Two-colour high-purity Einstein-Podolsky-Rosen photonic state

Abstract

We report a high-purity Einstein-Podolsky-Rosen (EPR) state between light modes with the wavelengths separated by more than 200 nm. We demonstrate highly efficient EPR-steering between the modes with the product of conditional variances [Formula: see text]. The modes display - 7.7 ± 0.5 dB of two-mode squeezing and an overall state purity of 0.63 ± 0.16. EPR-steering is observed over five octaves of sideband frequencies from RF down to audio-band. The demonstrated combination of high state purity, strong quantum correlations, and extended frequency range enables new matter-light quantum protocols.

Fig. 1. Experimental scheme and example of strong quadrature correlations.

a Setup.The 852 nm and 1064 nm lasers produce the local oscillators and the blue light used to pump the NOPO through the sum-frequency generation. The correlated modes at the two colours emerging from the NOPO are separated with a dichroic mirror, mixed with the LOs, and measured by the homodyne detectors. The photocurrents are recorded by the analog-to-digital converter (ADC) to obtain information on the joint system operators. b, c The experimental realizations of the photocurrents i₁ and i₂ showing strong non-classical correlations of {x₁, x₂} and {y₁, − y₂} for modes of two colours separated by 200 nm. Here the signals were demodulated at 200 kHz and integrated by a 10 kHz low-pass filter. The quadrature values are in vacuum state units.

Fig. 2. Spectra of the EPR quadratures normalized to shot-noise level (SN) for the frequency range 10 to 300 kHz.

The left plate shows the quantum noise suppression optimized for low spectral frequencies (10–50 kHz), while the right part corresponds to the best correlation level achieved in 50–300 kHz spectral range (see comments in the main text). The narrow peaks come from the phase noise of the lasers. The data are corrected for electronic noise which is 18.5 dB below the shot-noise level.