Cited by 1,407Quantum Information and CryptographyQuantum many-body systemsQuantum Computing Algorithms and Architecture

Quantum Communication through an Unmodulated Spin Chain

Open access
Bose, Sougato·2003·Physical Review Letters

Abstract

We propose a scheme for using an unmodulated and unmeasured spin chain as a channel for short distance quantum communications. The state to be transmitted is placed on one spin of the chain and received later on a distant spin with some fidelity. We first obtain simple expressions for the fidelity of quantum state transfer and the amount of entanglement sharable between any two sites of an arbitrary Heisenberg ferromagnet using our scheme. We then apply this to the realizable case of an open ended chain with nearest neighbor interactions. The fidelity of quantum state transfer is obtained as an inverse discrete cosine transform and as a Bessel function series. We find that in a reasonable time, a qubit can be directly transmitted with better than classical fidelity across the full length of chains of up to 80 spins. Moreover, our channel allows distillable entanglement to be shared over arbitrary distances.

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Written from the paper’s full text.

TL;DR

The paper proposes using an unmodulated, unmeasured spin chain as a channel for short-distance quantum communication by placing a qubit on one spin and retrieving it later on a distant spin. It derives simple fidelity and entanglement formulas and finds high-fidelity state transfer over chains up to 80 spins, plus distillable entanglement over arbitrarily large distances.

Key findings

  • For an open-ended nearest-neighbor Heisenberg chain, perfect quantum state transfer occurs for \(N=2\) and \(N=4\) (\(F=1.000\) to 3 decimal places), near-perfect for \(N=8\) (\(F=0.994\)), and fidelity exceeds \(0.9\) for \(N=7,10,11,13,14\); an \(N=80\) chain exceeds the classical transmission fidelity \(2/3\) within \(T_{\max}=4000/J\).
  • The channel can share distillable entanglement; for an 80-spin chain the maximum sharable entanglement is about \(E=0.45\). For very long chains with \(t_0=(N+0.8089N^{1/3})/2J\), \(E\) ranges from \(0.135\) for \(N=1000\) to \(1.35\times10^{-4}\) for \(N=10^{12}\), scaling as \(N^{-1/3}\).
  • For a ring of \(2N\) spins with diametrically opposite sites, the maxima of entanglement coincide with those of the line, so a 4-spin ring allows perfect communication between diametrically opposite sites.
  • General formulas are given for fidelity and entanglement in terms of the single transition amplitude \(f^N_{r,s}(t_0)=\langle r|\exp\{-iH_Gt_0\}|s\rangle\).

Methods

  • Theoretical protocol on an arbitrary graph of \(N\) spins with ferromagnetic isotropic Heisenberg interactions, static magnetic fields, and couplings; the chain is initially cooled to its ground state \(|00\ldots0\rangle\), Alice replaces the sender spin with an unknown qubit, and Bob retrieves the receiver spin after a chosen time \(t_0\).
  • For the linear open chain, the Hamiltonian uses \(J_{ij}=(J/2)\delta_{i+1,j}\) and \(B_i=B\); the transition amplitude is expressed via an inverse discrete cosine transform, and maximum \(|f^N_{N,1}(t_0)|\) is numerically evaluated for \(N=2\) to \(80\) over \(t_0\in[0,4000/J]\).
  • For very long chains, a Bessel-function expansion and Airy-function approximation are used to choose a fixed \(t_0\); the ring case is treated via an inverse discrete Fourier transform.

Limitations

  • The paper states no dedicated limitations section. It notes that the numerical search for \(t_0\) may return any of several times where the maxima of \(|f^N_{N,1}(t_0)|\) to 3 decimal places are attained, not necessarily the least time, and that direct state-transfer results hold only when directly transmitting over a distance; otherwise entanglement sharing can be distilled.
  • Evident from the text: the scheme assumes an initial ground state, detachable sender and receiver spins, no individual access or modulation of channel spins, and a magnetic-field choice making the phase a multiple of \(2\pi\); the quantitative results are for ideal Heisenberg models, with direct-fidelity numerics only up to \(N=80\).

