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arXiv:1101.2638 · Physical Review Letters

Decoherence and Disorder in Quantum Walks: From Ballistic Spread to Localization

A. Schreiber, K. N. Cassemiro, Václav Potoček, A. Gábris, Igor Jex, Christine Silberhorn

Published May 6, 2011• 389 citations
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Abstract

We investigate the impact of decoherence and static disorder on the dynamics of quantum particles moving in a periodic lattice. Our experiment relies on the photonic implementation of a one-dimensional quantum walk. The pure quantum evolution is characterized by a ballistic spread of a photon's wave packet along 28 steps. By applying controlled time-dependent operations we simulate three different environmental influences on the system, resulting in a fast ballistic spread, a diffusive classical walk, and the first Anderson localization in a discrete quantum walk architecture.

DOI
10.1103/physrevlett.106.180403

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We investigate the impact of decoherence and static disorder on the dynamics of quantum particles moving in a periodic lattice. Our experiment relies on the photonic implementation of a one-dimensional quantum walk. The pure quantum evolution is characterized by a ballistic spread of a photon's wave packet along 28 steps. By applying controlled time-dependent operations we simulate three different environmental influences on the system, resulting in a fast ballistic spread, a diffusive classical walk, and the first Anderson localization in a discrete quantum walk architecture.
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Abstract We experimentally investigate the impact of static disorder and dynamic disorder on the non-unitary dynamics of parity–time (PT)-symmetric quantum walks. Via temporally alternating photon losses in an interferometric network, we realize the passive PT-symmetric quantum dynamics for single photons. Controllable coin operations allow us to simulate different environmental influences, which result in three different behaviors of quantum walkers: a standard ballistic spread, a diffusive behavior, and a localization, respectively, in a PT-symmetric quantum walk architecture.
We put forward a versatile and highly scalable experimental setup for the realization of discrete two-dimensional quantum random walks with a single-qubit coin and tunable degree of decoherence. The proposed scheme makes use of a small number of simple optical components arranged in a multipath Mach-Zehnder-like configuration, where a weak coherent state is injected. Environmental effects (decoherence) are generated by a spatial light modulator, which introduces pure dephasing in the transverse spatial plane perpendicular to the direction of propagation of the light beam. By controlling the characteristics of this dephasing, one can explore a great variety of scenarios of quantum random walks: pure quantum evolution (ballistic spread), fast fluctuating environment leading to a diffusive classical random walk, and static disorder resulting in the observation of Anderson localization.
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Programmable two-particle quantum walks are crucial for advancing quantum simulation, computation, and information processing. Although disorder is traditionally associated with information loss, it can also facilitate emergent phenomena such as enhanced energy transport. Here, we experimentally realize a 12-step discrete-time quantum walk in programmable integrated photonic circuits, introducing tunable static and dynamic disorder to explore quantum transport dynamics. In periodic lattices, disorder induces light localization and drives a transition from quantum ballistic to classical diffusive behavior. In particular, quantum walks of correlated photons exhibit a disorder-induced bunching effect, accompanied by enhanced nonclassical correlations. Our platform provides a scalable framework for investigating multiparticle quantum dynamics in engineered environments, promoting the development of quantum optics toward large-scale applications.
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