Figure 3: Experimental set-up.
From: Continuous variable quantum key distribution with modulated entangled states
A squeezed state is generated in each of the two OPOs, operated below threshold. The squeezed states interfere at a beam splitter to form a two-mode squeezed state. The amplitude or the phase quadrature of the one mode is measured by Alice's homodyne detector. The other mode is carefully phase locked to a coherently modulated auxiliary mode. The auxiliary state is generated using a phase modulator (PM) and an amplitude modulator (AM), each of which are driven by a white noise generator. Alice acquires information about the modulation by measuring a part of the auxiliary state. The coherent state is purified by the highly asymmetric beamsplitter all of this to minimize the harmful preparation noise28. The modulated and conditionally squeezed state is transmitted through the channel to Bob's homodyne detector where one of the conjugate quadratures is measured. The resulting measurement outcomes are fed via a fast AD card to a computer for signal processing.
