Recent research has shown that multitasking is a myth. We have believed for years that the key to working smarter is to multitask, but recent research by Dan & Broadstreet (2011) show that people are not natural multitaskers. Their research also shows that even if you can do more things at once, you tend to do all of them at a lower standard.
Another concept that has gained prominence is “flow”. Referring to that period in work where you are in the “zone”. You are focused on the task at hand and have clarity of purpose and thinking.