- Near-adiabatic ramps ("slow quenches") in quantum many-particle systems
- Entanglement and topological order in quantum Hall states
- Edge-localized states in 1D quantum lattices
- Few-vortex dynamics in Bose condensates
- Entanglement between unusual partitionings of many-particle systems

Since a real-life ramp can never be infinitely slow, understanding
non-adiabatic dynamics during ramps is vital.
We are therefore studying the evolution of many-particle systems
during and after a sudden change (*quench*) or gradual change
(*ramp*) of parameter, *e.g.*, changes of interaction
strength or magnetic field, or (for cold-atom systems) trapping
potential. Varying the rate of change, one can study the whole range
between
*instantaneous* and *adiabatic* limits.

A grand challenge is to understand *deviations* from adiabaticity
in slow but finite ramps. I have explored this issue in a series of
calculations, aiming to provide intuition about how this deviation is
related to various system features, such as energy gap or gaplessness,
inhomogeneity due to trapping potentials, and presence of phase
transitions.

References:

[a] M. Haque and F.E. Zimmer;
Phys. Rev. A 87, 033613 (2013)

Title: `Slow interaction ramps in trapped many-particle systems: universal deviations
from adiabaticity.'

[b]
T. Venumadhav, M. Haque, and R. Moessner;
Phys. Rev. B 81, 054305 (2010).

Title: `Finite-rate quenches of site bias in the Bose-Hubbard dimer.'

[c] B. Dorá, M. Haque, and G. Zaránd;
Phys. Rev. Lett. 106, 156406 (2011).

Title: ` Crossover from adiabatic to sudden interaction quench in a Luttinger liquid.'

[d] F.E. Zimmer and M. Haque;
arXiv:1012.4492.

Title: `Non-adiabatic interaction ramps in a trapped Bose condensate.'

[e] M. Haque and H.T.C. Stoof;
Phys. Rev. A 71, 063603 (2005).

Title: `Dynamics of a molecular Bose-Einstein condensate near a Feshbach resonance.'

References:

[a] M. Haque, O. Zozulya, and K. Schoutens;
Phys. Rev. Lett. 98, 060401 (2007).

* Entanglement entropy of fermionic Laughlin states. *

[b] O. Zozulya, M. Haque, K. Schoutens, and E. H. Rezayi;
Phys. Rev. B 76, 125310 (2007).

* Bipartite entanglement entropy in fractional quantum
Hall states. *

[c] O. Zozulya, M. Haque and N. Regnault;
Phys. Rev. B 79, 045409 (2009).

* Entanglement signatures of Quantum Hall phase transitions. *

[d] A. M. Laeuchli, E. J. Bergholtz, J. Suorsa, and M. Haque;
Phys. Rev. Lett. 104, 156404 (2010).

* Disentangling Entanglement Spectra of Fractional Quantum Hall
States on Torus Geometries. *

[e] A. M. Laeuchli, E. J. Bergholtz, and M. Haque;
New Journal of Physics, 12, 075004 (2010).

* Entanglement Scaling of Fractional Quantum Hall states through
Geometric Deformations. *

Also available as
arXiv:1003.5656.

In one-dimensional quantum lattice models with open boundaries, examining few-particle dynamics led me to an edge-induced self-similar (`fractal') structure high up in the energy specturm, and associated out-of-equilibrium consequences.

The non-equilibrium consequences are a hierarchy of `edge-locking'
or edge-localization effects. This is a *collective* rather than
a single-particle effect, requiring at least three fermions or three
bosons.

Till now, I found and examined versions of the phenomenon in
three classic condensed-matter models: (1) the Bose-Hubbard
model; (2) the spinless fermion model with nearest-neighbor
repulsion; (3) the *XXZ* spin chain.

References:

[a] R. Pinto, M. Haque, S. Flach;
Phys. Rev. A 79, 052118 (2009).

* Edge-localized states in quantum one-dimensional lattices. *

[b] M. Haque;
Phys. Rev. A 82, 012108 (2010).

* Self-similar spectral structures and edge-locking hierarchy in open-boundary spin chains. *

The nonlinear Schroedinger equation (Gross-Pitaevskii equation), describing mean-field dynamics of Bose-Einstein condensates, possesses a remarkable range of rich dynamical phenomena. We are exploring the dynamics of condensates with a few vortices. For example, a vortex-antivortex pair (vortex dipole) in a trapped condensate displays stationary configurations and characteristic trajectories due to the interplay between mutually driven and inhomogeneity-driven motion.

References:

[a] W. Li, M. Haque and S. Komineas;
Phys. Rev. A 77, 053610 (2008).

* A vortex dipole in a trapped two-dimensional Bose
condensate. *

[b] J. A. Seman, E. A. L. Henn, M. Haque, R. F. Shiozaki, E. R. F. Ramos,
M. Caracanhas, P. Castilho, C. Castelo Branco, P. E. S. Tavares,
F. J. Poveda Cuevas, G. Roati, K. Magalhaes, and V. S. Bagnato;
Phys. Rev. A, 82, 033616 (2010).

* Three-vortex configurations in trapped Bose-Einstein condensates. *

The standard usage of entanglement estimators in condensed matter theory is through the entanglement between a spatially connected block and the rest of the system. Clearly, it is possible to ask about the entanglement between other kinds of partitions of a many-particle state. Our work demonstrates that several alternate types of partitionings can be fruitful and instructive for characterizing correlations in many-particle states.

References:

[a] O. Zozulya, M. Haque, and K. Schoutens;
Phys. Rev. A 78, 042326 (2008).

* Particle partitioning entanglement in itinerant
many-particle systems. *

[b] M. Haque, J.N. Bandyopadhyay and V. Ravi Chandra;
Phys. Rev. A 79, 042317 (2009).

* Entanglement and level crossings in finite
frustrated ferromagnetic chains. *

[c] (Review Article) M. Haque,
O. Zozulya, and K. Schoutens;
J. Phys. A: Math. Theor. 42, 504012 (2009).

*Entanglement between particle partitions in itinerant many-particle
states. *

Also available as
arXiv:0905.4024

Personal home page: Masud Haque.

Email (replace ATT by @ and remove spaces): haque ATT pks.mpg.de