Femtotechnology is a term used by some futurists to refer to structuring of matter on a femtometre scale, by analogy with nanotechnology and picotechnology. This involves the manipulation of excited energy states within atomic nuclei to produce metastable (or otherwise stabilized) states with unusual properties. In the extreme case, excited states of nucleons are considered, ostensibly to tailor the behavioral properties of these particles (though this is in practice unlikely to work as intended).

Practical applications of femtotechnology are currently considered to be unlikely. The spacings between nuclear energy levels require equipment capable of efficiently generating and processing gamma rays, without equipment degradation. The nature of the strong interaction is such that excited nuclear states tend to be very unstable (unlike the excited electron states in Rydberg atoms), and there are a finite number of excited states below the nuclear binding energy, unlike the (in principle) infinite number of bound states available to an atom's electrons. Similarly, what is known about the excited states of individual nucleons seems to indicate that these do not produce behavior that in any way makes nucleons easier to use or manipulate, and indicates instead that these excited states are even less stable and fewer in number than the excited states of atomic nuclei.

The most advanced form of molecular nanotechnology is often imagined to involve self-replicatingnucleons rather than atoms. For example, the astrophysicist Frank Drake once speculated about the possibility of self-replicating organisms composed of such nuclear molecules living on the surface of a neutron star, a suggestion taken up in the science fiction novel Dragon's Egg by the physicist Robert Forward. It is thought by physicists that nuclear molecules may be possible, but they would be very short-lived, and whether they could actually be made to perform complex tasks such as self-replication, or what type of technology could be used to manipulate them, is unknown. molecular machines, and there have been some very speculative suggestions that something similar might in principle be possible with "molecules" composed of

The hypothetical hafnium bomb can be considered a crude application of femtotechnology.