Special Seminar

מארגן/מארגנים: 
מארגן/מארגנים: 
Usual Time: 
Place: 

Previous Lectures

Dr. Yuval Ronen
06/07/2017 - 12:30

 In recent years, efforts to observe helical edge states in materials with large spin-orbit coupling have accelerated. These material, once in proximity to an s-wave superconductor may, under certain conditions, manifest a topological superconductive (TS) phase [1]. Consequently, Majorana fermions, allusive quasiparticles with a non-Abelian exchange statistic, are expected to emerge. Even more interesting are the fractional helical states, previously not observed, which manifest the more exotic para-fermion anyons. Though evidence for the presence of Majorana fermions accumulates, observations of helical edge transport, being a prerequisite for the formation of Majorana quasiparticles, are scarce. Encouraged by proposals that induce topological superconductivity in 2DEG at the quantum Hall effect (QHE) regime [2, 3], we succeeded to form such, the sought after, robust chiral helical edge modes in GaAs-AlGaAs heterostructures.In order to have two adjacent counter-propagating edge modes with opposite spin, the 2DEG is embedded in a unique quantum well structure, which hosts two weakly interacting electronic sub-bands. Gating the 2DEG with two half-plain gates, enable a scenario where two different filling factors are applied to the lower and upper sub-bands. Landau levels of different sub-bands cross at the interface between the two gates; thus forming overlapping, counter-propagating, chiral edge modes. Two counter-propagating edges with opposite spins, both in the integer and fractional regime were observed, propagating for more than 300 microns without mixing. In addition, spin protected tunneling was observed depending on spin orientation.

[1] L. Fu and C. Kane, PRL 100, 096407 (2008).

[2] N.H. Lindner, E. Berg, G. Refael and A. Stern, PRX 2, 041002 (2012).

[3] D.J. Clarke, J. Alicea and K. Shtengel, Nature. Communication 4, 1348 (2013).

QUEST Center event
Sir Michael Pepper
03/07/2017 - 12:00

It will be shown that the well known technique of Magnetic Focussing can be used to probe the spin configuration in a one dimensional electron channel. Spin polarization occurs which can be controlled by geometry, the relation to the 0.7 structure will be discussed. When the confinement is relaxed a single line of electrons will relax into two or more rows and here it will be shown that this can be detected and spin texture explored.

Prof. Richard Schoen ,University of California
08/06/2017 - 16:20

This will be a general lecture about the role that the scalar curvature plays in geometric problems. In particular, we will highlight connections to the Einstein equations and questions which arise from the physical side. We will also describe recent results which resolve some old issues in the subject.

Prof. David N. Jamieson
21/02/2017 - 14:00

Ion implanted phosphorus (31P) atoms in isotopically pure silicon devices have driven a sequence of discoveries reporting exceptionally long coherence times for the 31P nuclear spin quantum bit [1-4] with coherence times longer than 30 s [2].  To make the devices used for this work, a small number of 31P atoms are implanted into a nano-scale construction site on a 28Si substrate that is later surrounded by nanocircuitry for programming and read out of the qubit.   Post-implant donor selection by tuning gate electrodes is used to select a single 31P donor atom for the experiments.  However the next step requires achieving the key milestone of qubit entanglement in an ordered array of 31P dopant atoms placed with nanometer precision.  Deterministic implantation of atoms into such arrays is possible by counting the ion-implantation-induced transient pulse of electron-hole pairs created in the substrate that incorporates suitable detector electrodes.  The detector electrodes produce a gate pulse signalling the implantation of single ions that have a random arrival time.  Achieving the required spatial precision is difficult owing to straggling and channelling effects.  This can be addressed by low energy (<10 keV) implantation of 31P ions, but in this regime the signal from the generation of  electron-hole pairs in the substrate is close to the noise threshold of present charge-sensitive electronics.  This method could also be extended for the deterministic placement of colour centres in diamond provided the implanted-ion to colour-centre conversation problem is solved.  This presentation shows how these challenges are being addressed [5] both within CQC2T and in parallel developments in the UK, EU and USA.  Within CQC2T our approach will take this technology to the next stage by building deterministic arrays of single atoms with the goal of 6 nm positioning precision in new architectures that could form the building blocks of a future CMOS quantum computer fabricated with the standard tools of the semiconductor industry.

[1] Bell's inequality violation with spins in silicon, JP Dehollain, et al., Nature Nanotechnology 11 p242 (2016)

[2] Storing quantum information for 30 seconds in a nanoelectronic device, JT Muhonen, et al. Nature Nanotechnology 9, p986 (2014)

[3] High-fidelity readout and control of a nuclear spin qubit in silicon, JJ Pla, et al., Nature 496, p334 (2013)

[4] A single-atom electron spin qubit in silicon, JJ Pla, et al., Nature 489, p541 (2012)

Single-shot readout of an electron spin in silicon, A Morello, et al., Nature 467, p687 (2010)

[5] Single atom devices by ion implantation, JA van Donkelaar, et al., J. Phys. Cond. Mat. 27, 154204 (2015)

 

 

Dr. I. Protopopov, University of Geneva
13/02/2017 - 12:00

The many-body localized (MBL) phase is characterized by a complete set of quasi-local integrals of motion and area-law entanglement of excited eigenstates. We study the effect of non-Abelian continuous symmetries on MBL, considering the case of $SU(2)$ symmetric disordered spin chains. The $SU(2)$ symmetry imposes strong constraints on the entanglement structure of the eigenstates, precluding conventional MBL. We construct a fixed-point Hamiltonian, which realizes a non-ergodic (but non-MBL) phase characterized by eigenstates having logarithmic scaling of entanglement with the system size, as well as an incomplete set of quasi-local integrals of motion. We study the response of such a phase to local symmetric perturbations, finding that even weak perturbations induce multi-spin resonances. We conclude that the non-ergodic phase is generally unstable and that $SU(2)$ symmetry implies thermalization. The approach introduced in this work can be used to study dynamics in disordered systems with non-Abelian symmetries, and provides a starting point for searching non-ergodic phases beyond conventional MBL.

