Theory Seminars

Quantum Effects of Strong Magnetic Fields in Semimetallic Films and Wires

Speaker: 
Danny Bulmash
Event Date and Time: 
Mon, 2016-11-28 12:00 - 13:00
Location: 
Hennings318
Local Contact: 
Mracel Franz
Intended Audience: 
Graduate

Motivated by Weyl and Dirac semimetals, I will show theoretically that strong magnetic fields can induce novel quasi-lower-dimensional physics in semimetallic films and wires. First, I will propose that a thin film of Weyl or Dirac semimetal with a strong in-plane magnetic field becomes a quasi-two-dimensional Fermi liquid displaying quantum oscillations that depend on field angle in a highly unusual way. I will discuss the utility of these oscillations for probing Fermi arcs.

Milestones toward Majorana-based topological quantum computing

Speaker: 
Ryan Mishmash (Caltech)
Event Date and Time: 
Mon, 2016-11-21 12:00 - 13:00
Location: 
Hennings318
Local Contact: 
Marcel Franz
In this talk, I will introduce a new scheme for preparation, 
manipulation, and readout of Majorana zero modes in semiconducting wires 
coated with mesoscopic superconducting islands.  Our approach 
synthesizes recent materials growth breakthroughs with tools long 
successfully deployed in quantum-dot research, notably gate-tunable 
island couplings, charge-sensing readout, and charge pumping.

Quamtum Critical Dynamics in Many Body Systems

Speaker: 
Dr. Jianda Wu (University of California, San Diego)
Event Date and Time: 
Mon, 2016-09-19 12:00 - 13:00
Location: 
Hennings 318

Thermal and quantum fluctuations, as two fundamental powers, dominate overall thermodynamics and dynamics of many body systems. At zero temperature the many body systems is uniquely driven by quantum fluctuations, and quantum phase transitions arise when ground state energy meets non-analyticity via tuning a non-thermal parameter.

The emergence of geometry on the domain walls of topological phases

Speaker: 
Prof. Zhengcheng Gu (PI---> Chinese University of Hong Kong)
Event Date and Time: 
Thu, 2016-08-18 11:00 - 12:00
Location: 
Room 309 Hennings
Local Contact: 
Fei Zhou
Intended Audience: 
Graduate
In this talk, I will discuss how geometry degree of freedoms naturally arise on the domain walls of topological phases. In particular, I will study a simple example of domain wall theory between toric code model and double semion model. It turns out that the domain wall theory is indeed a SU(2)_1 conformal field theory at low energy . I will also discuss the general math framework for the emergence of geometry on the domain walls of topological phases.

Induced Vacuum Decay by Topological Solitons

Speaker: 
Manu Paranjape, Université de Montréal
Event Date and Time: 
Fri, 2015-10-16 11:00 - 12:00
Location: 
Henn 318
Local Contact: 
Gordon Walter Semenoff
Intended Audience: 
Graduate
We study the decay of the false vacuum mediated by meta-stable topological solitons. The symmetry broken vacuum is unstable to decay to the symmetry preserving vacuum via quantum tunnelling, but usually the rate of decay is very small. However, the existence of topological solitons can significantly enhance the disintegration rate. We consider monopoles, vortices and domain walls.

Novel quantum magnetism and Mott physics with Sp(2N) and SU(2N) symmetries - large spin ultra-cold fermions are different

Speaker: 
CongJun Wu (UCSD)
Event Date and Time: 
Mon, 2015-11-16 12:00 - 13:00
Location: 
Hennings 318
Local Contact: 
Fei ZHou
Intended Audience: 
Graduate
The large spin ultra-cold fermionic systems provide a whole new opportu-nity to investigate large symmetries, say, Sp(2N) and SU(2N), which are often studied in high energy physics. In our early works, we proved an exact and generic Sp(4), or, iso-morphically SO(5) symmetry in the hyperfine spin-3/2 systems without fine-tuning. This symmetry provides a unified framework to understand the competition between quantum magnetism, charge-density-wave, and superconductivity.

Quantitative Determination of the Pairing Interactions for High Temperature Superconductivity in Cuprates

Speaker: 
Chandra Varma (UCR)
Event Date and Time: 
Mon, 2015-11-09 12:00 - 13:00
Location: 
Hennings 318
Local Contact: 
andrea Damascelli
I will report report on the laser based angle-resolved photoemission data taken at IOP Beijing and its analysis. This has led to the first quantitative determination of the attractive effective interactions in the cuprates in the (d)- wave pairing symmetry, as well as their repulsive counterpart in the full symmetry of the lattice.

Classifying and detecting symmetry fractionalization in gapped 2D spin liquids

Speaker: 
Dr. Yang QI (PI, Waterloo)
Event Date and Time: 
Mon, 2015-09-21 12:00 - 13:00
Location: 
Hennings 318
Local Contact: 
Fei Zhou
Intended Audience: 
Graduate
Quantum spin liquid states with intrinsic topological orders supports fractionalized anyons excitations, and they can carry fractional quantum numbers of spin rotational symmetry, time reversal symmetry and crystal symmetries. This symmetry fractionalization distinguishes different topologically ordered spin liquid states.

Spontaneous Loop Currents and Chiral Topological States in Optical Lattices

Speaker: 
Dr. Xiaopeng Li (JQI, Maryland, USA)
Event Date and Time: 
Mon, 2015-09-28 12:00 - 13:00
Location: 
Hennings 318
Local Contact: 
Fei Zhou
Intended Audience: 
Graduate
Charged particles like electrons naturally couple to gauge fields, e.g., electromagnetic fields, and exhibit fascinating many-body phenomena such as Integer and Fractional Quantum Hall Effects. On the contrary, ultracold atoms are charge neutral and thus do not couple to the electromagnetic fields. At the same time, in recent optical lattice experiments, the methods of synthesizing artificial gauge fields with Raman schemes or lattice shaking have been developed.

Optimal control and optimal response in microscopic nonequilibrium systems

Speaker: 
David Sivak, SFU
Event Date and Time: 
Mon, 2014-11-17 12:00 - 13:00
Location: 
Hennings 318
Intended Audience: 
Graduate
Molecular machines are protein complexes that convert between different forms of energy, and they feature prominently in essentially any major cell biological process. A plausible hypothesis holds that evolution has sculpted these machines to efficiently transmit energy and information in their natural contexts, where energetic fluctuations are large and nonequilibrium driving forces are strong.
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