Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session L15: Focus Session: Progress toward Scalable Quantum Information Processing |
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Sponsoring Units: GQI Chair: Dana Berkeland, IARPA Room: Morial Convention Center 207 |
Tuesday, March 11, 2008 2:30PM - 3:06PM |
L15.00001: Ensemble encoding of quantum registers: it's easy if you can count to one Invited Speaker: We present a new encoding of qubits in multi-bit registers which makes use of the collective population of a set of internal states of an ensemble of identical quantum systems. This establishes a linear rather than exponential relationship between the number of bits and the internal state Hilbert space dimension of our basic physical system. The key requirement of our proposal is that we can count to one and restrict the collective populations to the values zero and unity. We propose physical implementations and recipes for one- and two-bit gates with ground state atoms interacting via Rydberg excited states, offering up to 14 bits in a small cloud of cesium atoms, and with polar molecules interacting via a stripline cavity field and a Cooper pair box, offering even larger register sizes. [Preview Abstract] |
Tuesday, March 11, 2008 3:06PM - 3:42PM |
L15.00002: Progress toward scalable optical quantum computing Invited Speaker: Quantum computing holds great promise for solving certain problems which would be intractable using classical computing architectures. Compared to other carriers of other quantum information (e.g., ions, spins, or superconductors) photons have the simultaneous advantage and disadvantage of interacting with the environment and each other only weakly. They are thus relatively immune to decoherence, but it is difficult to achieve the required qubit-qubit interactions. Fortunately, in 2001 Knill, Laflamme, and Milburn proposed a scheme that was scalable at least in principle, if not in practice (too many resources per gate were required). Since then, the ideas were merged with those of ``one-way quantum computing'' to realize a scalable approach based on ``cluster states'', with much more modest – though still very challenging - resource requirements. Here I will describe some of the challenges and recent successes, both in implementing the necessary resources (i.e., high-efficiency detectors, single- and entangled-photon sources, and fast logic), and in applying these to realize some basic quantum computing primitives (single- and two-qubit gates and some simple algorithms). [Preview Abstract] |
Tuesday, March 11, 2008 3:42PM - 3:54PM |
L15.00003: Experimental demonstration of decoherence-free one-way quantum information processing Robert Prevedel, Mark S. Tame, Andr\'e Stefanov, Mauro Paternostro, Myungshik Kim, Anton Zeilinger In recent years, one-way quantum computing has become an exciting alternative to existing proposals for quantum computers. In this specific model, coherent quantum information processing (QIP) is accomplished via a sequence of single-qubit measurements applied to an entangled resource known as cluster state. However, there has so far been no experimental realization of noise-resilient quantum computation in the one-way model. Here we report the experimental demonstration of a one-way quantum processor reliably operating under the effects of decoherence. Information is protected by a properly designed decoherence-free subspace in which the cluster states reside. We demonstrate our scheme in an all-optical setup by encoding the information into the polarization states of four photons. A one-way information-transfer protocol is performed with the photons exposed to severe symmetric phase damping noise. Remarkable protection of information is accomplished, delivering nearly ideal computational outcomes. [Preview Abstract] |
Tuesday, March 11, 2008 3:54PM - 4:06PM |
L15.00004: Entangling the optical frequency comb into multiple continuous-variable cluster states Olivier Pfister, Hussain Zaidi, Nicolas Menicucci, Steven Flammia, Russell Bloomer, Matthew Pysher A single multimode optical parametric oscillator (OPO) can be designed so that its nonlinear gain medium (typically a two-photon parametric amplifier) generates a particular network of entangling interactions between the eigenmodes of its optical cavity. We show how this can be formulated using nonstandard graph states and how these are related to the usual graph states, an example of which is the cluster state for one-way quantum computing. We also report on the progress of our very compact experimental implementation, in a single OPO with a single pump field, of a parallel quantum register comprising several independent quadripartite cluster states. [Preview Abstract] |
Tuesday, March 11, 2008 4:06PM - 4:18PM |
L15.00005: Experimental Teleportation-Based Quantum Gate Kai Chen, Alexander Goebel, Claudia Wagenknecht, Yu-Ao Chen, Jian-Wei Pan For large scale quantum computation, the coupling of physical qubits to the environment imposes a major challenge for a real- life implementation. Teleportation-based scheme offers an alternative way for scalable quantum computing. Most attractively, this architecture allows for realizations of universal quantum gates in a fault-tolerant manner as shown by Gottesman and Chuang, and in fact serves as an important basis for measurement-based quantum computing. We report a proof-in- principle experimental implementation of this architecture by demonstrating a teleportation based two-qubit CNOT (controlled NOT) gate through linear optics with 6-photon scheme. By preparation of high-fidelity four-photon cluster states and applying two Bell state measurements with an arbitrary input of two qubits, the desired quantum gate operations are teleported onto the remaining two qubits of the cluster states. Our novel architecture and experimental demonstration for teleportation- based linear optics quantum computing could serve as an essential basis toward resource-efficient, scalable quantum computation and yielding fault tolerance automatically. [Preview Abstract] |
Tuesday, March 11, 2008 4:18PM - 4:30PM |
