Bad Qubits — Learn Quantum by Doing

Multiple choice

For a free-particle wave packet, if you confine it to a narrower window in position space (smaller spread Delta x), what necessarily happens to the spread of its momentum distribution Delta p?

Delta p drops to zero, giving the particle a perfectly sharp momentum
Delta p must increase, since roughly Delta p ~ hbar/Delta x
Delta p is unaffected; position and momentum spreads are independent
Delta p must decrease by the same factor that Delta x decreases