Quench dynamics in interacting and disordered field theories in one-dimension
Aditi Mitra New York University (NYU)
PIRSA:14050087
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From locally covariant QFT to quantum gravity
Katarzyna Rejzner University of York
TBA
Antonello Scardicchio The Abdus Salam International Centre for Theoretical Physics (ICTP)
PIRSA:14050084Gravity waves from Kerr/CFT
Achilleas Porfyriadis Harvard University
Can Eigenstate Thermalization Breakdown without Disorder?
Matthew Fisher University of California, Santa Barbara
PIRSA:14050083Universal dynamics and topological order in many-body localized states
Ronen Vosk Weizmann Institute of Science
PIRSA:14050082A polynomial-time algorithm for the ground state of 1D gapped local Hamiltonians
Thomas Vidick Weizmann Institute of Science
PIRSA:14050039What can we learn from modifing gravity ?
Claudia de Rham Imperial College London
Many-body mobility edge in a mean-field quantum spin-glass
Arijeet Pal Harvard University
PIRSA:14050078
Quench dynamics in interacting and disordered field theories in one-dimension
Aditi Mitra New York University (NYU)
PIRSA:14050087I 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.(Robert Konik) Glimmers of a Quantum KAM Theorem: Insights from Quantum Quenches in One Dimensional Bose Gases
PIRSA:14050086We 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.From locally covariant QFT to quantum gravity
Katarzyna Rejzner University of York
Locally covariant quantum field theory (LCQFT) has proven to be a very successful framework for QFT on curved spacetimes. It is natural to ask, how far these ideas can be generalized and if one can learn something about quantum gravity, using LCQFT methods. In particular, one can use the relative Cauchy evolution to formulate the notion of background independence. Recently we have proven that background independence in this sense holds for effective quantum gravity, formulated as a perturbative QFT. Remarkably, the formalism of LCQFT can be extended to structures more general than spacetimes. The essential feature is the presence of the causal structure. An example application would be QFT on causal sets (work in progress).TBA
Antonello Scardicchio The Abdus Salam International Centre for Theoretical Physics (ICTP)
PIRSA:14050084Gravity waves from Kerr/CFT
Achilleas Porfyriadis Harvard University
Astronomical observation suggests the existence of near-extreme Kerr black holes whose horizons spin at nearly the speed of light. Properties of diffeomorphisms imply that the dynamics of the high-redshift near-horizon region of near-extreme Kerr, which includes the innermost-stable-circular-orbit (ISCO), is governed by an infinite-dimensional emergent conformal symmetry. This symmetry may be exploited to analytically, rather than numerically, compute a variety of potentially observable processes. In this talk I will show how we compute and study the conformal transformation properties of the gravitational radiation emitted by an orbiting massive object in the large-redshift near-horizon region. I will also use conformal symmetry of the near-horizon region to compute the gravitational radiation produced during the plunge phase following the object's crossing of the ISCO.Can Eigenstate Thermalization Breakdown without Disorder?
Matthew Fisher University of California, Santa Barbara
PIRSA:14050083We 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.Universal dynamics and topological order in many-body localized states
Ronen Vosk Weizmann Institute of Science
PIRSA:14050082It 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.A polynomial-time algorithm for the ground state of 1D gapped local Hamiltonians
Thomas Vidick Weizmann Institute of Science
PIRSA:14050039Computing ground states of local Hamiltonians is a fundamental problem in condensed matter physics. We give the first randomized polynomial-time algorithm for finding ground states of gapped one-dimensional Hamiltonians: it outputs an (inverse-polynomial) approximation, expressed as a matrix product state (MPS) of polynomial bond dimension. The algorithm combines many ingredients, including recently discovered structural features of gapped 1D systems, convex programming, insights from classical algorithms for 1D satisfiability, and new techniques for manipulating and bounding the complexity of MPS. Our result provides one of the first major classes of Hamiltonians for which computing ground states is provably tractable despite the exponential nature of the objects involved. /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-style-parent:""; font-size:11.0pt; font-family:"Calibri","sans-serif";}What can we learn from modifing gravity ?
Claudia de Rham Imperial College London
I will review models of modified gravity in the infrared and show how extra degrees of freedom present in these theories get screened via the Vainshtein mechanism. That mechanism comes hand in hand with its own share of peculiarities: classical superluminalities, strong coupling and perturbative non-analyticity of the S-matrix to name a few. From a traditional effective field viewpoint such effects are disastrous but I will present the first hints in understanding these theories beyond the traditional perspective and their implications not only for gravity but also for our understanding of a certain class of field theories.A Rigorous Result on Many-Body Localization
John Imbrie University of Virginia
PIRSA:14050079I will discuss a proof of many-body localization for a one-dimensional spin chain with random local interactions. The proof depends on a physically reasonable assumption that limits the amount of level attraction in the system. I construct a sequence of local rotations that completely diagonalizes the Hamiltonian and exhibits the local degrees of freedom.Many-body mobility edge in a mean-field quantum spin-glass
Arijeet Pal Harvard University
PIRSA:14050078Isolated, interacting quantum systems in the presence of strong disorder can exist in a many-body localized phase where the assumptions of equilibrium statistical physics are violated. On tuning either the parameters of the Hamiltonian or the energy density, the system is expected to transition into the ergodic phase. While the transition at "infinite temperature" as a function of system parameters has been found numerically but, the transition tuned by energy density has eluded such methods.
In my talk I will discuss the nature of the many-body localization-delocalization (MBLD) transition as a function of energy denisty in the quantum random energy model (QREM). QREM provides a mean-field description of the equilibrium spin glass transition. We show that it further exhibits a many-body mobility edge when viewed as a closed quantum system. The mean-field structure of the model allows an analytically tractable description of the MBLD transition. I will also comment on the nature of the critical states in this mean-field model.
This opens the possibility of developing a mean-field theory of this interesting dynamical phase transition.