 

Prof. Alexander Mirlin, University of Karlsruhe, Germany
30/11/2016 - 13:00 - 14:30

I will discuss the delocalization in a many-body system due to a power-law interaction. One experimentally relevant realization of this problem is the effect of Coulomb interaction in Anderson insulators. Particle-hole excitations built on localized electron states are viewed as two-level systems (“spins”) randomly distributed in space and energy and coupled due to electron-electron interaction. A small fraction of these states form resonant pairs that in turn build a complex network allowing for energy propagation. We identify the character of energy transport and evaluate the spin relaxation rate and the thermal conductivity. For physically relevant cases of two-dimensional and three-dimensional spin systems with 1/r^{3} dipole-dipole interaction (originating from the conventional 1/r Coulomb interaction between electrons), the found thermal conductivity κ scales with temperature as κ ∝ T^{3} and κ ∝ T^{4/3}, respectively. Our results are of relevance also to other realizations of random spin Hamiltonians with long-range interactions. We also determine the delocalization threshold for a finite-size system (“quantum dot” with localized single-particle states and power-law interaction). In this context, I will discuss a connection of this problem with Anderson localization on random regular graphs.  

Yossi Cohen
22/11/2016 - 10:30 - 11:30

The Poisson equation appears in many physical processes including electrostatics, fluid dynamics and fracture mechanics. Yet, pattern formation processes involving Poisson dynamics are not well-understood. Here we present a criterion for path selection for growing channels. We show that the growth of a channel in a Poisson field follows local symmetry in order to maximize the flux in its vicinity. We then use this criterion to reconstruct the history of a real network and to find the growth law associated with it. We also identify a cause for instability that results in a ramified structure in which the golden ratio prevails.

David E. Clemmer
25/07/2016 - 12:00

It is well accepted that a measurement of an ion's mobility through an inert gas can be compared with calculated mobilities for trial geometries to obtain insight about the abundances and overall shapes of specific ions. In these studies, energy can be added to induce structural transitions and follow changes in the abundances of different conformations that are favored before and after activation. Here, we extend this idea as a means of following structural transitions in solution, examining the well-studied model systems: bradykinin and polyproline. Our approach is to vary the solution composition from which ions are electrosprayed. Overall, we conclude that in some cases it appears that the solution phase structures are more or less preserved in the gas phase; in other cases, new structures are favored in the gas phase –but, these can be mapped back in order to obtain insight about populations of states that were favored in solution. In the case of bradykinin, we find evidence for ~10 different solution phase states that vary in abundance as the solution composition is changed. These populations largely arise from variations in the cis- and trans-configurations of three proline residues in the nonapeptide sequence. The polyproline system provides a chance to study such transitions in detail. When in relatively non-polar solvents such as propanol, polyproline forms a compact type PPI helix; when placed in water the polymer undergoes a series of cis-trans interconversions to produce a type PPII helix, in which water molecules intercalate along the peptide backbone, stabilizing a much more extended structure in solution. We find that although the PPII helix collapses in the gas phase, IMS-MS techniques provide an ideal means of studying the step-by-step transitions that connect these different structures.

Isao H. Inoue, National Institute of Industrial Science and Technology (AIST), 305-8565 Tsukuba, Japan
22/06/2016 - 12:00

Most of the people in the world have not given it a thought that our fully electronics-depended society is now really confronted a fatal problem called “miniaturisation limit” of transistors. By the time of Tokyo Olympic in 2020, it is anticipated a typical dimension of the transistor would reach 10 nm. Then, the channel contains only about 10 chemical dopants (origin of carriers), and the switching energy becomes smaller than the thermal noise limit (100 kBT ); “on/off” states are no more distinguished. The saviour from such a looming crisis is nothing but to use a chemical-doping-free FET, and to develop such electronics beyond the present Si ones is indeed an urgent challenge for condensed matter physicists.

In this talk, we demonstrate an ex- ample:   by  applying  an  electric  field, a quite insulating ‘non-doped’ SrTiO3 shows a two dimensional (2D) insulator- metal transition at the surface, and it actu- ally works as an excellent field effect tran- sistor (FET) with sufficiently good sub-threshold swing (170 mV/decade) and very large carrier mobility (10 cm2/Vs). 

SrTiO3 is well-known for its defect-prone surface, but by inserting a thin (6 nm) organic insulator Parylene-C between thesurface and the high-k gate insulator HfO2, we can avoid any damages on the surface during the device fabrication as well as during the application of the gate voltage. This clean interface between Parylene-C and SrTiO3 is not only promising for the electronic application of the SrTiO3-FET but also unexpected intriguing electronic properties of the SrTiO3 surface are getting revealed one after another.  We can accumulate 2D carriers more than 1014 cm2, which is surprisingly beyond the value expected from the capacitance of the gate insulator (the phenomenon is called “negative capacitance”[1]. By increasing the gate voltage VG, the channel resistance decreases, and the tem- perature dependence exhibits a clear insulator to metal transition with the boundary at the quantum resistance. Metallic channel shows the Kondo effect at low temperatures, as well as an anomaly of the Hall effect without hysteresis is accompanied. All these results suggest consistently the lifting of the three-fold degenerate t2g band, which is most probably caused by a strong Rashba effect at the surface. We will explain these phenomena with the experimental data, and discuss on the rich physics behind them.

