USC Physics Seminars

                                   Quantum Information – Condensed Matter – Biophysics

These seminars are scheduled on Fridays at 2:00pm, and the location is SSL 150, unless otherwise noted. Some of the seminars will be held jointly with UCLA and CALTECH.
For more information contact Lorenzo Campos Venuti (condensed matter) or Ben Reichardt (quantum information). Biophysics seminars are held the first Friday of each month and are indicated in blue.
UPC seminar location: Ahmanson Center for Biological Research, ACB 238. Location for remote viewing of HSC seminars: ACB 238
HSC seminar location: Herklotz seminar room, Zilkha Neurogenetic Institute HSC.  Location for remote viewing of UPC seminars: Herklotz

September 2, 2pm SSL150
Daniel Ben-Zion (UCSD)

SPT and SET physics from decorated string nets

It has been understood for some time now that quantum entanglement plays a central role in classifying phases of matter. Patterns of long range entanglement can distinguish two phases even when symmetries cannot; this is called topological order. One interesting question is: what possibilities are there in systems with both topological order and a global symmetry? On the other hand, even in the absence of topological order it is occasionally possible to have two phases which preserve all symmetries yet are nonetheless distinct. This phenomena is known as a 'symmetry protected topological' phase. In this talk, I will give a few explicit examples of models both with and without topological order, emphasizing the interplay with global symmetries. These models have the feature that domain walls are decorated with auxiliary degrees of freedom which arrange themselves into particular interesting states.

September 7, 2pm SSC319
Si-Hui Tan (CQT Singapore)

An encryption scheme for malleable quantum data with information-theoretic security

We introduce an approach to homomorphic encryption on quantum data. Homomorphic encryption is a cryptographic scheme that allows evaluations to be performed on ciphertext without giving the evaluator access to the secret encryption key. Random operations from an finite abelian unitary group chosen using an encryption key chosen uniformly at random perform the encryption, and operations that lie within the centralizer of the encryption group perform the computation. Since the latter operations commute with any evaluation in the encryption group by definition, applying the inverse of the encryption decrypts the evaluated state, and the decryption key depends only on the encryption key. We show that the group of operations that can be used for computation is isomorphic to a unitary group of a large dimension. Moreover our scheme is information theoretically secure, that is, given orthogonal inputs to our sceme, the evaluator can only extract some amount of classical information that is exponentially suppressed via the Holevo quantity. For a specific encoding, we show that our scheme is able to hide a constant fraction of bits that can be made arbitrarily close to unity.

October 14, 2pm SSL150
Fariborz Nasertorabi (Bridge Institute/USC)

Structure Biology Center at bridge  enables USC research labs to extend their research into structure biology

Structural biology center (SBC) has been established to enable all biology labs at USC to extend their research into the field of structural Bioloy. Here at Bridge Institute we have executed an unique center that can efficiently help labs to progress into structural biology at a minimal cost and without  any prior knowledge in structural biology.  We at the center will work with labs at USC to solve the structure of their protein of interest alone or in complex with ligands/drugs, DNA, RNA or protein. We can additionally do ligand search for the highest stabilizer of the targeted protein.  
During my talk, I will walk you through how the center is set up and how USC labs can best benefit from the center in their research.

October 21, 2pm SSL150
Gerd Bergmann (USC)

Introduction into Topological Semiconductors

Topological insulators are, at low temperatures, insulating in the bulk, but at the surfaces or edges they are conducting. Due to strong spin-orbit coupling the electron spin and momentum are locked. In the simplest cases the spin is oriented perpendicular to the momentum.  As a consequence a current carried by these states carries a net spin and introduces a spin polarization at the surface. For two-dimensional topological insulators one obtains one-dimensional edge states. A current along these edges is protected by spin-momentum locking and time-reversal symmetry and should be free of dissipation. It shows a spin quantum Hall effect. The 2016 Nobel prizes in Physics for Thouless and Haldane are mainly given for their pioneering work in introducing the concept of topology in solid state physics. An overview of the physics of topological insulators will be given.

