Venue May 25-26, 2018 Physics and Math Building, room 128 Department of Physics Duke University, Durham, NC Organizers Thomas Barthel,  Gleb Finkelstein,  Eduardo Mucciolo,  Denis Ullmo Program Friday, May 25 8:30 Opening remarks 9:00 A. Douglas Stone  (Yale University, USA) "Mesoscopic correlations of diffusive light: Transmission and focusing through opaque media" Weak localization and mesoscopic fluctuations in electron transport taught us that coherence effects have a critical influence on the propagation of electron waves in normal metals at low temperatures. In particular, interference effects induced by self-crossing paths generate correlations between diffusing waves that do not exist for diffusing particles, leading to anomalously large fluctuations. Specifically, the phenomenon of Universal Conductance Fluctuations [1,2] would not occur without these correlations. A further extraordinary implication of these correlations is that there always exist sample-specific input states ("open channels") that will propagate with unit transmission through a phase coherent diffusive wire, despite its low average transmission, = lt/L <<1 (lt is the transport mean free path, L is the length of the wire). The prediction of open channels was impossible to test directly with electron waves due to the lack of control of the relevant input states. However, it was appreciated many years ago that similar effects occur in transmission of light through strong scattering and weakly absorbing media ("white paint"), and recent instrumental advances in optics have made it possible to synthesize complex input states using a Spatial Light Modulator and to attempt to control the propagation of light in diffusive media via such interference effects. Strong enhancements of focused transmission and total transmission through a nominally opaque white sample have been demonstrated [3-5]. To describe theoretically the optimal control of diffusing light it is necessary to generalize the standard random matrix theory of disordered conductors to account for the loss of control of an input beam due to transverse diffusion [5,6]. I will present results from recent experiments that demonstrate control of diffusing light in very good agreement with that theory. [1]  "Universal Conductance Fluctuations in Metals", P. A. Lee and A. D. Stone, PRL 55, 1622 (1985) [2]  "Correlations and Fluctuations of Coherent Wave Transmission Through Disordered Media", S. Feng, C. Kane, P.A. Lee and A. Douglas Stone, PRL 61, 834 (1988) [3]  "Universal Optimal Transmission of Light Through Disordered Materials", I. M. Vellekoop and A. P. Mosk, PRL, 101, 120601 (2008) [4]  "Coherent control of transmission of light through disordered media", S. M. Popoff, A. Goetschy, S. F. Liew, A. D. Stone, and H. Cao, PRL, 112, 133903 (2014) [5]  "Correlation effects in focused transmission through disordered media", C. W. Hsu, S.-F. Liew, A. Goetschy, H. Cao and A. D. Stone, Nat. Phys., 13, 497-502 (2017) [6]  "Filtering random matrices: The effect of imperfect channel control in multiple-scattering", A. Goetschy and A. D. Stone, PRL, 111, 063901 (2013) 9:30 Martina Hentschel  (Technical University of Ilmenau, Germany) "Mesoscopic optics - from billiards for light towards future photonic devices" The investigation of the propagation of light in mesoscopic systems is a rich subject ranging from billiards for light to new schemes for realizing directional emission from microcavity lasers. The concept of quantum-classical, here wave-ray, correspondence, proves to be as useful as for the originally studied electronic mesoscopic systems such as quantum dots. There are, however, deviations from the naive ray-picture expectation, for example in form of semiclassical deviations from Snell's law in the reflection and refraction of light at dielectric interfaces. We illustrate these effects and discuss their impact on the far-field emission characteristics of optical microcavities. The propagation of electromagnetic waves in realistic, three-dimensional optical microcavities requires to pay attention to the evolution of the light's polarization as a new degree of freedom. In systems like dielectric Möbius strips or cone-shaped microtube cavities, the polarization state of resonant whispering gallery-type modes may differ strongly from the reference case of homogeneous cylinders. Whereas we find that the polarization of the electromagnetic field follows the wall orientation in thin Möbius strips, thereby reflecting the accumulated geometric phase, we observe that light ignores the Möbius topology when the strip's thickness is increased. Breaking of symmetries further influences the morphology of resonances and can induce a transition from linear to elliptical polarization. In an outlook we will discuss the potential for applications like sensors emerging in the field of mesoscopic optics. 