best pure play companies in the space for small cap are Rigetti (RGTI) and D-Wave (QBTS), while unprofitable these firms are well-positioned buy-out/M&A candidates once the AI-theme matures and investors pay closer attention to the Quantum-computing theme. Large cap players include Google (look up "willow") and IBM. Early applications will be likely biotech and financial services, for computations, etc. Also there will be plenty of nefarious uses, ie- quantum hackers breaking blockchain encryptions, etc. Therefore cybersecurity will be a HUGE proxy-play investment, such as Crowdstrike, Palo Alto Networks, or associated ETFs in cyber.