[1] N. Kumar, A. Kitoh and I. H. Inoue, Scientific Reports 6, 25789 (2016).

Isao H. Inoue received BSc, MSc, and DSc degrees in Physics from the University of Tokyo in 1990, 1992 and 1998, respectively. He became a tenure researcher of the Electrotechnical Laboratory (ETL) in 1992 and a senior researcher in 1999. From 1999 to 2001, he was a visiting scholar at Cavendish Laboratory, University of Cambridge. In 2001, ETL was re-organized to the National Institute of Advanced In- dustrial Science and Technology (AIST); since then, he has been a senior researcher of AIST. He studied in a wide range of research field: from the high-energy spec- troscopies and fermiology of strongly correlated materials to the development of the Mott transistor, ReRAM, and other electronic devices, which utilise functional oxides, where electron correlations play a crucial role.

 

Prof. Igor Aronson , Materials Science Division Argonne National Laboratory
29/05/2016 - 14:00

Bacteria are among the oldest and most abundant living species on Earth, and their activity influences the planet’s environmental dynamics in multiple ways. Bacteria often migrate en masse over large distances, moving in dense groups in a highly organized, collective fashion known as “swarming motility.” The flow dynamics of dense bacterial colonies can be very complex and, because of the interaction between the bacteria and the fluid, remarkably different from those predicted by conventional fluid models. In particular, turbulent swimming patterns often emerge, characterized by chaotic motions and the formation of vortices, even in situations where liquids should exhibit laminar flow. But these complex phenomena are difficult to characterize experimentally, and a predictive model that describes them has not emerged to date. Additional complications arise when the suspending medium is anisotropic exemplified by lyotropic liquid crystals. In my talk I will survey the most recent progress in experimental and theoretical studies of manipulation of bacterial swimming trajectories in liquid crystals1,2 We also demonstrated that shear flow created by rotating magnetic particle leads to surprisingly rapid depletion of bacterial concentration near the particle3. Our observation highlights that the expulsion of bacteria is not caused by the centrifugal forces but rather a non-trivial interplay between shear induced alignment and locomotion of bacteria.

 

References

1. S. Zhou, A. Sokolov, O.D. Lavrentovich, and I.S. Aranson, PNAS 111, 1265 (2014)

2. A. Sokolov, S. Zhou, O.D. Lavrentovich, and I.S. Aranson, Phys. Rev. E 91, 013009 (2015)

3. A. Sokolov and I.S. Aranson, Nature Communications, 2016

 

Dvira Segal from Uni of Toronto
22/12/2015 - 12:00

I will describe our research interests in the area of quantum dynamics and molecular conduction. I will present two seemingly simple models for charge and heat transfer in molecular junctions and discuss our efforts in developing and benchmarking appropriate simulation tools. The first model concerns charge transfer in a two-site electronic junction with electron-vibration interaction effects and energy dissipation to secondary phonons [1]. The second model, the so called nonequilibrium spin-boson model, allows us to study principles of quantum energy flow in anharmonic systems [2].

I will outline different methodologies that we have been advancing for calculating transport characteristics in these interacting models: An iterative influence functional path integral approach and perturbative tools, quantum master equation, the nonequilibrium Green's function approach. I will explain our efforts in developing these methods in a consistent manner, and exemplify nontrivial function, diode behavior, thermoelectric energy conversion, and negative differential thermal conductance.


[1] B. K. Agarwalla, J.-H. Jiang and D. Segal,
Full counting statistics of vibrationally-assisted electronic conduction: transport and fluctuations of the thermoelectric efficiency,
arXiv:1508.02475, Phys. Rev. B in press.

[2] N. Boudjada and D. Segal,
From dissipative dynamics to studies of heat transfer at the nanoscale: Analysis of the spin-boson model,
J. Phys. Chem. A, 118 (47), 11323-11336 (2014).

Prof. Igor Lukyanchuk ,University of Picardie, Amiens, France
28/10/2015 - 14:00 - 15:00

Functionalization of ferroelectric materials emerged the growing interest in exploration of such nano-scale self-organized structures as polarization domains. For a long time it was believed that the regular domain patterns can appear only in ferromagnetic systems.

However, it was convincingly demonstrated over the last decade that the steady Landau-Kittel polarization domains do arise in the nano-scale strained films, superlattices nanoroads and nanodots.
Several recent results concerning their dynamic and static properties will be reviewed.
First, we consider the formation of domains in ultrathin films and superlattices of ferroelectric oxides and report a comprehensive description of their electrodynamic response. In particular we demonstrate that the field-induced domain wall motion can be in the origin of the recently observed fascinating “negative capacitance effect” effect.
Then, we show that the frequency-dependent permittivity of such system reveals the collective resonance mode in the near-terahertz frequency range that can be excited and detected by the methods of reflection absorption spectrometry. This finding can provide an important impact for the development of the ferroelectric-based terahertz optics and plasmonics.
Finally we consider the unconventional multibit polarization switching in ferroelectric nanodots, with formation of the intermediate domain states or/and chiral polarization skyrmions that can be useful for design of the memory-storage devices.

