General way to define tunneling time

With the development of attosecond science, tunneling time can now be measured experimentally with the attoclock technique. However, there are many different theoretical definitions of tunneling time and no consensus has been achieved. Here, we bridge the relationship between different definitions of tunneling time based on a quantum travel time in one-dimensional rectangular barrier tunneling problem. We find that the real quantum travel time t_Re is equal to the Bohmian time t_Bohmian, which is related to the resonance lifetime of a bound state. The total quantum travel time τ_t can perfectly retrieve the transversal time t_x and the Büttiker-Landauer time τ_BL in two opposite limits, regardless of the particle energy.