Quantum states can jump long distances without particle interaction, this includes energy transfer (you just need a measurable latent possibility for particle interaction!)
The scifi answer that makes sense is that the space curvature around portal and shifting the object between two frames of reference (perhaps through frame dragging effects / gravity-wave like space warping) imparts momentum and it is conveyed from the portal as it is the thing which has to put in energy to correctly warp space for the object transfer.