Southwest Quantum Information and Technology

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

Full Program | Thursday | Friday | Saturday | All Sessions

SESSION 9c: Break-out 3: Atoms and Photons
4:00pm - 4:30pm	Hector Sosa Martinez, University of Arizona
	New Tools for Unitary Control of Cold Atom Qudits
	Abstract. Accurate and robust quantum control of single or coupled qubit systems is a key element of quantum information science. In practice, the actual physical building blocks (atoms, ions, superconducting devices) are often qudits with state space dimension d>2, and the available auxiliary levels have proven useful for information processing tasks such as implementing Toffoli gates with two-body interactions. More generally, large internal state spaces may prove a useful resource if good laboratory tools for qudit manipulation can be developed. As a laboratory test bed for such development, we have implemented a protocol to perform arbitrary unitary transformations in the 16 dimensional ground hyperfine manifold of individual 133Cs atoms, by driving this system with phase modulated rf and microwave magnetic fields and using the tools of optimal control to find appropriate control waveforms. Similar to what can be achieved for qubits, we show that accurate unitary control can be achieved in the presence of simultaneous static and dynamical perturbations and imperfections in the control fields, simply by optimizing with respect to the appropriate cost function when designing control waveforms. We anticipate this approach to prove helpful for control in less than ideal environments, such as atoms moving around in the light shift potential of a dipole trap. We are currently exploring the prospects for inhomogeneous quantum control, with the goal of performing different unitary transformations on qudits that see different light shifts from an optical addressing field. Ultimately this may lead to addressable unitary control similar to what has been demonstrated for atomic qubits in optical lattices.
4:30pm - 5:00pm	David Rideout, University of California, San Diego
	Quantum optics experiments at Earth-orbital scales and beyond
	Abstract. A number of national and international entities are racing to set up satellite-based quantum communication infrastructure, which would allow the construction of a global network for quantum key distribution. The construction of such a network poses numerous technological challenges, considering that quantum entanglement has not yet been demonstrated at such scales. I will provide some details of a Canadian Space Agency funded mission to demonstrate quantum entanglement between the Earth's surface and Low Earth Orbit, and sketch some tests of fundamental physics which could be enabled by such satellites, ranging from verification of quantum mechanics to tests of spacetime discreteness from quantum gravity.
5:00pm - 5:30pm	Matthias Lang, University of New Mexico
	Optimal quantum-enhanced interferometry using a laser power source
	Abstract. We consider an interferometer powered by laser light (a coherent state) into one input port and ask the following question: what is the best state to inject into the second input port, given a constraint on the mean number of photons this state can carry, in order to optimize the interferometer’s phase sensitivity? This question is the practical question for high-sensitivity interferometry. We answer the question by considering the quantum Cramer-Rao bound for such a setup. The answer is squeezed vacuum, if there are no photon losses in the interferometer. For a lossy interferometer, the squeezed vacuum is the best choice for the practical case where the laser power is much bigger than the power put into the squeezing.
5:30pm - 6:00pm	Collin Trail, University of Calgary
	On generating macroscopic superpositions via nonlinear dynamics of stopped light in a two-component Bose-Einstein condensate
	Abstract. We investigate a method for generating nonlinear phase shifts on superpositions of photon number states. The light is stored in a Bose-Einstein condensate via electromagnetically-induced transparency memory techniques. The atomic collisions are exploited to generate a nonlinear evolution for the stored state. The stored light is then revived with the nonlinear phase shift imprinted upon it. For the special case of a coherent state input we find that this method can be used to generate an optical cat state. We investigate the validity of using the Thomas-Fermi and mean-field approximations.