Dmitri Feldman
21/09/2015 - 14:00 - 15:00

Several topological orders have been proposed to explain the quantum Hall plateau at ν=5/2. The observation of an upstream neutral mode on the sample edge [Bid et al., Nature (London) 466, 585 (2010)] supports the non-Abelian anti-Pfaffian state. On the other hand, the tunneling experiments [Radu et al., Science 320, 899 (2008); Lin et al., Phys. Rev. B 85, 165321 (2012); Baer et al., Phys. Rev. B 90, 075403 (2014) ] favor the Halperin 331 state which exhibits no upstream modes. We find a topological order, compatible with the results of both types of experiments. That order allows both finite and zero spin polarizations. It is Abelian but its signatures in Aharonov-Bohm interferometry can be similar to those of the non-Abelian Pfaffian and anti-Pfaffian states. 

Prof. Daniel J. Gauthier
07/09/2015 - 10:30

The field of quantum information science aims to leverage the properties of quantum mechanics to realize new approaches for computing and communication.  In this presentation, I will review the basic building blocks of a classical optical communication system.  From there, I will describe a communication system in which the photonic wavepackets have less than one photon - and hence entering the quantum regime.  Surprisingly,  the number of bits that can be encoded on a single quanta is nearly limitless.  I will show how this property, along with the indistinguishability of certain quantum states, can be used to realize a quantum communication system for sharing a secret key between two parties.  This system is secure against an attack by an eavesdropper due to the fundamental properties of quantum mechanics.

Dr. Yaron Caspi, bio-nanoscience department of the Technical University of Delft
23/08/2015 - 12:00

The Min system is one of the two known mechanisms that are responsible for the accurate positioning of the division apparatus in Escherichia coli. Quite fascinatingly, the Min proteins achieve this by forming a dynamic concentration gradient that shuttles constantly from pole to pole. It is believed that this behavior depends only on the mutual interaction of three components - two proteins and the cell membrane. One of the important features of the Min system is its typical length scale of a couple of microns. Extensive research in the past years resulted in a detailed mathematical model that can reproduce the in vivo Min system behavior quite accurately.

However, reconstituted in vitro studies have resulted in the formation of patterns such as surface waves and oscillations that – though fascinating in its own right – have a typical length scale that is an order of magnitude larger that the in vivo observed one. It is highly important to understand this difference, both from a basic-science point of view and if one wants to use this system in the context of synthetic cells.

We study the Min system behavior in fully enclosed microfluidic compartments (coated with a supported lipid membrane). This setup enables us for the first time a full control on the characteristics of the system. We show that the compartment geometry is a major determinant of the dynamical mode that the system will adopt. We find that dominant mode in the major part of the phase diagram are spirals. Waves is the dominate behavior only for long or large chambers while oscillations is the dominate mode for narrow chambers or these with a large aspect ratio. Notably, the geometrical phase-diagram that we discover does not correspond to the in vivo observed behavior. Various additional parameters such as the temperature and crowding of the bulk media or of the membrane do not bridge the gap between the in vivo vs. in vitro pattern formation differences.

Our results strongly suggests that in spite of the good correspondence between the mathematical model and the in vivo behavior of the Min system, we still lack a real understanding of this important model system. In particular, we suggest that additional components probably contribute to the Min system dynamical pattern formation in vivo. 

Alexander Figotin
06/07/2015 - 10:30

Plasmonics has grown in recent years into a well established area of research with a great potential. Our interest to this area roots in mechanisms involved in plasmonic resonance responses and implied pretty narrow spatial dimension range between 1nm and 25nm. We entertain an idea that the very existence of surface plasmons with sizes in that range suggest a possibility of a new fundamental scale such as the size 5nm of a free electron in our neoclassical theory. This theory features a new spatial scale - the size a_e of a free electron. This scale is special to our theory and does not appear in either classical EM theory nor in the quantum mechanics where electron is always a point-like object. Our current assessed value for this scale is a_e≈100a_B where a_B is the Bohr radius, and consequently a_e≈5 nm. In our theory any elementary charge is a distributed in space quantity. Its size is understood as the localization radius which can vary depending on the situation. For instance, if an electron is bound to a proton in the Hydrogen atom then its the size of is approximately 1 Bohr radius, that is a_B≈0.05 nm, and when the electron is free its size is

a_e≈100a_B≈5 nm.

Interestingly, the upper bound 25 nm is the skin depth and that implies that a nanosystem of size smaller than 25nm is transparent to the external field. The same transparency should hold for a nanostructured surface indicating such a surface is better for nearly ideal field electron emission. There is an experimental evidence showing that the highest current densities were obtained for nanotips with sizes ∼1nm yet another important fact supporting a possibility of a fundamental nonoscale.

Dr. Oleg Gang, Center for Functional Nanomaterials, Brookhaven National Laboratory
22/06/2015 - 16:00

In the last decades nanoscale inorganic objects emerged as a novel type of matter with unique functional properties and a plethora of prospective applications. Although a broad range of nano-synthesis methods has been developed, our abilities to organize these nano-components into designed architectures and control their transformations are still limited. In this regard, an incorporation of bio-molecules into a nano-object structure allows establishing highly selective interactions between the components of nano-systems. Such bio-encoding may permit programming of complex and dynamically tunable systems via self-assembly: biomolecules act as site-specific scaffolds, smart assembly guides and reconfigurable structural elements.

