Measurement Induced Synthesis of Coherent Quantum Batteries

Abstract

Quantum coherence represented by a superposition of energy eigenstates is, together with energy, an important resource for quantum technology and thermodynamics. Energy and quantum coherence however, can be complementary. The increase of energy can reduce quantum coherence and vice versa. Recently, it was realized that steady-state quantum coherence could be autonomously harnessed from a cold environment. We propose a conditional synthesis of N independent two-level systems (TLS) with partial quantum coherence obtained from an environment to one coherent system using a measurement able to increase both energy and coherence simultaneously. The measurement process acts here as a Maxwell demon synthesizing the coherent energy of individual TLS to one large coherent quantum battery. The measurement process described by POVM elements is diagonal in energy representation and, therefore, it does not project on states with quantum coherence at all. We discuss various strategies and their efficiency to reach large coherent energy of the battery. After numerical optimization and proof-of-principle tests, it opens way to feasible repeat-until-success synthesis of coherent quantum batteries from steady-state autonomous coherence.

Experimental demonstration of optimal probabilistic enhancement of quantum coherence

“…We have tested one of the scenarios considered in Ref. [38], where the lowest energy state is completely filtered out, a = 0, and b is optimized to maximize the output state coherence. Note that these filters belong to the class of filters optimal for the energy enhancement, c.f.…”

“…1(d,h). For states with non-vanishing initial coherence and low enough mean energy the quantum filtering can simultaneously increase both energy and coherence [38]. In particular, in the above example the filter MC,1 is optimal for both energy and coherence improvement.…”

“…If the filtered state is produced in larger number of copies, it may serve as improved coherent source of energy (fuel) for more efficient quantum machines [36,37]. Input states formed by several subsystems such as N two-level systems [38] are of particular interest, because the optimal enhancement of coherence may require filtering that introduces quantum correlations between the elementary subsystems.…”

Achieving local coherence in thermal states by intra-system coupling

“…Quantum coherence is responsible for many fundamental effects and is the essential resource of upcoming quantum technology. It is, therefore, the subject of intensive basic research that culminated from the mathematical side in the formulations of resource theory of coherence [1,2] and experimentally, by coherence manipulations with diverse systems [3,4,5,6,7,8]. The potential role and impact of quantum coherence is known to be extremely wide, ranging from quantum biology [9,10], to quantum computing [11,12,13,14], quantum gravity [15] and quantum thermodynamics [16,17,1,18].…”

Floquet Engineering to Reactivate a Dissipative Quantum Battery

“…Ideal QB scheme.-A battery is a device that stores and converts energy. The basic idea of a QB is to use the discrete energy levels of a quantum system for energy storage and conversion [32][33][34][35][36][37][38]. Without loss of general-ity, we consider a two-level system as the QB [3,7,30,31].…”