Quantum Dynamics of LowDimensional Systems Workshop
In memoriam
Adilet Imambekov (1981  2012)
"You should strive to solve the most challenging problem and get a result which is most valuable from the intellectual
point of view. You cannot try to publish every paper in the best possible journal. There is simply too little time."
Dates: September 21st and 22nd, 2013
Location: 17 Oxford Street, Jefferson Lab room 250, Cambridge, MA 02138 (map)
Information/Scheduling: Jennifer Bastin
Tentative schedule
Saturday 21 September 2013

Sunday 22 September 2013

Participants (with titles & abstracts as provided):
Lev Ioffe (Rutgers)
Title: Josephson ladders implementing quantum critical onedimensional model and their applications.
Abstract: I present the novel type of Josephson ladders that can be mapped onto the quantum one dimensional models with tunable criticality and their applications for the implementation of a tunable superinductor, the element that is characterized by a purely inductive response and impedance much larger than quantum (6.5 kOm). In particular I will show the ladders that allow an experimental realization of the one dimensional φ^{4} theory with the mass that changes sign with magnetic field. Close to the critical point the low energy excitations in this theory can be described by Ising model in transverse field. The solution of this model shows that these excitations are Majorana fermions. I will show the spectroscopy data that display the spectral lines that are due to these fermionic excitations. I also show that slight variation of the ladder design allows one to implement other Hamiltonians that can be mapped to different quantum critical models. The applications of these ladders range from the current standard to the studies of the nonequilibrium properties of almost integrable quantum problems.
Jun Kono (Rice)
Title: Superfluorescence from a QuantumDegenerate TwoDimensional ElectronHole Gas
Matteo Rizzi (Mainz)
Title: Robustness of quantum memories based on Majorana zero modes
Abstract: We analyze the rate at which quantum information encoded in zeroenergy Majorana modes is lost in the presence of perturbations. We find that under certain conditions it can survive for times that scale exponentially with the size of the chain, for both quenching and timedependent dephasing perturbations, even when the latter have spectral components above the system's energy gap. The origin of the robust storage, namely the fact that a sudden quench aects in the same way both parity sectors of the original spectrum, is discussed, together with the memory performance at finite temperatures and in the presence of particle exchange with a bath.
Alexei Tsvelik (Brookhaven)
Title: A tractable model of bad metals
Abstract: We discuss the model Kondo type Hamiltonian representing an analytically tractable version of the model used by Yin {\it et.al.}, Phys. Rev. B{\bf 86}, 2399 (2012) to explain a nonFermi liquid behavior of iron chalcogenides and ruthenates in the intermediate energy region. It is suggested that the complete screening of the local degrees of freedom proceeds in two stages described by two characteristic temperatures $T_K^{orb} >> \epsilon^*$. The first energy scale marks a screening of the orbital degrees of freedom and the second one marks a crossover to the regime with coherent propagation of quasiparticles. Our calculations show that the latter regime is not a Landau Fermi liquid since the imaginary part of the electron self energy $\Im m\Sigma(\omega) \sim \omega^{b}, ~~ 1< b <2$.
Karyn Le Hur (Paris)
Title: Dissipative and NonEquilibrium SpinBoson Systems
Abstract: In this Talk, we focus on Entanglement and Dynamical properties of SpinBoson Systems consisting of Spins coupled to Bosonic Environments. The case of a boson bath with Ohmic dissipation will be thoroughly addressed with applications in Cold Atoms and Photon Systems for example. This case is particularly interesting since it reveals a quantum phase transition, nontrivial features in the spin dynamics and connections with other models such as the Kondo model and the Ising model with longrange forces. Entanglement properties of the system can be exactly evaluated using the Bethe Ansatz approach. Concerning driven SpinBoson systems, we apply the nonperturbative stochastic scheme discussed in the paper, P. P. Orth, A. Imambekov and K. Le Hur, Phys. Rev. B 87, 014305 (2013) and address a few applications.
Aditya Shashi (Rice)
Title: Interaction quench in the 1D Bose gas
Abstract: We obtain results on interaction quenches in a nonquadratic continuum system, the 1D Bose gas described by the integrable LiebLiniger model, and we show that in the long time limit integrability leads to significant deviations from the predictions of the grand canonical ensemble. I will briefly describe how we take into account the conserve charges associated with the integrability of the model to formulate the Generalized Gibbs Ensemble which correctly predicts the asymptotic steady state.
Anatoli Polkovnikov
Title: Classifying and measuring geometry of quantum phases
Abstract: Using transverse field Ising model as a primary example I will show that its phase diagram can be characterized using Riemannian geometry based on the FubiniStudy metric. I will show there are robust geometric invariants based on the integrated Gauss curvature, which are protected against small perturbations. I will show that one can classify critical points and special singular symmetry directions based on the independent of parametrization Gauss curvature. I will identify three generic types of singularities: removable, conical and curvature. At the end I will discuss how the metric tensor can be measured as a standard dynamical response and as a leading nonadiabatic response in energy.
Joerg Schmiedmayer (Vienna Center for Quantum Science and Technology (VCQ), Atominstitut, TUWien)
Title: How does an isolated 1d quantum system relax?
Abstract: One of the biggest challenges in probing nonequilibrium dynamics of manybody quantum systems is that there is no general approach to characterize the resulting quantum states. Interference experiments give access to the phase of the order parameter. The full distribution functions of the interference amplitude [1,2], and the full phase correlation functions allows us to study the relaxation dynamics in onedimensional quantum systems. Starting form a coherently split 1d quantum gas, the initial coherence slowly dies. Due to the approximate conserved quantities in our nearly integrable system, this relaxation leads to a prethermalized state [3], which is characterized by thermal like distribution functions but exhibits an effective temperature much lower than the kinetic temperature of the initial system. A detailed study of the correlation functions reveals that these thermallike properties emerge locally in their final form and propagate through the system in a lightconelike evolution [4].
[1] A. Polkovnikov, et al. PNAS 103, 6125 (2006); V. Gritsev, et al., Nature Phys. 2, 705 (2006);
[2] S. Hofferberth et al. Nature Physics 4, 489 (2008);
[4] M. Gring et al., Science 337, 1318 (2012); D. Adu Smith et al. NJP 15, 075011 (2013).
[5] T. Langen et al. Nature Physics DOI: 10.1038/nphys2739 (2013) arXiv:1305.3708.
Onlasyn Imambekov & Aigerim Kabdiyeva (Almaty)
Leonid Glazman (Yale)
Alexey Gorshkov (NIST)
Title: Propagation of information in systems with longrange interactions
Misha Lukin (Harvard)
Subir Sachdev (Harvard)
Title: Angular fluctuations of a multicomponent order describe the pseudogap regime of the cuprate superconductors
Abstract: The holedoped cuprate high temperature superconductors enter the pseudogap regime as their superconducting critical temperature, T_c, falls with decreasing hole density. Experiments have probed this regime for over two decades, but we argue that decisive new information has emerged from recent Xray scattering experiments. The experiments observe incommensurate charge density wave fluctuations whose strength rises gradually over a wide temperature above T_c, but then decreases as the temperature is lowered below T_c. We propose a theory in which the superconducting and chargedensity wave orders exhibit angular fluctuations in a 6dimensional space. The theory provides a natural quantitative fit to the Xray data, and is consistent with other observed characteristics of the pseudogap.
Mohhamad Hafezi (JQI Maryland)
J.S. Caux (University of Amsterdam)
Title: An exact solution for the BEC to repulsive interaction quench in the 1D Bose gas