I will discuss our advances in addressing the challenge of programmable assembly using the DNA platform, in which a high degree of addressability of nucleic acids is used to direct the formation of structures from nanoscale inorganic components. Our work explores the major leading parameters determining a structure formation and methods for creating targeted architectures. The principles and practical approaches developed by our group allow for assembly of well-defined three-dimensional superlattices, two-dimensional membranes and finite-sized clusters from the multiple types of the components. I will also discuss how interplay of polymeric and colloidal effects can result in the novel interactions effects in these systems.  Our recent progress on the assembly by-design, including super-lattices with pre-defined crystallographic symmetries and particle clusters with pre-determined architectures will be demonstrated.  Finally, I will present several approaches for the dynamical control of assemblies, which allow for the post-assembly structural manipulation and selective triggering of system transformations. 

 Research is supported by the U.S. DOE Office of Science and Office of Basic Energy Sciences under contract No. DE-AC-02-98CH10886.

Justin Wells, Trondheim University
15/06/2015 - 15:00 - 16:00
From its origins as a curious illustration of the photo-electric effect (Einstein, ca. 1905) and later as a tool for chemical analysis (Siegbahn, ca. 1967), photoemission spectroscopy has more recently developed into a very versatile tool for solid state physics. A continually improving understanding, paralleled by continually improving instrumentation is both increasing the prominence of photoemission, and broadening its relevance.

In this talk, I will use our recent research to illustrate a broad range of photoemission-based techniques: 

1. The role of XPS and resonant XPS in understanding materials as diverse as graphene, chemotherapy drugs [1] and intermediate band photovoltaics.

2. ARPES as a tool for understanding surface and non-surface localised confined states for organic electronics and quantum computation applications [2].

3. Spin-resolved ARPES for a fundamental understanding of topological insulators and spin-orbit coupled systems [3,4].

4. Engineering novel confined systems using photoemission microscopy, and 

5. Creating and understanding novel phonon interactions through a combination of ARPES, many-body simulations and transport measurements [5,6].

 
References:
[1] Silver catalyzed Fluorouracil degradation; a promising new role for graphene, Mazzola et al., arXiv preprint arXiv:1411.2096 and 2D materials, accepted (2015).
 
[2] Valley Splitting in a Silicon Quantum Device Platform, Miwa et al., Nano letters 14 (3), 1515-1519 (2014)
 
[3] One-dimensional spin texture of Bi (441): Quantum spin Hall properties without a topological insulator,  Bianchi, et al., Physical Review B 91:165307 (2015)
 
[4] Direct observation of spin-polarized bulk bands in an inversion-symmetric semiconductor, Riley et al., Nature Physics 10 (11), 835-839 (2014)
 
[5] Kinks in the σ Band of Graphene Induced by Electron-Phonon Coupling, Mazzola et al., Physical review letters 111 (21), 216806 (2013)
 
[6] Disentangling phonon and impurity interactions in δ-doped Si (001), Mazzola et al., Applied Physics Letters 104 (17), 173108 (2014).
Adar Sonn-Segev School of Chemistry, Tel Aviv University
10/06/2015 - 10:30 - 11:50

The viscoelastic response of actin networks is length- and time-scale dependent, encoding information on intrinsic dynamic correlations and mesoscopic structure. Over sufficiently large distances the network responds as a continuous medium, characterized by frequency-dependent viscoelastic moduli. But how large should the distance be for this asymptotic bulk limit to hold?

We report the observation of a large-distance intermediate response in an experimental system of F-actin networks. The tools of 1-point and 2-point microrheology were used to characterize the local and distance-dependent responses of the actin networks, respectively. The 2-point response at intermediate distances, arising from the effect of mass displacement rather than momentum diffusion, is enhanced by the much softer local microenvironment of the tracers compared to the bulk properties of the gel. Consequently, the cross-over to the bulk behavior is pushed to surprisingly large distances, much larger than the mesh size, , of the actin gel.

By developing a new analysis scheme for microrheology experiments, combining both 1-point and 2-point measurements, we were able to characterize the intermediate response, which in turn allows extracting the material’s structural properties. We use this newfound understanding to extract structural information of active in-vitro reconstituted cytoskeleton networks, in which such analysis can be done in a controlled fashion.

Gabriel Seiden (Max Planck Institute for the Physics of Complex Systems, Dresden, Germany)
10/03/2015 - 12:00

Geographic tongue (GT) is a medical condition affecting approximately 2% of the population, whereby the papillae (i.e., tiny hair-like protrusions) covering the upper part of the tongue are lost due to a slowly expanding inflammation. The resultant dynamical appearance of the tongue has striking similarities with well known out-of-equilibrium phenomena observed in excitable media, such as forest fires, cardiac dynamics and chemically driven reaction-diffusion systems. Here we explore the dynamics associated with GT from a dynamical systems perspective, utilizing cellular automata simulations. Our results shed light on the evolution of the inflammation and suggest a practical way to classify the severity of the condition, based on the characteristic patterns observed in GT patients.

Prof. Benjamin Lev, Stanford University
25/01/2015 - 14:00

Investigations of many-body physics in an AMO context often employ a static optical lattice to create a periodic potential. Such systems, while capable of exploring, e.g., the Hubbard model, lack the fully emergent crystalline order found in solid state systems whose stiffness is not imposed externally, but arises dynamically. We will discuss our multimode cavity QED experiment to explore the spontaneous continuous symmetry breaking observed in compliant crystallization, providing an environment to observe effects pertinent to soft condensed matter systems including frustration and liquid crystalline topological defects concomitant with superfluidity. Associative memory and spin-glasses also may form due to cavity-mediated long-range, oscillatory, and frustrated spin-spin interactions

This is the first time that Prof. Lev comes to Israel and an exceptional occasion to meet it.

