104 research outputs found
BGLS: A Python Package for the Gate-by-Gate Sampling Algorithm to Simulate Quantum Circuits
The classical simulation of quantum computers is in general a computationally
hard problem. To emulate the behavior of realistic devices, it is sufficient to
sample bitstrings from circuits. Recently, arXiv:2112.08499 introduced the
so-called gate-by-gate sampling algorithm to sample bitstrings and showed it to
be computationally favorable in many cases. Here we present bgls, a Python
package which implements this sampling algorithm. bgls has native support for
several states and is highly flexible for use with additional states. We show
how to install and use bgls, discuss optimizations in the algorithm, and
demonstrate its utility on several problems.Comment: 7 pages, 9 figures, included in Workshops of The International
Conference on High Performance Computing, Network, Storage, and Analysis
(SC-W 2023
Digital zero noise extrapolation for quantum error mitigation
Zero-noise extrapolation (ZNE) is an increasingly popular technique for
mitigating errors in noisy quantum computations without using additional
quantum resources. We review the fundamentals of ZNE and propose several
improvements to noise scaling and extrapolation, the two key components in the
technique. We introduce unitary folding and parameterized noise scaling. These
are digital noise scaling frameworks, i.e. one can apply them using only
gate-level access common to most quantum instruction sets. We also study
different extrapolation methods, including a new adaptive protocol that uses a
statistical inference framework. Benchmarks of our techniques show error
reductions of 18X to 24X over non-mitigated circuits and demonstrate ZNE
effectiveness at larger qubit numbers than have been tested previously. In
addition to presenting new results, this work is a self-contained introduction
to the practical use of ZNE by quantum programmers.Comment: 11 pages, 7 figure
Testing platform-independent quantum error mitigation on noisy quantum computers
We apply quantum error mitigation techniques to a variety of benchmark
problems and quantum computers to evaluate the performance of quantum error
mitigation in practice. To do so, we define an empirically motivated,
resource-normalized metric of the improvement of error mitigation which we call
the improvement factor, and calculate this metric for each experiment we
perform. The experiments we perform consist of zero-noise extrapolation and
probabilistic error cancellation applied to two benchmark problems run on IBM,
IonQ, and Rigetti quantum computers, as well as noisy quantum computer
simulators. Our results show that error mitigation is on average more
beneficial than no error mitigation - even when normalized by the additional
resources used - but also emphasize that the performance of quantum error
mitigation depends on the underlying computer
Quantum-assisted quantum compiling
Compiling quantum algorithms for near-term quantum computers (accounting for
connectivity and native gate alphabets) is a major challenge that has received
significant attention both by industry and academia. Avoiding the exponential
overhead of classical simulation of quantum dynamics will allow compilation of
larger algorithms, and a strategy for this is to evaluate an algorithm's cost
on a quantum computer. To this end, we propose a variational hybrid
quantum-classical algorithm called quantum-assisted quantum compiling (QAQC).
In QAQC, we use the overlap between a target unitary and a trainable
unitary as the cost function to be evaluated on the quantum computer. More
precisely, to ensure that QAQC scales well with problem size, our cost involves
not only the global overlap but also the local
overlaps with respect to individual qubits. We introduce novel short-depth
quantum circuits to quantify the terms in our cost function, and we prove that
our cost cannot be efficiently approximated with a classical algorithm under
reasonable complexity assumptions. We present both gradient-free and
gradient-based approaches to minimizing this cost. As a demonstration of QAQC,
we compile various one-qubit gates on IBM's and Rigetti's quantum computers
into their respective native gate alphabets. Furthermore, we successfully
simulate QAQC up to a problem size of 9 qubits, and these simulations highlight
both the scalability of our cost function as well as the noise resilience of
QAQC. Future applications of QAQC include algorithm depth compression,
black-box compiling, noise mitigation, and benchmarking.Comment: 19 + 10 pages, 14 figures. Added larger scale implementations and
proof that cost function is DQC1-har
Variational Quantum Linear Solver
Previously proposed quantum algorithms for solving linear systems of
equations cannot be implemented in the near term due to the required circuit
depth. Here, we propose a hybrid quantum-classical algorithm, called
Variational Quantum Linear Solver (VQLS), for solving linear systems on
near-term quantum computers. VQLS seeks to variationally prepare
such that . We derive an operationally meaningful
termination condition for VQLS that allows one to guarantee that a desired
solution precision is achieved. Specifically, we prove that , where is the VQLS cost function and is the
condition number of . We present efficient quantum circuits to estimate ,
while providing evidence for the classical hardness of its estimation. Using
Rigetti's quantum computer, we successfully implement VQLS up to a problem size
of . Finally, we numerically solve non-trivial problems of size
up to . For the specific examples that we consider, we
heuristically find that the time complexity of VQLS scales efficiently in
, , and the system size .Comment: 13 + 8 pages, 15 figures, 7 table
Framing and visual type: Effect on future Zika vaccine uptake intent
Introduction: The Zika virus is associated with the birth defect microcephaly, and while a vaccine was not available in early- 2017, several were under development. This study’s purpose was to identify effective communication strategies to promote uptake of a new vaccine, particularly among women of reproductive age.Design and methods: In order to study the effects of Zika message framing (gain vs. loss) and visual type (photo vs. infographic) on future Zika vaccine uptake intent, a 2×2 between-subjects experiment was performed via an online survey in 2017 among 339 U.S. women of reproductive age (18-49 years). Participants were exposed to one of four messages, all resembling Instagram posts: gain-framed vs. loss-framed infographic, and gain-framed vs. loss-framed photo. These messages were followed by questions about Zika vaccine uptake intent as well as intermediate psychosocial variables that could lead to intent. Results: There was no interaction between framing and visual type (P=0.116), and there was no effect for framing (P=0.185) or visual type (P=0.724) on future Zika vaccine uptake intent, which is likely indicative of insufficient dosage of the intervention. However, when focusing on intermediate psychosocial constructs that are known to influence behavior and intent, gain-framed messages were more effective in increasing subjective norms (P=0.005) as related to a future Zika vaccine, as well as perceived benefits (P=0.016) and self-efficacy (P=0.032). Conclusions: Gain-framed messages seem to be more effective than loss-framed messages to increase several constructs that could, in turn, affect future Zika vaccine uptake intent. This is a novel finding since, traditionally, loss-framed messages are considered more beneficial in promoting vaccine-related health behaviors
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