Condensed Matter Theory at Caltech

Gil Refael Lesik Motrunich

Quantum Information & IQIM

John Preskill Alexei Kitaev (on leave at KITP)

Quantum Condensed Matter

Jason Alicea

http://www.iqim.caltech.edu/

   

* Thursday, March 27 1:30-2:30: Social hour with refreshments (cookies, drinks,

coffee) in the Bridge Annex common area/patio. We are planning to have posters just outside in the corridors of Bridge Annex and West Bridge.

The social is co-hosted with all IQIM groups.

2:30-4:30: "Lab tours" - students visiting our offices and talking individually. The quantum information group will return to Annenberg and will be available to students to talk more.

4:30-5:30: Department-wide poster session just outside West Bridge (under the East Bridge portico).

* Friday, March 28 1:30-4:30: CMP-T "Lab tours" (same as Thursday)

CMP & QI visiting day schedule

   

Quantum Condensed Matter

Quantum mechanics underlies most properties of materials – subject of Solid State Physics and broader Condensed Matter Physics (including superfluids and other liquids).CMP: study electronic, optical, magnetic,..., properties of materials, phases of matter and their transformations, ...

Quantum Condensed Matter at Caltech: * emergent behaviors in quantum many-body systems; * topological phases and exotic phases in strongly-correlated systems; * understanding and harnessing exotic quantum behaviors in materials and artificial systems

Put

to work!

Quantum Information Science

   

Quantum Information ScienceBig Questions:HEP:What underlying theory explains the observed elementaryparticles and their interactions, including gravity?

QIS:Can we control complex quantum systems and if so whatare the scientific and technological implications?

Not the frontier of short (subnuclear) distances or long(cosmological) distances, but rather the frontier of highlycomplex quantum states: The entanglement frontier

Also: emergence of classicality, security of quantum cryptographicprotocols, foundations of statistical mechanics and thermalization,information theoretic principles illuminating the foundations of quantumphysics, information processing by e.g. black holes, etc.

IQIM blog: http://quantumfrontiers.com/author/preskill/

   

Gil Refael: topology, disorder, and dynamics

Dynamical topological phenomena

- Floquet topological insulators (TI) in 2d and 3d in realistic systems

- Photocurrents on TI surfaces

Non-ideal topological insulators

- Transport in metal-TI hybrid systems

- Disordered topological metals

Majorana physics

- Exotic Josephson signatures of Majorana physics

- Boosted Majoranas in wires

Topological Insulators; quest for Majorana fermions

   

2005-2006 - Revolution in Condensed Matter Physics:Band structures in materials can be topological!

Topological Insulators

M. Z. Hasan and C. L. Kane

Rev. Mod. Phys. 82:3045, 2010

   

Topological Phases* Material realizations * Complete mathematical

classification for free ferms

“periodic table”

* Novel physics and potential applications!

   

Topological superconductor in 1d and 2d

2d p+ip superconductors;=5/2 FQH (Jim Eisenstein's lab);

-> Majorana fermion inside a vortex-> quasi-particles with non-abelian statistics and possibilities for topologically protected quantum computation (Alexei Kitaev's idea)

Gil and collaborators: 1d topological phase can be realized with solid state technology!

Phys. Today 64, March 2011

Much current experimental effort to realize Majoranas driven by this proposal!

   

Non-abelian statistics and topological quantum information processing in 1d

wire networks

-proposed by Jason, Gil, and collaboratorsNature Physics doi:10.1038/nphys1915

   

Jason Alicea: Engineering exotic phases of matter for quantum information applications

   

Jason Alicea: Engineering exotic phases of matter for quantum information applications

   

Jason Alicea: Engineering exotic phases of matter for quantum information applications

   

Jason Alicea: Engineering exotic phases of matter for quantum information applications

Ongoing efforts:

1) Developing proposal for engineering analog of Read-Rezayi states using

filling factor 2/3 states coupled to SCs (holy grail for topological quantum

computation!)

2) Classification of spin liquid phases in strongly spin-orbit coupled

frustrated magnets

3) Exploring new schemes/viewpoints for braiding Majoranas

4) Studying magnetic field effects in possible topological Kondo insulator

SmB6

   

Lesik Motrunich: topological phases, spin liquids, and gapless fractionalized phases

Strongly correlated electronic systems and frustrated magnets:

* Unusual quantum phases/gapless fractionalized phases - spin liquid Mott insulators (fractionalization) - gapless spin liquids (spin Bose-metals) and Mott transition - metallic non-Fermi liquids (high-Tc cuprates) * Symmetry-protected topological phases - thinking in terms of topological defects (vortices, hedgehogs, monopoles) - exact realizations of SPT and SET phases - Monte Carlo studies

   

Mott Insulators of electrons

Metal: electronsmove around

Mott insulator: electrons are localized one per site because of Coulomb repulsion

What do the spins do?-> Quantum Magnetism

Valence Bond Solid order120-degree Magnetic Order

Quantum magnetism: interacting spins

Symmetry breaking:

   

Anderson's Resonating Valence Bond Spin Liquid

- macroscopic analogy to Pauling's resonating chemical bond picture, e.g. for benzene:

Quantum superposition of many different valence bond configurations like this:

   

Spin-charge separation (fractionalization)

Excitation with spin-1/2, charge-0 - fraction of the electron!

   

Spin-charge separation (fractionalization)

Excitation with spin-1/2, charge-0 - fraction of the electron!

   

Spin-charge separation (fractionalization)

Excitation with spin-1/2, charge-0 - fraction of the electron!

   

There is also a spin-0 vortex-like excitation and subtle topological order!

Spin-charge separation (fractionalization)

Excitation with spin-1/2, charge-0 - fraction of the electron!

   

In several experimental spin liquid materials, spinons behave as if they are fermions in a metallic state - Spin Bose-metal!

Transition from metal to such spin liquid Mott Insulator can be continuous, by electrons shedding their charge while their spin part propagates as fermionic particles.

   

Lesik Motrunich: topological phases, spin liquids, and gapless fractionalized phases

Strongly correlated electronic systems and frustrated magnets:

* Unusual quantum phases/gapless fractionalized phases - spin liquid Mott insulators (fractionalization) - gapless spin liquids (spin Bose-metals) and Mott transition - metallic non-Fermi liquids (high-Tc cuprates) * Symmetry-protected topological phases - thinking in terms of topological defects (vortices, hedgehogs, monopoles) - exact realizations of SPT and SET phases - Monte Carlo studies

   

* Thursday, March 27 1:30-2:30: Social hour with refreshments (cookies, drinks,

coffee) in the Bridge Annex common area/patio. We are planning to have posters just outside in the corridors of Bridge Annex and West Bridge.

The social is co-hosted with all IQIM groups.

2:30-4:30: "Lab tours" - students visiting our offices and talking individually. The quantum information group will return to Annenberg and will be available to students to talk more.

4:30-5:30: Department-wide poster session just outside West Bridge (under the East Bridge portico).

* Friday, March 28 1:30-4:30: CMP-T "Lab tours" (same as Thursday)

CMP & QI visiting day schedule