Southwest Quantum Information and Technology

Thirteenth Annual Meeting, February 17-20, 2011
Boulder, Colorado

Full Program | Thursday | Friday | Saturday | Sunday | All Sessions

SESSION 11: Ion Trap QIP
Session Chair:
8:30am-9:00am	Christian Ospelkaus, National Institute of Standards and Technology, Boulder
	Quantum information processing with trapped ions at NIST
	Abstract. We discuss experiments towards scalable Quantum Information Processing (QIP) in the Ion Storage Group at NIST Boulder. The architecture we pursue is based on quantum information stored in internal (hyperfine) states of the ions. Laser beams are used to induce both single-qubit gates and multi-qubit gates through the Coulomb interaction between ions held in the same potential well. Transport of ions allows for keeping the number of ions per trap zone small and for individual addressing. We first describe a set of experiments that demonstrate these basic techniques with two qubits in a scalable way to realize a programmable quantum processor. Based on current efforts towards scalable surface-electrode trap arrays, we discuss the integration of the various experimental techniques, for example integrated fiber-optic readout. We also discuss studies on decoherence and efforts to improve the fidelity of entangling operations. Moreover, we explore techniques that go beyond the established scheme of laser-based multi-qubit gates on ions held in a common trap. We demonstrate Coulomb coupling between two ions (mechanical oscillators) held in individual traps separated by 40 μm and observe oscillations of single energy quanta between the two ions. Furthermore, we explore a microwave near-field approach to quantum control. In particular we observe microwave single-qubit rotations with pi times of less than 20 ns, motional sideband transitions, and cooling of the ion motion. These two techniques could open new experimental perspectives for quantum simulation in surface-electrode trap arrays, for novel entangling schemes for QIP, and for precision spectroscopy. In related work our group explores multiqubit entanglement of ions in Penning traps and applications of quantum information protocols to optical atomic clocks. This work has been supported by IARPA, DARPA, NSA, ONR, and the NIST Quantum Information Program.
9:00am-9:30am	Kihwan Kim, Joint Quantum Institute and University of Maryland
	Quantum simulation with trapped atomic ions
	Abstract. As Feynman proposed a couple of decades ago, a well-controlled quantum system called a "quantum simulator" can efficiently simulate other interesting and complex quantum systems that are otherwise intractable. For a collection of spins subject to a fully-connected frustrated Ising interaction, current conventional computations can simulate no more than about 20-30 spins. A crystal of trapped ions system is one of most promising quantum systems for the realization of such a quantum simulator. We demonstrate the quantum simulation of a frustrated Ising Hamiltonian in a transverse field with 3 spins [1] and increase the number of spins up to 9 for the case of all ferromagnetic interactions [2]. This is an important benchmark as the system is fast approaching a level where classical simulation will not be possible. In the experiment with up to 9 spins, we observe several technical imperfections such as state detection efficiencies, spontaneous emissions, AC stark shift fluctuations, qubit decoherence of qubits, and heating of motion. We find that these errors do not appreciably affect the observation of the magnetic order while crossing a phase transition from paramagnetism to ferromagnetism as the system size increases. We finally speculate on how this system can be scaled to models that cannot be simulated using classical computers. This research was supported by the DARPA OLE program under ARO contract, IARPA through ARO contract, the NSF PIF Program, the AQUTE program, and the NSF Physics Frontier Center at JQI. [1] K. Kim, et al., Nature 465, 590 (2010). [2] In preparation
9:30am-10:00am	Thomas Noel, University of Washington
	Rapid Adiabatic Passage on a Trapped Ion with a Noisy Laser
	Abstract. We report experimental investigation of rapid adiabatic passage (RAP) in a trapped ¹³⁸Ba⁺ system. RAP is implemented on the transition from the ¹³⁸Ba⁺ ground state to a metastable D state by applying a laser at 1.76 μm. We focus on the interplay of laser noise and laser power in shaping the effectiveness of RAP, which has been shown to be a robust tool for state detection of ionic qubits. However, we note that reaching high state transfer fidelity requires a combination of small laser linewidth and large rabi frequency.