A novel post-selection scheme is proposed to generate squeezed vacuum pulses using noisy fiber laser pulses at 1550 nm. By selecting only coherent pulses with low excess noise, quadrature squeezing is obtainable with conditional homodyne detection.
Photon-number squeezing and quadrature squeezing were studied using ultrafast fibre nonlinear optics pumped by 1.5 µm femtosecond laser pulses. To obtain quadrature squeezing using an Erbium doped fibre amplifiers (EDFA) light source, we developed temporal homodyne technology to exclude the excess noise of an EDFA light source. We also performed a quadrature squeezing experiment using an optical parametric oscillator light source in stead of an EDFA light source exhibiting substantially high excess noise. Although the photon-number squeezing of -3dB was obtained from an asymmetric Sagnac fibre loop, the quadrature noise could not decrease to less than the Shot noise level without cooling the fibre, which is presumably due to GAWBS. To suppress guided acoustic wave Brillouin scattering, we refrigerated the fibre loop by liquid nitrogen, and squeezing at -0.7 dB was obtained by cooling the fiber at liquid nitrogen temperature.
Purification of quadrature squeezed vacuum pulses at the wavelength of 1.5 µm generated from a Sagnac loop fiber interferometer is experimentally demonstrated using linear optics and conditional homodyne detection. The anti-squeezed quadrature variance degraded by guided acoustic wave Brillouin scattering in the fiber is significantly improved from 12.6 to 4 dB after the post selection, while the squeezed quadrature variance of -0.7 dB slightly decreases to -0.3 dB due to the linear optical loss caused by a beam splitter. This result agrees well with the theory.
Squeezed light is a key resource in quantum metrology and quantum information science. It is primarily generated through nonlinear optical interactions, where the degree of squeezing is set by the nonlinearity of the medium. Here, we modulate the third-order nonlinear response of a dielectric with strong ultrafast laser fields to control squeezed light generation on attosecond time scales. By tuning a sub-cycle phase delay between the input femtosecond pulses, we switch the generated light between amplitude-squeezed and phase-squeezed states. We measure the quantum noise using a frequency-resolved balanced homodyne detection scheme that extracts field quadratures in many frequency modes simultaneously. From these measurements we obtain the complete coherency matrix containing quadrature correlations across the frequency modes of the pulse. These results enable quantum light sources with sub-cycle control of squeezing and open a route to transduction of dynamical quantum correlations in matter to quantum correlations in electric fields.