We introduce an open quantum battery protocol using dark states to achieve both superextensive capacity and power density, with only local interactions. Further, our power density actually scales with the of number of spins N in the battery. We show that the enhanced capacity and power is correlated with entanglement. Whilst connected to the charger, the charged state of the battery is a steady state, stabilised through quantum interference in the open system.

By coupling controllable quantum systems into larger structures we introduce the concept of a quantum metamaterial. Conventional meta-materials represent one of the most important frontiers in optical design, with applications in diverse fields ranging from medicine to aerospace. Up until now however, metamaterials have themselves been classical structures and interact only with the classical properties of light. Here we describe a class of dynamic metamaterials, based on the quantum properties of coupled atom-cavity arrays, which are intrinsically lossless, reconfigurable, and operate fundamentally at the quantum level. We show how this new class of metamaterial could be used to create a reconfigurable quantum superlens possessing a negative index gradient for single photon imaging. With the inherent features of quantum superposition and entanglement of metamaterial properties, this new class of dynamic quantum metamaterial, opens a new vista for quantum science and technology.

We derive the gravitonic Casimir effect with non-idealised boundary conditions. This allows the quantification of the gravitonic contribution to the Casimir effect from real bodies. We quantify the meagreness of the gravitonic Casimir effect in ordinary matter. We also quantify the enhanced effect produced by the speculated Heisenberg-Couloumb (H-C) effect in superconductors, thereby providing a test for the validity of the H-C theory, and consequently the existence of gravitons.PACS numbers: 14.70. Kv,74.20.Fg One of the most remarkable consequences of the nonzero vacuum energy predicted by quantum field theory, is the Casimir effect. In its most basic form, the Casimir effect is the attraction between two perfectly reflecting surfaces as a result of the restriction of allowed modes in the vacuum between them (Fig. 1). Real bodies however are not perfectly reflecting, and the generalisation of these ideal boundary conditions to more realistic ones have been derived for the electromagnetic (EM) field, resulting in the Lifshitz formula at zero temperature [1]. The EM field of course, is not the only field that produces the Casimir effect; in theory all fields of the quantum vacuum contribute to the Casimir effect. In fact the contribution to the Casimir effect from any massless field which is opaque to the plates should be significant (mass quickly weakens the Casimir effect [2]). Therefore one may imagine plates which are opaque to the gravitational field, so that the Casimir effect would then be a manifestation of the quantisation of the gravitational field, or gravitons. The difficulty is in finding such a medium, as ordinarily materials are transparent to the gravitational field [3].Recently however, there have been suggestions that the properties of quantum fluids (superconductors, superfluids, quantum Hall fluids, Bose-Einstein condensates) may enhance the interaction with gravitational waves (GW). The novel effects of the interaction of a gravitational field with a quantum fluid was first investigated by DeWitt [4] and Papini [5], who calculated that a Lense-Thirring field should induce a current in the superconductor. Following this, further analyses were made into the interaction of GW with superconductors [6,7], proposing superfluids as a medium for gravitational antennae [8], superconducting circuits as GW detectors [9], transducers [10,11] and mirrors [12]. These idea have not been met without controversy [13,14]. Although a few experiments have attempted to test the proposed enhanced GW interaction [15,16], none have produced clear and unambiguous outcomes. This is perhaps because of the small magnitude of some of the theorised effects coupled with the practical challenges in producing the environment capable of their detection [16].

We study entanglement entropy (EE) as a signature of quantum chaos in ergodic and non-ergodic systems. In particular we look at the quantum kicked top and kicked rotor as multi-spin systems, and investigate the single spin EE which characterizes bipartite entanglement of this spin with the rest of the system. We study the correspondence of the Kolmogorov-Sinai entropy of the classical kicked systems with the EE of their quantum counterparts. We find that EE is a signature of global chaos in ergodic systems, and local chaos in non-ergodic systems. In particular, we show that EE can be maximised even when systems are highly non-ergodic, when the corresponding classical system is locally chaotic. In contrast, we find evidence that the quantum analogue of Kolmogorov-Arnol'd-Moser (KAM) tori are tori of low entanglement entropy. We conjecture that entanglement should play an important role in any quantum KAM theory.