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Quantum Information –
Condensed Matter – Biophysics
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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. UPC location for remote viewing of HSC seminars: To be determined.

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 netsIt 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 biologyStructural 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

RaziehMohseninia(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 B,93(3), 035127.

November 11, 2pm SSL150

Barry Sanders (IQST,Caltech)

Machine Learning for Quantum ControlQuantum 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)

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