Tag Archives: quantum computing

Q+ Hangout: Daniel Gottesman

Here are the details of the next Q+ hangout. To watch live, visit this link at the appointed hour.

Date/time: Tue. May 20th 2014 2pm BST/UTC+1

Speaker: Daniel Gottesman (Perimeter Institute)

Title: Fault-tolerant quantum computation with constant overhead

Abstract: The threshold theorem for fault tolerance tells us that it is possible to build arbitrarily large reliable quantum computers provided the error rate per physical gate or time step is below some threshold value. Most research on the threshold theorem so far has gone into optimizing the tolerable error rate under various assumptions, with other considerations being secondary. However, for the foreseeable future, the number of qubits may be an even greater restriction than error rates. The overhead, the ratio of physical qubits to logical qubits, determines how expensive (in qubits) a fault-tolerant computation is. Earlier results on fault tolerance used a large overhead which grows even larger (albeit slowly) with the size of the computation. I show that it is possible in principle to do fault-tolerant quantum computation with the overhead constant in the size of the computation, and with a low constant at that. The result depends on recent progress on quantum low-density parity check codes.

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Q+ Hangout: Troels Frimodt Rønnow

Here are the details of the next Q+ hangout

Date: 28th January 2014

Time: 2pm UTC/GMT

Speaker: Troels Frimodt Rønnow (ETH Zurich)

Title: Quantum annealing on 503 qubits

Abastract: Quantum speedup refers to the advantage of quantum devices can over classical ones in solving classes of computational problems. In this talk we show how to correctly define and measure quantum speedup in experimental devices. We show how to avoid issues that might mask or fake quantum speedup. As illustration we will compare the performance of a D-Wave Two quantum annealing device on random spin glass instances to simulated classical and quantum annealers, and other classical solvers.

To watch the talk live go to http://gplus.to/qplus at the appointed hour.

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Q+ Hangout: Dietrich Leibfried (NIST)

Here are the details of the next Q+ hangout. This is our “Nobel Prize” lecture. Dietrich is a long time colleague of David Wineland at NIST and will tell us about the latest research from the Ion Storage Group. Please note the unusual start time of 5pm BST(UTC+1)

To join the hangout or watch the livestream go to http://gplus.to/qplus at the appointed hour.

Date: 23rd April 2013 5pm BST(UTC+1)

Speaker: Dietrich Leibfried (NIST)

Title: Towards scalable quantum information processing and quantum simulation with trapped ions

Abstract:
Quantum information processing (QIP) and Quantum Simulation (QS) can potentially provide an exponential speedup for certain problems over the corresponding (known) algorithms on conventional computers. QIP makes use of the counter-intuitive properties of quantum mechanics, like entanglement and the superposition principle (being in more states than one simultaneously). On the way towards a useful QIP device these properties, mostly subject of thought experiments so far, will have to become a practical reality. I will discuss experiments towards Quantum Information Processing (QIP) and Quantum Simulation (QS) with trapped ions. Most requirements for QIP and QS have been demonstrated in this system, with two big challenges remaining: Improving operation fidelity and scaling up to larger numbers of qubits.

The architecture pursued at the Ion Storage Group at NIST is based on quantum information stored in long lived internal (hyperfine) states of the ions. We investigate the use of laser beams and microwave fields to induce both single-qubit rotations and multi-qubit gates mediated by the Coulomb interaction between ions. Moving ions through a multi-zone trap architecture allows for keeping the number of ions per zone small, while sympathetic cooling with a second ion species can remove energy and entropy from the system.

After a brief introduction to these elements, I will present the current status of experiments and some future perspectives for QIP and QS.

This work has been supported by IARPA, DARPA, ARO, ONR, and the NIST Quantum Information Program.

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Q+ Hangout: Joe Fitzsimmons

Speaker: Joe Fitzsimons, Centre for Quantum Technologies, Singapore

Date: Tuesday 29th May 2012

Time: 14:00 British Summer Time

Title: Universal blind quantum computation

Abstract:

Blind Quantum Computing (BQC) allows a client to have a server carry out a quantum computation for them such that the client’s inputs, outputs and computation remain private. In this talk I will present a protocol for universal unconditionally secure BQC, based on the conceptual framework of the measurement-based quantum computing model. In this protocol the client only needs to be able to prepare single qubits in separable states randomly chosen from a finite set and send them to the server, who has the balance of the required quantum computational resources. This scheme has recently been implemented in a quantum optics setting. I will finish with a discussion of variants of the scheme allowing the client to detect deviations from the protocol by a malicious server.

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