October 28, 2pm SSL150
Mohseninia (Sharif University of Technology)
Quantum non-Abelian Potts model and its exact solution

We introduced the one-dimensional non-Abelian Potts model, which is the generalized form of the one-dimensional Potts model to the case where the symmetry group is a non-Abelian finite group. In this talk, I make a rather detailed study of its properties. I determine the complete energy spectrum, i.e., the ground states and all the excited states with their degeneracy structure and also the partition function which means that the model is an exactly solvable model. Finally I determine the entanglement properties of the ground states and show that this model has a quantum nature, that is its spectrum of energy eigenstates consists of entangled states.
In the same way that the Ising and Potts models have led to a large number of applications in physics, it may also be the case that the non-Abelian case, in view of its richer structure, may find such applications.

Mohseninia, R., & Karimipour, V. (2016). Quantum non-Abelian Potts model and its exact solution. Physical Review B93(3), 035127.

November 11, 2pm SSL150

Barry Sanders (IQST,Caltech)
Machine Learning for Quantum Control

Quantum control is valuable for quantum technologies such as high-fidelity quantum gates, adaptive quantum-enhanced metrology, and ultra-cold atom manipulation. Although both supervised and reinforcement learning are used to optimize control parameters in classical systems, quantum control for parameter optimization is mainly achieved via gradient-based greedy algorithms. However, greedy algorithms can yield poor results for quantum control, especially for highly constrained large-dimensional quantum systems. We employ differential evolution algorithms to circumvent the stagnation problem of non-convex optimization, and we average over the objective function to improve quantum control fidelity for noisy systems. To reduce computational cost, we introduce heuristics for early termination of runs and for adaptive selection of search subspaces. Our implementation is massively parallel and vectorized to reduce run time even further. We demonstrate our methods with two examples, namely quantum phase estimation and quantum gate design, for which we achieve superior fidelity and scalability than obtained using greedy algorithms.

November 18, 2pm SSL150
Fabio Traversa (UCSD)

Practical Realization of Memcomputing Machines with Self-Organizing Logic Gates

Memcomputing is a novel computing paradigm based on (non-von Neumann) architectures that employ interconnected memory cells capable of using the collective state of the network to compute.
The computational power of these machines can be substantially increased if we embed in the network some extra information related to the problem to solve. We call this feature "information overhead’’. By taking advantage of this embedded information we can exponentially reduce the complexity of many problems such as the Non-deterministic Polynomial (NP) ones. In fact, the latter ones can be solved by a memcomputing machine with only polynomial resources (in time, space, energy).
A practical realization of these machines can be obtained by employing “self-organizing logic gates’’, i.e., logic gates that can accept inputs from all terminals, including the conventional output terminals and self-organize to satisfy their logic propositions. I will show how to use these gates to solve specific NP problems with polynomial resources. These novel logic gates and circuits can be realized with available nanotechnology components and are scalable.

December 9, 2pm SSL150
David Beratan (Duke University)

January 27, 2pm SSL150
Victor Martin-Mayor (Complutense University of Madrid)
Why are hard-to-solve problem instances so hard?

The difficulty of solving the small problem instances that one can submit to DW2 processors is very heterogeneous, ranging from easy to impossible [1,2]. This difficulty is controlled (to a large extent) by a physical effect named "temperature chaos" (TC). The best quantitative description of TC is provided by the performance of the Parallel Tempering, a Markov-chain Monte Carlo algorithm, on the system under study. TC controls the performance of simulated annealing and that of Selby's algorithm as well. It is only natural to guess that TC points to some topological features of the instance's energy landscape. In this talk, we try to unearth these topological features that underlie computational hardness by borrowing ideas from the Physics of supercooled liquids and glasses. We consider two ensembles of problem instances. On the one hand, our "control experiment" instances are  usual problem instances filtered according to their degree of TC. On the other hand, we consider quantum-protected instances, namely an ensemble of problem instances designed to increase the robustness of the Quantum Annealing algorithm, yet just as hard to solve with classical algorithms as  the "control experiment" instances. As it could be expected, DW2 is found to perform better on the ensemble of quantum-protected instances. However, we succeed in finding an "energy-landscape predictor" that quantitatively explains the  performance of DW2 both for the standard and the quantum-protected instances[3].

