No. Not happening. With all we have done in the field, we still haven’t succeeded with fusion, and that’s projects the size of a shopping mall. As for fission, that’s been done at about 50 pounds, but almost none of that weight is miniaturizable electronics - it’s fissile material, explosives, and scaffolding to maintain the geometry.
Shiva used lasers the size of buildings (okay, that was mostly the capacitors to store the charge for firing the lasers, but the lasers themselves were huge and had to be huge to deliver that much power). Nova was even more powerful and even larger.
National Ignition Facility is also gigantic, with enough concrete to cover a football field to a depth of more than 30 yards, plus enough steel to build a large warship. You need that much structure for stability. The hydrogen isotope targets hit by the laser are small, but you cannot deliver power above a certain threshold from a small laser - the air ionizes and no longer transmits power to a single point. Alternately, if you try to do it in a vacuum, there is a limit to how much power can be transmitted within the laser cavities before you run into the same issues. Put the lasers outside the vacuum, and you cannot transmit power through the windows into the vacuum. Put the lasers inside the vacuum, and your vacuum chamber has to be heavy (and huge).
Whether you use solid lasers (neodymium or similar) or gas (CO2) lasers, random variation in molecular motion places limits on power transmission. Do the math on laser fusion project, and you run into these limits. I’ve seen the facilities, which are by necessity large. Fusion cannot be miniaturized to anywhere near the level discussed.
As for fission, yes, there are isotopes with relatively small critical masses. There are complex designs that can take advantage of those isotopes. However, miniaturizing the explosives for fusion to get something “compact enough to fit into a pocket or purse and weigh about 5 pounds” is absurd. Even if your delivery system is a suicide bomber, you cannot beat the mass ratios imposed by physics. You need a certain amount of explosive relative to your critical mass, and you need a certain amount of support structure relative to your amount of explosives. Even with the electronics miniaturized, the rest of the device mass is limited by physics to several times the size mentioned.
I left out some details for obvious reasons, but the bottom lime is simple: Not happening.
Indeed, good explanation.
Most drivels about “nanotech”, a trendy, all-purposes but meaningless word are fake news. “Nanotech” always triggers my BS alarm.