Principal Investigator Jeffrey Shapiro
Co-investigator Franco Wong
Professors Chuang and Yamamoto showed that the cross-Kerr effect (cross-phase modulation) could be used, in principle, to create an optical CNOT gate in dual-rail quantum logic, thus completing a universal gate set for all-optical quantum computation. They used a single-mode model for the cross-phase modulation interaction, and presumed that a single photon propagating in one mode of a dual-rail qubit could induce a p-rad phase shift on a single photon propagating in one mode of another dual-rail qubit. We have used multi-mode continuous-time analysis to show that the causal, non-instantaneous behavior of any c(3) nonlinearity is enough to preclude high-fidelity operation of such a gate, owing to the phase noise that is required by commutator-bracket preservation. We are now exploring the limitations this noise imposes on quantum computation architectures that rely on weak nonlinearities, and we are studying the relationship between our theory and cross-phase modulation created via electromagnetically-induced transparency.