L15.00006: Generation arbitrary permutation symmetric state with projection Fangwen Sun, Chee Wei Wong We proposed a scheme to generate arbitrary permutation symmetric multi-partite state. The system contains N equally single quantum particles (We use atoms for these particles) which may interact with single photon to generate entanglement between them. This entanglement can be obtained by the transition from three-level $\Lambda $ atom's exited state to different low levels and emitting corresponding polarized photon, or by inputting a single-photon to a trapped atom to gain different phase shift . After preparing N photon-atom entangled states, the N photons are coupled into same path mode to erase the \textit{Welcher-Weg} information. By postselection ($\frac{N}{2}+k$) photons in one polarization state and ($% \frac{N}{2}-k$) photons in its orthogonal polarization state with N-fold coincidence counts, we can generate the atom Dicke state $\left\vert \frac{N% }{2},k\right\rangle $. Moreover, the arbitrary superposition of these Dicke states can be generated by constructing corresponding projection measurements, which includes multi-atom GHZ state. Based on the discussion on the entanglement between different degrees of freedom, we will show that the projection measurement can also be constructed in the far- field region without combining all photons in one path mode. [Preview Abstract] |
Tuesday, March 11, 2008 4:30PM - 4:42PM |
L15.00007: Single photon Mach-Zehnder interferometer for quantum networks based on the Single Photon Faraday Effect: principle and applications Hubert Seigneur, Michael Leuenberger, Winston Schoenfeld Combining the recent progress in semiconductor nanostructures along with the versatility of photonic crystals in confining and manipulating light, quantum networks allow for the prospect of an integrated and low power quantum technology. Within quantum networks, which consist of a system of waveguides and nanocavities with embedded quantum dots, it has been demonstrated in theory that many-qubit states stored in electron spins could be teleported from one quantum dot to another via a single photon using the Single Photon Faraday Effect. However, in addition to being able to transfer quantum information from one location to another, quantum networks need added functionality such as (1) controlling the flow of the quantum information and (2) performing specific operations on qubits that can be easily integrated. In this paper, we show how in principle a single photon Mach-Zehnder interferometer, which uses the concept of the single photon Faraday Effect to manipulate the geometrical phase of a single photon, can be operated both as a switch to control the flow of quantum information inside the quantum network and as various single qubit quantum gates to perform operations on a single photon. Our proposed Mach-Zehnder interferometer can be fully integrated as part of a quantum network on a chip. [Preview Abstract] |
Tuesday, March 11, 2008 4:42PM - 4:54PM |
L15.00008: High threshold 2D nearest neighbor quantum computation. Austin Fowler, Peter Groszkowski, Robert Raussendorf We describe a quantum computation scheme on a 2D nearest neighbor coupled square lattice of qubits that requires relatively few physical qubits per logical qubit, permits logical operations between arbitrarily distant logical qubits in almost constant time and has a physical gate threshold error rate of almost 1{\%}. To the best of our knowledge, no other quantum computation scheme simultaneously possesses all of these desirable properties. [Preview Abstract] |
Tuesday, March 11, 2008 4:54PM - 5:06PM |
L15.00009: A Universal Operator Theoretic Framework for Quantum Fault Tolerance. Gerald Gilbert, Robert Calderbank, Vaneet Aggarwal, Michael Hamrick, Yaakov Weinstein We introduce a universal operator theoretic framework for quantum fault tolerance. This incorporates a top-down approach that implements a system-level criterion based on specification of the full system dynamics, applied at every level of error correction concatenation. This leads to more accurate determinations of error thresholds than could previously be obtained. The basis for the approach is the Quantum Computer Condition (QCC), an inequality governing the evolution of a quantum computer. In addition to more accurate determination of error threshold values, we show that the QCC provides a means to systematically determine optimality (or non-optimality) of different choices of error correction coding and error avoidance strategies. This is possible because, as we show, all known coding schemes are actually special cases of the QCC. We demonstrate this by introducing a new, operator theoretic form of entanglement assisted quantum error correction. [Preview Abstract] |
Tuesday, March 11, 2008 5:06PM - 5:18PM |
L15.00010: Structure and quantum-dynamics relationship in spin networks Luis Cajamarca, Luis Quiroga We report on the relationship of the spin dynamics with the quantum network topology. The network consists of N-1 spins-1/2 arranged along a circle, also referred to as a ring, equidistant to a central spin (Heisenberg star or ring topology). Every spin along the ring interacts with its first neighbors by means of a coupling constant J2, as well as with the central spin by means of a constant coupling J1. Both couplings are of antiferromagnetic nature and the competition among these incorporates the well known magnetic frustration behavior, which is characteristic of this type of systems. A full analysis of the quantum system's dynamics is carried out for the two limiting cases of coupling constants. We analyze the ground state transitions of the system as well as correlations between any pair of spins including the temperature dependence. The time evolution of the central spin is also analyzed for a given preparation state of the whole spin network. Finally, an stochastic element is incorporated into the system by disconnecting the central spin with any spin along the ring in a random manner. Such dynamics is referred to as dilution and allows us to describe how quantum quantities, such as spin coherences, entanglement and general quantum correlations, depend on the different path topologies between the considered spins (classical structural quantities). Extensions to more complex network topologies are also addressed. [Preview Abstract] |
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