Armed with a doctorate in financial engineering, 34-year-old Timo Schlaefer was on his way to a promising career at Goldman Sachs in London. Previously with the bank’s mergers and acquisitions team, he became an executive director of credit quantitative modeling at Goldman, where quants like Schlaefer are highly valued. In February he gave that up, and launched a company called Crypto Facilities Ltd, a bitcoin derivatives trading platform, which now has six employees.