[1] V.M-M. and Itay Hen, Scientific Reports 5, Article number: 15324 (2015).
[2] Jeff Marshall, V.M-M. and Itay Hen, Phys. Rev. A 94, 012320 (2016).
[3] Mohammad Amin,  Evgeny Andriyash, Jeff Marshall, Itay Hen and V.M-M., manuscript in preparation.

January 27, 2pm UPC
Andre Kosmerlj, Ph.D. (Princeton)
Aggregation of Proteins: Growth of Glucagon Fibrils and Bacterial Growth

February 3, 2pm SSL150
Eli Kapon (Ecole Polytechnique Fédérale de Lausanne (EPFL) Switzerland)
Quantum Photonics with Ordered Quantum Dot and Quantum Wire Systems

Quantum wire (QWR) and quantum dot (QD) systems offer means for tailoring the electronic structure of semiconductors thanks to multi-dimensional quantum confinement.  By placing them in confined photonic structures (waveguides, cavities) it is possible to tailor light-matter interaction via the introduced modifications in the density of states of excitons and photons.  We review the technology of ordered QWR and QD structures grown by metallolrganic vapor phase epitaxy on patterned substrates and their integration with photonic components.  Tailoring exciton wavefunctions, controlling their recombination dynamics, and observing cavity quantum electrodynamic effects in the integrated structures are described.  Applications in quantum information technology and ultralow threshold lasers are discussed.

Eli Kapon received his Ph.D. in physics from Tel Aviv University, Israel in 1982. He then spent two years at the California Institute of Technology, Pasadena, as a Chaim Weizmann Research Fellow, and then nine years at Bellcore, New Jersey, as member of technical staff and District Manager. Since 1993 he has been Professor of Physics of Nanostructures at the Swiss Federal Institute of Technology in Lausanne (EPFL), where he heads the Laboratory of Physics of Nanostructures. In 1999-2000 he was a Sackler Scholar at the Mortimer and Raymond Sackler Institute of Advanced Studies in Tel Aviv University, Israel.  During that period he helped establishing the Tel Aviv University Center for Nanoscience and Nanotechnology and served as its first Director from 2000 to 2002.  In 2001 he founded the start up BeamExpress, serving as its Chief Scientist. His research interests include quantum- and nano-photonics, low-dimensional semiconductors, and vertical cavity semiconductor lasers. Prof. Kapon is Fellow of the Optical Society of America, the Institute of Electrical and Electronics Engineers, and the American Physical Society of America, a recipient of a 2007 Humboldt Research Award, and a Photonics Society Distinguished Lecturer for 2105-2017.


February 8, 2pm HSC

From Ion Selectivity to Drug Design in Transmembrane Proteins

February 17, 12:00 SSC 319
Abhinav Prem (Boulder, Colorado)
Multiply quantised vortices in fermionic superfluids: angular momentum, unpaired fermions, and spectral asymmetry

We compute the orbital angular momentum $L_z$ of an $s$-wave paired superfluid in the presence of an axisymmetric multiply quantised vortex. For vortices with winding number $|k| > 1$ we find that in the weak-pairing BCS regime, $L_z$ is significantly reduced from its value $\hbar N k/2$ in the BEC regime, where $N$ is the total number of fermions. This deviation results from the presence of unpaired fermions in the BCS ground state, which arise as a consequence of spectral flow along the vortex sub-gap states. We support our results analytically and numerically by solving the Bogoliubov-de-Gennes equations within the weak-pairing BCS regime.

Thursday March 9, 4pm EEB 123
Peter Shor (MIT)
Capacities for Quantum Communication Channels

In 1948, Shannon discovered his famous formula for the capacity of a communication channel. This formula does not apply, however, to channels with significant quantum effects. For quantum channels, the question of capacity is much more complicated, as there are different capacities for sending classical information and for sending quantum information. We will discuss the capacities of quantum channels, and survey the historical development of the subject.
Peter Shor received a B.S. in Mathematics from Caltech in 1981, and a Ph.D. in Applied Mathematics from M.I.T. After a one-year postdoctoral fellowship at the Mathematical Sciences Research Institute in Berkeley, he took a job at AT&T Bell Laboratories, and stayed at AT&T until 2003.  In 2003, he went to M.I.T., where he is the Morss Professor of Applied Mathematics.

