The no cloning theorem lies at the heart of quantum mechanics and is a direct consequence of the Heisenberg's uncertainty relation. While trying to measure an unknown quantum state, we necessarily perturb it. While this feature has been put to good use to provide for unconditional security in quantum cryptography, it is an annoyance in many quantum protocols, especially so when we realise that most quantum states are fragile and prone to decoherence. For example, it was long (and correctly) believed that the no cloning theorem forbids the implementation of an ideal quantum repeater and quantum noiseless linear amplifier. This is a major obstacle in the extending the range of quantum networks since the quantum signals would degrade after say 100 kilometres of optical fibre and cannot be recovered.
If we give up determinism, however, we can implement near noiseless linear amplification. The implementation becomes better at the expense of a lower probability of success. This protocol has a finite probability of success so that on average, the Heisenberg uncertainty relation is still satisfied. Nevertheless, the successfully noiselessly amplified quantum states can be heralded and thus useful in extending the range of loss-sensitive protocols.
Recently, we have shown that under certain conditions, the NLA could be performed via a Gaussian post-selection such that the classical outputs of a physical NLA and the postselection process are identical. We use this technique to realise quantum cloners, quantum amplifiers and extend the range of quantum cryptography.
The project covers both experimental and theoretical aspects. We are looking for candidates with a background in optics, electronics, quantum mechanics, quantum and classical information, labview and matlab, although they would certainly acquire these skills during this project