Generation of continuous-wave broadband entangled beams using periodically poled lithium niobate waveguides

Continuous-wave light beams with broadband quantum entanglement are created with two independent squeezed light beams generated by two periodically poled lithium niobate waveguides and a symmentric beam splitter. The quantum entanglement is confirmed with a sufficient criterion Δ A,B 2 = 〈 [Δ (x A - x B)] 2 〉 + 〈 [Δ (p A + p B)] 2 〉 <1 and the observed Δ A,B 2 is 0.75 over the bandwidth of 30 MHz. Although the bandwidth is limited by that of the detector so far, it would be broadened up to 10 THz which would be only limited by the bandwidth of phase matching for the second-order nonlinear process.