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1103/physrevlett.91.207901

Cites

7 of 7 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

0 of 10 cited sources checked · 0 supported · 0 flagged

  • Findingown data
    § Quantum Communication Through an Unmodulated Spin Chain · p. 3

    For N=8, the open-ended chain gives near perfect quantum state transfer with fidelity F=0.994.

    “N = 8 gives near perfect ( F = 0 . 994).”
    Quote in the paperSubstantial claim
    • The authors state this as an assumption: The spin chain is initially cooled to its ground state |0...0>, with each spin in the spin-down state aligned along the -z direction.
    • The authors state this as an assumption: The sender and receiver spins are detachable from the chain.
    • The authors state this as an assumption: The magnetic fields B_i can be chosen such that γ is a multiple of 2π for any given t0.
  • Findingown data
    § Quantum Communication Through an Unmodulated Spin Chain · p. 3

    For open-ended chains up to N=21, fidelities are lower when N is divisible by 3 compared to N+1 and N+2.

    “Till N = 21 we observe that the fidelities are lower when N is divisible by 3 in comparison to the fidelities for N +1 and N +2.”
    Quote in the paperNot a substantial claim
    • The authors state this as an assumption: The spin chain is initially cooled to its ground state |0...0>, with each spin in the spin-down state aligned along the -z direction.
    • The authors state this as an assumption: The sender and receiver spins are detachable from the chain.
    • The authors state this as an assumption: The magnetic fields B_i can be chosen such that γ is a multiple of 2π for any given t0.
  • Findingcitation
    § Quantum Communication Through an Unmodulated Spin Chain · p. 4

    For benzene molecules with J_ij = δ_{i⊕1,j}/4 + δ_{i⊕2,j}/(12√3) + δ_{i⊕3,j}/32, the fidelity F for r-s=3 at t0=130 is 0.793.

    “Benzene molecules (with NMR probes possible) with J ij = δ i ⊕ 1 ,j 4 + δ i ⊕ 2 ,j 12 √ 3 + δ i ⊕ 3 ,j 32 , still have | ˜ m 〉 R as eigenstates [16]. F can thus be calculated by an IDFT to be 0 . 793 for r -s = 3 at t 0 = 130.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [16] G. J. Bowden, J. Math. Chem. 31 , 363 (2002).

      Not checked in the free run.

  • Findingown data
    § Quantum Communication Through an Unmodulated Spin Chain · p. 3

    For N=4, the open-ended chain gives perfect quantum state transfer with fidelity F=1.000 to 3 decimal places.

    “N = 4 gives perfect ( F = 1 . 000) quantum state transfer to 3 decimal places”
    Quote in the paperNot a substantial claim
    • The authors state this as an assumption: The spin chain is initially cooled to its ground state |0...0>, with each spin in the spin-down state aligned along the -z direction.
    • The authors state this as an assumption: The sender and receiver spins are detachable from the chain.
    • The authors state this as an assumption: The magnetic fields B_i can be chosen such that γ is a multiple of 2π for any given t0.
  • Findingreasoning
    § Quantum Communication Through an Unmodulated Spin Chain · p. 3

    For an open-ended chain with nearest-neighbor interactions of equal strength and uniform magnetic field, the transition amplitude f^N_{r,s}(t0) is given by an inverse discrete cosine transform.

    “where, v m = a m cos { π 2 N ( m -1)(2 r -1) } e -iE m t 0 and IDCT s ( v m ) = ∑ N m =1 a m v m cos { π 2 N ( m -1)(2 s -1) } is the s th element of the inverse discrete cosine transform of the vector { v m } .”
    Quote in the paperSubstantial claim
    • The authors state this as an assumption: The spin chain is initially cooled to its ground state |0...0>, with each spin in the spin-down state aligned along the -z direction.
    • The authors state this as an assumption: The sender and receiver spins are detachable from the chain.
    • The authors state this as an assumption: The magnetic fields B_i can be chosen such that γ is a multiple of 2π for any given t0.
  • May combine two claims. 5
  • The quote only partly states this claim. 1
  • Classified as probably not a substantial claim. 2
  • May combine two claims. The quote only partly states this claim.

