Cited by 1,738Quantum Computing Algorithms and ArchitectureQuantum Information and CryptographyQuantum Mechanics and Applications

The DOI matches its Crossref record; 33 of the 34 references it cites were found in a registry or an index; none of the 15 sources its claims cite is checked for support yet.

Experimental realization of Shor's quantum factoring algorithm using nuclear magnetic resonance

Open access

Abstract

The number of steps any classical computer requires in order to find the prime factors of an l-digit integer N increases exponentially with l, at least using algorithms known at present. Factoring large integers is therefore conjectured to be intractable classically, an observation underlying the security of widely used cryptographic codes. Quantum computers, however, could factor integers in only polynomial time, using Shor's quantum factoring algorithm. Although important for the study of quantum computers, experimental demonstration of this algorithm has proved elusive. Here we report an implementation of the simplest instance of Shor's algorithm: factorization of N = 15 (whose prime factors are 3 and 5). We use seven spin-1/2 nuclei in a molecule as quantum bits, which can be manipulated with room temperature liquid-state nuclear magnetic resonance techniques. This method of using nuclei to store quantum information is in principle scalable to systems containing many quantum bits, but such scalability is not implied by the present work. The significance of our work lies in the demonstration of experimental and theoretical techniques for precise control and modelling of complex quantum computers. In particular, we present a simple, parameter-free but predictive model of decoherence effects in our system.

Overview

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TL;DR

The paper reports an NMR implementation of Shor’s quantum factoring algorithm, factoring N = 15 into 3 and 5 using seven spin-1/2 nuclei as qubits. It also presents a parameter-free decoherence model that reproduces the main non-ideal features of the measured spectra.

Key findings

  • Shor’s algorithm was experimentally executed for N = 15 with two parameter choices: a = 11 (“easy” case) and a = 7 (“difficult” case). The output spectra gave period r = 2 for a = 11 and r = 4 for a = 7, yielding gcd(11^2/2 ± 1, 15) = 3, 5 and gcd(7^4/2 ± 1, 15) = 3, 5, respectively.
  • The quantum computer used seven spin-1/2 nuclei: five ^19F and two ^13C, manipulated by room-temperature liquid-state NMR. The difficult case used a sequence of ∼300 spin-selective RF pulses, with the complete Shor sequence lasting up to ∼720 ms.
  • A parameter-free decoherence model, using measured T1 and T2 values and treating generalized amplitude damping and phase damping sequentially, agreed well with the large non-idealities in the data. The paper states this is the first NMR quantum computation experiment for which decoherence is the dominant source of errors.
  • The authors state that scalability to many qubit systems is not implied by this work; the significance lies in demonstrating experimental and theoretical techniques for precise control and modelling of complex quantum computers.

Methods

  • Experiments were performed at IBM Almaden with an 11.7 T (500 MHz) magnet, a custom-modified four-channel Varian Unity INOVA spectrometer, and a Nalorac HFX probe. The molecule was a custom-synthesized perfluorobutadienyl iron complex with the inner two carbons ^13C-labeled, at 0.88 ± 0.04 mole % in diethyl ether-d10, with all experiments at 30 °C.
  • The seven-qubit effective pure state was created by a two-stage temporal averaging scheme summing 4 × 9 = 36 experiments, with state preparation sequences ∼200 ms long. The algorithm was implemented with spin-selective Hermite-180 and Gaussian-90 pulses, shaped in 256 steps, and read out by NMR spectroscopy of the first three qubits.
  • The modular exponentiation and inverse QFT were implemented with a simplified quantum circuit for N = 15, including controlled additions and swaps, followed by spectral analysis to determine the period and factors.

Limitations

  • The paper states that scalability of this NMR approach to many qubit systems is not implied by the present work.
  • The decoherence model assumes independent stochastic relaxation with correlation times ≪ 1/ω_i, uses phenomenological Bloch equations with only T1 and T2 per spin, and treats non-commuting processes as commuting/sequential; the authors note remaining discrepancies due to model approximations and experimental imperfections such as RF inhomogeneity, imperfect calibrations, incomplete field drift compensation, and incomplete unwinding of coupled evolution during RF pulses.
  • The experiment used an ensemble of independent quantum computers, so measurement gives the bitwise average value of 8c/r rather than a sample of 8c/r; this was sufficient for the present experiment, but for larger N a continued fractions algorithm would need to be performed on the quantum computer, requiring additional qubits.

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Integrity signals

Registry

Crossref · 10.1038/414883a

Cites

33 of 33 references verified0 citation errors · 0 not checkable

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Verification

Claims the paper makes

0 of 15 cited sources checked · 0 supported · 0 flagged

Show all 7 claims

  • The quote only partly states this claim. 1
  • It may state two separate claims as one. 11
  • Probably not a substantial claim. 1
13 of 13
  • The authors state this as an assumption.

    Each spin experiences independent stochastic relaxation with correlation time scales much less than 1/ω_i.

    “In order to get a first estimate of the impact of decoherence during the factoring pulse sequence we assume that each spin experiences independent stochastic relaxation with correlation time scales ≪ 1 /ω i .”
  • The authors state this as an assumption.

    The non-commuting GAD, PD, and ideal unitary evolution processes can be treated as commuting transformations so that simultaneous processes can be modeled sequentially.

    “However, GAD does not commute with e -i H t , and PD and GAD do not commute with the ideal unitary evolution during RF pulses. Nevertheless, we have treated these as commuting transformations, such that all of the processes which occur simultaneously can be modeled sequentially.”
  • The paper relies on this without support.

    An effective pure ground state of all seven spins had never been created before.

    “To create an effective pure ground state of all seven spins, which has never been done before, we used a two-stage extension of the scheme of Ref. [9], necessary because ω 13 C is very different from ω 19 F .”
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Citations

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1 of the 34 references couldn’t be matched to a known paper.

Research works printed but not linked: 2

  1. Schulman, L. & Vazirani, U. in Proc. 31st ACM Symp. on Theory of Computing 322–329 (Association for Computing Machinery, New York, 1999).
  2. Freeman, R. Spin Choreography (Spektrum, Oxford, 1997).

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Metadata

Authors
Vandersypen, L. M. K., Steffen, M., Breyta, G., Yannoni, C. S., Sherwood, M. H., & Chuang, I. L.
Affiliations
IBM Research - Almaden (US)
Venue
Nature
Published
2001-12
Volume
414
Issue
6866
Pages
883-887
ISSN
  • 0028-0836 (ISSN-L)
  • 1476-4687
OpenAlex
W2159226773
Cited by
1,738
References
34
Citations by year
2026: 37 · 2025: 41 · 2024: 66 · 2023: 97 · 2022: 82 · 2021: 75 · 2020: 58 · 2019: 96 · 2018: 41 · 2017: 79 · 2016: 65 · 2015: 55 · 2014: 60 · 2013: 56 · 2012: 74
FWCI
83.11
Type
journal article
Language
en
Open access
Locations
  • Nature (publishedVersion)
  • PubMed (publishedVersion)
  • arXiv (Cornell University) (acceptedVersion)
  • RePEc: Research Papers in Economics (submittedVersion)
  • arXiv (Cornell University)
Topics
  • Physical Sciences › Computer Science › Artificial Intelligence › Quantum Computing Algorithms and Architecture
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Quantum Information and Cryptography
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Quantum Mechanics and Applications
Keywords
Shor's algorithm, quantum factoring, integer factorization, nuclear magnetic resonance, quantum computing, spin-1/2 nuclei, decoherence, qubits

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