To schedule a meeting with the speaker: doodle.com/zk7cgrbtfrcpeq28

Local contact: Emanuele Dalla Torre, Emanuele.dalla-torre@biu.ac.il

More info: “LevLab Where Quantum Matters” – levlab.stanford.edu

 

Mordecai D. Rosen, Lawrence Livermore National Laboratory
30/12/2014 - 10:00 - 12:30

ההרצאה תועבר בשני חלקים בנות 45 דקות כל אחת עם הפסקה של כ- 10 דקות ביניהן.

 

Prof. Arjun Yodh, University of Pennsylvania
29/10/2014 - 11:00

I will discuss soft matter experiments with colloidal suspensions which reveal new phenomena associated with a surprisingly broad range of problems. Some of these experiments, for example, have enabled us to learn about first steps of crystal melting [1] and about intermediate steps of solid-solid phase transitions [2]. Other experiments explore the ways in which colloidal particle shape can modify the so-called coffee ring effect [3].

References
[1] A.M. Alsayed, M.F. Islam, J. Zhang, P.J. Collings, A.G. Yodh, Science 309, 1207 (2005).
[2] Peng Y, Wang F, Wang Z, Alsayed AM, Zhang Z, Yodh AG, Han Y. Nat Mater. 2014 Sep 14. doi: 10.1038/nmat4083.
[3] P.J. Yunker, T. Still, M. Lohr, Yodh, A.G., Nature 476, 308 (2011); P.J. Yunker, M. Gratale, M. Lohr, T. Still, T. C. Lubensky, A.G. Yodh, Phys. Rev. Lett. 108, 228303 (2012); P.J. Yunker, M. Lohr, T. Still, A. Borodin, D.J. Durian, A.G. Yodh, Phys. Rev. Lett. 110, 035501 (2013). 
Prof. Yodh is one of the scientific leaders in the field of colloidal physics, as also in a whole bunch of other soft-matter-related fields. His current interests span fundamental and applied questions in condensed matter physics, medical and biophysics, and the optical sciences. Areas of ongoing research include: soft materials, complex fluids and networks, carbon nanotubes, laser spectroscopy, optical microscopy & micromanipulation, biomedical optics, functional imaging and spectroscopy of living tissues, photodynamic therapy and nonlinear optics.

Some information on Prof. Yodh's work can be found here:
http://www.physics.upenn.edu/yodhlab/

Prof. Maxim Olshanii, Department of Physics, University of Massachusetts Boston, USA
14/07/2014 - 10:30

We study relaxation in a one-dimensional two-mass mixture of hard-core particles. A special attention is payed to the region of light-to-heavy mass ratios around m/M = sqrt(5)-2 = 0.236... . At this mass ratio, each heavy-light-heavy subsystem constitutes a little known non-equal-mass generalization of the Newton Cradle, and an anomalous slow-down of relaxation is expected as a result. We further list and classify all other instances of integrability in the one-dimensional three-body hard-core systems; there, integrability is especially prominent at the quantum level, leading to the famous "scattering without diffraction" phenomenon. The principal experimental application of our results is the two-specie mixtures in optical lattices; there, the effective masses---that can be controlled at will---are assumed to replace the real ones.

Itamar Shani
17/06/2014 - 11:00 - 12:30

Many-body systems with long-range interactions that are driven out of equilibrium are common in Nature. For example, stellar motion, charged particles in plasma and sedimentation of particles in a fluid under gravity. Yet, their complex behavior is hard to explain, since each constituent effectively interacts with all the others. I will present a study of the dynamics of microfluidic droplet ensembles flowing in a two-dimensional channel and governed by long-range hydrodynamic dipolar interactions1,2. While the ensemble is spatially disordered, the droplet velocities exhibit strong long-range correlations proportional to 1/r^2, with a four-fold angular symmetry3. The two-droplet correlation is explained by representing the entire ensemble as a third droplet. The velocity fluctuations amplitude is non-monotonous with the ensemble’s density owing to excluded-volume effects. The summation over the long-range interactions converges thanks to the low-dimensionality of the system facilitating a theoretical description of the velocity fluctuations and correlations in such a complicated system.
1.           Beatus, T., Tlusty, T. & Bar-Ziv, R. Phonons in a one-dimensional microfluidic crystal. Nat. Phys. 2, 743–748 (2006).
2.           Beatus, T., Bar-Ziv, R. H. & Tlusty, T. The physics of 2D microfluidic droplet ensembles. Phys. Rep. 516, 103–145 (2012).
3.           Shani, I., Beatus, T., Bar-Ziv, R. H. & Tlusty, T. Long-range orientational order in two-dimensional microfluidic dipoles. Nat. Phys. 10, 140–144 (2014).

Prof. Alexey Kryukov
07/04/2014 - 14:00

A mathematical framework that uses rigged Hilbert spaces to unify the standard formalisms of classical mechanics, relativity and quantum theory will be introduced. In the framework states of a classical particle are identified with Dirac delta functions. The classical space (or space-time)  is "made" of these functions and is a submanifold in a Hilbert space of quantum states of the particle. The resulting embedding of the classical space into the space of states is highly non-trivial and accounts for numerous deep relations between classical and quantum physics and relativity. One of the most striking results is the proof that the normal probability distribution of position of a macroscopic particle (equivalently, position of the corresponding delta state within the classical space submanifold) yields the Born rule for probability of transitions between arbitrary quantum states.

