  Error correction is a significant step in postprocessing of
continuous-variable quantum key distribution system, which is used to make two
distant legitimate parties share identical corrected keys. We propose an
experiment demonstration of high speed error correction with multi-edge type
low-density parity check (MET-LDPC) codes based on graphic processing unit
(GPU). GPU supports to calculate the messages of MET-LDPC codes simultaneously
and decode multiple codewords in parallel. We optimize the memory structure of
parity check matrix and the belief propagation decoding algorithm to reduce
computational complexity. Our results show that GPU-based decoding algorithm
greatly improves the error correction speed. For the three typical code rate,
i.e., 0.1, 0.05 and 0.02, when the block length is $10^6$ and the iteration
number are 100, 150 and 200, the average error correction speed can be
respectively achieved to 30.39Mbits/s (over three times faster than previous
demonstrations), 21.23Mbits/s and 16.41Mbits/s with 64 codewords decoding in
parallel, which supports high-speed real-time continuous-variable quantum key
distribution system.
