Speaker: Terence Rudolph (Imperial College London)

Title: A photonic cluster state machine gun

Cluster states are multi-qubit entangled states which have the remarkable property that, once prepared, they can be used to perform quantum computation by making only single qubit measurements.

The problem of constructing a quantum computer therefore reduces to that of preparing these states. Over the last few years one of the more promising architectures for doing so has been single photon optics. However the resource requirements are still prohibitive. In this talk I will discuss a way of turning a single photon source - in particular one built from a self-assembled quantum dot - into a device capable of firing out long strings of entangled cluster state. Remarkably this device can be fired for times much longer than the typical decoherence times of the electron, because any errors on the spin become localized on the emitted photons instead. Such a device would reduce the resource requirements for optical quantum computing by many orders of magnitude.

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Speaker: Chris Monroe (University of Maryland)

Title: Quantum Networks with Ions, Phonons, and Photons

Trapped atomic ions are among the most promising candidates for quantum information processing. All of the fundamental quantum operations have been demonstrated on this system, and the central challenge now is how to scale the system to larger numbers of qubits. By entangling atomic qubits through both deterministic phonon and probabilistic photon interfaces, the trapped ion system can be scaled in various ways for applications in quantum communication, quantum computing, and quantum simulations. I will discuss several options and issues for such atomic quantum networks, along with state-of-the-art experimental progress.

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Speaker: Anthony Laing (University of Bristol )

Title: Quantum Process Discrimination, Waveguides, and Fault Tolerant Quantum Processes

Given the emerging potential of quantum information science where devices including photonic quantum circuits are being miniaturized, making their identification challenging, quantum process discrimination (QPD) has pragmatic, as well as foundational, considerations. Discrimination between unknown quantum processes chosen from a finite set is experimentally shown to be possible even in the case of nonorthogonal processes. We demonstrate unambiguous deterministic QPD of nonorthogonal processes using properties of entanglement, additional known unitaries, or classical communication.

Single qubit measurement and unitary processes, and multipartite unitaries (where the unitary acts nonseparably across two distant locations) acting on photons are discriminated with a confidence of at least 97% in all cases.

In principle these discrimination protocols can be realised with 100% confidence, however the usual imperfect input states and imperfect processes contribute to experimental errors and our discrimination confidence of 97% is not perfect. In this spirit, we go on to discuss recent improved tests of quantum photonic devices (waveguides) and report unprecedented fidelities, which demonstrate that these devices can operate within the fault tolerant regime, by some accepted measures.

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Speaker: Christoph Simon (University of Calgary)

Title: Quantum Repeaters

Coauthors: N. Sangouard, H. de Riedmatten, M. Afzelius, N. Gisin, M. Staudt, J. Minar, H. Zbinden, B. Zhao, Y.-A. Chen, J.-W. Pan, R. Dubessy

I will briefly describe recent progress on the development of practical quantum repeater architectures, where the most immediate goal is to outperform the direct transmission of quantum states. I will focus on architectures using solid-state atomic ensembles as quantum memories, which may allow very efficient temporal multiplexing through the implementation of multimode memories. I will also discuss a promising approach based on trapped ions, which builds on the impressive experimental progress achieved with the goal of quantum computation in mind.

Paper reference: PRL 98, 190503; PRA 76, 050301; PRA 77, 062301; Nature 456, 773; PRA 79, 042340; PRA 79, 052329