Typical Weekly Events:

Seminars:  February 2012

• Tue 2/28, 3:30PM in Room 184                   print event

  Akimasa Miyake, Perimeter Institute for Theoretical Physics
  Correlations, information, and complexity in quantum many-body systems

  The advent of quantum information science brought an emergent perspective to quantum many-body systems, and to their distinctive collective phenomena such as magnetism. For instance, the recent research focusing on quantum correlations (or entanglement) is useful to invent new simulation methods on conventional computers, and helps us to analyze better strongly-correlated systems. On the other hand, people are looking for exotic, collective phenomena, convenient for practical applications of quantum information processing, since quantum many-body systems seem to have own mechanism to handle information and to order their correlations. A famous example would be so-called topologically ordered phases of matter as robust quantum memory. It gets clearer by now that quantum many-body physics is more intertwined with the intrinsic complexity of quantum systems than it may have been imagined. In this talk, I like to push this perspective one step further. I would ask, is there a possible, direct way to harness, both conceptually and practically, naturally-occurring quantum many-body correlations for the main-stream goals of quantum information processing? Quantum many-body systems could be seen as excellent, natural resource of complexity, once we learn to release their intrinsic potential to process quantum information. Here I illustrate the idea along with quantum magnetism. It is suggested that quantum correlations, exhibited in the 2D valence bond solid phase (or certain quantum liquid phase) of a quantum Heisenberg-type antiferromagnet, are capable of simulating universal quantum computation with the aid of single-spin measurements.

• Thu 2/23, 3:30PM in Room 190                   print event

  Iman Marvian, Perimeter Institute for Theoretical Physics
  TBA

  TBA

• Tue 2/21, 3:30PM in Room 184                   print event

  Ying-Dan Wang, McGill University
  Quantum state engineering in macroscopic quantum systems

  Is quantum mechanics a universal theory which dominates over the subatomic scale, as well as our macroscopic world? While this old debate is still far from being settled, technical innovations of our times have pushed the quest for quantum coherence into the mesoscopic/macroscopic regime. Among several well-designed systems exhibiting macroscopic quantum coherence, what particularly interests me are opto-mechanical devices and superconducting circuits. These systems have demonstrated great potential in the realization of quantum information and quantum computing. Starting with a brief review of experimental progress, I will discuss our theoretical studies on quantum state engineering of these systems in the presence of environmental noise and their prospects for quantum information processing. Especially, I will show that by making use of quantum interference, a significant improvement can be achieved to transfer quantum states in opto-mechanical systems.

• Tue 2/14, 3:30PM in Room 184                   print event

  Steven Flammia, University of Washington
  Verification and characterization of quantum states and processes

  Recent years have witnessed tremendous progress in laboratory experiments which prepare highly entangled states of quantum many-body systems. As the complexity of these states increases, however, so too does the difficulty in verifying the quality of the experiment by some objective measure and in characterizing any undesired noise processes. In this talk I will discuss several new methods which address both tasks -- verification and characterization -- using far fewer resources than traditional methods. I will begin by discussing compressive sensing, a result from classical signal processing which can drastically reduce the required number of samples to reconstruct the spectrum of a time-dependent signal. By adapting and extending these methods to the setting of quantum mechanical systems, I will show how to verify and characterize a broad class of quantum experiments using quadratically fewer measurement settings than traditional methods, an improvement which is provably optimal. Next, I will show how ideas from quantum information theory and condensed matter physics allow us to efficiently reconstruct the ground state of any local Hamiltonian of a gapped one-dimensional interacting quantum many-body system. Finally, I will show how to directly verify the quality of any experiment which prepares a pure quantum state using only a constant number of measurement settings, independent of the size of the system.

• Tue 2/7, 3:30PM in Room 184                   print event

  Liang Jiang, Caltech
  Quantum information processing using spins and topological quantum systems

  Recently, there are exciting breakthroughs in quantum information science. However, quantum systems suffer from decoherence due to the unavoidable system-environment interaction, which poses a major obstacle to quantum information applications. Nevertheless, conventional quantum systems like spins can be protected from decoherence via dynamical decoupling. I will present some recent results of diamond-based spin systems that can be used for high-resolution nano-magnetometers and room-temperature quantum computers. Another promising approach to suppressing decoherence is to use topological quantum systems, which emerge from condensed matter physics and are insensitive to local perturbations. I will discuss some new ideas to create and probe topological quantum systems, and propose a hybrid platform between topological and conventional quantum systems that can combine the advantages from both.