04.30.+p Entanglement in phase transitions

Practical Entanglement Estimation for Spin-System Quantum Simulators

Date: 
2015-07-09 - 2016-03-09
Author(s): 

O. Marty, M. Cramer, and M. B. Plenio

Reference: 

Phys. Rev. Lett. 116, 105301

We present practical methods to measure entanglement for quantum simulators that can be realized with trapped ions, cold atoms, and superconducting qubits. Focusing on long- and short-range Ising-type Hamiltonians, we introduce schemes that are applicable under realistic experimental conditions including mixedness due to, e.g., noise or temperature. In particular, we identify a single observable whose expectation value serves as a lower bound to entanglement and that may be obtained by a simple quantum circuit.

Criticality in translation-invariant parafermion chains

Date: 
2015-03-18
Author(s): 

Wei Li, Shuo Yang, Hong-Hao Tu, and Meng Cheng

Reference: 

Phys. Rev. B 91, 115133 (2015)

In this work we numerically study critical phases in translation-invariant Z_N parafermion chains with both nearest- and next-nearest-neighbor hopping terms. The model can be mapped to a Z_N spin model with nearest-neighbor couplings via a generalized Jordan-Wigner transformation and translation invariance ensures that the spin model is always self-dual.

All spin-1 topological phases in a single spin-2 chain

Date: 
2015-05-19
Author(s): 

Augustine Kshetrimayum, Hong-Hao Tu, and Roman Orus

Reference: 

Phys. Rev. B. 91, 205118 (2015)

Here we study the emergence of different Symmetry-Protected Topological (SPT) phases in a spin-2 quantum chain. We consider a Heisenberg-like model with bilinear, biquadratic, bicubic, and biquartic nearest-neighbor interactions, as well as uniaxial anisotropy.

Irreversible processes without energy dissipation in an isolated Lipkin-Meshkov-Glick model

Date: 
2014-04-24 - 2015-07-02
Author(s): 

R. Puebla, A. Relaño

Reference: 

Phys. Rev. E 92, 012101

For a certain class of isolated quantum systems, we report the existence of irreversible processes in which the energy is not dissipated. After a closed cycle in which the initial energy distribution is fully recovered, the expectation value of a symmetry-breaking observable changes from a value differing from zero in the initial state to zero in the final state. This entails the unavoidable loss of a certain amount of information and constitutes a source of irreversibility.

Spin liquid phases of alkaline-earth-metal atoms at finite temperature

Date: 
2013-10-11 - 2013-12-05
Author(s): 

P. Sinkovicz, A. Zamora, E. Szirmai, M. Lewenstein, G. Szirmai

Reference: 

Phys. Rev. A 88, 043619 (2013)

We study spin liquid phases of spin-5/2 alkaline-earth-metal atoms on a honeycomb lattice at finite temperatures. Our analysis is based on a Gutzwiller projection variational approach recast to a path-integral formalism. In the framework of a saddle-point approximation we determine spin liquid phases with lowest free energy and study their temperature dependence.

Projected entangled-pair states can describe chiral topological states

Date: 
2013-10-23
Author(s): 

T.B. Wahl, H.-H. Tu, N. Schuch, J.I. Cirac

Reference: 

Physical Review Letters 111, 236805 (2013)

We show that Projected Entangled-Pair States (PEPS) in two spatial dimensions can describe chiral topological states by explicitly constructing a family of such states with a non-trivial Chern number. They are ground states of two different kinds of free-fermion Hamiltonians: (i) local and gapless; (ii) gapped, but with hopping amplitudes that decay according to a power law. We also prove that they are necessarily non-injective, and cannot correspond to exact ground states of gapped, local parent Hamiltonians.

Projected BCS states and spin Hamiltonians for the SO(n)1 Wess-Zumino-Witten model

Date: 
2013-01-14
Author(s): 

Hong-Hao Tu

Reference: 

URL: http://link.aps.org/doi/10.1103/PhysRevB.87.041103
DOI: 10.1103/PhysRevB.87.041103
PACS: 75.10.Pq, 03.65.Fd, 11.25.Hf

We propose a class of projected BCS wave functions and derive their parent spin Hamiltonians. These wave functions can be formulated as infinite matrix product states constructed by chiral correlators of Majorana fermions. In one dimension, the spin Hamiltonians can be viewed as SO(n) generalizations of Haldane-Shastry models. We numerically compute the spin-spin correlation functions and Rényi entropies for n=5 and 6. Together with the results for n=3 and 4, we conclude that these states are critical and their low-energy effective theory is the SO(n)1 Wess-Zumino-Witten model.

Dipolar Molecules in Optical Lattices

Date: 
2012-03-13
Author(s): 

T. Sowiński, O. Dutta, P. Hauke, L. Tagliacozzo, M. Lewenstein

Reference: 

URL: http://link.aps.org/doi/10.1103/PhysRevLett.108.115301
DOI: 10.1103/PhysRevLett.108.115301
PACS: 67.85.Hj, 37.10.Jk

We study the extended Bose-Hubbard model describing an ultracold gas of dipolar molecules in an optical lattice, taking into account all on-site and nearest-neighbor interactions, including occupatio

Critical properties and Renyi entropies of the spin-3/2 XXZ chain

Date: 
2012-04-06
Author(s): 

M. Dalmonte, E. Ercolessi and L. Taddia

Reference: 

Phys. Rev. B 85, 165112 (2012)
doi:10.1103/PhysRevB.85.165112

We discuss entanglement and critical properties of the spin-3/2 XXZ chain in its entire gapless region. Employing density-matrix renormalization-group calculations combined with different methods based on level spectroscopy, correlation functions, and entanglement entropies, we determine the sound velocity and the Luttinger parameter of the model as a function of the anisotropy parameter.

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