the microscopic structure\ud of the environment, in addition to its noise spectrum, is relevant for the dynamics of quantum correlations and\ud may be a valid starting point for the engineering of non-Gaussian colored environments
We describe an efficient theoretical criterion, suitable for indistinguishable particles to quantify the quantum correlations of any pure two-fermion state, based on the Slater rank concept. It represents the natural generalization of the linear entropy used to treat quantum entanglement in systems of non-identical particles. Such a criterion is here applied to an electron-electron scattering in a two-dimensional system in order to perform a quantitative evaluation of the entanglement dynamics for various spin configurations and to compare the linear entropy with alternative approaches. Our numerical results show the dependence of the entanglement evolution upon the initial state of the system and its spin components. The differences with previous analyses accomplished by using the von Neumann entropy are discussed.The evaluation of the entanglement dynamics in terms of the linear entropy results to be much less demanding from the computational point of view, not requiring the diagonalization of the density matrix.
We perform the quantitative evaluation of the entanglement dynamics in scattering events between two insistinguishable electrons interacting via Coulomb potential in 1D and 2D semiconductor nanostructures. We apply a criterion based on the von Neumann entropy and the Schmidt decomposition of the global state vector suitable for systems of identical particles. From the time-dependent numerical solution of the two-particle wavefunction of the scattering carriers we compute their entanglement evolution for different spin configurations: two electrons with the same spin, with different spin, singlet, and triplet spin state. The procedure allows to evaluate the mechanisms that govern entanglement creation and their connection with the characteristic physical parameters and initial conditions of the system. The cases in which the evolution of entanglement is similar to the one obtained for distinguishable particles are discussed.
We address the effect of classical noise on the dynamics of quantum correlations, entanglement and quantum discord, of two non-interacting qubits initially prepared in a Bell state. The effect of noise is modeled by randomizing the single-qubit transition amplitudes. We address both static and dynamic environmental noise corresponding to interaction with separate common baths in either Markovian and non-Markovian regimes. In the Markov regime, a monotone decay of the quantum correlations is found, whereas for non-Markovian noise sudden death and revival phenomena may occur, depending on the characteristics of the noise. Entanglement and quantum discord show the same qualitative behavior for all kind of noises considered. On the other hand, we find that separate and common environments may play opposite roles in preserving quantum correlations, depending on the noise regime considered.
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