Quantum process tomography and the search for decoherence-free subspaces

Optimal Quantum Tomography

“…One should realize that the whole technology of quantum information crucially depends on the reliability of processes, source and detectors, and on precise knowledge of sources of noise and errors. For example, all error correction techniques are based on the knowledge of the noise model, which is a prerequisite for an effective design of correcting codes [70], [71], [72], and Quantum Process Tomography allows a reliable reconstruction of the noise and its decoherence free subspaces without recurring to prior assumptions on the noisy channels [73]. The increasingly high confidence in the tomographic technique, with the largest imaginable flexibility of data-processing, and expanding outside the optical domain in the whole physical domain, grew the appetite of experimentalists and theoreticians posing increasingly challenging problems.…”

Experimental study of decoherence of the two-mode squeezed vacuum state via second harmonic generation

“…Among these prior experimental studies on decoherence, some are of particular interest to us due to the fact that they were conducted in an 'all-optical' manner, for instance, Kwiat et al used polarization entangled photon pairs produced by spontaneous parametric downconversion to search for decoherence-free subspaces [13]; Almeida et al also used polarization entangled photon pairs to demonstrate that quantum entanglement may suddenly disappear although the environment-induced decay is asymptotic [14]. Both experiments employed the sophisticated quantum state tomography [32,33] to characterize the effect of decoherence. In this paper, we report a novel all-optical experimental scheme for studying the effect of decoherence.…”