Cited by 89Quantum Computing Algorithms and ArchitectureQuantum Information and CryptographyQuantum and electron transport phenomena

Speed limits for quantum gates in multiqubit systems

Open access
Ashhab, S., de Groot, P. C., Nori, Franco·2012·Physical Review A

Abstract

We use analytical and numerical calculations to obtain speed limits for various unitary quantum operations in multiqubit systems under typical experimental conditions. The operations that we consider include single-, two-, and three-qubit gates, as well as quantum-state transfer in a chain of qubits. We find in particular that simple methods for implementing two-qubit gates generally provide the fastest possible implementations of these gates. We also find that the three-qubit Toffoli gate time varies greatly depending on the type of interactions and the system's geometry, taking only slightly longer than a two-qubit controlled-not (cnot) gate for a triangle geometry. The speed limit for quantum-state transfer across a qubit chain is set by the maximum spin-wave speed in the chain.

Integrity signals

Registry

Crossref · 10.1103/physreva.85.052327

Cites

32 of 32 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

0 of 11 cited sources checked · 0 supported · 0 flagged

  • Findingown data

    In a triangle geometry, the Toffoli gate takes only a little more time than a CNOT gate.

    “taking only slightly longer than a two-qubit controlled-NOT (CNOT) gate for a triangle geometry.”
    • Also stated in: § Chain · plain
      “for the triangle geometry, we find Toffoli gate times that are smaller than twice the minimum time required for a CNOT gate with the same coupling strength.”
    Quote in the paperSubstantial claim
  • Findingown data

    The time needed for the three-qubit Toffoli gate depends strongly on the interaction type and the geometry of the system.

    “We also find that the three-qubit Toffoli gate time varies greatly depending on the type of interactions and the system's geometry”
    Quote in the paperSubstantial claim
  • Findingown data

    For the iSWAP gate with Ising interactions, the fixed-parameter numerical estimate is about 25% larger than the tunable estimate.

    “The speed limit that we find numerically for the fixed-case is about 25% higher than that for the tunable-case.”
    Quote in the paperNot a substantial claim
  • Findingown data

    In a chain geometry, the Toffoli gate requires about three times the minimum CNOT gate time.

    “The Toffoli gate requires approximately three times the minimum time required for a CNOT gate in a chain geometry”
    Quote in the paperSubstantial claim
  • Findingown data

    For a triangle geometry, the Toffoli gate time found here is less than twice the CNOT gate time with the same coupling strength.

    “for the triangle geometry, we find Toffoli gate times that are smaller than twice the minimum time required for a CNOT gate with the same coupling strength.”
    Quote in the paperSubstantial claim
  • May combine two claims. 4
  • Classified as probably not a substantial claim. 2
  • May combine two claims.

    Interpretationnone given

    Reaching the maximum wave speed is not enough for high-fidelity state transfer; the state must also be transferred without distortion.

    “Even though the maximum wave speed sets an upper limit to the speed of quantum-state transfer, one still needs to make sure that the quantum state is transferred without distortion.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Study design and conductown data

    The numerical Toffoli gate times may be substantially larger than the true minimum because the results depend on guess pulses and do not yield smooth fitting functions.

    “we would like to point out that the results of the calculations also showed stronger dependence on the guess pulses than in the case of two-qubit gates (the data also did not result in smooth fitting functions as shown in Fig. 2).We therefore cannot exclude the possibility that some of the expressions in Table II are substantially larger than the true minimum gate time.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Premisereasoning

    A CNOT gate can be built from a CZ gate plus two π/2 pulses on the target qubit, so its time with Ising interactions is about π/(4J).

    “The CNOT gate can be obtained by combining the CZ gate with two single-qubit gates.These are π/2 pulses applied to the target qubit before and after the CZ gate.As a result, the amount of time required to obtain the CNOT gate using this approach is approximately equal to the amount of time required for the CZ gate, i.e., π/(4J ) with Ising interactions.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [14] source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    An optimal-control calculation found a Toffoli gate time of about 2.2 times the CNOT gate time for qubits in a triangle geometry.

    “An optimal-control-theory-related calculation based on certain forms of pulses has found a gate time of about 2.2 times the CNOT gate time for qubits coupled in a triangle geometry [3].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [3] source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationcitation

    The Heisenberg minimum transfer time expression agrees with the one given in Ref. [11].

    “This expression is essentially the same as the one given in Ref. [11].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [11] source

      Not checked in the free run.

  • May combine two claims.

    Interpretationnone given

    The speed-limit expressions derived here agree with known analytical results and with recent numerical results.

    “The expressions that we find agree with analytical results known in the literature and also with recent numerical results.”
    Quote in the paperNot a substantial claim
6 of 6
  • The authors state this as an assumption.

    Qubits can be described using only two quantum states.

    “With the assumption of two-state qubits, the single-qubit Hamiltonian can be expressed in terms of the two-dimensional Pauli matrices σα (with α = x, y, or z):”
  • The authors state this as an assumption.

    Any arbitrary driving signal can be applied to the system.

    “We shall assume that any arbitrary driving signal can be applied to the system.”
  • The paper relies on this without support.

    Single-qubit Hamiltonian parameters are typically much larger than the interqubit coupling strength.

    “The parameters of the single-qubit Hamiltonian are typically much larger than the interqubit coupling strength, i.e., J , .”
  • The paper relies on this without support.

    Single-qubit gate durations are typically negligibly short compared with two- or multiqubit gate durations.

    “Furthermore, performing single-qubit gates typically requires a negligibly short duration compared to the duration required for performing a two-or multiqubit gate”
  • The authors state this as an assumption.

    For the Heisenberg state-transfer analysis, the system contains only one excitation.

    “Taking J , = 0, and assuming only one excitation in the system”
5 of 5

Cites

Flagged first, then by citations

Research works printed but not linked: 2

  1. L. Mandelstam, 1945, J. Phys. USSR, 9, 249
  2. V. V. Shende, 2009, Quantum Inf. Comp., 9, 461

Cited by

Sorted by citations

Authors
Ashhab, S., de Groot, P. C., & Nori, F.
Affiliations
University of Michigan (US)
Venue
Physical Review A
Published
2012-05-29
Volume
85
Issue
5
ISSN
  • 0556-2791 (ISSN-L)
  • 1050-2947
  • 1094-1622
OpenAlex
W2138618971
Cited by
89
References
32
Citations by year
2026: 6 · 2025: 9 · 2024: 13 · 2023: 8 · 2022: 6 · 2021: 3 · 2020: 7 · 2019: 6 · 2018: 7 · 2017: 6 · 2016: 4 · 2015: 3 · 2014: 6 · 2013: 3 · 2012: 2
FWCI
4.41
Type
journal article
Language
en
Open access
Locations
  • Physical Review A (publishedVersion)
  • arXiv (Cornell University) (submittedVersion)
  • Research Repository (Delft University of Technology) (submittedVersion)
  • Data Archiving and Networked Services (DANS) (submittedVersion, other-oa)
  • arXiv (Cornell University)
Funders
National Science Foundation
Topics
  • Physical Sciences › Computer Science › Artificial Intelligence › Quantum Computing Algorithms and Architecture
  • Physical Sciences › Computer Science › Artificial Intelligence › Quantum Information and Cryptography
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Quantum and electron transport phenomena
Keywords
quantum speed limit, multi-qubit systems, quantum gates, two-qubit gates, CNOT gate, quantum state transfer, qubit chains, spin waves, triangle geometry

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