Southwest Quantum Information and Technology

Sixteenth Annual Meeting, February 20-22, 2014
Santa Fe, New Mexico

Full Program | Thursday | Friday | Saturday | All Sessions

SESSION 8: Quantum Simulation, Digital and Analog
1:45pm - 2:30pm	Alan Aspuru-Guzik, Harvard University (invited)
	Towards practical quantum simulators for quantum chemistry
	Abstract. My first talk about quantum computing for chemistry was at SQUINT 2005. Back then, I presented a gate-model approach for the simulation of quantum chemistry. In this talk, almost a decade later, I will present two approaches that are much less demanding on the requirements of the quantum device, yet are able to simulate Fermionic Hamiltonians such as those of molecular quantum chemistry. First, I will talk about the variational quantum eigensolver approach for solving chemistry problems in an arbitrary {\sl hardware ansatz}. I will follow by describing an approach for the simulation of quantum chemistry using adiabatic quantum computers. Both approaches are scalable and good candidates for an early implementation of quantum devices that could carry out a simulation of practical relevance to medical or industrial applications.
2:30pm - 3:00pm	Krysta Svore, Microsoft Research
	Repeat-Until-Success: Non-deterministic decomposition of single-qubit unitaries
	Abstract. We present a non-deterministic circuit decomposition technique for approximating an arbitrary single-qubit unitary to within distance epsilon that requires significantly fewer non-Clifford gates than deterministic decomposition techniques. We develop ``Repeat-Until-Success" (RUS) circuits and characterize unitaries that can be exactly represented as an RUS circuit. Our RUS circuits operate by conditioning on a given measurement outcome and using only a small number of non-Clifford gates and ancilla qubits. We construct an algorithm based on RUS circuits that approximates an arbitrary single-qubit Z-axis rotation to within distance epsilon, where the number of T gates scales as 1.26log_2(1/\epsilon) - 3.53, an improvement of roughly three-fold over state-of-the-art techniques. We then extend our algorithm and show that a scaling of 2.4 log_2(1/\epsilon) - 3.28 can be achieved for arbitrary unitaries and a small range of epsilon, which is roughly twice as good as optimal deterministic decomposition methods.
3:00pm - 3:30pm	Heather Partner, Physikalisch-Technische Bundesanstalt
	Topological defect formation and dynamics in ion Coulomb crystals
	Abstract. Topological defects (kinks) in laboratory systems have attracted recent interest because of their universal nature. In our system, kinks form during nonlinear quenches from the linear to zigzag phase in Coulomb crystals of about 30 172Yb+ ions in a segmented linear trap. I will present our experimental study of probabilistic kink creation in the context of the Kibble-Zurek mechanism, which predicts a scaling for defect creation as a function of quench rate, and discuss the effects of inhomogeneity and finite size in such systems. In addition, I will describe the dynamics of such defects and how they can be controllably modified. These methods provide a toolbox for using kinks to study phase transitions and soliton physics, and as a potential carrier of quantum information.