Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session Q32: Invited Session: Quantum Computing Architectures |
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Sponsoring Units: GQI Chair: Andrew Landahl, Sandia National Laboratories Room: 708-712 |
Wednesday, March 5, 2014 2:30PM - 3:06PM |
Q32.00001: Quantum Compiling for Topological Quantum Computing Invited Speaker: Krysta Svore In a topological quantum computer, universality is achieved by braiding and quantum information is natively protected from small local errors. We address the problem of compiling single-qubit quantum operations into braid representations for non-abelian quasiparticles described by the Fibonacci anyon model. We develop a probabilistically polynomial algorithm that outputs a braid pattern to approximate a given single-qubit unitary to a desired precision. We also classify the single-qubit unitaries that can be implemented exactly by a Fibonacci anyon braid pattern and present an efficient algorithm to produce their braid patterns. Our techniques produce braid patterns that meet the uniform asymptotic lower bound on the compiled circuit depth and thus are depth-optimal asymptotically. Our compiled circuits are significantly shorter than those output by prior state-of-the-art methods, resulting in improvements in depth by factors ranging from 20 to 1000 for precisions ranging between $10^{-10}$ and $10^{-30}$. [Preview Abstract] |
Wednesday, March 5, 2014 3:06PM - 3:42PM |
Q32.00002: Error correction for adiabatic quantum computing Invited Speaker: Kevin Young Adiabatic quantum computing (AQC) is an alternative to the standard circuit model of quantum computation, wherein a quasistatic Hamiltonian, whose ground state at time T = 0 is simple and easily prepared, evolves slowly so that by the final time T = 1 the ground state encodes the answer to a problem. This procedure admits a novel set of natural algorithms for optimization problems, and is computationally equivalent to the circuit model in the absence of noise. But noise, and its effect on computational power, cannot be ignored. In light of this, AQC is particularly intriguing, possessing an intrinsic resilience to certain kinds of errors, including flawed time-dependent control Hamiltonians, dephasing in the energy basis, and energy relaxation. But these are far from the only errors afflicting quantum information processors, and any practical model of computation must be fault-tolerant to all expected forms of noise and error. With respect to this broader class of errors, true fault tolerance for AQC has remained elusive. In this talk we will discuss our progress towards this goal: (1) we identified and solved a variety of challenges on the road to error correction and fault tolerance in AQC; and (2) we identified a couple of major roadblocks, which appear insurmountable, and make us ultimately pessimistic that fault-tolerant AQC will ever be achieved. [Preview Abstract] |
Wednesday, March 5, 2014 3:42PM - 4:18PM |
Q32.00003: Architectures for measurement-based quantum computation Invited Speaker: Robert Raussendorf As our experience so far shows, building a quantum computer is not going to be easy. There are fundamental difficulties to overcome, such as decoherence, and suitable technologies and materials need to be identified. In between those two extremes lies the challenge of quantum computer architecture. Shall or shall we not envision a quantum computer as a von-Neumann type device, with CPU here and memory there? How are the qubits supposed to be wired? How do realistic physical constraints such translation invariance, planarity or bounded degree of the qubit connectivity graph affect quantum computer architecture? I will discuss these questions from the angle of measurement-based quantum computation. [Preview Abstract] |
Wednesday, March 5, 2014 4:18PM - 4:54PM |
Q32.00004: Synthesizing Logic in Fault-Tolerant Quantum Computers Invited Speaker: Cody Jones Quantum computers hold the promise of solving problems believed to be intractable using conventional computation, but this potential is impeded by the apparent difficulty in engineering reliable quantum hardware. One solution is quantum error correction (QEC), which enables fault-tolerant computation at the expense of a sizable overhead in qubits and gates. In this talk, I discuss several recent advancements in QEC to reduce the resource overhead in contemporary error-correction schemes like the surface code. Quantum logic can be encoded into so-called ``magic states,'' and the burden of error correction is shifted to verifying a well-characterized state, instead of protecting an arbitrary quantum process from errors. I discuss some of the recent work in magic-state distillation and its extensions to multi-qubit gates like Toffoli, which are ubiquitous in quantum algorithms. For operations in the surface code, resource overheads are improved by as much as two orders of magnitude. [Preview Abstract] |
Wednesday, March 5, 2014 4:54PM - 5:30PM |
Q32.00005: The quest for self-correcting quantum memory Invited Speaker: Olivier Landon-Cardinal A self-correcting quantum memory is a physical system whose quantum state can be preserved over a long period of time without the need for any external intervention. The most promising candidates are topological quantum systems which would protect information encoded in their degenerate groundspace while interacting with a thermal environment. Many models have been suggested but several approaches have been shown to fail due to no-go results of increasingly general scope. In this presentation, I will explain the desiderata for self-correction, review the recent advances and no-go results, and describe the current endeavours to define a self-correcting system in 2D and 3D. [Preview Abstract] |
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