| |
USC Quantum Information and Condensed Matter Physics Seminars |
For more information contact Stephan Haas (condensed matter) (213) 740-4528, or Daniel Lidar (quantum information) (213) 740-0198.
Random Walk to Graphene
Andre Geim (University of Manchester)
January 27, 2pm
Probing "inside" quantum collapse with solid-state qubits
Sasha Korotkov (UCR)
We discuss what is "inside" the quantum state collapse due to measurement, and what happens if the collapse is stopped half-way. For particular setups with solid-state qubits the answer is rather simple: the qubit state changes in accordance with gradually acquired information, without loss of its purity (no decoherence). The simple theory of such measurement leads to a number of experimentally testable predictions. So far three such experiments have been realized with superconducting qubits: partial collapse, uncollapse (measurement reversal), and persistent Rabi oscillations. These effects can be potentially useful, for example for quantum feedback and decoherence suppression.
February 3, 2pm
Visibility of the Higgs (amplitude) mode in condensed matter
Daniel Arovas (UCSD)
The amplitude mode is a ubiquitous collective excitation in condensed-matter systems with a broken continuous symmetry. It is expected in antiferromagnets, short coherence length superconductors, charge density waves, and lattice Bose condensates. Its detection is a valuable test of the corresponding field theory, and its mass gap measures the proximity to a quantum critical point. However, since the amplitude mode can decay into low-energy Goldstone modes, its experimental visibility has been questioned. Here we show that the visibility depends on the symmetry of the measured susceptibility. The longitudinal susceptibility diverges at low frequency as Im ? ~ 1/? (d = 2) or log(1/|?|) (d = 3), which can completely obscure the amplitude peak. In contrast, the scalar susceptibility is suppressed by four extra powers of frequency, exposing the amplitude peak throughout the ordered phase. We also discuss experimental setups for measuring the scalar susceptibility. Reference: D. Podolsky, A. Auerbach, and D. P. Arovas, Phys. Rev. B 84, 174522 (2011)
February 10, 2pm
Nano-plasmonics and Nano-photonics: Applications to Enhanced Single Photon Sources, and Mid-Infrared Photonics
Irfan Bulu (Harvard)
Applications to Enhanced Single Photon Sources, and Mid-Infrared Photonics Abstract: Plasmonics and photonics at the nano-scale offer new possibilities for improving the performance of photonic devices such as lasers, creating new functionality, and building chip-scale integrated optical devices. In the first part of my talk, I will present our recent experimental and theoretical work on plasmonic nano-cavities for efficient, room temperature single photon sources based on nitrogen-vacancy (NV) color centers in diamond. NV center is a stable single photon source even at room temperature, and exhibits long coherence times for both electronic and nuclear spins. As a result, it is a robust quantum system for applications ranging from quantum information processing to nano-scale magnetometry. These applications benefit from large single photon rates, which can be improved by the use of nano-photonic devices. I will discuss various plasmonic cavity designs and show that the emission rate, excitation rate, and collection efficiency from single NV centers can be improved significantly in an extremely small footprint device. Furthermore, I show that our scalable, top-down nanofabrication technique maintains the crucial properties of embedded NV centers, and is therefore compatible with requirements needed for realization of quantum systems based on diamond. In the second part of the talk, I will discuss our work on mid-infrared photonics. The mid-infrared is an exciting wavelength range for on chip photonic devices, with important applications in spectroscopy and gas sensing. We recently developed record high-Q (45,000) photonic crystal cavities on a CMOS compatible platform for trace gas sensing applications. I will discuss some of the methods that we developed in order to improve the quality factors of photonic crystal cavities at mid-infrared (4.5 µm), and report the observation and origin of optical bi-stability at this wavelength range. Finally, I will discuss the prospects for future devices ranging from all-optical signal processing to on chip frequency combs at the mid-infrared.
February 17, 2pm
Let's get physical: statistical physics dynamic models of crassly biological functions
Brad Foley and Reza Dehestani (USC Molecular Biology)
TBA
February 24, 2pm
Physical principles are the basis for molecular mechanisms in biology
Remo Rohs (USC)
Many biological processes depend on the correct readout of DNA sequences by proteins, a phenomenon called binding specificity. Previously, it was thought that specificity solely arises from hydrogen bonds between protein side chains and functional groups of the base pairs but those interactions are not sufficient in explaining specificity. Proteins have been shown to recognize DNA shape or the three-dimensional DNA structure rather than just a linear code of the letters A, C, G, and T. Nucleotides are complex assemblies of atomic groups and charges that affect the structure of DNA beyond its local environment. This phenomenon explains why nucleotides that are not contacted by the protein still contribute to specificity by giving rise to a sequence-dependence of DNA shape. Since experimental data on DNA structure is limited, a Monte Carlo sampling approach was implemented for predicting DNA shape. The sequence-dependent double helix can be viewed as a clay model with a dielectric boundary between the DNA molecule and the solvent. When the shape of the dielectric boundary is varied, the electrostatic potential surrounding DNA is affected, which in turn is recognized by proteins. Such variations are calculated by solving the Poisson-Boltzmann equation. The talk will demonstrate how electrostatic potential affects protein-DNA binding specificity and thus biological processes including development and cancer. Recent advances in predicting DNA shape on a high-throughput basis make it now possible to connect physical principles as the basis for specificity with whole-genome sequences.
March 2, 2pm
TBA
TBA
TBA
March 9, 2pm
TBA
hold for Rajiv
TBA
March 16, 2pm
TBA
TBA
TBA
March 23, 2pm
TBA
hold for Rajiv
TBA
March 30, 2pm
TBA
hold for Moh's visitor
TBA
April 6, 2pm
TBA
Arjun Yodh (University of Pennsylvania)
TBA
April 13, 2pm
TBA
Robert Westervelt (Harvard)
TBA
April 20, 2pm
TBA
hold for Rajiv
TBA
April 27, 2pm
TBA
hold for Rajiv
TBA
June 8, 2pm
TBA
Domenico D'Alessandro (Iowa State)
TBA
USC 
Caltech
UCLA ITP