March 10, 2pm SSL150
Christian Majenz (Caltech)
Quantum supremacy with random circuits

Quantum supremacy has been a trending topic in the last years, with experimentalists eager to try problems on their small scale quantum computing devices which are likely hard for a classical computer as a benchmark, however useless they may be in practice. In this talk, I will review the development of theoretical quantum supremacy results with random circuits and explain the main ingredients and difficulties of supremacy results for sampling problems. Finally I will present some initial results towards a clearer framework for supremacy with random circuits.

Tuesday April 4, 2pm EEB 248
Matthew J. Gilbert (Urbana-Champaign)
Topological Energy Transduction

Within the CMOS architecture, the interconnected devices may either be categorized as an “active” device, which produces energy in the form of a current or a voltage, or a “passive” device, which stores or maintains energy in the form of a current or voltage. The societal demand for smaller sized electronic devices, such as computers and cellular phones, with improved functionality has forced not only the sizes of the constituent components of CMOS information processing technology to rapidly shrink, but for the operational frequencies to increase. While it has been possible to reduce the size of active CMOS devices, passive devices have not seen the same reduction in size. Of the passive devices (e.g. resistors, capacitors and inductors) used in CMOS technologies, the circuit element that consumes the most area on a circuit board while simultaneously finding the least success in miniaturization is the inductor. In this talk, we will present a novel method for energy transduction that utilizes the interplay between magnetism and topology on the surface of a newly discovered materials, referred to as time-reversal invariant topological insulators, to create a paradigmatically different inductor. Using a novel self-consistent simulation that couples AC non-equilibrium Green functions to fully electrodynamic solutions of Maxwell's equations, we demonstrate excellent inductance densities up to terahertz frequencies thereby providing a potential solution to an eminent grand challenge.

Wednesday April 5, 2pm KAP 209
Matthew J. Gilbert (Urbana-Champaign)
Unconventional Superconductivity in Topological Heterostructures

The search for materials and systems that exhibit unconventional superconductivity, or superconductivity beyond the canonical s-wave pairing as predicted in BCS theory, is one of the most active areas within condensed matter physics. This effort has been reinvigorated by the interesting properties inherent to a new class of materials that possess topological phases. A topological phase is unique in that it does not break any of the underlying symmetries of the system and cannot be described by a local order parameter. In other words, the inherent properties of the system cannot be changed by adiabatic shifts in materials parameters unless the system passes a quantum critical point associated with a phase transition. More recently, this search has taken on additional significance due to the fact that systems that possess unconventional superconductivity may enable a new type of fault tolerant quantum information processing that may significantly increase computing power when compared to traditional information processing. In this talk, I will discuss the appearance and signatures of unconventional superconductivity and review some of the most prominent systems that have been predicted to exhibit unconventional superconductivity. In particular, I will focus on heterostructures containing s-wave superconductors and proximity-coupled 3D time-reversal invariant topological insulators. I will explain some of the experimentally relevant conditions that must be satisfied in order to observe the features of unconventional superconductivity and conclude by examining the potential for finding unconventional superconductivity in emergent topological materials such as semimetals and crystalline insulators.

March 31, 2pm UPC
Xiaojiang Chen, Ph.D. (USC)
DNA Remodeling and Modification By Nucleic Acid Transaction Enzymes: Helicases and Deaminases

April 28, 2pm UPC
Sima Setayeshgar, Ph.D. (Indiana)

October 27, 2pm HSC
April 28, 2pm UPC
Ralf Langen, Ph.D. (USC)

November 17, 2pm UPC
April 28, 2pm UPCEmily Liman, Ph.D. (USC)


Januar 2015 - July 2016

January-August 2015

More seminars


USC | Department of Physics and Astronomy
How to get to USC