OP: I can't address your question directly since: (1) I'm from the US, and got my education here. I am aware that graduate programs in physics, particularly with respect to masters programs, is substantially different between the US and Europe. (2) Job markets vary with locality; in particular, the demand in industry for candidates with an MS in X will vary widely. Job markets can also be quite fickle over time. So there is an element of luck when it comes to the job market when you graduate (see below).
But, I'll offer a couple of general caveats. [Many decades ago, I got my PhD in physics, concentration in solid-state physics; upon graduation, I got a job in an industrial R&D lab, working on optoelectronic devices.]
(a) It's natural that you are concerned about employment prospects after graduation. From what I can gather, you are leaning more towards quantum optics, because you believe the job prospects are stronger there. Is that correct? But you haven't mentioned whether you are interested in quantum optics. It's too early in your life to be tied to a job you're not interested in (later on in your life, other constraints may dictate that you be tied to a job you're not interested in; but you shouldn't start your career in such a scenario).
(b) As I've pointed out in previous posts, job markets can invert quickly. I'll repeat my pet example. In late 1999, there was a shortage of R&D staff (internationally) for optoelectronic devices, fueled by the Internet Bubble and the demand for high-bandwidth lightwave telecommunications systems. At the time I was mentoring students, including one completing a physics masters program in Europe (concentrating in optoelectronics). I had no problems placing her with a US company; under normal times, she likely would not have been in the running without a PhD. Other colleagues asked me whether I could refer other students to them. But within a year, the Internet Bubble had started to deflate, and hiring practically stopped (with exceptions here and there). By mid 2001, there were massive layoffs and looming bankruptcies.
(c) In the US, you typically get your degrees in (unqualified, plain-old) physics [with the exception of some specialized programs such as applied physics, engineering physics, medical physics, and interdisciplinary programs such as (some) biophysics]. You get a broad-based physics education. Solid-state physics is a subset of physics; and quantum optics (as applied to optoelectronic devices) is a subset of solid-state physics. A deep specialization is advantageous when looking for a job if that specialization is "hot". But what if it isn't? Or, suppose it is "hot" when you graduate and you do get a job; but a few years, or even many years, down the road it grows "cold"? Then what? A broader background allows you more flexibility to pivot when you need to.