Broadband realtime measurement of optical Einstein–Podolsky–Rosen states using optical parametric amplifiers

Entanglement is a key resource for various quantum technologies. Besides the purity of entanglement, the available bandwidth also plays a crucial role in quantum information processing with light, as it directly determines the clock speed of processing. While many efforts have been made to enhance the bandwidth of optical entanglement resources, they have generally been limited to a few tens of MHz at best. In this work, we report the real-time measurement of EPR states over a broad bandwidth of 60 GHz, achieved using a fast homodyne detection technique supplemented by phase-sensitive amplification. The quantum correlation level exceeds 4.5 dB at its peak, which is sufficient for applications of several quantum technologies. This research marks a significant milestone in the advancement of high-speed optical quantum information processing.