10:00 Evgenii Narimanov  (Purdue University, USA) "Optical hyperspace: Light in (meta) materials with hyperbolic dispersion" Metamaterials with hyperbolic dispersion (where two eigenvalues of the dielectric permittivity tensor have opposite signs) exhibit a broad bandwidth singularity in the photonic density of states, with resulting manifestations in a variety of phenomena, from spontaneous emission to light propagation and scattering. 10:30 Coffee break 11:00 Rodolfo Jalabert  (Université de Strasbourg, France) "The semiclassical tool for old and new problems of mesoscopic and quantum physics" The power of the semiclassical approximations is presented and illustrated through a few relevant examples: the quantum transport in nanostructures, the magnetic response of metallic nanoparticles, and the out-of-time order correlators of Hermitian operators. 11:30 Klaus Richter  (University of Regensburg, Germany) "Out-of-time-order correlators and post-Ehrenfest interference in quantum-chaotic many-body systems" Out-of-time-order correlation (OTOC) functions have recently received a lot of interest as tools to analyze the dynamics of interacting many-body systems and to quantify the scambling of information in these systems. They exhibit a characteristic exponential growth as a function of time until the Ehrenfest time, where they saturate. Following and extending semiclassical paths in condensed matter pioneered by Harold Baranger et al., we will show for quantum chaotic many-body (Bose-Hubbard) systems that this saturation arises from quantum interference effects. This is non-perturbatively achieved by expressing the OTOC in terms of coherent sums over interfering solutions of the corresponding classical mean-field equations, thereby including correlation effects. Moreover, we devise a semiclassical propagator for large-N Bose-Hubbard systems far-out-of equilibrium that allows us to calculate with high precision many-body quantum interference in Fock space on time scales far beyond the Ehrenfest time (work in cooperation with J. Rammensee, P. Schlagheck, S. Tomsovic, D. Ullmo, J.D. Urbina). 12:00 Bertrand Georgeot  (CNRS and Université Paul Sabatier, France) "Multifractality and nonergodicity in complex quantum systems" In many contexts, it is important to assess the ergodicity properties of quantum states, with important consequences for transport, quantum statistical mechanics or the quantum manifestations of classical chaos. Ergodic states are extended, with random-like fluctuations, while e.g. Anderson localized states or states of integrable systems are localized on specific regions of phase space. Multifractal states represent a specific type of nonergodic quantum states, associated to scale-invariant fluctuations. Several models where quantum wave functions display multifractal properties have been recently identified. The talk will review recent results on the effect of perturbation on multifractal states, and on the ergodicity of quantum states on random graphs. (work done in collaboration with R. Dubertrand, I. García-Mata, O. Giraud, G. Lemarié and J. Martin) 12:30 Lunch break 2:00 Pier Mello  (UNAM, Mexico) "Transport though disordered conductors and waveguides: the density inside the sample" The single-parameter scaling hypothesis relating the average and variance of the logarithm of the conductance is a pillar of the theory of electronic transport. We use a maximum-entropy ansatz to explore the logarithm of the energy density, ln W(x), at a depth x into a random one-dimensional system. Single-parameter scaling would be the special case in which x = L (the system length). We find the result, confirmed in microwave measurements and computer simulations, that the average of ln W(x) is independent of L and equal to -x/l, with l the mean free path. At the beginning of the sample, var[ln W(x)] rises linearly with x and is also independent of L, with a sublinear increase near the sample output. At x = L we find a correction to the value of var[ln T] predicted by single-parameter scaling. 