Demonstration of an ultrafast logic gate by interference of coherent transients

We demonstrate an ultrafast three-port all-optical Taffoli logic gate by us ing interference of femtosecond laser pulses with two-pulse photon echo in dye-doped polymer films at low temperatures. The gate performs an operation of "controlled controlled NOT" on the time scale of less than 1 ps, using one spatial spot. We show that an important condition for this gate is the causal nature of the coherent transient response. Relevant truth table is i mplemented only if pulses coming later in time do not influence the interfe rence of the pulses applied earlier in time. The other special property of the gate is coherent phase memory about the input pulses. We suggest that i f the excited electronic state coherence time is much longer than the durat ion of the pulses, then it is possible to implement a coherent logic gate w ith a large number of inputs.