A stroll down “Quantum Boulevard” reveals one of the world’s tightest concentrations of bleeding-edge technology firms. Dozens of companies feed a quantum-computing supply chain that did not exist a few years ago. Their wares include some of the most advanced commercialised technology on the planet. The district is hardly a decade old; not long ago the most modern tech in the area was farming equipment. And it is in an unlikely spot: Hefei, the capital of Anhui, one of China’s less fancied provinces. China’s growth is flagging, but its economic miracle appears alive and well in Hefei. Home to about…