Bulletin of the American Physical Society
Inaugural Fall 2009 Meeting of the Prairie Section of the APS
Volume 54, Number 17
Thursday–Saturday, November 12–14, 2009; Iowa City, Iowa
Session D2: AMO and Plasma I |
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Chair: Robin Santra, Argonne National Laboratory Room: IMU 243 (Ballroom) |
Friday, November 13, 2009 8:30AM - 8:42AM |
D2.00001: Scalable Quantum Information Processing with Ultracold Neutral Atoms Arjun Sharma, Kathy-Anne Brickman Soderberg, Kara Lamb, Peter Scherpelz, Nathan Gemelke, Cheng Chin Remarkable experimental progress has been made over the last decade in realizing the necessary requirements for quantum information processing. Of all the approaches, cold atoms are at the forefront due to the precise control possible over both the external trapping potential and the atoms' internal structure. Two key issues are scaling up the number of quantum bits (qubits) and individually addressing qubits for targeted operations. We present an experiment able to overcome these difficulties. Two species of ultra cold neutral atoms confined in independent, overlapping optical lattices are the basis of our computer. One atomic species is loaded into a lattice with unit filling and act as qubits. The other species, less densely populated in a second lattice, are messenger atoms that allow for individual qubit addressing and aid in entangling operations. By translating the lattices, the messenger and qubits are brought into contact for qubit operations. This makes the scheme scalable to entangle any two distant qubits. [Preview Abstract] |
Friday, November 13, 2009 8:42AM - 8:54AM |
D2.00002: In situ Microscopy of an Ultracold Atomic Gas near a Quantum Phase Transition Xibo Zhang, Chen-Lung Hung, Nathan Gemelke, Cheng Chin In situ observation of quantum phases in ultracold atoms realizes a key step in experimental many-body physics. By identifying coexisting local phases in an inhomogeneous system, in situ imaging holds promise for studying quantum criticality and dynamics. Here we study the bosonic superfluid (SF) to Mott insulator (MI) transition by applying high resolution imaging to a large 2D sample to identify the emergence of new phase domains near the critical point. Starting from a cesium 133 BEC loaded into a 2D potential, we drive the SF to MI transition by ramping up a 2D optical lattice. The surface density is measured by absorption imaging along the tightly confined direction. To identify the phases, we compute the local compressibility from the averaged density profile. As the final lattice depth is increased, the cloud center develops a flattened density plateau with almost zero compressibility, indicating a MI phase. We also observe suppressed density fluctuation in the MI domain, which is consistent with the fluctuation-dissipation theorem. Our technique can be extended to explore quantum fluctuations, correlations, thermodynamics, and dynamics in the quantum critical regime. [Preview Abstract] |
Friday, November 13, 2009 8:54AM - 9:06AM |
D2.00003: The breakdown of one-dimensional fermionic and bosonic vaccua in strong fields M. Ware, T. Cheng, Q. Su, R. Grobe We compare the creation rates for particle-antiparticle pairs produced by a supercritical force field for fermionic and bosonic model systems. The rates obtained from the Dirac and Klein-Gordon equations can be computed directly from the quantum mechanical transmission coefficients describing the scattering of an incoming particle with the supercritical potential barrier. We provide a unified framework that shows that the bosonic rates can exceed the fermionic ones, as one could expect from the Pauli exclusion principle for the fermion system. This imbalance for small but supercritical forces is associated with the occurrence of negative bosonic transmission coefficients of arbitrary size for the Klein-Gordon system, while the Dirac coefficient is positive and bound by unity. We confirm the transmission coefficients with time-dependent scattering simulations. For large forces, however, the fermionic and bosonic pair creation rates are surprisingly close to each other. The predicted pair-creation rates also match the slopes of the time-dependent particle probabilities obtained from large-scale ab initio numerical simulations based on quantum field theory. [Preview Abstract] |
Friday, November 13, 2009 9:06AM - 9:18AM |
D2.00004: Computational approach to pair-creation processes Q. Su, M. Ware, T. Cheng, R. Grobe We examine the spontaneous breakdown of the matter vacuum triggered by an external force of arbitrary strength and spatial and temporal variations. We derive a non-perturbative framework that permits for the first time the computation of the complete time evolution of various multiple electron-positron pair probabilities. These time-dependent probabilities can be computed from a generating function as well as from solutions to a set of rate-like equations with coupling constants determined by the single-particle solutions to the time-dependent Dirac equation. This approach might be of relevance to the planned experiments to observe for the first time the laser-induced breakdown process of the vacuum. [Preview Abstract] |
Friday, November 13, 2009 9:18AM - 9:54AM |
D2.00005: Space-time resolved quantum field theory Invited Speaker: We have solved simplified model versions of the time-dependent Dirac and Yukawa equation numerically to study the time evolution of electrons, positrons and photons with full spatial resolution. The goal is to better understand how various particle creation and annihilation processes that require quantum field theory can be visualized. There are many open ended questions that we will address. Are particles and their antimatter companions created instantly, or do they require a certain minimum amount of time? Are they created at precisely the same location? What is the difference between a bare and a physical particle? Forces between two particles are usually understood on a microscopic level as the result of an exchange of bosonic particles. How can the same microscopic exchange mechanism lead to a repulsion as well as an attraction? Do these force intermediating particles ``know'' about the charges of the two interacting particles? How can one visualize this exchange? Does it really make sense to distinguish between virtual and real particles? We also examine how a bare electron can trigger the creation of a cloud of virtual photons around it.\\[4pt] In collaboration with R. Wagner, Intense Laser Physics Theory Unit, Illinois State University; C. Gerry, Lehman College and ILP-ISU; T. Cheng and Q. Su, Intense Laser Physics Theory Unit, Illinois State University. [Preview Abstract] |
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