Non-Markovian Dynamics of Geometric Quantum Discord in a Double Quantum Dot System

In this paper, we study the geometric quantum discord dynamics of the double quantum dot charge qubit in the non-Markovian environment. We apply the non-perturbative non-Markovian quantum state diffusion method to obtain the exact master equation of the double quantum dot system coupled to two independent non-zero temperature electronic baths. Then, we use this master equation to investigate the effects of non-Markovianity, inter-dot coupling strength and bath temperature on the dynamics of geometric quantum discord. Our studies show that the geometric quantum discord of a double quantum dot system can be modified and enhanced in some cases via these factors.

Superconductor qubits hamiltonian approximations effect on quantum state evolution and control

Microwave IQ-mixer controllers are designed for the three approximated Hamiltonians of charge, phase and flux qubits and the controllers are exerted both on approximate and precise quantum system models. The controlled qubits are for the implementation of the two quantum-gates with these three fundamental types of qubits, Quantum NOT-gate and Hadamard-gate. In the charge-qubit, for implementation of both gates, in the approximated and precise model, we observed different controlled trajectories. But fortunately, applying the controller designed for the approximated system over the precise system leads to the passing of the quantum state from the desired state sooner that the expected time. Phase-qubit and flux qubit have similar behaviour under the control system action. In both of them, the implementation of NOT-gate operation led to same trajectories which arrive at final goal state at different times. But in both of those two qubits for implementation of Hadamard-gate, desired trajectory and precise trajectory have some angle of deviation, then by exerting the approximated design controller to precise system, it caused the quantum state to approach the goal state for Hadamard gate implementation, and since the quantum state does not completely reach the goal state, we can not obtain very high gate fidelity.

Superconductor Qubits Hamiltonian Approximations Effect on Quantum State Evolution and Control

Quantum state on Bloch sphere for superconducting charge qubit, phase qubit and flux qubit for all time in absence of external drive is stable to initial state. By driving the qubits, approximation of charge and flux Hamiltonian lead to quantum state rotation in Bloch sphere around an axis completely differ from rotation vector of exact Hamiltonian. The trajectory of quantum state for phase qubit for approximated and exact Hamiltonian is the same but the expectation of quantum observable has considerable errors as two other qubits. microwave drive control is designed for approximated Hamiltonian and exerted on actual systems and shows completely different trajectory with respect to desired trajectory. Finally a nonlinear control with external µV voltage control and nA current control is designed for general qubit which completely stabilizes quantum state toward a desired state.

Preparation of a superposition of squeezed coherent states of a cavity field via coupling to a superconducting charge qubit

The generation of nonclassical states of a radiation field has become increasingly important in the past years given its various applications in quantum communication. It has been recently proposed a way to engineer quantum states using a SQUID charge qubit inside a cavity with a controllable interaction between the cavity field and the charge qubit. Since decoherence is known to affect quantum effects uninterruptedly and decoherence process are working even when the quantum state is being formed, therefore, is interesting to envisage processes through which quantum superpositions are generated as fast as possible. We succeed in linearizing the Hamiltonian of the system through the application of an appropriate unitary transformation and for certain values of the parameters involved, we show that it is possible to obtain specific Hamiltonians. In this work we will use this approach for preparing superposition of two squeezed coherent states.

Preparation of a superposition of squeezed coherent states of a cavity field via coupling to a superconducting charge qubit

The generation of nonclassical states of a radiation field has become increasingly important in the past years given its various applications in quantum communication. It has been recently proposed a way to engineer quantum states using a SQUID charge qubit inside a cavity with a controllable interaction between the cavity field and the charge qubit. Since decoherence is known to affect quantum effects uninterruptedly and decoherence process are working even when the quantum state is being formed, therefore, is interesting to envisage processes through which quantum superpositions are generated as fast as possible. We succeed in linearizing the Hamiltonian of the system through the application of an appropriate unitary transformation and for certain values of the parameters involved, we show that it is possible to obtain specific Hamiltonians. In this work we will use this approach for preparing superposition of two squeezed coherent states.