Entangling capabilities and unitary quantum games

TL;DR

This paper analyzes a quantum game where two players manipulate a shared quantum register, revealing how entanglement advantages influence the game's outcome and the effectiveness of different strategies under various conditions.

Contribution

It introduces the concept of quantum advantage in entangling capabilities and explores its impact on the second mover advantage in quantum energy games.

Findings

Quantum advantage can significantly reduce second mover advantage.

Random unitaries are effective when maximally entangled states are unavailable.

Mixed initial states allow strategies based on quantum battery ergotropy.

Abstract

We consider a class of games between two competing players that take turns acting on the same many-body quantum register. Each player can perform unitary operations on the register, and after each one of them acts on the register the energy is measured. Player A aims to maximize the energy while player B to minimize it. This class of zero-sum games has a clear second mover advantage if both players can entangle the same portion of the register. We show, however, that if the first player can entangle a larger number of qubits than the second player (which we refer to as having quantum advantage), then the second mover advantage can be significantly reduced. We study the game for different types of quantum advantage of player A versus player B and for different sizes of the register, in particular, scenarios in which absolutely maximally entangled states cannot be achieved. In this case, we also study the effectiveness of using random unitaries. Last, we consider mixed initial preparations of the register, in which case the player with a quantum advantage can rely on strategies stemming from the theory of ergotropy of quantum batteries.