Paper 4, Section I, B

Quantum Mechanics
Part IB, 2009

The wavefunction of a Gaussian wavepacket for a particle of mass mm moving in one dimension is

ψ(x,t)=1π1/411+it/mexp(x22(1+it/m))\psi(x, t)=\frac{1}{\pi^{1 / 4}} \sqrt{\frac{1}{1+i \hbar t / m}} \exp \left(-\frac{x^{2}}{2(1+i \hbar t / m)}\right)

Show that ψ(x,t)\psi(x, t) satisfies the appropriate time-dependent Schrödinger equation.

Show that ψ(x,t)\psi(x, t) is normalized to unity and calculate the uncertainty in measurement of the particle position, Δx=x2x2\Delta x=\sqrt{\left\langle x^{2}\right\rangle-\langle x\rangle^{2}}.

Is ψ(x,t)\psi(x, t) a stationary state? Give a reason for your answer.

[\left[\right. You may assume that eλx2dx=πλ]\left.\int_{-\infty}^{\infty} e^{-\lambda x^{2}} d x=\sqrt{\frac{\pi}{\lambda}} \cdot\right]