We study the decoherence of quantum trits (qutrits) when transferred through noisy channels. The qutrits are represented by the polarization of biphotons – pairs of indistinguishable photons which were generated by spontaneous parametric down-conversion. The biphotons were sent through a controllable depolarizer which is composed of birefringent crystals and wave-plates [1]. The depolarized states were fully characterized by two-photon four-dimensional quantum state tomography and compared successfully to the theoretical prediction. We measured the leakage of the qutrit population to the singlet subspace, and verified experimentally the incoherence between the symmetric and asymmetric subspaces [2]. We also studied the entanglement dynamics that the biphoton exhibits in the presence of decoherence processes, and demonstrated the loss of entanglement while the single qubit coherence still prevails.

[1] A. Shaham and H. S. Eisenberg, Phys. Rev. A 83, 022303 (2011).

[2] R. B. A. Adamson, L. K. Shalm, M. W. Mitchell, and A. M. Steinberg, Phys. Rev. Lett. 98, 043601 (2007).