Real-time observation of picosecond-timescale optical quantum entanglement toward ultrafast quantum information processing

TL;DR

This paper demonstrates real-time observation of ultrafast optical entanglement at a picosecond timescale, significantly advancing the speed of quantum information processing and enabling practical high-speed quantum applications.

Contribution

It introduces a method for real-time measurement of picosecond-scale optical entanglement using a broadband waveguide amplifier, surpassing previous nanosecond-scale observations.

Findings

Achieved 4.5 dB quantum correlation below shotnoise at 40-ps wavepackets

Demonstrated real-time amplitude measurement of ultrafast entanglement

Enabled entanglement observation 1000 times faster than prior CW systems

Abstract

Entanglement is a fundamental resource of various optical quantum-information-processing (QIP) applications. Towards high-speed QIP system, entanglement should be encoded in short wavepackets. We report real-time observation of ultrafast optical Einstein-Podolsky-Rosen (EPR) correlation at a picosecond timescale in a continuous-wave (CW) system. Optical phase-sensitive amplification using 6-THz-bandwidth waveguide-optical-parametric amplifier enhances the effective efficiency of 70-GHz-bandwidth homodyne detectors, mainly used in 5th-generation telecommunication, enabling its use in real-time quantum-state measurement. While power measurement using frequency scanning, i.e., optical spectrum analyzer, is not performed in real-time, our observation is demonstrated through real-time amplitude measurement and can be directly employed in QIP applications. Observed EPR states show quantum correlation of 4.5 dB below shotnoise level encoded in wavepackets with 40-ps period, equivalent to 25-GHz repetition -- ${10^3}$ times faster than previous entanglement observation in CW system. The quantum correlation of 4.5 dB is already sufficient for several QIP applications, and our system can be readily extended to large-scale entanglement. Moreover, our scheme has high compatibility with optical communication technology such as wavelength-division multiplexing, and femtosecond-timescale observation is also feasible. Our demonstration is paradigm shift in accelerating accessible quantum correlation, the foundational resource of all quantum applications, from the nanosecond to picosecond timescale, enabling ultra-fast optical QIP.