We demonstrate that a translation invariant chain of interacting quantum systems can be used for high efficiency transfer of quantum entanglement and the generation of multi-particle entanglement over large distances and between arbitrary sites without the requirement of precise spatial or temporal control. The scheme is largely insensitive to disorder and random coupling strengths in the chain. We discuss harmonic oscillator systems both in the case of arbitrary Gaussian states and in situations when at most one excitation is in the system. The latter case which we prove to be equivalent to an xy-spin chain may be used to generate genuine multi particle entanglement. Such a 'quantum data bus' may prove useful in future solid state architectures for quantum information processing. PACS numbers: 03.67.-a,03.67.HkThe realization of quantum communication and computation requires at various stages the mapping between stationary and flying qubits and the subsequent transfer of quantum information between different units of our quantum information processing devices. Traditionally the stationary forms of qubits are massive systems such as atoms, ions, quantum dots or Josephson junctions while the flying qubit is a photon, ie radiation. Photons might be optimal when considering long distance communication where they may travel through free space or optical fibres. In very small quantum information processing devices such as condensed matter systems however, this is difficult as the length scale both of the component parts and their separation will generally be below optical wavelengths. In this situation, it is worth considering novel approaches for the communication of quantum information and the generation of entanglement. To this end it is of interest to consider the properties of interacting quantum systems and here in particular those of harmonic systems that are realized in various condensed matter physics settings such as nano-mechanical oscillators. While static harmonic (or spin) systems near their ground state do not exhibit long distance entanglement [1], the situation changes drastically when considering time-dependent properties of interacting quantum systems [2]. Indeed, solid state devices such as arrays of nano-mechanical oscillators, described as interacting harmonic oscillators, allow for the generation [3], transfer and manipulation of entanglement [4] with a minimum of spatial and temporal control. However, in translation invariant systems the efficiency for this transfer decreased with distance. This can be overcome either by making the coupling strengths between neighboring systems position dependent [4,5] or by active steps such as quantum repeater stages [6] or conclusive transfer [7]. Nevertheless, active steps or the fabrication of precisely manufactured spatially dependent couplings are difficult in practice and will require a significant degree of control. Furthermore, the precise value of the coupling parameters and the timing of the operations will depend on the distance across which one ai...

By making use of a recently proposed framework for the inference of thermodynamic irreversibility in bosonic quantum systems, we experimentally measure and characterize the entropy production rates in the nonequilibrium steady state of two different physical systems -a micro-mechanical resonator and a Bose-Einstein condensate -each coupled to a high finesse cavity and hence also subject to optical loss. Key features of our setups, such as cooling of the mechanical resonator and signatures of a structural quantum phase transition in the condensate are reflected in the entropy production rates. Our work demonstrates the possibility to explore irreversibility in driven mesoscopic quantum systems and paves the way to a systematic experimental assessment of entropy production beyond the microscopic limit.Entropy is a crucial quantity for the characterisation of dynamical processes: it quantifies and links seemingly distant notions such as disorder, information, and irreversibility across different disciplinary boundaries [1,2]. Every finitetime transformation results in some production of entropy, which signals the occurrence of irreversibility. Quantifying the amount of irreversible entropy produced by a given process is a goal of paramount importance: entropy production is a key quantity for the characterisation of non-equilibrium processes, and its minimisation improves the efficiency of thermal machines. The second law of thermodynamics can be formulated in terms of a universal constraint on the entropy production, which can never be negative [3,4]. In turn, this leads to the following rate equation for the variation of the entropy S [5]where Π(t) and Φ(t) are the irreversible entropy production rate and the entropy flux from the system to the environment, respectively. When the system reaches a non-equilibrium steady-state (NESS) these quantities take values Π s and Φ s respectively, such that Π s = Φ s > 0 [see Fig. 1 (a)]. Under these conditions, entropy is produced and exchanged with the local baths at the same rate. Only when both terms vanish (Π s = Φ s = 0) one recovers thermal equilibrium. The entropy production rate directly accounts for the irreversibility of a process and uncovers the non-equilibrium features of a system. The link between the entropy production rate Π s and irreversibility becomes particularly relevant in small systems subjected to fluctuations, for which a microscopic definition of entropy production based on stochastic trajectories of the system has been given [6]. Experimentally, this notion has been used to test fluctuation theorems in a variety of classically operating systems such as a single-electron box [7], a two-level system driven by a time-dependent potential [8], and a levitated nanoparticle undergoing relaxation [9]. However, in order to harness the working principles of thermodynamic machines working at the quantum level, and pinpoint the differences between their performances and those of their classical counterparts, it is important to analyse the entropy generated thro...

In this paper, we study the role of collective vibrational motion in the phenomenon of electronic energy transfer (EET) along a chain of coupled electronic dipoles with varying excitation frequencies. Previous experimental work on EET in conjugated polymer samples has suggested that the common structural framework of the macromolecule introduces correlations in the energy gap fluctuations which cause coherent EET. Inspired by these results, we present a simple model in which a driven nanomechanical resonator mode modulates the excitation energy of coupled quantum dots and find that this can indeed lead to an enhancement in the transport of excitations across the quantum network. Disorder of the on-site energies is a key requirement for this to occur. We also show that in this solid state system phase information is partially retained in the transfer process, as experimentally demonstrated in conjugated polymer samples. Consequently, this mechanism of vibration enhanced quantum transport might find applications in quantum information transfer of qubit states or entanglement.

We address the problem of heat transport in a chain of coupled quantum harmonic oscillators, exposed to the influences of local environments of various nature, stressing the effects that the specific nature of the environment has on the phenomenology of the transport process. We study in detail the behavior of thermodynamically relevant quantities such as heat currents and mean energies of the oscillators, establishing rigorous analytical conditions for the existence of a steady state, whose features we analyze carefully. In particular, we assess the conditions that should be faced to recover trends reminiscent of the classical Fourier law of heat conduction and highlight how such a possibility depends on the environment linked to our system.