Light-cone-like spreading of correlations in a quantum many-body system

• Published in: Nature (London) Vol. 481; no. 7382; pp. 484 - 487
• Main Authors: Cheneau, Marc, Barmettler, Peter, Poletti, Dario, Endres, Manuel, Schauß, Peter, Fukuhara, Takeshi, Gross, Christian, Bloch, Immanuel, Kollath, Corinna, Kuhr, Stefan
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 26.01.2012; Nature Publishing Group
• Subjects: 639/766/400/482; 639/766/483; Classical and quantum physics: mechanics and fields; Computational efficiency; Condensed Matter; Correlation; Dynamical systems; Dynamics; Exact sciences and technology; Gases; Humanities and Social Sciences; letter; Mathematical analysis; multidisciplinary; Optical lattices; Phase transitions; Physics; Propagation; Quantum computation; Quantum Gases; Quantum information; Quenching; Science; Science (multidisciplinary); Spreading; Studies; Quantum system; Propagation velocity; Light velocity; N body system; Quasiparticles; Relaxation; Closed systems; Dynamics; Correlations; Short-range interactions; Relativistic quantum field theory; Light cones; Quantum information; Quantum gaz
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature10748

No limit to the speed of information propagation exists in non-relativistic quantum field theory, but finite-velocity transport of correlations is now found in a system of ultracold atoms in an optical lattice, aiding fundamental understanding of closed quantum systems far from equilibrium. Spread the word In relativistic quantum field theory, information propagation is bounded by the speed of light. No such limit exists in the non-relativistic case, although in real physical systems, short-range interactions may be expected to restrict the propagation of information to finite velocities. The existence of a maximal velocity has been shown theoretically to exist in several interacting many-body systems, but has never been observed experimentally. Here Cheneau et al . detect finite-velocity transport correlations in a system of ultracold atoms in an optical lattice. The results aid fundamental understanding of closed quantum systems far from equilibrium, and may be important for engineering efficient quantum channels necessary for fast quantum computations. In relativistic quantum field theory, information propagation is bounded by the speed of light. No such limit exists in the non-relativistic case, although in real physical systems, short-range interactions may be expected to restrict the propagation of information to finite velocities. The question of how fast correlations can spread in quantum many-body systems has been long studied 1 . The existence of a maximal velocity, known as the Lieb–Robinson bound, has been shown theoretically to exist in several interacting many-body systems (for example, spins on a lattice 2 , 3 , 4 , 5 )—such systems can be regarded as exhibiting an effective light cone that bounds the propagation speed of correlations. The existence of such a ‘speed of light’ has profound implications for condensed matter physics and quantum information, but has not been observed experimentally. Here we report the time-resolved detection of propagating correlations in an interacting quantum many-body system. By quenching a one-dimensional quantum gas in an optical lattice, we reveal how quasiparticle pairs transport correlations with a finite velocity across the system, resulting in an effective light cone for the quantum dynamics. Our results open perspectives for understanding the relaxation of closed quantum systems far from equilibrium 6 , and for engineering the efficient quantum channels necessary for fast quantum computations 7 .