Decoherence and entanglement of a pair of coupled qubits

János K. Asbóth, Петер Адам, Mátyás Koniorczyk +1 more

Nikola Burić

Numerical solutions of the stochastic Schr\"odinger equation given by quantum state diffusion approach to open quantum systems is used to study dynamics of nearest neighbor qubit pairs in systems of small number of qubits on rings with Heisenberg and transverse Ising interaction and under the influence of the thermal environment. In particular, the dependence of the pair entanglement dynamics on the temperature, number of qubits, the type of coupling, and the type of entanglement in the initial state was analyzed for systems of up to $N=10$ qubits. Periodic recurrence of relatively large values of the pair entanglement with dumping due to decoherence by the thermal noise is observed. It is concluded that the pair entanglement in rings with transverse Ising coupling and prepared in a separable initial state is the most resistant on the decoherence effects of the thermal noise, compared to the Heisenberg coupling or initial states with different types of entanglement.

Mohammad Mehdi Sahrapour, Nancy Makri

We use numerically exact iterative path integral methods to investigate the decoherence and entanglement dynamics of a tunneling pair of two coupled qubits (spins) system interacting with a dissipative bath. We find that decoherence is generally accompanied by the destruction of entanglement, although the specifics of this destruction depend sensitively on the parameters of the Hamiltonian (qubit-qubit coupling and/or energy bias), the strength of dissipation, the temperature, and the choice of initial condition. We also observe that dissipation can in some cases generate a substantial amount of entanglement. Finally, if an entangled eigenstate exists which does not couple to the environment, the long-time entanglement can significantly exceed the value corresponding to the Boltzmann equilibrium state.

Yang-Le Wu, S. Das Sarma

We study a pair of capacitively coupled singlet-triplet spin qubits. We characterize the two-qubit decoherence through two complementary measures, the decay time of coupled-qubit oscillations and the fidelity of entangled state preparation. We provide a quantitative map of their dependence on charge noise and field noise, and we highlight the magnetic field gradient across each singlet-triplet qubit as an effective tool to suppress decoherence due to charge noise.

Gabriele Campagnano, Alioscia Hamma, Ulrich Weiß