  The continuous-variable version of quantum key distribution (QKD) offers the
advantages (over discrete-variable systems) of higher secret key rates in
metropolitan areas as well as the use of standard telecom components that can
operate at room temperature. An important step in the real-world adoption of
continuous-variable QKD is the deployment of field tests over commercial
fibers. Here we report two different field tests of a continuous-variable QKD
system through commercial fiber networks in Xi'an and Guangzhou over distances
of 30.02 km (12.48 dB) and 49.85 km (11.62 dB), respectively. We achieve secure
key rates two orders-of-magnitude higher than previous field test
demonstrations. This is achieved by developing a fully automatic control system
to create stable excess noise and by applying a rate-adaptive reconciliation
protocol to achieve a high reconciliation efficiency with high success
probability. Our results pave the way to achieving continuous-variable QKD in a
metropolitan setting.