2:30 Julia Meyer  (Université Grenoble Alpes, France) "Spontaneous spin polarization of non-equilibrium quasiparticles in mesoscopic superconductors" Experimentally, the concentration of quasiparticles in gapped superconductors always largely exceeds the equilibrium one at low temperatures. Since these quasiparticles are detrimental for many applications, it is important to understand the origin of the excess. We demonstrate that the dynamics of quasiparticles localized at spatial fluctuations of the gap edge becomes exponentially slow. This may give rise to the observed excess quasiparticles in the presence of a vanishingly weak nonequilibrium agent. Furthermore, we show that, in a mesoscopic system, the spin dependence of the recombination process may lead to the spontaneous polarization of the residual quasiparticles, if the spin relaxation is sufficiently slow. 3:00 Inanc Adagideli  (Sabanci University, Turkey) "Landau Levels and Equilibrium Chiral Magnetic Effect in a Weyl Superconductor" The massless fermions of a Weyl semimetal come in two species of opposite chirality, in two cones of the band structure. As a consequence, the current j induced in one Weyl cone by a magnetic field B (the chiral magnetic effect, CME) is cancelled in equilibrium by an opposite current in the other cone. Here we show that superconductivity offers a way to avoid this cancellation, by means of a flux bias that gaps out a Weyl cone jointly with its particle-hole conjugate. The remaining gapless Weyl cone and its particle-hole conjugate represent a single fermionic species, with renormalized charge e* and a single chirality set by the sign of the flux bias. As a consequence, the CME is no longer cancelled in equilibrium, but appears as a supercurrent response |dj/dB|=(ee*/h^2)mu along the magnetic field at chemical potential mu for a mesoscopic sample. For a macroscopic sample, the presence of the CME depends on whether the mixed phase of a gapless superconductor can support a Landau level, a celebrated problem in the context of d-wave superconductivity, with a negative answer. Here we show that the same question has a positive answer for a Weyl superconductor: The chirality of the Weyl fermions protects the zeroth Landau level by means of a topological index theorem. As a result, the heat conductance parallel to the magnetic field has the universal value G=g0 Phi/(2 Phi0), with Phi the magnetic flux through the system, Phi0 the superconducting flux quantum, and g0 the thermal conductance quantum and in the flux biased regime the chiral magnetic response becomes universal with value |dj/dB|=(e^2/h^2)mu. 3:30 Coffee break 4:00 Manuel Houzet  (CEA and Université Grenoble Alpes, France) "Andreev and Majorana Weyl crossings in multi-terminal Josephson junctions" We analyze the Andreev spectrum in a four-terminal Josephson junction between conventional and topological superconductors. We find that a topologically protected crossing in the space of three superconducting phase differences can occur between the two Andreev bound states with lower energy. We discuss the possible detection of this crossing through the nonlocal conductance quantization between two voltage-biased terminals. 4:30 Michael Wimmer  (Technical University of Delft, Netherlands) "Numerical transport simulations and how they can help Majorana experiments" I will give a brief introduction into how state-of-the-art numerical transport calculations work, and how they are implemented in the software package kwant. I will then give an example of how numerical transport calculations can give insight into current Majorana experiments and give some new insights how topological properties may be probed even with trivial states. 5:00 Gonzalo Usaj  (Bariloche Atomic Center, Argentina) "Topology in driven quantum systems: from graphene to Josephson junctions" Periodic time dependent potentials can induce topological properties in an otherwise topologically trivial material. Similar to ordinary topological insulators. the so-called Floquet topological insulators present a bulk gap in their (quasi-) energy spectrum and chiral states at their edges/surfaces or at the interfaces with other materials. In this talk I will discuss the paradigmatic example of graphene where we characterized the bulk topological properties and the hierarchy of chiral edge states that appear and show how they lead to a Hall signal. Finally, I will comment on how similar effects appear in a three-terminal Josephson junction with a quantum dot leading to a realization of a Haldane-like model. 