Improved measurement of multimode squeezed light via eigenmode decomposition

Summary form only given. We find that the quantum statistics of multimode squeezed fields are easily obtained and simply understood via an eigenmode description. The eigenmode description of squeezed light is based on our finding that the squeezing matrix /spl Gamma/ can always be diagonalized by a physical transformation of the fields - either a change of basis or linear unitary evolution. Each eigenmode possesses single-mode squeezing statistics, and the corresponding eigenvalue is the effective squeezing parameter for that mode. The squeezing eigenmodes are completely uncoupled from one another (at the quantum level) and represent independent channels (pixels) useful for carrying noise-sensitive data. We show how an eigenmode description of a squeezed field allows one to easily calculate noise statistics of the field upon diffraction and/or propagation through any sequence of lossless linear optical elements. We further show that the eigenmodes define the shape of the local oscillator which must be used in order to obtain the smallest quantum noise in balanced homodyne or heterodyne measurements. Finally, we use the theory to model pulsed optical parametric downconversion in a /spl chi//sup (2)/ medium with a classical pump field of arbitrary bandwidth, allowing for the possibility of phase and/or group velocity mismatch.