Decoherence and quantum computation

The practical implementation of any quantum information protocol has to face the problem of the unavoidable
coupling of quantum processors with their environment. Indeed, real systems can never be perfectly isolated from the surrounding world. It is therefore important to understand the impact of the coupling with a noisy environment on the stability of quantum protocols. In particular, the simulation
of these protocols including realistic models of noise, promises to give useful insights for the design and future construction of quantum hardware.
Teleportation in a noisy environment

We have studied [1] the fidelity of quantum teleportation for the situation in which quantum logic gates are used to provide the long distance entanglement required in the protocol, and where the effect of a noisy environment is modeled by means of a generalized amplitude damping channel.
Our results demonstrate the effectiveness of the quantum trajectories approach, which allows the simulation of open systems with a large number of qubits (up to 24).
This shows that the method is suitable for modeling quantum information protocols in realistic environments.

We have also investigated the effects of quantum noise on the stability of a quantum algorithm simulating the quantum dynamics of a paradigmatic model of chaos, the baker's map. As a result of this study, the time scales for reliable quantum computation in a dissipative environment have been found [2].




Fidelity of teleportation in the presence of a dissipative environment.

References
[1] G.G. Carlo, G. Benenti and G. Casati, Teleportation in a noisy environment: a quantum trajectories approach, Phys. Rev. Lett. 91, 257903 (2003).
[2] G.G. Carlo, G. Benenti, G. Casati and C. Mejia-Monasterio, Simulating noisy quantum protocols with quantum trajectories, Phys. Rev. A 69, 062317 (2004).