"has significantly improved" is correct and usable in written English. You can use it when describing a change (such as an improvement) that has been made. For example: Over the last year, research funding for pediatric cancer research has significantly improved.
The city has significantly improved over the last decade".
We have noticed that the vine strength has significantly improved.
This policy has significantly improved people's retirement savings.
This new approach has significantly improved the prediction accuracy.
Over the last four months, her English has significantly improved.
Lithuania has significantly improved its social service system since independence.
Perhaps only Levante have significantly improved.
We've significantly improved our Net Promoter Score.
Hard to say, "but some appear to have significantly improved their circumstances," according to the Times.
Ms. Collins said she believed the changes had significantly improved the measure.
Though cooperation with Mexico had significantly improved, the officials said, it was still far from perfect.
Awesome tool! I started using it one year ago and I never had to look for another app
Ha Thuy Vy
MA of Applied Linguistic, Maquarie University, Australia