 

Dr. John Kitching Atomic Devices and Instrumentation Group NIST, Time and Frequency Division Boulder, Colorado, USA
17/02/2014 - 14:00

Coherent population trapping is a phenomenon in which atoms are prepared and detected in superpositions of their ground state energy levels through illumination by bichromatic optical fields. We describe the use of coherent population trapping in the development of compact atomic clocks based on both room temperature vapors and laser cooled ensembles. The use of coherent population trapping allows for a high degree of miniaturization as well as some performance advantages such as a reduction in the first-order Doppler shift.

Dr. John Kitching Atomic Devices and Instrumentation Group NIST, Time and Frequency Division Boulder, Colorado, USA
17/02/2014 - 10:30

We describe work a NIST to develop precision instruments based on atomic spectroscopy, advanced semiconductor lasers and micro-electro-mechanical systems (MEMS). These millimeter-scale instruments achieve useful levels of stability or sensitivity but with reduced power consumption and potentially reduced manufacturing cost compared to their larger counterparts. Physics packages for atomic frequency references with fractional frequency stabilities in the range of 10-11 over one hour have been demonstrated. Using similar device designs and processing, magnetometers with sensitivities below 10 fT/ÖHz have been demonstrated, making them competitive with commercial SQUID-based sensors without the need for cryogenic cooling. The design, fabrication and performance of these instruments will be described, as well as a number of applications to which the devices are well-suited. 

Note: Dr. Kitching will give a more specialized seminar, later on the same day at Resnick bulg.

Prof. Vincent Desjacques, Department of Theoretical Physics University of Geneva
03/02/2014 - 10:30

Upcoming galaxy surveys will enable us to test the assumptions of the standard cosmological model which pertain to the nature of dark matter and dark energy, the origin of the primeval fluctuations and the law of gravity. In this talk, I will describe recent observational and theoretical developments, with an emphasis on the complications that arise from the complex relationship between luminous galaxies and the matter distribution.

 

Prof. Michael Shlesinger, Office of Naval Research
26/01/2014 - 11:00

The search problem played an important role in the development of the field of operations research in the 1940's.  We study the search problem under a variety of circumstances where different search patterns are available and can be alternated and the search time is fixed.

Dr. Baruch Barzel 
13/01/2014 - 14:30 - 16:00

One of the major achievements of statistical mechanics is the development of theoretical tools to bridge between the microscopic description of a system and its observed macroscopic behavior, tracking the emergence of large-scale phenomena from the mechanistic description of the system’s interacting components. A key factor in determining this emergent behavior is associated with the underlying geometry of the system’s interactions - a natural notion when treating structured systems, yet difficult to generalize when approaching complex systems. Indeed, social, biological and technological systems feature highly random and non-localized interaction patterns, which challenge the classical connection between structure, dimensionality and dynamics, and hence confront us with a potentially new class of dynamical behaviors. To observe these behaviors we focus, both empirically and theoretically, on the system's response to external perturbations, helping us uncover the unique dynamical universality classes that characterize complex systems.

Relevant papers: 
Universality in network dynamics Nature Physics. 9, 673–681 (2013) doi:10.1038/nphys2741
Network link prediction by global silencing of indirect correlations, Nature Biotechnology 31, 720–725 (2013) doi:10.1038/nbt.2601
Also featured in 2physics.com - Presenting key developments in physics: http://www.2physics.com/search/label/Complex%20System%203

 

Dr. Michael Stern
02/01/2014 - 14:30 - 16:00

The flux qubit is often considered as a major design for the future of quantum integrated circuits and its properties have triggered intense interest in the last decade [1-2]. This superconducting circuit behaves as a two-level system, each level being characterized by the direction of a macroscopic permanent current flowing in the loop of the qubit.  The permanent current, typically of the order of several hundreds of nAs, generates a large magnetic dipole, which offers interesting prospects for hybrid quantum circuits [3]. However, the flux qubit suffers from limited and irreproducible lifetimes which prevent these potential applications. Recently, a novel architecture where qubits are placed in a three dimensional cavity was introduced for transmon qubit [4]. It was shown that coherence properties can be greatly improved.

 

I will present the first measurements of flux qubits in a three dimensional cavity and show that they can reach long and more reproducible T1. The qubits were fabricated on a sapphire substrate and were measured by coupling them inductively to an on-chip superconducting resonator embedded in a three dimensional copper cavity. All the measured flux qubits exhibit an intrinsic T1 comprised between 5 and 13 us.

 

These long and reproducible depolarization times are a key element to reach the strong coupling limit with a single spin as suggested in [3]. I will describe our current experimental efforts towards this long term objective.

 

[1] I. Chiorescu et al., Science, 299, 5614 (2003).

[2] J. Bylander et al., Nature Physics, 7, 565 (2011).

[3] D. Marcos et al., PRL , 105, 210501 (2010).

[4] H. Paik et al., Phys. Rev. Lett., 107, 240501 (2011).

Dr. Yuval Lubashevsky
29/12/2013 - 12:30 - 14:00

The presence of optical polarization anisotropies, such as Faraday/Kerr effects, linear birefringence, and magnetoelectric birefringence are evidence for broken symmetry states of matter. The recent discovery of a Kerr effect using near-IR light in the pseudogap phase of the cuprates can be regarded as a strong evidence for a spontaneous symmetry breaking and the existence of an anomalous long-range ordered state. In this work we present a high precision study of the polarimetry properties of the cuprates in the THz regime. While no Faraday effect was found in this frequency range to the limits of our experimental uncertainty (1.3 milli-radian or 0.07∘), a small but significant polarization rotation was detected that derives from an anomalous linear dichroism. In YBa2Cu3Oy the effect has a temperature onset that mirrors the pseudogap temperature T∗ and is enhanced in magnitude in underdoped samples. In x=1/8 La2−xBaxCuO4, the effect onsets above room temperature, but shows a dramatic enhancement near a temperature scale known to be associated with spin and charge ordered states. These features are consistent with a loss of both C4 rotation and mirror symmetry in the electronic structure of the CuO2 planes in the pseudogap state.

