Quantum Many-Body Dynamics

Universal dynamics and topological order in many-body localized states

Ronen Vosk
Weizmann Institute of Science

May 15, 2014

PIRSA:14050082
Can Eigenstate Thermalization Breakdown without Disorder?

Matthew Fisher
University of California, Santa Barbara

May 15, 2014

PIRSA:14050083
TBA

Antonello Scardicchio
The Abdus Salam International Centre for Theoretical Physics (ICTP)

May 15, 2014

PIRSA:14050084
(Robert Konik) Glimmers of a Quantum KAM Theorem: Insights from Quantum Quenches in One Dimensional Bose Gases

May 16, 2014

PIRSA:14050086
Quench dynamics in interacting and disordered field theories in one-dimension

Aditi Mitra
New York University (NYU)

May 16, 2014

PIRSA:14050087
(Lea Santos) General Features of the Relaxation Dynamics of Isolated Interacting Quantum Systems

May 16, 2014

PIRSA:14050088

Universal dynamics and topological order in many-body localized states

Ronen Vosk
Weizmann Institute of Science

May 15, 2014

PIRSA:14050082

It has been argued recently that, through a phenomenon of many-body localization, closed quantum systems subject to sufficiently strong disorder would fail to thermalize. In this talk I will describe a real time renormalization group approach, which offers a controlled description of universal dynamics in the localized phase. In particular it explains the ultra-slow entanglement propagation in this state and identifies the emergent conserved quantities which prevent thermalization. The RG analysis also shows, that far from being a trivial dead state, the MBL state admits phase transitions between distinct dynamical phases. For example, I will discuss the universal aspects of a transition between a paramagnetic localized state to one which exhibits spin-glass order. Finally, I will present a development of the RG scheme, defined on an effective coarse grained model, which allows to capture the transition from a many-body localized to a thermalizing state.
Can Eigenstate Thermalization Breakdown without Disorder?

Matthew Fisher
University of California, Santa Barbara

May 15, 2014

PIRSA:14050083

We describe a new diagnostic for many-body wavefunctions which generalizes the spatial bipartite entanglement entropy. By was of illustration, for a two-component wavefunction of heavy and light particles, a partial (projective) measurement of the coordinates of the heavy (but not light) particles is first performed, and then the entanglement entropy of the projected wavefunction for the light particles is computed. If the two-component wavefunction has a volume law entanglement entropy, yet the post measurement wavefunction of the light particles is disentangled with an area law entanglement, we refer to the original wavefunction as a “Quantum Disentangled State”. This diagnostic can be generalized to include other partial measurements, such as measuring the charge, but not spin, for finite-energy density eigenstates of Fermion Hubbard-type model. Quantum disentanglement results if the post measurement spin-wavefunction has an area law entanglement entropy. Recent numerics searching for such Quantum Disentangled States in 1d Hubbard-type models will be discussed in detail.
TBA

Antonello Scardicchio
The Abdus Salam International Centre for Theoretical Physics (ICTP)

May 15, 2014

PIRSA:14050084
(Robert Konik) Glimmers of a Quantum KAM Theorem: Insights from Quantum Quenches in One Dimensional Bose Gases

May 16, 2014

PIRSA:14050086

We consider quantum quenches in one dimensional Bose gases where we prepare the gas in the ground state of a parabolic trap and then release it into a small cosine potential. This cosine potential breaks the integrability of the 1D gas which absent the potential is described by the Lieb-Liniger model. We explore the consequences of this cosine potential on the thermalization of the gas. We argue that the integrability breaking of the cosine does not immediately lead to ergodicity inasmuch as we demonstrate that there are residual quasi-conserved quantities post-quench. We demonstrate that the quality of this quasi-conservation can be made arbitrarily good.
Quench dynamics in interacting and disordered field theories in one-dimension

Aditi Mitra
New York University (NYU)

May 16, 2014

PIRSA:14050087

I will present results for the quench dynamics of one-dimensional interacting bosons under two circumstances. One is when the bosons are in the vicinity of the superfluid-Mott quantum critical point, while the second is when the bosons are in a disordered potential which can drive the system into a Bose glass phase. I will show that the dynamics following a quench can be quite complex by being characterized by three regimes. One is a short time perturbatively accessible regime which depends on microscopic parameters, the second is an intermediate time prethermalized regime where inelastic effects are weak and correlation functions can show universal scaling behavior which is quantified by a nonequilibrium generalization of the Callan-Symanzik equations. The third is a long time regime where inelastic effects become important. For the dynamics in the inelastic regime I will construct a novel quantum kinetic equation that accounts for multi-particle scattering between bosons, and discuss how the combined effect of interactions and (weak) disorder can thermalize the system.
(Lea Santos) General Features of the Relaxation Dynamics of Isolated Interacting Quantum Systems

May 16, 2014

PIRSA:14050088

We consider isolated interacting quantum systems that are taken out of equilibrium instantaneously (quenched). We study numerically and analytically the probability of finding the initial state later on in time (the so-called fidelity or Loschmidt echo), the relaxation time of the system, and the evolution of few-body observables. The fidelity decays fastest for systems described by full random matrices, where simultaneous many-body interactions are implied. In the realm of realistic systems with two-body interactions, the dynamics is slower and dependent on the energy of the initial state. The fastest fidelity decay in this case is Gaussian and can persist until saturation. The fidelity also plays a central role in the short-time dynamics of few-body observables that commute with the system Hamiltonian before the quench. Our analyses are mainly developed for initial states that can be prepared in experiments with cold atoms in optical lattices.

Title	Speaker(s)	Date	Talk Type	Info
Universal dynamics and topological order in many-body localized states	Ronen Vosk	2014-05-15	Conference	View details
Can Eigenstate Thermalization Breakdown without Disorder?	Matthew Fisher	2014-05-15	Conference	View details
TBA	Antonello Scardicchio	2014-05-15	Conference	View details
(Robert Konik) Glimmers of a Quantum KAM Theorem: Insights from Quantum Quenches in One Dimensional Bose Gases		2014-05-16	Conference	View details
Quench dynamics in interacting and disordered field theories in one-dimension	Aditi Mitra	2014-05-16	Conference	View details
(Lea Santos) General Features of the Relaxation Dynamics of Isolated Interacting Quantum Systems		2014-05-16	Conference	View details

Quantum Many-Body Dynamics

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