The value of De Broglie wavelength is λ = h/mv, 

Where h is a universal constant, Plancks constant

m is mass and v is velocity.

If λ is same for Bith it means the same value of mv

By equating momentum for Both we can easily find that velocity of Proton will be four times that of Alpha particle Because alpha particle is four times Heavies than that of Proton.