    Findingreasoning
    § Quantum Communication Through an Unmodulated Spin Chain · p. 2

    For an arbitrary Heisenberg ferromagnet, the fidelity of quantum state transfer and the amount of entanglement sharable between any two sites are given by simple expressions in terms of the single transition amplitude f^N_{r,s}(t0).

    “Eqs.(6) and (8) are exceptionally simple formulas for the fidelity of quantum communications and the entanglement shared through our spin-graph channel in terms of single transition amplitude f N r,s ( t 0 ).”
    Quote in the paperSubstantial claim
    • The authors state this as an assumption: The spin chain is initially cooled to its ground state |0...0>, with each spin in the spin-down state aligned along the -z direction.
    • The authors state this as an assumption: The sender and receiver spins are detachable from the chain.
    • The authors state this as an assumption: The magnetic fields B_i can be chosen such that γ is a multiple of 2π for any given t0.
  • May combine two claims.

    Premisecitation
    § Quantum Communication Through an Unmodulated Spin Chain · p. 2

    The entanglement shared through the channel can be distilled into pure singlets and used for teleportation.

    “This entanglement, being that of a 2 × 2 system, can also be distilled [7] into pure singlets and used for teleportation.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [7] M. Horodecki, P. Horodecki, and R. Horodecki, Phys. Rev. Lett. 78 , 574-577 (1997). source

      Not checked in the free run.

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

    Interpretationcitation
    § Quantum Communication Through an Unmodulated Spin Chain · p. 4

    The scheme's principles should be testable in simulated open-ended Heisenberg chains in a 1D optical lattice.

    “Principles of the scheme should also be testable in simulated open ended Heisenberg chains in a 1D optical lattice [17].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [17]

      Not checked in the free run.

  • May combine two claims.

    Interpretationcitation
    § Quantum Communication Through an Unmodulated Spin Chain · p. 1

    The spin-chain channel does not require the ability to switch interactions on and off, nor does it require modulation by external fields.

    “neither does the spin chain channel require the ability to switch interactions 'on' and 'off' (often a problem in quantum computer implementations [4, 5]), nor does it require any modulation by external fields (essential for quantum computation).”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [4] X. Zhou et. al. , Phys. Rev. Lett. 89 , 197903 (2002). source

      Not checked in the free run.

    • cites [5] S. C. Benjamin and S. Bose, Phys. Rev. Lett.(2003). source

      Not checked in the free run.

  • May combine two claims.

    Interpretationreasoning
    § Quantum Communication Through an Unmodulated Spin Chain · p. 4

    For large N, the maximum entanglement E scales as N^{-1/3} and is achieved at a time t0 linear in N.

    “Thus for any fi nite N , however large, the chain allows us to distribute entanglement of the order N -1 / 3 in a time t 0 linear in N .”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [13] source

      Not checked in the free run.

    • The authors state this as an assumption: The spin chain is initially cooled to its ground state |0...0>, with each spin in the spin-down state aligned along the -z direction.
    • The authors state this as an assumption: The sender and receiver spins are detachable from the chain.
    • The authors state this as an assumption: The magnetic fields B_i can be chosen such that γ is a multiple of 2π for any given t0.
  • Classified as probably not a substantial claim. May combine two claims.

    Interpretationnone given
    § Quantum Communication Through an Unmodulated Spin Chain · p. 4

    The scheme can be implemented in Josephson junction arrays, excitons in quantum dots, and real 1D magnets without the elaborate control required for quantum computation.

    “Our scheme can be implemented in such systems without the elaborate control required for quantum computation.”
    Quote in the paperSubstantial claim
6 of 6
  • The authors state this as an assumption.

    The spin chain is initially cooled to its ground state |0...0>, with each spin in the spin-down state aligned along the -z direction.

    “We assume that initially the system is initially cooled to its ground state | 0 〉 = | 000 ... 0 〉 where | 0 〉 denotes the spin down state (i.e., spin aligned along -z direction) of a spin.”
  • The authors state this as an assumption.

    The sender and receiver spins are detachable from the chain.

    “It is also assumed that the sender and receiver spins are detachable from the chain.”
  • The authors state this as an assumption.

    The magnetic fields B_i can be chosen such that γ is a multiple of 2π for any given t0.

