The authors propose a universal mechanism for the environment-assisted quantum transport effect - where the interaction with an external environment Increases the transport efficiency of quantum particles - and show that it is different from a competition between Anderson localization and a Zeno effect
The way in which energy is transported through an interacting system governs fundamental properties in nature such as thermal and electric conductivity or phase changes. Remarkably, environmental noise can enhance the transport, an effect known as environment-assisted quantum transport (ENAQT). In this Letter, we study ENAQT in a network of coupled spins subject to engineered static disorder and temporally varying dephasing noise. The interacting spin network is realized in a chain of trapped atomic ions, and energy transport is represented by the transfer of electronic excitation between ions. With increasing noise strength, we observe a crossover from coherent dynamics and Anderson localization to ENAQT and finally a suppression of transport due to the quantum Zeno effect. We find that in the regime where ENAQT is most effective, the transport is mainly diffusive, displaying coherences only at very short times. Further, we show that dephasing characterized by non-Markovian noise can maintain coherences longer than white noise dephasing, with a strong influence of the spectral structure on the transport efficiency. Our approach represents a controlled and scalable way to investigate quantum transport in many-body networks under static disorder and dynamic noise.
We demonstrate that repeated measurements in disordered systems can induce a quantum anti-Zeno effect under certain conditions to enhance quantum transport. The enhancement of energy transfer is really exhibited in multisite models under repeated measurements. The optimal measurement interval for the anti-Zeno effect and the maximal efficiency of energy transfer are specified in terms of the relevant physical parameters. Since the environment acts as frequent measurements on the system, the decoherence-induced energy transfer, which has been discussed recently for photosynthetic complexes, may be interpreted in terms of the anti-Zeno effect. We further find an interesting phenomenon in a specific three-site case, where local decoherence or repeated measurements may even promote entanglement generation between the nonlocal sites.
Environment-assisted quantum transport (ENAQT) is a unique situation where environmental noise can, counterintuitively, enhance the transport of an open quantum system. In this paper, we investigate how the presence of a one-dimensional single-particle mobility edge can generate strong ENAQT. For this purpose, we study the energy current of a generalized Aubry-Andr\'e-Harper tight binding model coupled at its edges to spin baths of differing temperature and dephasing noise along the system. We find that the ENAQT increases by orders of magnitude and depends on the number of localized eigenstates and disorder strength nonmonotonically. We show that this enhancement is the result of the cooperation between population uniformization and localization.
We study the environment-assisted enhancement of the excitation-transport efficiency across a network of interacting quantum particles or sites. Our study reveals a crucial influence of the network configuration - and especially its degree of connectivity - on the amount of environment-supported enhancement. In particular, we find a significant interplay of direct and indirect connections between excitation sending and receiving sites. On the other hand, the non-Markovianity induced by memory-bearing, finite sized environments does not seem to provide a critical resource for the enhanced excitation-transport mechanism.
The transport of excitations governs fundamental properties of matter. Particularly rich physics emerges in the interplay between disorder and environmental noise, even in small systems such as photosynthetic biomolecules. Counterintuitively, noise can enhance coherent quantum transport, which has been proposed as a mechanism behind the high transport efficiencies observed in photosynthetic complexes. This effect has been called ``environment-assisted quantum transport''. Here, we propose a quantum simulation of the excitation transport in an open quantum network, taking advantage of the high controllability of current trapped-ion experiments. Our scheme allows for the controlled study of various different aspects of the excitation transfer, ranging from the influence of static disorder and interaction range, over the effect of Markovian and non-Markovian dephasing, to the impact of a continuous insertion of excitations. Our paper discusses experimental error sources and realistic parameters, showing that it can be implemented in state-of-the-art ion-chain experiments.
Abstract Nontrivial quantum effects in biological systems are of high interest among physicists over the past decade. They allow for information and energy to be exchanged with near-unity efficiency despite hindered by the warm, wet, and noisy environment. Several models suggests that the efficient quantum energy transport is due to the interplay between dephasing dynamics and unitary evolution of the disordered biological systems i.e in photosynthetic complex. However, the proposed models have not yet included the driving force depicting the external perturbation used in the experiment such as laser in 2D spectroscopy involved in the detection of the exciton transfer or an artificial quantum transport experiments. Here, we resolve this issue by subjecting the dephasing assisted transport model by Plenio and Huelga [New J. Phys. 10, 11 (2012)] to a driving force. We analyze dynamical evolution of the driven system and show that further efficiency enhancement achieved by driving the transport site. We also discuss some experimental realizations of the quantum transport system.