Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session J3: Recent Progess in Quantum Physics and Quantum Information |
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Sponsoring Units: GQI Chair: Anthony Leggett, University of Illinois Room: LACC 515B |
Tuesday, March 22, 2005 11:15AM - 11:51AM |
J3.00001: Superconducting quantum bits Invited Speaker: Superconducting qubits are solid state electrical circuits fabricated using techniques adapted from conventional integrated circuits. They are based on the Josephson tunnel junction, the only non-dissipative, strongly non-linear circuit element compatible with low temperature operation. In contrast to microscopic entities such as spins or atoms, these qubits tend to be well coupled to other circuits, an appealing feature for readout and 2-qubit gate implementation. Very recently, new circuit topologies have solved the problem of qubit isolation from unwanted extrinsic electromagnetic noise, yielding coherence quality factors in excess of 10,000. Current experiments are addressing the intrinsic decoherence mechanisms in tunnel junctions circuits and whether the Preskill criterion of 10,000 coherent 1- and 2-qubit gate operations can be met. [Preview Abstract] |
Tuesday, March 22, 2005 11:51AM - 12:27PM |
J3.00002: Small quantum algorithms realized in an ion trap array Invited Speaker: Atomic ions confined in an array of traps represent a potentially scalable approach to quantum computing. All basic requirements have been experimentally demonstrated in one and two qubit experiments. The remaining task is to scale the system to hundreds and later thousands of qubits while minimizing and correcting errors in the system. While this requires extremely challenging technological improvements, no fundamental roadblocks are currently foreseen. I will give a survey of recent progress in implementing simple two and three-qubit quantum algorithms with ions in trap arrays. In particular, implementations of quantum teleportation,~quantum error correction and the quantum Fourier transform will be discussed. I will also summarize the prospects and challenges of scaling this particular approach towards a large scale computing device. [Preview Abstract] |
Tuesday, March 22, 2005 12:27PM - 1:03PM |
J3.00003: Photonic Quantum Communication and One-Way Quantum Computation Invited Speaker: A century after Einstein's invention of the photon concept and 80 years after the introduction of entangled states by Einstein-Podolsky-Rosen and by Schrodinger, entangled photon states have become important in quantum communication and quantum computation schemes. Quantum communication with entangled states is approaching large distances and experiments involving even satellite-bases systems become possible. In some schemes like teleportation and entanglement swapping active feed forward of Bell state measurement results is an essential part of the scheme: together with the intrinsic randomness of the individual measurement result a violation of Einstein relativity is avoided that way. Active feed forward then plays a central role in the completely novel concept of one-way quantum computation as proposed by Raussendorf and Briegel. That concept is qualitatively different from all quantum computer concepts where a sequence of one- and two-qubit quantum gates acts on a suitably chosen input state. In contrast the one-way quantum computer scheme starts with a sufficiently complex and general highly entangled initial state, a cluster state. The specific calculation performed is then defined as a specific sequence of measurements performed on that initial state. An important point is that the specific choice of later measurements is defined by the results of earlier measurements. Using such active feed-forward the one-way quantum computer overcomes the problem of the intrinsic randomness of the individual results in quantum measurement. For photons, the one-way quantum computer can be seen as an extension of the linear optics quantum computation proposal by Knill, Laflamme and Milburn. Recently we realized a one-way quantum computer using four- photon entangled cluster states (P. Walther, K. J. Resch,, T. Rudolph, E. Schenk, H. Weinfurter, V. Vedral, M.Aspelmeyer {\&} A. Zeilinger, submitted to Nature). The state was characterized by full four-qubit tomography. Using various types of cluster states a universal set of 1- and 2-qubit operations was demonstrated. Finally, a Grover search algorithm was implemented. [Preview Abstract] |
Tuesday, March 22, 2005 1:03PM - 1:39PM |
J3.00004: Probabilities From Envariance: Born's Rule (And More) From Entanglement Invited Speaker: Wojciech Hubert Zurek I shall discuss consequences of envariance (environment - assisted invariance), a symmetry exhibited by entangled quantum states [1]. I shall focus on the implications of envariance for the understanding of the origins and nature of ignorance, and, hence, for the origin of probabilities in physics. While the derivation of Born's rule for probabilities ($p_k = |\psi_k|^2$) is the principal accomplishment [1-3] of this research, I shall discuss the possibility that essentially all other symptoms of the quantum - classical transition that are now justified using decoherence (e.g. pointer states, einselection, etc.) can be understood as a direct consequence of envariance, without invoking Born's rule explicitly or implicitly (that is, without using ``trace" or reduced density matrices). Thus, envariance appears to supply a new and deep foundation for the origin of quantum probabilities and, more generally, leads to a new understanding of the quantum origins of the classical [5]. [1] W. H. Zurek, PRL 90, 120404 (2003); RMP 75, 715 (2003). [2] H. Barnum, quant-ph/0312150; M. Shlosshauer \& A. Fine, quant-ph/0312058 [3] W. H. Zurek, quant-ph/0405161 [Preview Abstract] |
Tuesday, March 22, 2005 1:39PM - 2:15PM |
J3.00005: Bell Nonlocality and Retrospective Error Correction for Noisy Channels Invited Speaker: Using a channel similar to one side of a Bell inequality experiment, we show how the auxiliary resources of shared sender:receiver entanglement and classical back communication, neither of which increases the forward capacity of any classical channel, can greatly increase both the quantum and classical capacities of some quantum channels. Joint work with Igor Devetak, Peter Shor, and John Smolin. [Preview Abstract] |
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