Abstract
We report a large area photo-diode based homodyne detector for free-space quantum coherent communication. The detector's performance is studied in terms of detection bandwidth and electronic noise for shot-noise limited quantum signal detection. Using large area photo-diodes increases signal collection efficiency from turbulent atmospheric channels, in comparison with typical fibre based free-space homodyne detectors. Under identical atmospheric turbulence and receiver aperture conditions, our homodyne detector based on 1mm diameter photo-diode experiences 0dB loss due to turbulence while a 10um fibre based detector experiences 13.5dB of signal loss over a 700km free-space link, at 90 degree elevation angle.
Highlights
In coherent communication systems, optical signals carry information on both their amplitude and phase[1]
Thereafter, error correction followed by privacy amplification are employed to generate a secure key[6]
We show that using larger area detectors, it is possible to achieve higher signal collection efficiency for CVQKD in atmospheric channels
Summary
Optical signals carry information on both their amplitude and phase[1]. Many techniques have been proposed and are being developed in order to overcome the losses and to extend the transmission distance, such as measurement device independent (MDI)-QKD[7, 8], use of quantum repeaters[9] and, most recently, Twin Field (TF)-QKD [10]. All of these methods require an intermediate node(or nodes) between the users.
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