5:30 Break / Duke Gardens tour 6:30 Banquet Saturday, May 26 9:00 Gergely Zaránd  (BME, Hungary) "Noise in a chargeless Fermi liquid" We study the charge of carriers close to the singlet-doublet (parity changing) transition of a superconductor-quantum dot- normal metal junction. Our goal is, in particular, to understand if this charge is influenced by strong interactions. As a first step, we establish a mapping to the Anderson model, and generalize Nozieres' Fermi liquid theory to this latter. We then use our generalized Fermi liquid theory to describe transport in the superconducting device. Though quasiparticles do not have a definite charge in the emerging "chargeless" Fermi liquid theory, a hidden U(1) symmetry - unrelated to the real charge of excitations - and a corresponding pseudo-charge still emerges. In contrast to other correlated Fermi-liquids, the back scattering noise reveals an effective charge equal to the charge of Cooper pairs, e* = 2e, which remains completely unrenormalized by interactions. We also predict a strong suppression of (non-linear) noise at resonance. 9:30 Mireille Lavagna  (CEA and Université Grenoble Alpes, France) "Emission noise in an interacting quantum dot: role of inelastic scattering and asymmetric coupling to the reservoirs" I will discuss the quantum current noise in an interacting quantum dot connected to two reservoirs with any symmetry of the coupling. The theory is developed based on the Keldysh non-equilibrium Green function technique. Both the current autocorrelators (inside a single reservoir) and the current cross-correlators (between the two reservoirs) are expressed as a function of the transmission amplitudes and of some effective transmission coefficients which include inelastic scattering contributions. The results are interpreted in terms of the transmission of an electron-hole pair to the concerned reservoir where it emits an energy after recombination. The interactions are then treated by solving the self-consistent equations of motion for the Green functions. We have found [1,2] that the noise derivative is zero until the voltage reaches a threshold value, set by the measuring frequency beyond which a Kondo peak appears when the system is in the Kondo regime. Our findings are discussed in the light of recent measurements performed in carbon nanotube quantum dots [3]. [1]  A. Crépieux, S. Sahoo, T.Q. Duong, R. Zamoum, and M. Lavagna, Phys. Rev. Lett. 120, 107702 (2018) [2]  R. Zamoum, M. Lavagna, and A. Crépieux, Phys. Rev. B 93, 235449 (2016) [3]  R. Delagrange, J. Basset, H. Bouchiat, and R. Deblock, Phys. Rev. B 97, 041412(R) (2018) 10:00 Harold Baranger  (Duke University, USA) "Many-body states through quantum noise: Rescuing a quantum phase transition and an unpaired Majorana zero mode" It is natural to suppose that decoherence produced by quantum noise will suppress quantum effects, and in particular inhibit or destroy interesting quantum states. In contrast, I shall discuss how quantum noise can be used as a resource to create delicate many-body states. My first example concerns two quantum dots in series with two resistive leads. The leads couple charge flow through the dots to the electromagnetic environment, the source of quantum noise. While charge transport inhibits a quantum phase transition, the quantum noise suppresses charge transport and restores the transition. For strong noise, it is similar to the fixed point of the two-impurity Kondo model. Second, I discuss a topological superconducting wire with a nonlocal fermion shared between its ends coupled to a quantum dot with resistive leads. It has been observed (Finkelstein group) that such a dot supports an effective two-channel Kondo (2CK) state in its charge degree of freedom. The decoupled Majorana degree of freedom associated with this 2CK state can hybridize with one Majorana of the non-local fermion. At the other end of the wire, one obtains a single decoupled Majorana zero mode. 10:30 Coffee break 11:00 Albert Chang  (Duke University, USA) "Tales from a long-time colleague, from quantum chaos to a search for Wigner "crystal" correlations in quantum point contacts" As one of the older colleagues to participate in this 60th birthday celebration for Harold, I have the opportunity to speak on the pleasure of having shared interests and having collaborated for over 30 years. In this 30 minute talk, I will briefly reivew three topics, on which we had collaborated back in the 1980's at Bell Labs, when we were both young and able: (i) quenching of the Hall resistance in ballistic junctions, (ii) weak localization in non-chaotic and chaotic cavities, and (iii) Coulomb blockade peak height distribution in quantum dots. I will then move onto a more recent topic, that of correlation in ballistic quantum point contacts. I will present evidence that perhaps, something unusual is happening apart from the "0.7" e^2/h effect, which at face value, does not appear to be caused by residual disorder. I will speculate that we might be seeing a hint of Wigner-crystal-like correlations, of the sort proposed by Matveev and Baranger and their colleagues. The unifying theme in all these topics is that in clean 2DEG's, such as in GaAs/AlGaAs heterostructures, geometry matters, whether in the presence or absence of interaction. The recent findings suggest that graphene systems would be an interesting direction to pursue for investigating correlations in the 1- to few channel limit. 