BEIJING—New U.S. Ambassador Nicholas Burns has arrived to take up his post in Beijing amid heightened tensions between China and the United States over Taiwan, trade, human rights, and the war in Ukraine. Burns arrived Friday with his wife Libby and a group of other U.S. diplomats and their families and will undergo three weeks of quarantine at his official residence as the Chinese regime requires, according to a U.S. Embassy spokesperson. During his quarantine, the ambassador will virtually meet with U.S. Mission staff, the spokesperson said. The post had been empty since Terry Branstad departed in October 2020. Burns is a career diplomat, former State Department spokesperson, ambassador to NATO, and leading academic, teaching most recently at the Harvard Kennedy School and serving as a foreign policy adviser to Joe Biden’s presidential campaign. He has framed the U.S. relationship with China as manageable, saying Americans should “have confidence in …