First UQUAM Topical Workshop on. Open Quantum Systems. April 13-15, 2016 Israel

Transcription

1 First UQUAM Topical Workshop on April 13-15, 2016 Israel

2 Program Wednesday, April 13 Thursday, April 14 Friday, April 15 08:45 Transport from Hotel to WIS 09:30-10:15 Mykola Maksymenko Jorge Yago Malo 10:15-11:00 Benoit Vermersch Eyal Leviatan 11:00-11:30 Coffee Break 11:30-12:15 Markus Heyl Wojciech de Roeck 12:15-13:00 Henrik Lüschen Lukas Sieberer Trip! 13:00-14:30 Lunch 14:30-17:00 Discussions Discussions Transport to Hotel (17:00) Mizlala (19:30) Music by the Pond then Transport to Hotel (18:30) LaShuk (20:00) Participants Sumilan Banerjee, Weizmann Institute of Science Markus Heyl, TU München Eyal Leviatan, Weizmann Insitute of Science Henrik Lüschen, LMU München Mykola Maksymenko, Weizmann Institute of Science Wojciech de Roeck, KU Leuven Lukas Sieberer, Weizmann Institute of Science Benoit Vermersch, IQOQI Jorge Yago Malo, University of Strathclyde Organizers Marcello Dalmonte, IQOQI Mark H Fischer, Weizmann Institute of Science

3 Abstracts Quantum trajectories with matrix product states and its application to many-body localization Mykola Maksymenko Weizmann Institute of Science Quantum trajectories combined with the matrix product states algorithms can be a convenient tool to study real-time dynamics of open dissipative quantum systems. I will outline the main idea of the method and its implementation and provide an example of its application to disordered systems. Different regimes of weak and strong disorder reveal advantages and downsides of the method. MPS simulations with absorbing boundary conditions and applications for the study of Markovian/Non- Markovian spin networks Benoit Vermersch IQOQI I will present our recent results about the theory of Chiral quantum networks consisting in qubits connected to optical fibers with broken left-right symmetry in the couplings. Beyond applications from a Quantum Information perspective, such networks allow for example the driven dissipative preparation of pure, entangled steady-states. I will show in this presentation how one can model such network via finite spin chains, allowing to access in particular the Non-Markovian regime, beyond standard quantum-optics tools. Moreover, I will explain how the use of losses at the edges of our spin chain allows to mimic an infinite waveguide and, combined with MPS approach, to study the longtime behavior of long-delayed quantum networks.

4 Transport in many-body localized systems from driven dissipative boundaries Markus Heyl TU München While many-body localization (MBL) has emerged as a robustly nonergodic quantum phase of matter with vanishing DC transport, studying the transport properties for specific systems analytically or numerically remains a challenge. In this talk I will discuss a general scheme to (numerically) access transport in MBL systems by imposing dissipative boundaries, i.e., to couple the system to incoherent external particle sources and drains on two ends. I will also point out that this might be seen as a quantum generalization of a paradigmatic model for transport in classical systems: the simple exclusion process (SEP). Experimental studies on open MBL systems Henrik Lüschen LMU München The paradigm of Many Body Localization (MBL) describes a localized phase where closed many body systems in the presence of disorder fail to act as their own heat bath. However, any small coupling to the environment will thermalize a MBL system, making true experimental implementations, which will always have a finite coupling, impossible. We can, however, learn to extrapolate properties of true MBL systems from imperfectly isolated experiments by systematically studying the effects of small bath couplings. Cold gases experiments are known to create very well isolated systems, making them ideally suited for such studies. I will present recent results on systematically opened MBL systems via I) Coupling of many MBL systems II) Photon Scattering III) Lattice shaking and IV) give an outlook on the possibility of implementing baths with a two band model.

5 Dissipative engineering of ultracold atoms in optical lattices Jorge Yago Malo University of Strathclyde In the last few years, a huge effort has been made towards the characterization and description of dissipative processes that occur inevitably in a cold-atom experimental setup. Inspired by quantum optics, plenty of proposals have tried to not only incorporate those non-unitary processes but also engineer them in a way that new exciting physical phenomena can be studied in the context of manybody systems. Current techniques push the limits of the available numerical tools to simulate Linbladian dynamics. I will discuss some of the most successful techniques to tackle dissipative dynamics using the density matrix renormalization group (DMRG), combining it with quantum trajectories methods. In particular, I will apply it to two particularly relevant problems: the dissipative generation of entangled states for metrology purposes and the study of particle losses in the optical lattice; trying to observe the key differences between bosonic and fermionic emission. Is the long-time quantum dynamics of a many-body system computable? Eyal Leviatan Weizmann Institute of Science Computing the time evolution of closed ergodic systems is a formidable task because all the exponentially large Hilbert space of the system is in principle reachable from a generic initial states. Even if we start from a product state, thermalization involves build up of highly non local quantum correlations or entanglement in the system, which cannot be captured by modern methods such as DMRG. But do we really need to accurately keep track of non-local quantum correlations? We know that at long times a thermalizing system should be characterized by an emergent classical behavior dominated by hydrodynamic transport of conserved quantities. In this talk I will discuss how this quantum to classical crossover that occurs during the time evolution can be described and utilized to formulate a systematic approximation scheme for the dynamics of many-body quantum systems. I will comment on the relation between the loss, or scrambling, of quantum information during thermalization to black hole information paradoxes.

6 Temperature profiles in localized chains Wojciech de Roeck KU Leuven Localized systems are isolators, yet upon connection to baths, they still have a small conductivity (vanishing exponentially in system size). One can ask for the temperature profile established in such a system. It turns out that these temperature profiles are step functions on a macroscopic scale, jumping in the middle of the chain between the temperatures set by the baths. For the case of noninteracting localized systems (Anderson localization), there is also a spectacular breakdown of local equilibrium; in the middle of the chain, and on a microscopic scale, the temperature jumps wildly between adjacent sites. It is not clear to us whether this is also true in interacting localized systems. This is work joint with Abishek Dhar, francois Huveneers, and Marius Schuetz. Time permitting, I will take the opportunity to make some general comments on Markovian dissipation models in the many-body context. In my opinion, there is a surprising lack of Markovian models that are healthy from a thermodynamic point of view. I will describe some tentative work towards clarifying these issues: solutions/no-go theorems. This is work with Marius Schuetz. Coherence, superfluidity, and vortex unbinding in two-dimensional driven-dissipative condensates Lukas Sieberer Weizmann Institute of Science Fluids of exciton-polaritons, excitations of two-dimensional semiconductor microcavities, show collective phenomena akin to Bose condensation. However, a fundamental difference from standard condensates stems from the finite lifetime of these excitations, which necessitate continuous driving to maintain a steady state. A basic question is how the paradigm of two-dimensional Bose condensation in thermal equilibrium, comprising algebraic order, superfluidity, and the loss of these features in a KT transition associated with the unbinding of vortices, is modified under non-equilibrium conditions. We show that fluctuations of the phase of a driven-dissipative condensate, which are governed by the KPZ equation lead to the destruction of algebraic order, even if the possible presence of vortices is not taken into account. Remarkably, despite the absence of algebraic order, a finite superfluid density persists. In a second step of our analysis, we account for vortices in the phase field through a duality mapping between the compact KPZ equation and a theory of non-linear electrodynamics coupled to charges. Using the dual theory we derive renormalization group equations that describe vortex unbinding in these media. We find that vortices always unbind, and we predict the finite size scaling behavior of the superfluid stiffness in the crossover governed by vortex unbinding showing its clear distinction from the scaling associated with the equilibrium KT transition.