Postgraduate @ Seoul National University (SNU)

Friday July 1 – 8.45 BST

Quantum Charging Advantage Cannot Be Extensive Without Global Operations 

Quantum batteries are thermal devices, which store energy at quantum states and convert it to usable energy. They have numerous possibilities to be applied significant technology, due to their speed of charging and releasing energy which has at most quadratic scaling with cells over the classically achievable linear scaling. The paper, “Quantum Charging Advantage Cannot Be Extensive Without Global Operations” (going to be published at Physical Review Letters as Editors’ Suggestion) shows the general bound of charging speed and the necessary condition to reach the quadratic scaling derived from the bound. 
Quantum batteries’ state storing energy at the battery Hamiltonian $\hat{H}$ is evolved by the driving Hamiltonian $\hat{V}$. This is the basic protocol of Quantum batteries and gives a crucial bound for us. We show that the maximum energy change $\Delta E$ by the first time perturbation term $\hat{V}t$ decide the bound of the power. It is simply written as equation $|P|\leq \Delta E \|\hat{V}\|$ which gives the condition to obtain quadratic scaling. 
To achieve quadratic scaling, a global charging protocol, which charges all the cells collectively, needs to be employed. Meanwhile, It is not a sufficient condition. We found a case that the batteries evolved by the global operator have the power increasing with linearly with cells. 
We showed the significant condition for quantum batteries. This concludes the quest on the limits of charging power of quantum batteries and adds to other results in which quantum methods are known to provide at most quadratic scaling over their classical counterparts. 
cf. I changed my academic name as Ju-Yeon Gyhm from Juyeon Kim. The First author of the paper referred to in the abstract is me. 
Kim, J., Rosa, D., & Šafránek, D. (2021). Quantum Charging Advantage Cannot Be Extensive Without Global Operations. arXiv preprint arXiv:2108.02491. 

Categories: Talks Friday July 1