Government Policy? Maybe a bit crazy for HN...
Price controls = supply shortages. Basic principal of market economics.
Remember, this is Switzerland, so you need to convince the population that this is a good idea otherwise they will block it with a popular vote. So confiscation of property or forced labour or increased taxes are all out of the question.
Change zoning rules. Incentives for co-living. Reduce flat sizes. Rebuilt office spaces. Or look to Vienna: a big stock of goverment-owned flats with low prices which makes it hard to charge more than those.