There is no apparent memory leak. What is it that you are trying to see here? It says 340MB and that is not much, especially for a 64bit program which by their nature already have a larger memory footprint. There's really nothing unusual here. The program itself needs to be loaded and PS traditionally always reserves memory for history states, undos, swap space and so on. You know, computers don't run on thin air. All that data has to go somewhere... No offense, but you are really misinterpreting things here and don't seem to understand how any of this works, especially with regards to the specifics of PS' memory and swap file management. That 49% is not just Photoshop, BTW, that's all your processes currently active in memory...
You're converting from MB to GB incorrectly.
It's using 340MB of RAM, which is approx .34GB of RAM. Not 3.4GB of RAM.
As Mylenium states, 340MB of RAM usage is expected.
Photoshop holds onto the memory it allocates in the course of working. It will never free it once it's open. This is done on purpose, and the expressed intent is to allow it to meet its future memory needs out of its own allocation, which is more efficient than allowing the OS to manage it.
Whether you or I believe it's the "best behaved" way to act is inconsequential. It will allocate and hold up to the amount of RAM you allow it in the Performance preferences, and Adobe does not appear to be ready to consider changing strategy.
This is nothing new; it has always done this.
If it bothers you, you have some options:
1. Close Photoshop after every edit. This will free resources for other applications to use.
2. Lower Photoshop's RAM limit. This will, of course, reduce Photoshop performance.
3. Get more RAM and stop worrying. More is better, much more is much better.