1,428 research outputs found
Noise thresholds for optical cluster-state quantum computation
In this paper we do a detailed numerical investigation of the fault-tolerant
threshold for optical cluster-state quantum computation. Our noise model allows
both photon loss and depolarizing noise, as a general proxy for all types of
local noise other than photon loss noise. We obtain a threshold region of
allowed pairs of values for the two types of noise. Roughly speaking, our
results show that scalable optical quantum computing is possible for photon
loss probabilities less than 0.003, and for depolarization probabilities less
than 0.0001. Our fault-tolerant protocol involves a number of innovations,
including a method for syndrome extraction known as telecorrection, whereby
repeated syndrome measurements are guaranteed to agree. This paper is an
extended version of [Dawson et al., Phys. Rev. Lett. 96, 020501].Comment: 28 pages. Corrections made to Table I
QuEST and High Performance Simulation of Quantum Computers
We introduce QuEST, the Quantum Exact Simulation Toolkit, and compare it to
ProjectQ, qHipster and a recent distributed implementation of Quantum++. QuEST
is the first open source, OpenMP and MPI hybridised, GPU accelerated simulator
of universal quantum circuits. Embodied as a C library, it is designed so that
a user's code can be deployed seamlessly to any platform from a laptop to a
supercomputer. QuEST is capable of simulating generic quantum circuits of
general single-qubit gates and multi-qubit controlled gates, on pure and mixed
states, represented as state-vectors and density matrices, and under the
presence of decoherence. Using the ARCUS Phase-B and ARCHER supercomputers, we
benchmark QuEST's simulation of random circuits of up to 38 qubits, distributed
over up to 2048 compute nodes, each with up to 24 cores. We directly compare
QuEST's performance to ProjectQ's on single machines, and discuss the
differences in distribution strategies of QuEST, qHipster and Quantum++. QuEST
shows excellent scaling, both strong and weak, on multicore and distributed
architectures.Comment: 8 pages, 8 figures; fixed typos; updated QuEST URL and fixed typo in
Fig. 4 caption where ProjectQ and QuEST were swapped in speedup subplot
explanation; added explanation of simulation algorithm, updated bibliography;
stressed technical novelty of QuEST; mentioned new density matrix suppor
Deep Quantum Circuit Simulations of Low-Energy Nuclear States
Numerical simulation is an important method for verifying the quantum
circuits used to simulate low-energy nuclear states. However, real-world
applications of quantum computing for nuclear theory often generate deep
quantum circuits that place demanding memory and processing requirements on
conventional simulation methods. Here, we present advances in high-performance
numerical simulations of deep quantum circuits to efficiently verify the
accuracy of low-energy nuclear physics applications. Our approach employs
several novel methods for accelerating the numerical simulation including 1-
and 2-qubit gate fusion techniques as well as management of simulated
mid-circuit measurements to verify state preparation circuits. We test these
methods across a variety of high-performance computing systems and our results
show that circuits up to 21 qubits and more than 115,000,000 gates can be
efficiently simulated
Resource costs for fault-tolerant linear optical quantum computing
Linear optical quantum computing (LOQC) seems attractively simple:
information is borne entirely by light and processed by components such as beam
splitters, phase shifters and detectors. However this very simplicity leads to
limitations, such as the lack of deterministic entangling operations, which are
compensated for by using substantial hardware overheads. Here we quantify the
resource costs for full scale LOQC by proposing a specific protocol based on
the surface code. With the caveat that our protocol can be further optimised,
we report that the required number of physical components is at least five
orders of magnitude greater than in comparable matter-based systems. Moreover
the resource requirements grow higher if the per-component photon loss rate is
worse than one in a thousand, or the per-component noise rate is worse than
. We identify the performance of switches in the network as the single
most influential factor influencing resource scaling
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