11:30 Konstantin Matveev  (Argonne National Laboratory, USA) "Viscosity of one-dimensional quantum liquids" I will discuss viscous dissipation in a single-channel one-dimensional quantum liquid. This system is commonly described in terms of the Luttinger liquid theory, in which elementary excitations are non-interacting bosons. This simplest model does not describe relaxation of elementary excitations, and will be modified to account for the coupling of the bosonic degrees of freedom. The resulting theory is formulated in terms of excitations with Fermi statistics with very long life times. I will then apply this approach to the evaluation of the bulk viscosity of the system. Unlike the three-dimensional Fermi liquid, in which the bulk viscosity vanishes in the low temperature limit, our result diverges as 1/T^3. 12:00 Igor Aleiner  (Columbia University, USA) "Saturation of strong electron-electron umklapp scattering at high temperature" 12:30 Lunch break 2:00 Gilles Montambaux  (Université Paris-Sud, France) "Artificial graphenes: Dirac matter beyond condensed matter" After the discovery of graphene and its so many fascinating properties, there has been a growing interest for the study of "artificial graphenes". These are totally different and novel systems which bear exciting similarities with graphene. Among them are lattices of ultracold atoms, microwave or photonic lattices or "molecular graphene". The advantage of these artificial structures is that they serve as new playgrounds for measuring and testing physical phenomena which may not be reachable in graphene, in particular: the possibility of controlling the existence of Dirac points (or Dirac cones) existing in the electronic spectrum of graphene, of performing interference experiments in reciprocal space (Landau-Zener-Stückelberg interferometry), of probing geometrical properties of the wave functions, of manipulating edge states, etc. These cones, which describe the band structure in the vicinity of the two connected energy bands, are characterized by a topological "charge". They can be moved in reciprocal space by appropriate modification of external parameters (pressure, twist, sliding, stress, etc.). They can be manipulated, created or suppressed under the condition that the total topological charge be conserved. The merging between two Dirac cones is thus a topological transition that may be described by two distinct universality classes, according to whether the two cones have opposite or like topological charges. In this presentation, I will discuss several aspects of the scenarios of merging or emergence of Dirac points as well as the experimental investigations of these scenarios in condensed matter and beyond. 2:30 Ribhu Kaul  (University of Kentucky, USA) "Interaction induced Dirac fermions in bilayer graphene" We revisit the effect of local interactions on the quadratic band touching (QBT) of Bernal stacked bilayer graphene models using renormalization group (RG) arguments and quantum Monte Carlo simulations of the Hubbard model. We present an RG argument which predicts, contrary to previous studies, that weak interactions do not flow to strong coupling even if the free dispersion has a QBT. Instead they generate a linear term in the dispersion, which causes the interactions to flow back to weak coupling. Consistent with this RG scenario, in unbiased quantum Monte Carlo simulations of the Hubbard model we find compelling evidence that antiferromagnetism turns on at a finite U/t, despite the U=0 hopping problem having a QBT. The onset of antiferromagnetism takes place at a continuous transition which is consistent with a dynamical critical exponent z=1 as expected for 2+1 d Gross-Neveu criticality. We conclude that generically in models of bilayer graphene, even if the free dispersion has a QBT, small local interactions generate a Dirac phase with no symmetry breaking and that there is a finite-coupling transition out of this phase to a symmetry-broken state. 