A great many of your bigger companies require new hires to sign contracts that convey to the employers any "Intellectual Property" that the workers "make or conceive" during the term of employment. Courts treat such assignments as valid in spite of the at-will nature of the relationship.

But what happens if a worker conceives an invention before starting the new

Russian scientists come up with a way to make an ozone-friendly agent that helps prepare materials useful in making units that store hot or cold.  They tell the American company that hired them about the results of their study.  And the U.S. firm starts using the process that their Russian colleagues discovered.

Does the U.S. outfit qualify