    “Assuming this special choice of magnetic field value (which can always be made for any given t 0 ) to be a part of our protocol”
3 of 3

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

  • By tailoring hopping rates between waveguides of an array to match the matrix elements of the J_x angular momentum operator, perfect quantum state transfer becomes possible.

    “Inspired by spin chains [100-102] (see figure 12(a)), by tailoring the hopping rates between the waveguides of an array to match the matrix elements of the J x angular momentum operator, such a task becomes possible.”

    From Integrated photonic quantum walks (2020) · cites this paper as [100]

    The paper reports perfect state transfer for certain short spin chains (p. 3), so it supports that limited outcome. But its open-chain model uses equal-strength nearest-neighbor interactions (p. 2); it does not describe waveguide hopping rates tailored to Jₓ matrix elements as the means of achieving transfer. (LLM, conf=0.83)

    Experimental — accuracy not yet measured
  • Imperfect QST over a uniform spin chain is impossible for long chains.

    “Imperfect QST [8, 9] over a uniform spin chain was studied numerically, showing that perfect state transfer is impossible for long chains.”
  • The speed limit for 1D QST could be overcome by increasing either network complexity or Hamiltonian complexity if not confined to nearest-neighbor interactions in one dimension.

    “We lastly comment that such speed limit, if not confined with nearest-neighbor interactions in one dimension, could be overcome by increasing either the network complexity [9] or the Hamiltonian complexity [26].”

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • General-site transition amplitude replaced by an end-to-end amplitude

    Minor

    The paper says its fidelity formula applies to transfer between arbitrary sender and receiver sites s and r, but then says to replace that transition amplitude with the amplitude specifically from site 1 to site N. Choosing the magnetic field to remove a phase does not make those different site-to-site amplitudes equal.

1 of 1

Cites

Flagged first, then by citations

Research works printed but not linked: 9

  1. 10.1038/35005001 · DOI · Paper page
  2. 10.1038/nature00784 · DOI · Paper page
  3. 10.1103/PhysRevLett.90.247901 · DOI · Paper page
  4. 10.1103/PhysRevLett.78.574 · DOI · Paper page
  5. 10.1103/PhysRevA.60.1888 · DOI · Paper page
  6. 10.1038/30156 · DOI · Paper page
  7. G. J. Bowden, 2002, J. Math. Chem., 31, 363, 10.1023/A:1021068521256 · DOI
  8. 10.1103/PhysRevLett.91.090402 · DOI
  9. A. M. Childs, Proceedings of the 35th ACM Symposium on Theory of Computing (STOC 2003), San Diego, CA

Cited by

Sorted by citations

Authors
Bose, S.
Affiliations
California Institute of Technology (US)
Corresponding author
Bose, Sougato
Venue
Physical Review Letters
Published
2003-11-10
Volume
91
Issue
20
Pages
207901-207901
ISSN
  • 0031-9007 (ISSN-L)
  • 1079-7114
OpenAlex
W1983655155
Cited by
1,407
References
7
Citations by year
2026: 42 · 2025: 78 · 2024: 54 · 2023: 70 · 2022: 71 · 2021: 59 · 2020: 64 · 2019: 68 · 2018: 52 · 2017: 67 · 2016: 74 · 2015: 72 · 2014: 64 · 2013: 73 · 2012: 69
FWCI
35.81
Type
journal article
Language
en
Open access
Locations
  • Physical Review Letters (publishedVersion)
  • PubMed (publishedVersion)
  • arXiv (Cornell University) (submittedVersion)
  • CERN Document Server (European Organization for Nuclear Research) (submittedVersion)
  • UCL Discovery (University College London) (submittedVersion)
  • arXiv (Cornell University)
Topics
  • Physical Sciences › Computer Science › Artificial Intelligence › Quantum Information and Cryptography
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Quantum many-body systems
  • Physical Sciences › Computer Science › Artificial Intelligence › Quantum Computing Algorithms and Architecture
Keywords
quantum state transfer, Heisenberg ferromagnet, quantum channels, entanglement distribution, distillable entanglement, fidelity, discrete cosine transform, Bessel function series, nearest-neighbor interactions

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