Quantum Mechanics
Motion in a potential: Free particle

Minimum uncertainty wave packet

A wave packet for which minimum uncertainty in both the position and the momentum is attained. In one dimension it satisfies Delta x * Delta p_x = hbar / 2, where

Delta x

is the root-mean-square deviation from the mean position and

Delat p_x

is the root-mean-square from the mean momentum. The solution to the mathematical problem of finding the wave function that satisfies Delta x * Delta p_x = hbar / 2 is left as an exercise. The result is

Psi (x,0)

where sigmais the root-mean-square deviation from the mean position x_0 and hbar * k_0 is the mean momentum of the particle. The initial probability distribution P(x,0) is given by Gaussian function

P(x,0)

a Gaussian function. P(x,0) is a positive real number. The Gaussian function

Gaussian

Two-dimensional Gaussian functionis shown on the right. The curve has the same shape as the normal distribution with a standard deviation sigma. In two or three dimensions the minimum uncertainty wave packet takes the form of a product of one-dimensional minimum uncertainty wave packets. For a particle moving in a plane the probability distribution looks like the one shown in the picture on the right.