Efficient tomography of quantum-optical Gaussian processes probed with a few coherent states

TL;DR

This paper presents a method for efficiently performing quantum process tomography on quantum-optical Gaussian processes using only a few coherent states, avoiding common approximations and significantly reducing experimental complexity.

Contribution

The authors introduce an exact tomography technique for Gaussian processes that requires only a limited set of coherent states, improving efficiency over existing methods.

Findings

Complete identification of Gaussian processes with few coherent states

Exponential reduction in the number of test states for multimode processes

Avoidance of energy cut-off approximations in quantum process tomography

Abstract

An arbitrary quantum-optical process (channel) can be completely characterized by probing it with coherent states using the recently developed coherent-state quantum process tomography (QPT) [Lobino et al., Science 322, 563 (2008)]. In general, precise QPT is possible if an infinite set of probes is available. Thus, realistic QPT of infinite-dimensional systems is approximate due to a finite experimentally-feasible set of coherent states and its related energy-cut-off approximation. We show with explicit formulas that one can completely identify a quantum-optical Gaussian process just with a few different coherent states without approximations like the energy cut-off. For tomography of multimode processes, our method exponentially reduces the number of different test states, compared with existing methods.