Quasiprobability representations of quantum mechanics with minimal negativity

TL;DR

This paper investigates the minimal negativity in quasiprobability representations of quantum mechanics, revealing that representations with minimal negativity are linked to symmetric informationally complete measurements and exhibit a tradeoff with symmetry.

Contribution

It introduces three measures of negativity and shows they all identify the same minimal negativity representations, connecting them to SIC measurements and symmetry properties.

Findings

Minimal negativity representations correspond to SIC measurements.

Most minimal negativity representations are covariant with Heisenberg-Weyl groups.

A tradeoff exists between negativity and symmetry in these representations.

Abstract

Quasiprobability representations, such as the Wigner function, play an important role in various research areas. The inevitable appearance of negativity in such representations is often regarded as a signature of nonclassicality, which has profound implications for quantum computation. However, little is known about the minimal negativity that is necessary in general quasiprobability representations. Here we focus on a natural class of quasiprobability representations that is distinguished by simplicity and economy. We introduce three measures of negativity concerning the representations of quantum states, unitary transformations, and quantum channels, respectively. Quite surprisingly, all three measures lead to the same representations with minimal negativity, which are in one-to-one correspondence with the elusive symmetric informationally complete measurements. In addition, most representations with minimal negativity are automatically covariant with respect to the Heisenberg-Weyl groups. Furthermore, our study reveals an interesting tradeoff between negativity and symmetry in quasiprobability representations.