Can one achieve success by being just positive and not put in the hard work ? Of course not. It is only a part of the whole process. Most of the time, just being positive or hard working or dedicated or wishing or believing isn't enough. One can achieve success only by bringing all of these qualities together. Staying positive throughout is probably a bit more important because without it, the person is not motivated to work hard or show dedication.
A positive attitude is most certainly a cornerstone for success - however I would not say a person who is positive, will be successful in Quantum Computing - No matter how much they think positively about it.
The positive vibes could be channeled into improving ones' skills to reach their desired destination, that would definitely mean that the attitude was the key to success; However attitude alone will not mean a successful person.