IonQ (IONQ 6.88%) stock is posting big gains in Friday's trading despite sell-offs for the broader market. The quantum computing specialist's share price was up 7.2% as of 2:45 p.m. ET and had been up as much as 12.3% earlier in the session. Meanwhile, the S&P 500 index and the Nasdaq Composite index were both down 1.4%.IonQ saw big sell-offs earlier this week after Nvidia (NVDA -3.00%) CEO said he thought it was unlikely that a very useful quantum computer would be ready within the next 15 years. But IonQ' ...