Power of Quantum Entanglement

Jozef Gruska, Hiroshe Imai, Hiroshi Imai

Guan, Zhe, Huan He, Yong‐Jian Han +2 more

Fernando Galve \emph{et al.} $[Phys. Rev. Lett. \textbf{110}, 010501 (2013)]$ introduced discording power for a two-qubit unitary gate to evaluate its capability to produce quantum discord, and found that a $π/8$ gate has maximal discording power. This work analyzes the entangling power of a two-qubit unitary gate, which reflects its ability to generate quantum entanglement in another way. Based on the renowned Cartan decomposition of two-qubit unitary gates, we show that the magic power of the $π/8$ gate produces maximal entanglement for a general value of purities for two-qubit states.

Tianxuan Feng, Zhiying Song, Tong Wu +2 more

Nowadays, with the continuous development of optical quantum sensor technology, the importance of the quantum entanglement source is increasing day by day. As an indispensable part of optical quantum systems, the quantum entanglement source has a wide prospect of application in quantum communication, quantum imaging, quantum computing, life science and so on. However, the current power consumption and preparation cost of quantum entanglement sources are relatively huge, which impedes further integration and expansion. In view of these problems, we establish a quantum entanglement source model pumped by a low-power laser diode based on spontaneous parametric down-conversion (SPDC) theory and phase matching technology, to effectively analyze the influence of components and characteristics of each module of quantum entanglement source on its performance. Furthermore, we prepare a quantum entanglement source with a 10mW laser diode and a typical type-II barium metaborate (BBO) crystal to conduct experiment whose result is 2053 counts per second in average which is in desirable agreement with the model. To some extent, the low-power and low-cost goal of quantum entanglement source has been achieved, which has made a significant contribution to the practical application of quantum entanglement lighting, and is conducive to the popularization of optical quantum systems in the future.

Liesel K. Hill

Ju-Yeon Gyhm, Uwe R. Fischer

We establish a general implementation-independent approach to assess the potential advantage of using highly entangled quantum states between the initial and final states of the charging protocol to enhance the maximum charging power of quantum batteries. It is shown that the impact of entanglement on power can be separated from both the global quantum speed limit associated with an optimal choice of driving Hamiltonian and the energy gap of the batteries. We then demonstrate that the quantum state advantage of battery charging, defined as the power obtainable for given quantum speed limit and battery energy gap, is not an entanglement monotone. A striking example we provide is that, counterintuitively, independent thermalization of the local batteries, completely destroying any entanglement, can lead to larger charging power than that of the initial maximally entangled state. Highly entangled states can thus also be potentially disadvantageous when compared to product states. We also demonstrate that taking the considerable effort of producing highly entangled states, such as W or k-locally entangled states, is not sufficient to obtain quantum-enhanced scaling behavior with the number of battery cells. Finally, we perform an explicit computation for a Sachdev–Ye–Kitaev battery charger to demonstrate that the quantum state advantage allows the instantaneous power to exceed its classical bound.