Abstract

When N quanta are partitioned with a 50%–50% linear beamsplitter, the two outputs are quantum-mechanically uncorrelated both in particle number and in wave phase. The rootmean-squared uncertainty of the number difference is $\text{δ}N\equiv {〈{\left[\Delta \left(N_A-N_B\right)\right]}^2〉}^{1/2}=\sqrt{N}$ and that of the phase difference is$\text{δ}\varphi \equiv {〈{\left[\Delta \left({\varphi }_{\text{A}}-{\varphi }_{\text{B}}\right)\right]}^2〉}^{1/2}\approx 1/\sqrt{N}$. This is the standard quantum limit (SQL) of correlations in equal partition. Here, δϕ determines the interferometric phase sensitivity, while δN may impose a fundamental limit in information processing if the number of quanta is small.

© 1992 IQEC