Quantum coherent transceivers toward Holevo-limited communications

The Holevo limit quantifies the upper boundary of potential utilisation of channel capacity in communication channels that include the use of quantum states for information encoding and quantum measurements for information decoding. To realise the limit, quantum-limited transceivers are essential, which either generate quantum states of light or perform quantum-limited measurements. This work focuses on the advancing and benchmarking of the first integrated photonic-electronic quantum-limited coherent receiver (QRX). The QRX displayed an impressive achievement of 14.0 dB shot noise clearance (SNC), 520 µW knee power, 2.57 GHz 3-dB bandwidth and 90.2 dB common-mode rejection ratio (CMRR). The scalability of the design is demonstrated by the 32-channel QRX array, which, through

automated post-fabrication adjustment, realised a median SNC of 26.6 dB and a median CMRR of 76.8 dB. The combined system of the integrated QRX with the fibre-optic transmitter demonstrated a shot noise limited performance of 0.15 ± 0.01 dB of squeezing (off-chip losses are the current limiting factor). This work proposes a communication scheme with squeezed light that aims to exceed the classical Shannon limit and provides a pathway for the quantum communication systems to achieve the Holevo limit.

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