Mutually unbiased bases with free parameters

TL;DR

This paper introduces a systematic method to incorporate free parameters into sets of mutually unbiased bases in quantum systems, revealing new degrees of freedom and constructing maximal sets with adjustable entanglement properties.

Contribution

It provides a novel systematic approach to introduce free parameters into mutually unbiased bases, including explicit constructions and bounds in various dimensions.

Findings

Any set of m real mutually unbiased bases in dimension N>2 admits (m-1)N/2 free parameters.

Constructed maximal sets of mutually unbiased bases with free parameters for two- and three-qubit systems.

Established upper bounds for the number of mutually unbiased bases in any dimension.

Abstract

We present a systematic method to introduce free parameters in sets of mutually unbiased bases. In particular, we demonstrate that any set of m real mutually unbiased bases in dimension N>2 admits the introduction of (m-1)N/2 free parameters which cannot be absorbed by a global unitary operation. As consequence, there are m=k+1 mutually unbiased bases in every dimension N=k^2 with k^3/2 free parameters, where k is even. We construct the maximal set of triplets of mutually unbiased bases for two-qubits systems and triplets, quadruplets and quintuplets of mutually unbiased bases with free parameters for three-qubits systems. Furthermore, we study the richness of the entanglement structure of such bases and we provide the quantum circuits required to implement all these bases with free parameters in the laboratory. Finally, we find the upper bound for the maximal number of real and complex mutually unbiased bases existing in every dimension. This proof is simple, short and it considers basic matrix algebra.