A simple realization of Weyl-Heisenberg covariant measurements

TL;DR

This paper presents a simple, systematic method for physically implementing Weyl-Heisenberg covariant informationally complete measurements in finite-dimensional quantum systems, facilitating laboratory realization.

Contribution

It introduces an algorithm to realize Naimark extensions for rank-one Weyl-Heisenberg covariant IC measurements using a reduced unitary, enabling practical optical implementations.

Findings

Explicit calculations for qubit, qutrit, and ququart SIC-POVMs

Block-circulant structure of the unitary interaction

Framework suitable for laboratory implementation of IC measurements

Abstract

Informationally complete (IC) measurements are fundamental tools in quantum information processing, yet their physical implementation remains challenging. By the Naimark extension theorem, an IC measurement may be realized by a von Neumann measurement on an extended system after a suitable interaction. In this work, we elaborate on a simple algorithm for realizing Naimark extensions for rank-one Weyl-Heisenberg covariant informationally complete measurements in arbitrary finite dimensions. Exploiting Weyl-Heisenberg covariance, we show that the problem reduces to determining a $d \times d$ unitary from which the full $d^2 \times d^2$ unitary interaction can be constructed. The latter unitary enjoys a block-circulant structure which allows e.g., for an elegant optical implementation. We illustrate the procedure with explicit calculations for qubit, qutrit, and ququart SIC-POVMs. Finally, we show that from another point of view, this method amounts to preparing an ancilla system according to a so-called fiducial state, followed by a generalized Bell-basis measurement on the system and ancilla. These results provide a straightforward framework for implementing informationally complete measurements in the laboratory suitable for both qubit and qudit based systems.