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arXiv:1711.04105

Unfolding multi-particle quantum correlations hidden in decoherence

Ke-Ji Chen, Ho Kwan Lau, Hon Ming Chan, Dajun Wang, Qi Zhou

Published Nov 11, 2017• 1 citation
arXivHTMLPDF

Abstract

Quantum coherence is a fundamental characteristic to distinguish quantum systems from their classical counterparts. Though quantum coherence persists in isolated non-interacting systems, interactions inevitably lead to decoherence, which is in general believed to cause the lost of quantum correlations. Here, we show that, accompanying to the single-particle decoherence, interactions build up quantum correlations on the two-, three-, and multi-particle levels. Using the quantitative solutions of the quantum dynamics of a condensate occupying two modes, such as two bands of an optical lattice, we find out that such dynamically emergent multi-particle correlations not only reveal how interactions control the quantum coherence of a many-body system in a highly intriguing means, but also evince the rise of exotic fragmented condensates, which are difficult to access at the ground state. We further develop a generic interferometry that can be used in experiments to measure high order correlation functions directly.

DOI
10.48550/arxiv.1711.04105

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Quantum coherence is a fundamental characteristic to distinguish quantum systems from their classical counterparts. Though quantum coherence persists in isolated non-interacting systems, interactions inevitably lead to decoherence, which is in general believed to cause the lost of quantum correlations. Here, we show that, accompanying to the single-particle decoherence, interactions build up quantum correlations on the two-, three-, and multi-particle levels. Using the quantitative solutions of the quantum dynamics of a condensate occupying two modes, such as two bands of an optical lattice, we find out that such dynamically emergent multi-particle correlations not only reveal how interactions control the quantum coherence of a many-body system in a highly intriguing means, but also evince the rise of exotic fragmented condensates, which are difficult to access at the ground state. We further develop a generic interferometry that can be used in experiments to measure high order correlation functions directly.
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Abstract Quantum coherence, the physical property underlying fundamental phenomena such as multi-particle interference and entanglement, has emerged as a valuable resource upon which modern technologies are founded. In general, the most prominent adversary of quantum coherence is noise arising from the interaction of the associated dynamical system with its environment. Under certain conditions, however, the existence of noise may drive quantum and classical systems to endure intriguing nontrivial effects. In this vein, here we demonstrate, both theoretically and experimentally, that when two indistinguishable non-interacting particles co-propagate through quantum networks affected by non-dissipative noise, the system always evolves into a steady state in which coherences accounting for particle indistinguishabilty perpetually prevail. Furthermore, we show that the same steady state with surviving quantum coherences is reached even when the initial state exhibits classical correlations.
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Locally constrained gauge theories underpin our understanding of fundamental interactions in particle physics and the emergent behaviour of quantum materials. In strongly correlated systems, they can give rise to quantum spin liquids that lack conventional order and are defined by coherent superpositions of an extensive number of many-body configurations. Realising and probing such exotic states experimentally is an outstanding challenge both in solid-state and synthetic quantum systems, not least due to the difficulty of detecting the fragile coherences between many-body states. Here, we report a large-scale (>3,000 sites) realisation of a two-dimensional U(1) lattice gauge theory with ultracold atoms in a square optical superlattice and demonstrate non-equilibrium preparation of extended regions of U(1) quantum spin liquids. We demonstrate Gauss's law validity in a quench experiment, enabled by a new microscopy technique for detecting doubly occupied sites. We observe characteristic real-space correlations and momentum-space pinch points, hallmarks of the emergent U(1) gauge structure. Using round-trip interferometric protocols, we directly observe large-scale coherence between many-body configurations, providing strong evidence for quantum spin liquid regions extending over ~100 lattice sites. Our results establish non-equilibrium quantum simulation protocols as a powerful route for accessing and probing exotic, highly-entangled states beyond those hosted by the engineered Hamiltonian in thermal equilibrium.