The US Commerce Department is looking into whether DeepSeek – the Chinese company whose AI model's performance rocked the tech world – has been using US chips that are not allowed to be shipped to China, a person familiar with the matter said. China's DeepSeek last week launched a free assistant it says uses less data at a fraction of the cost of US models. Within days, it became the most downloaded app in Apple's App Store and stirred concerns about the United States' lead in AI, wiping around $1 trillion off US technology stocks. Current restrictions on Nvidia artificial…