# Does the principle of superposition hold for open quantum systems?

In closed systems, the dynamical equation is the Schrödinger equation, for which the principle of superposition holds.

In open quantum systems, does the principle of superposition hold?

• Maybe this is obvious to people who have studied the topic more than I, but what differentiates an open quantum system from a closed one? My first instinct is that your definition of open will either trivially prove superposition does not hold by invoking a behavior at the border that isn't in line with Schrodinger's equation, or will trivially prove it holds by letting the system reduce to something that is in line. – Cort Ammon - Reinstate Monica Nov 4 '19 at 21:09

I looked up "open quantum systems", because I could not understand how a quantum system could be "open" as it needs the boundary conditions to define the wavefunction.

In physics, an open quantum system is a quantum-mechanical system which interacts with an external quantum system, the environment or bath

As the "open" boundary is a quantum system the answer is yes, superposition holds, as with all quantum systems.