A technique for information transfer using phase squeezed states of light is considered. The optimal squeezing that minimizes the quantum decoding error is calculated. The minimum phase uncertainty is determined.
The origin of quantum noise is addressed and it can be eliminated when the quantum state is optimally prepared for the single measured observable. Minimum uncertainty states are reviewed using Q (α) -representation, which include squeezed states and number-phase minimum uncertainty states. Squeezing is a concept of trading quantum uncertainties between two conjugate observables to optimize the state for the measurement. Need for optical nonlinearity to achieve squeezing is induced. Principles and experimental results for squeezing quadrature amplitude and photon number are delineated. Applications to optical communications and optical precision measurement are briefly stated.
In order to improve the error probability of generating entanglement by communication for quantum computation, we propose the use of squeezed light. When generating entanglement between two atoms by communication, the error probability can be reduced by increasing the distance between quantum states of probe light in phase space. The phase rotation of light depends on the atom-photon coupling strength and the light amplitude, which are limited in practice. A large error probability has been expected for coherent probe light. If we assume typical values of light amplitude and phase rotation, $\ensuremath{\alpha}=100$ and $\ensuremath{\theta}=0.01$, the error probability is estimated to be Pcoh(min)=0.14 and Pcoh(hom)=0.23 for minimum error discrimination and homodyne measurements. The error probability can be reduced to ${P}_{\mathrm{squ}}^{(\mathrm{min})}=1.73\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ and ${P}_{\mathrm{squ}}^{(\mathrm{hom})}=4.09\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ using squeezed coherent light, where the same values of the mean photon number and the phase rotation angle are assumed for the coherent light probe. These values satisfy the requirements for scalable quantum computation.