This series consists of talks in the area of Quantum Information Theory.
Based on the joint work with Sergey Bravyi, IBM Watson. We show that any topologically ordered local stabilizer model of spins in three dimensional lattices that lacks string logical operators can be used as a reliable quantum memory against thermal noise. It is shown that any local process creating a topologically charged particle separated from other particles by distance $R$, must cross an energy barrier of height $c \log R$. This property makes the model glassy.
In this talk, I will briefly review the recent progress on quantum computation and simulation in the trapped ion system, with particular emphasis on the idea of scaling (how to scale up the number of qubits). I will discuss ideas towards large-scale quantum computation/simulation based on the network approach or the use of transverse phonon modes in anharmonic traps and then review the recent experimental progress along this direction. At the end of the talk, I will also briefly mention recent activities in Tsinghua-Michigan Joint Institute for quantum information.
Quantum field theory provides the framework for the Standard Model of particle physics and plays a key role in many areas of physics. However, calculations are generally computationally complex and limited to weak interaction strengths. I shall describe a polynomial-time algorithm for computing, on a quantum computer, relativistic scattering amplitudes in massive scalar quantum field theories. The quantum algorithm applies at both weak and strong coupling, achieving exponential speedup over known classical methods at high precision or strong coupling.
One of the major obstacles in quantum information processing is to prevent a quantum bit from decoherence. One powerful approach to protect quantum coherence is dynamical decoupling. I will present some recent progress of diamond-based quantum information processing using dynamical decoupling. The other promising approach is to use topological quantum systems, which are intrinsically insensitive to local perturbations. I will discuss some ideas to create and probe topological quantum systems.
Relativistic quantum information theory uses well-known tools coming from quantum information and quantum optics to study quantum effects provoked by gravity and to learn information about the spacetime. One can take advantage of our knowledge about quantum optics and quantum information theory to analyse from a new perspective the effects produced by the gravitational interaction.
The model of an arbitrarily varying quantum channel will be introduced in strict analogy to the classical definition by Blackwell, Breiman and Thomasian. We will then consider the task of entanglement transmission over such a channel and take a look at the methods, both from classical and quantum information theory, that enter the direct part of our proof of a quantum version of Ahlswede's dichotomy for the capacity of classical arbitrarily varying channels. Differences to the classical setting will be pointed out.
A symmetric informationally complete positive-operator-valued measure (SIC POVM) is a special POVM that is composed of d^2 subnormalized pure projectors with equal pairwise fidelity. It may be considered a fiducial POVM for reasons of its high symmetry and high tomographic efficiency. Most known SIC POVMs are covariant with respect to the Heisenberg-Weyl (HW) group. We show that in prime dimensions the HW group is the unique group that may generate a SIC POVM.
We review situations under which a standard quantum adiabatic condition fails. We reformulate the problem of adiabatic evolution as the problem of Hamiltonian eigenpath traversal, and give convergence conditions in terms of the length of the eigenpath and the minimum energy gap of the Hamiltonians. We introduce a randomized evolution method that can be used to traverse the eigenpath and prove its convergence and cost. We then describe more efficient methods for the same task and show that their implementation complexity is close to optimal.