Southwest Quantum Information and Technology

Eleventh Annual Meeting, February 19-22, 2009
Seattle, Washington

Full Program | Thursday | Friday | Saturday | Sunday

SESSION 10: Breakout III - Decoherence
Session Chair:
3:30-4:00	Mark Byrd, Southern Illinois University
	Creating and manipulating quantum decoherence-free, or noiseless, systems of qudits
	Abstract. Qudits are promising candidates for many quantum information processing tasks. They can be more entangled than qubits, can share a larger fraction of the entanglement in some cases, and may be required for some quantum information processing tasks. I will show how to make entangled qutrit states using photons which form a decoherence-free subspace and show how, in principle, we can manipulate qudit decoherence-free subspaces comprised of quDits.
4:00-4:30	Michael Biercuk, NIST - Ion Storage Group
	Dynamical Decoupling in a Model Quantum Memory
	Abstract. We present results on the application of Dynamical Decoupling (DD) pulse sequences for the suppression of phase errors in a qubit array consisting of a laser-cooled crystal of trapped Beryllium ions. We study various DD sequences including CPMG and the recently discovered Uhrig DD sequence. Our results demonstrate the ability of UDD and CPMG to strongly suppress phase errors in the presence of ambient magnetic field noise, and show strong agreement with theoretical predictions for qubit decoherence. We also generate noise artifically and compare the efficacy of these DD sequences in Ohmic, 1/f and 1/f^2 noise environments -- making our qubit array a model quantum system capable of emulating solid state noise environments. Finally, we demonstrate real-time experimental optimization of DD pulse sequences without any required knowledge of the ambient noise environment.
4:30-5:00	Sergio Boixo, California Institute of Technology
	Quantum computing through decoherence
	Abstract. A computation in adiabatic quantum computing is achieved by traversing a path of nondegenerate eigenstates of a continuous family of Hamiltonians. We introduce a method that traverses a discretized form of the path: at each step we evolve with the instantaneous Hamiltonian for a random time. The resulting decoherence approximates a projective measurement onto the desired eigenstate, achieving a version of the quantum Zeno effect. For bounded error probability, the average evolution time required by our method is O(L^2 /D), where L is the length of the path of eigenstates and D the minimum spectral gap of the Hamiltonian. The randomization also works in the discrete-time case, where a family of unitary operators is given, and each unitary can be used a finite amount of times. Applications of this method for unstructured search and quantum sampling are considered. We discuss the quantum simulated annealing algorithm to solve combinatorial optimization problems. This algorithm provides a quadratic speed-up (in the gap) over its classical counterpart implemented via Markov chain Monte Carlo.
5:00-5:30	Cesar Rodriguez-Rosario, Harvard University
	Non-Markovian Environmental Contributions to the Efficiency of Energy Transfer
	Abstract. Non-Markovian environmental effects have been experimentally observed in the Fenna-Matthews-Olson photosynthetic complex, but their role is not understood. We study the dynamical contribution of the environment to the efficiency of energy transfer by considering a non-Markovian environment and its interplay with the system Hamiltonian. We focus on the role of memory effects of different orders in time, and their competition that affect the energy transfer by defining the efficiency of the non-Markovian process. This efficiency measure has applications to the study of the quantum transport efficiency and engineering of light-harvesting devices.