between the position operator x and momentum operator p x in the x direction of a point particle in one dimension, where [ x , p x ] = x p x − p x x is the commutator of x and p x , i is the imaginary unit, and ℏ is the reduced Planck constant h /2π, and I is the unit operator. In general, position and momentum are vectors of operators and their commutation relation between different components of position and momentum can be expressed as [ x ^ ^ i , p ^ ^ j ] = i ℏ ℏ δ δ i j , where δ δ i j is the Kronecker delta.