Thomas Symul

High efficiency error reconciliation, typically achieved by using Multi Edge Low Density Parity Codes (ME-LDPC), is necessary for CV-QKD to reach large transmission distance. The commonly accepted definition of the efficiency, however, is problematic as it does not take into account the Frame Error Rate (FER) of LDPC, and therefore is theoretically and provably unbounded (i.e. can tend to infinity), if one can accept increasingly larger FER. Here we report new ME-LDPC code construction allowing high efficiency (>0.91) with very low FER (<0.008), allowing for a large effective efficiency, over a large continuous range of SNR (between -20.5dB to -6dB).

We present a robust real time quantum random number generator based on broadband measurements of the quantum fluctuations of the vacuum field. Even though ANY optical measurements may contain potentially untrusted technical noise, we show that suitable algorithms can transform the digitised photo-current into a unique string of random numbers that are immune to environmental tempering and are absolutely indeterministic. Our device achieves a continuous generation bandwidth of 5.7 Gb/s, and is verified using statistical randomness tests.

We demonstrate continuous variable Gaussian entanglement distillation using a measurement-based noiseless linear amplifier. Our scheme relies on a heterodyne detection scheme, followed by a classical non-deterministic post selection of the measurements. We demonstrate that we are able to extract a subset of data presenting a stronger entanglement than the original resource, and that we can recover entanglement after transmission loss.