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arXiv:0803.0760 · Europhysics Letters (EPL)

Phase transitions, entanglement and quantum noise interferometry in cold atoms

Florian Mintert, Ana María Rey, Indubala I. Satija, Charles W. Clark

Published Apr 1, 2009• 9 citations
arXivHTMLPDF

Abstract

We show that entanglement monotones reveal the pronounced enhancement of entanglement at a quantum phase transition, when they are sensitive to long-range high-order correlations. Such monotones are found to develop a sharp interferometric peak at the critical point, and to exhibit universal scaling. We demonstrate that similar features are shared by noise correlation spectra, and verify that these experimentally accessible quantities encode entanglement information and probe separability. We give a prescription, for mesoscopic scale systems of how to extract the pronounced enhancement of entanglement at a quantum phase transition from limited accessible experimental data.

DOI
10.1209/0295-5075/86/17003

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We show that entanglement monotones reveal the pronounced enhancement of entanglement at a quantum phase transition, when they are sensitive to long-range high-order correlations. Such monotones are found to develop a sharp interferometric peak at the critical point, and to exhibit universal scaling. We demonstrate that similar features are shared by noise correlation spectra, and verify that these experimentally accessible quantities encode entanglement information and probe separability. We give a prescription, for mesoscopic scale systems of how to extract the pronounced enhancement of entanglement at a quantum phase transition from limited accessible experimental data.
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In this work, we study the two-point entanglement S ( i , j ), which measures the entanglement between two separated degrees of freedom ( ij ) and the rest of system, near a quantum phase transition. Away from the critical point, S ( i , j ) saturates with a characteristic length scale ξ E , as the distance | i − j | increases. The entanglement length ξ E agrees with the correlation length. The universality and finite size scaling of entanglement are demonstrated in a class of exactly solvable one-dimensional spin model. By connecting the two-point entanglement to correlation functions in the long range limit, we argue that the prediction power of a two-point entanglement is universal as long as the two involved points are separated far enough.
Abstract Entanglement plays a key role in quantum physics, but how much information it can extract from many-body systems is still an open question, particularly regarding quantum criticalities and emergent symmetries. In this work, we systematically study the entanglement entropy (EE) and derivative entanglement entropy (DEE) near quantum phase transitions in various quantum many-body systems. A one-parameter scaling relation between the DEE and system size at the critical point has been derived for the first time, which successfully obtains the critical exponent via data collapse. Furthermore, we find that the EE peaks at the (emergent) symmetry-enhanced first-order transition, reflecting higher symmetry breaking. This work provides a new paradigm for quantum many-body research from the perspective of EE and DEE.
Spatial entanglement of quantum states has become a central paradigm of many-body physics. Here, we unearth a fundamentally different form of entanglement, the entanglement between imaginary time scales. This time-scale entanglement is accessible through quantics tensor train diagnostics (QTTD), where the bond dimension of an nnn-particle correlator encodes the coupling between temporal scales. Our central result is that time-scale entanglement is generically enhanced in the vicinity of phase transitions and crossovers. At quantum critical points, it becomes scale-invariant. We demonstrate time-scale entanglement across a range of systems, including finite-size Hubbard rings, the transverse-field Ising model, the single-impurity Anderson model, and the Mott transition in the Hubbard model. Remarkably, the enhanced time-scale entanglement is largely independent of the specific observable, establishing QTTD as a universal and unbiased diagnostic of criticality.
Non-equilibrium phase transitions of open quantum systems generically exhibit diverging classical but not quantum correlations. Still entanglement -- characterizing the latter correlations -- can be sensitive to the phase transition. Furthermore, mutual information, bounding the total correlations, should exhibit critical scaling at the transition. In this work, we study these quantities in the steady state of open quantum Ising chains with power-law interactions (with the exponent 0≤α≤30\le α\le 30≤α≤3) where spins are subject to spontaneous emission. The bulk of this paper is dedicated to a detailed analytical as well as numerical analysis of the infinite-range model (α=0α=0α=0), a model that is closely related to the paradigmatic open Dicke model. Our main findings are that the entanglement, while being finite, peaks, exhibits a kink and takes a universal value at the transition, while the mutual information exhibits critical scaling not only at the transition but well into the ordered phase, underscoring a hidden criticality that is not captured by (two-point) correlations. We consider three distinct entanglement measures: logarithmic negativity; quantum Fisher information; and, spin squeezing. Specifically, we show that the collective spin operator that maximizes the quantum Fisher information can be identified with the \textit{gapless} mode of the phase transition, while the squeezed direction is that of the \textit{gapped} mode. Finally, we investigate power-law interacting models using matrix product states where we find comparable bounds on squeezing even when no phase transition is expected (for larger ααα), thus the connection to the phase transition does not appear to hold for shorter-range interactions.
The Dicke model is a paradigmatic setting for collective light-matter physics and the superradiant phase transition. Yet extracting the critical exponents is challenging at experimentally accessible mesoscopic sizes, due to the slow divergence of the correlation time under all-to-all coupling and a photon-loss-driven crossover to a distinct dissipative universality class. Here, we perform a large-NNN analysis that identifies distinct coherent and dissipative fixed points for the closed and open Dicke models. We then develop a unified mesoscopic scaling framework that incorporates the leading irrelevant correction and, going beyond static and spectral probes, brings ramping dynamics under the same scaling description. It recovers the corresponding exponents, verifies Kibble-Zurek scaling, and clarifies how finite size, dissipation, and speed compete in the ramping dynamics. Our work thus establishes a unified framework for resolving static and dynamical critical scaling in closed and open quantum systems, with broader applicability to mesoscopic systems with long-range interactions.