Southwest Quantum Information and Technology

Twelfth Annual Meeting, February 18-21, 2010
Santa Fe, New Mexico

Full Program | Thursday | Friday | Saturday | Sunday

SESSION 6: Neutral Atom QI
Session Chair:
8:30-9:15	Dieter Meschede, Universitaet Bonn
	"Quantum Interference Experiments with One and More Neutral Atoms"
	Abstract. The wave properties of material particles are one of the most widely known features of quantum physics. Wave properties become apparent in diffraction and perhaps most strikingly in interference phenomena. In this talk I will present experiments where we trap and control up to a dozen neutral atoms by means of optical dipole forces. I will show how to selectively address individual atoms, how to transport and sort them, and how to store and retrieve information from the atomic qubits. Recently, we have have taken the atoms to the full quantum regime, i.e. to the observation of matter wave interferences at the single trapped atom level. We have demonstrated the quantum analogue of Brownian motion, the quantum walk, a concept of relevance in quantum information science. We have furthermore obtained excellent control of atomic motion using microwaves, including cooling to the vibrational ground levels and the creation of single particle entangled states. In a separate line of experiments we have been able to read out the spin quantum states in dispersive manner. I will discuss the options to create correlated many atom quantum states based on the available protocols.
9:15-9:45	David Moehring, Sandia National Laboratories
	Single-Atom Single-Photon Quantum Interface
	Abstract. We report on the implementation of a deterministic protocol where a single rubidium atom trapped within a high-finesse optical cavity is entangled with a single emitted photon. After a chosen time, the atomic state is mapped onto a second photon, thus generating an entangled photon pair. Compared to previous experiments, the long trapping times of exactly one atom in the mode of the cavity allow for 10^5 times more entangled photons per atom. The entanglement is verified by a Bell inequality measurement and via quantum state tomography, both showing a clear violation of classical physics. The combination of two independent atom-cavity systems may further allow for the efficient generation of remote-atom entanglement in the near future. *The presented work was completed at the Max Planck Institute of Quantum Optics in the group of Gerhard Rempe.
10:15-10:45	Brian Mischuck, University of New Mexico
	Quantum Control of Neutral Atoms Qudits and Transport
	Abstract. Quantum control offers a variety of techniques to manipulate quantum systems in order to perform a desired evolution. We describe the application of these ideas to two different problems in the control of neutral atoms. In the first problem, we consider control of the hyperfine spin manifold a cloud of cold atoms driven by microwave and radio-frequency fields. The large number of spin states available in individual atoms makes them candidates for a qudit based quantum computer. Because the Hamiltonians that drive the system may vary spatially and/or temporally, collections of atoms form ensembles of distinguishable qudits. Borrowing from ideas originally developed for NMR, we show how to drive the ensembles through a given desired evolution. This allows for robust control and spatial selectivity of ensembles of atoms. In the second problem we show how atoms’ transport in an optical lattice can be controlled through polarization control of the optical lattice and global microwave pulses. This control is a necessary first step in many of the neutral atom based schemes for quantum computation and simulation, as well as a realization of a quantum walk. We show that with the available global control, any unitary or state synthesis consistent with translational invariance may be performed.
10:45-11:15	Aaron Smith, University of Arizona
	Quantum State Mapping in the Cs 133 Full Hyperfine Ground Manifold
	Abstract. Aaron Smith, Brian E. Anderson, Poul Jessen: Center for Quantum Information and Control, College of Optical Sciences, University of Arizona Quantum systems with Hilbert space dimension greater than two (qudits) are often thought of as carriers of quantum information, usually by isolating a convenient pair of states (qubit) and working entirely within this two dimensional embedded subspace. Quantum control of the entire qudit system could prove to be very useful for information processing tasks allowing for the implementation of novel protocols for robust qubit manipulation and error correction. Quantum control of systems with large Hilbert space dimension, especially collective spins, also has near-term applications in quantum metrology. We will describe a method in which to achieve universal quantum control of the entire 16 dimensional hyperfine ground manifold of Cesium using a nearly decoherence free protocol involving the application of static, RF, and microwave magnetic fields. A simple numerical optimization routine can be used to design time dependent control fields that map any initial state onto any target state. We have implemented this control protocol in our experiment and have successfully mapped our initial state, \|F=4, m=4>, onto all 16 magnetic eigenstates. We measure the fidelity of the state mapping using Stern-Gerlach analysis and we have achieved fidelities in the range ~ 94% - 98% which is limited almost entirely by errors in the control fields. Our next step is to implement a weak measurement in combination with dynamical control, and to perform quantum state reconstruction based on the resulting measurement record.
11:15-11:45	Katharina Gillen, California Polytechnic State University, San Luis Obispo
	A neutral atom quantum memory created by diffraction of laser light at an array of pinholes
	Abstract. We present an idea for a new quantum memory for neutral atom quantum computing: Atom traps formed behind an array of pinholes. The diffraction pattern directly behind a circular aperture exhibits localized intensity maxima and minima that can serve as red-detuned or blue-detuned dipole traps for cold atoms, respectively. Previous calculations [1] suggest that the trap frequencies (kHz to 10s of kHz) achieved for even moderate laser powers (~100 mW) are theoretically sufficient for trapping atoms with low decoherence rates from motional heating and trap light scattering. This approach can be extended to an array of pinholes, thereby creating a 2D array of trapping sites that can be used as a quantum memory. The 2D geometry allows addressing of individual trapping sites with a focused laser beam for performance of single qubit operations. In addition to trapping atoms in the sites of this pattern, the polarization-dependence of atoms in certain atomic substates [2] can be exploited to bring pairs of atoms together and apart to facilitate two-qubit quantum gates. We will discuss our latest computational results on these trap arrays and the ability of bringing pairs of traps together and apart for quantum operations. [1] G. D. Gillen, et al., Phys. Rev. A 73, 013409 (2006), [2] I. H. Deutsch, et al., Phys. Rev. A, 57 (3), 1972-1986 (1998).