Quantum entanglement in condensed matter systems

심흥선

Yang Ming, Zijian Wu, Xikui Hu +2 more

Condensed matter systems are potential candidates to realize the integration of quantum information circuits. Surface phonon polariton (SPhP) is a special propagation mode in condensed matter systems. We present an investigation on the entanglement of SPhP modes. The entangled pairs are generated from entangled photons injected to the system. Quantum performances of entangled SPhPs are investigated by using the interaction Hamiltonian and the perturbation theory. The wave mechanics approach is taken to describe the coupling process as a comparison. Finally, the correlation of system is examined. A whole set of descriptions of SPhP entanglement thus are presented.

Ann B. Kallin

At the interface of quantum information and condensed matter physics, the study of entanglement in quantum many-body systems requires a new toolset which combines concepts from each. This thesis introduces a set of computational methods to study phases and phase transitions in lattice models of quantum systems, using the Renyi entropies as a means of quantifying entanglement. The scaling of entanglement entropy can give valuable insight into the phase of a condensed matter system. It can be used to detect exotic types of phases, to pinpoint transitions between phases, and can give us universal information about a system. \nThe first approach in this thesis is a technique to measure entanglement in finite size \nlattice systems using zero-temperature quantum Monte Carlo simulations. The algorithm \nis developed, implemented, and used to explore anomalous entanglement scaling terms in \nthe spin-1/2 Heisenberg antiferromagnet. \nIn the second part of this thesis, a new and complementary numerical technique is introduced to study entanglement not just in finite size systems, but as we approach the thermodynamic limit. This “numerical linked-cluster expansion” is used to study two different systems at their quantum critical points — continuous phase transitions occurring at zero temperature, at which these systems exhibit universal properties. Remarkably, these universal properties can be reflected in the scaling of entanglement. \nEntanglement offers a new perspective on condensed matter systems, one which takes us closer to genuinely understanding what goes on in these materials at the quantum mechanical level. This thesis demonstrates the first steps in developing an extensive list of computational tools that can be used to study entanglement over a wide range of interacting quantum many-body systems. With the ever increasing computational power available, it may be only a matter of time before these tools are used to create a comprehensive framework for the characterization of condensed matter phases and phase transitions.

J. W. Clark, Hessam Habibian, Aikaterini Mandilara +1 more

Artur Sowa

C. A. Chatzidimitriou‐Dreismann

Abstract. The “anomalous ” scattering of neutrons and electrons from protons in the electron-volt energy range is described, and related experimental results are presented. Due to the very short characteristic scattering time, there is no well defined separation of time scales of electronic and protonic motions. An outline of a proposed theoretical interpretation is presented, which is based on the fact that scattering protons represent open quantum systems. PACS number: 03.65.Ud 1 Introductory Remarks The counter-intuitive phenomenon of entanglement [1] between two or more quantum systems has emerged as the most emblematic feature of quantum me-chanics. Experiments investigating entanglement, however, are mainly focused on collections of few simple (two- or three-level) quantum systems thoroughly isolated from their environment (e.g., atoms in high-Q cavities and optical lat-tices). These experimental conditions are necessary due to the decoherence of entangled states [2, 3]. In short, decoherence refers to the suppression of quan-tum superpositions caused by the environment. By contrast, quantum entanglement (QE) in condensed and/or molecular mat-ter at ambient conditions is usually assumed to be inaccessible experimentally. However, applying two new scattering techniques (NCS and ECS, see below) which operate in the sub-femtosecond time scale, we provided results indicating that short-lived entangled states may affect measurements in condensed matter even at room temperature [4–6]. The first direct experimental evidence of short-lived (that is, attosecond) QE involving protons in condensed matter was provided by means of the novel neu-tron Compton scattering (NCS) method. Starting in 1995, our experiments on 1310–0157 c © 2006 Heron Press Ltd. 193