3:00 Thomas Barthel  (Duke University, USA) "Typical 1d quantum systems at finite temperatures can be simulated efficiently on classical computers" It is by now well-known that ground states of gapped one-dimensional (1d) quantum-many body systems with short-range interactions can be studied efficiently using classical computers and matrix product state techniques. A corresponding result for finite temperatures was missing. For 1d systems that can be described by 1+1d field theory, I show that the cost for the classical simulation at finite temperatures grows in fact only polynomially with the inverse temperature and is system-size independent -- even for gapless systems. In particular, the thermofield double state (TDS), a purification of the equilibrium density operator, can be obtained efficiently in matrix-product form. The argument is based on the scaling behavior of Rényi entanglement entropies in the TDS. At finite temperatures, they obey the area law. For gapless conformally invariant systems, the Rényi entropies are found to grow only logarithmically with inverse temperature. The field-theoretical results are tested and confirmed by quasi-exact numerical computations for integrable and non-integrable spin systems, and interacting bosons. [1]  T. Barthel, arXiv:1708.09349 (2017) 3:30 Coffee break 4:00 Serge Florens  (CNRS and Université Grenoble Alpes, France) "Exploring many-body non-linear effects in superconducting waveguides" I will present a generic platform to engineer bosonic impurity models in the context of superconducting waveguides. Long Josephson arrays coupled to non-linear elements (such as transmon qubit, or small Josephson "defects") are investigated experimentally, and studied theoretically by a mixture of quantum modeling and classical microwave simulation tools. Advanced many-body techniques based on multimode coherent states are also developed to account for non-linear dynamical processes at ultra-strong coupling. We illustrate this method on particle production in a scattering setup beyond the linear response, and demonstrate that non-particle conserving processes dominate the inelastic response. 4:30 Amit Ghosal  (IISER Kolkota, India) "Glassy behavior associated with melting of two-dimensional Coulomb clusters" We present responses of a small number of Coulomb-interacting particles in two-dimensional confinements, across the crossover from their solid- to liquid-like behaviors. Here, irregular confinements emulate the role of disorder. Focusing first on the thermal melting, where zero-point motion of the particles are frozen, we explore the signatures of a "hexatic-glass" like behavior. While static correlations, which investigate the translational and bond orientational order [1,2], indicate a hexatic-like phase at low temperatures, dynamical correlations show considerably slow relaxations. Using density correlations we probe intriguing inhomogeneities arising from the interplay of the irregularity in the confinement and long-range interactions. The relaxation at multiple time scales show stretched-exponential decay of spatial correlations for Coulomb-particles in irregular traps [1,3]. Temperature dependence of characteristic time scales, depicting the structural relaxation of the system, show strong similarities with those observed for the glassy systems. Our results indicate that some of the key features of supercooled liquids emerge in confined systems. more so with irregular confinements. The analysis of normal modes [4] elucidates how long time behavior of the system is encoded in the quasi-localized modes. Time permitting, we extend our discussions to include the effects of quantum fluctuations. Our results, using quantum Monte Carlo techniques for Boltzmann particles, seem to indicate complementary mechanism for the quantum and thermal crossovers in Wigner molecules [5]. We will also discuss our recent analyses upon including the effects of quantum statistics. [1]  B. Ash, J. Chakrabarti and A. Ghosal, Phys. Rev. E 96, 042105 (2017) [2]  D. Bhattacharya and A. Ghosal, Eur. Phys. J. B 86, 499, (2013) [3]  B. Ash, J. Chakrabarti and A. Ghosal, Euro. Phys. Lett., 114, 4, (2016) [4]  B. Ash, C. Dasgupta and A. Ghosal (Preprint) [5]  D. Bhattacharya, A. V. Filinov, A. Ghosal and M.Bonitz, Eur. Phys. J. B 89, 60, (2016) 5:00 Shailesh Chandrasekharan  (Duke University, USA) "The bag approach to strongly correlated fermions" The auxiliary field method is the traditional method of choice to perform quantum Monte Carlo calculations in strongly correlated fermion systems. Over the past decade we have developed an alternate method, called "the fermion bag approach" that is complementary to the auxiliary field method. In this talk we discuss the essential ideas behind this approach and show how it allows us to solve some sign problems that seem impossible to solve with the auxiliary field methods. We also show some results from large scale Monte Carlo calculations near a semi-metal-insulator transition that were obtained using the bag approach. 5:30 Closing remarks have a nice day!