Abstract

In practicable CV-QKD systems one major challenge is to synchronise the time scales of the free running electronics at Alice (A) and Bob’s (B) site and the free running true local oscillator (TLO) in the coherent receiver. For the correct phase estimation of the discrete symbols and the mitigation of the phase noise of the lasers some phase reference is required. Reference signals can be multiplexed with the quantum signal in time, frequency or polarisation domain [1]. In some CV-QKD experiments this is achieved by using an extra wavelength which requires additional hardware [2]. In [3] we proposed the use of auxiliary signals in an 8-PSK 40 MBd system. The advantage of this pilot-assisted clock recovery is that it works independently of the quantum signal and without training symbols. On the other hand, the necessary second pilot occupies DAC and ADC bandwidth. In the receiver DSP constructive interference of both pilots must be realized. This requires knowledge of the clock ratio before phase noise compensation. To simplify the signal processing, we propose to use two very stable Rubidium clocks at A and B which can be disciplined with the time reference broadcast by GPS [4].

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