The phrase "actually an experiment" is correct and usable in written English.
You can use it when clarifying that something is indeed an experiment, often in a context where there may be confusion or doubt about its nature.
Example: "What you thought was a simple test is actually an experiment designed to gather data on user behavior."
Alternatives: "truly an experiment" or "genuinely an experiment".
"Something like Namatjira is actually an experiment in an intercultural exchange," he says.
The 1998 concert was unusual in that the featured "artistic" performance was actually an experiment for Teresa Marrin Nakra's doctoral thesis at the MIT Media Laboratory.
So just to mention a couple of others, the model, the experiment we ran in the class last time is called the double auction, and the experiment I told you about and had you do was actually an experiment that has been run before.
RT: For me, because this was one that I wrote, it was actually an experiment in positivity, trying not to be cynical in any way or having a dark side to it, but unapologetically writing a song about a person who's had a really hard time and needs to go to a club on a Saturday night and dance.
Similarly, the first paragraph of the survey instructions explained that this HIT is actually an experiment, and that only native speakers of U.S. English should take it because nonnative speakers could contaminate the data.
Furthermore, after we've actually performed an experiment and recorded its outcome, all that matters is the actual ratio of likelihoods for that outcome.
Actually, try an experiment, and you'll find it very illuminating.
So one reason, of course, was illustrated, actually, by an experiment that set out to show why children were so smart.
Bob Dylan, 64, is forever on the road, though this may actually be an experiment to establish how badly he can maul his old songs before his fans walk out.
I won the district fair — in part, I suspect, because the judges' pool was heavily populated by members of the military — even though I had violated one of the cardinal rules of science fairs: I hadn't actually done an experiment.
I only stay late if I'm actually doing an experiment.