 

דר' סטס בורוב
24/12/2013 - 14:30

This talk will describe quantitative analyses of particle tracking data for 
systems with cytoskeletally associated motors to better understand the 
motions contributing to intracellular transport and, more generally, means 
for characterizing systems far from equilibrium. We exploit stochastic properties 
of single particle trajectories to establish "sanity" tests for experimentally 
collected data. Development of simple order parameters for 2d motion 
and studying its behavior for different models of transport in disordered media 
permits us to distinguish between random motion inside dense physical systems 
and molecular motors mediated transport. Furthermore, the stochastic properties 
of insulin-containg vesicles transport in beta cells provide a simple mechanism for how 
important beta cell functioning (biphasic insulin secretion) can arise.

Dr. Amir Rosenthal
16/12/2013 - 14:00 - 15:30

In the last several decades, ultrasound detection has become almost synonymous with piezoelectric technology. In the field of medical sonography, the piezoelectric array, commercialized in the early 1970s, is still the core technology of contemporary devices. Nonetheless, with the emergence of new ultrasound-based technologies such as optoacoustic tomography and surface-acoustic-wave (SAW) microfluidics, a new need has arisen for novel ultrasound detectors with a level of miniaturization unattainable by piezoelectric technology. While optical detectors of ultrasound have long been considered an alternative to conventional technology, they have mostly remained a niche owing to their susceptibility to mechanical vibrations and the lack of effective schemes for parallel detector read-out

 

In this talk I will present a new paradigm for optical detection of ultrasound that can overcome the deficiencies of conventional optical techniques. At the heart of the new detection scheme is a sensor interrogation method called pulse interferometry, which achieves the fundamental shot-noise detection limit and is robust against mechanical vibrations. Sensor miniaturization is achieved by the use of light confinement in grating structures in fibers and silicon waveguides. Two applications are demonstrated: an all-optical optoacoustic imaging catheter and a silicon-based SAW detector. Finally, the potential of scaling the new technology to achieve ultra-small detector arrays will be discussed

Ronny Bartsch, Harvard Medical School
03/11/2013 - 14:00

The human organism is an integrated complex network of interconnected and interacting organ  systems, where the behavior of one system may affect the dynamics of all other systems.  Due to these interactions, failure of one system can trigger a breakdown of the entire network.  We introduce a systematic method to identify a network of interactions between diverse physiologic  systems, to quantify the hierarchical structure and dynamics of this network, and to track its  evolution under different physiologic states. We find a robust relation between network structure  and physiologic states: every state is characterized by specific network topology, node connectivity  and links strength -- a behavior we consistently observe across individual subjects. Further, we find  that transitions from one physiologic state to another trigger a markedly fast reorganization of physiologic
interactions on time scales of just a few minutes, indicating high network flexibility in response to  perturbations. Surprisingly, this reorganization occurs simultaneously and globally in the entire  network as well as at the level of individual network nodes, while preserving a hierarchical order in  the strength of network links. In the context of sleep-stage transitions, we demonstrate that  network connectivity and overall strength of physiologic interactions are significantly higher during  wake and light sleep, intermediate during rapid eye movement (REM) sleep and much lower during  deep sleep -- a stable stratification pattern which indicates that physiologic systems are highly and
strongly connected during light sleep, and practically disconnected during deep sleep. Such
pronounced difference in network organization during light and deep sleep is in contrast to the similarity  in the output dynamics of individual physiologic systems during these sleep stages. Our findings  highlight the need of an integrated network approach to understand physiologic function, since the framework we develop provides new information which can not be obtained by studying individual systems.

Professor Steven Prawer - University of Melbourne
15/07/2013 - 10:30

Professor Prawer is the director of the Melbourne Materials Institute, a multidisciplinary research initiative dedicated to using advanced materials science and technology to address problems of

). He has a world wide reputation in advanced http://materials.unimelb.edu.au global significance.

diamond science and technology with over 25 years of experience and over 250 scientific publications.

 

Professor Prawer is currently a senior leader one of Australia’s most prestigious national projects dedicated to the development of a bionic eye. He leads the team to develop the high density electrode array plus encapsulation strategy capable of delivering a high acuity device which will enable profoundly blind people to once again be able to recognize the faces of loved ones and read large print.

 

In 2000 he spearheaded The University of Melbourne’s entry into the world of quantum computing and nanotechnology becoming the inaugural Director of the Melbourne node of the Special Research Centre for Quantum Computer Technology  He has developed the technology for the fabrication for practical, diamond based quantum devices, such as single photon sources for secure communications, and room temperature read-out for spintronics for use in advanced quantum sensing. In 2005 he cofounded Quantum Communications Victoria

), which produced the first prototype commercial single photon http://qcvictoria.com/)

source, for use in quantum key distribution for ultra-secure communications.

 

Professor Prawer has been the recipient of numerous awards including the Lady Davis Visiting Professorship, The David Syme Research Prize, a Fulbright Senior visiting fellowship, visiting fellowship at Woolfson College Inin Oxford, and the Royal Society of Victoria Research medal. In  2010 he was elected to the Australian Academy of Science in recognition of his seminal contributions to diamond science and technology.