Cited by 77Quantum Computing Algorithms and ArchitectureTopological Materials and PhenomenaQuantum many-body systems

Quantum Simulation of the Majorana Equation and Unphysical Operations

Open access
Casanova, J., Sabín, C., León, J., Egusquiza, I. L., Gerritsma, R., Roos, C. F., García-Ripoll, J. J., Solano, E.·2011·Physical Review X

Abstract

Charge conjugation, complex conjugation, and time reversal of wave functions are theoretical concepts fundamental to quantum mechanics, but do not correspond to physical processes in the real world. Simulating them in a real physical setting seems then out of the question. A Spanish-Austrian team come up with a new toolbox for rendering the seemingly impossible possible.

AI snapshot

Written from the paper’s full text.

TL;DR

The paper proposes an analog quantum-simulation scheme for the non-Hamiltonian Majorana equation by mapping complex conjugation and other unphysical operations onto unitary operations in an enlarged Hilbert space. It outlines a trapped-ion implementation using two ions and gives measurement protocols for observables such as pseudohelicity.

Key findings

  • Complex conjugation, charge conjugation, and time reversal can be implemented as unitary operations on an enlarged real Hilbert space via the mapping \( \psi \in \mathbb{C}^n \to \Xi \in \mathbb{R}^{2n} \), using an auxiliary two-level system.
  • In \(1+1\) dimensions, the non-Hermitian Majorana equation for a complex spinor becomes a \(3+1\)-dimensional Dirac equation for a four-component real bispinor, Eq. (5).
  • The proposed trapped-ion implementation uses two trapped ions and laser couplings to simulate the \(1+1\)-dimensional Majorana dynamics; coupled Majorana neutrinos are suggested with three ions and two vibrational modes.
  • Numerical scattering examples use parameters \(m=0.5\), \(c=1\), and \(V(x)=x\) in dimensionless units, showing time reversal refocusing, charge conjugation converting a repulsive potential to attractive, and a Majorana wave packet penetrating a barrier.

Methods

  • Theoretical design: introduces a complex-to-real mapping that turns antiunitary operations into local unitaries on an ancillary qubit, then applies it to the Majorana equation and discrete symmetries \(C\), \(T\), and \(K\).
  • Trapped-ion scheme: derives an interaction-picture Hamiltonian for two ions with center-of-mass and stretch modes, specifying laser frequencies, phases, and Rabi frequencies in Eq. (8) to recover the simulated Majorana Hamiltonian.
  • Measurement and numerics: gives a protocol to measure pseudohelicity via state-dependent displacement and spin measurements, and uses conventional numerical tools to study wave-packet scattering against a linearly growing potential.

Limitations

  • The paper does not state explicit limitations.
  • Evident from the text: the work is a theoretical proposal, not an experimental realization; the detailed implementation is presented for \(1+1\) dimensions with two trapped ions, while higher-dimensional and coupled-neutrino cases are only outlined.
  • Evident from the text: the scattering examples are numerical, use dimensionless parameters, and are not experimental data.

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

Integrity signals

Registry

Crossref · 10.1103/physrevx.1.021018

Cites

20 of 20 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

0 of 5 cited sources checked · 0 supported · 0 flagged

  • Findingown data

    A Majorana particle wave packet penetrates the barrier, showing a counterintuitive insensitivity to its presence.

    “While there are no plane wave solutions in the Majorana equation, we can still see a wave packet penetrating the barrier, showing a counterintuitive insensitivity to the presence of it.”
    Quote in the paperSubstantial claim
  • Findingreasoning

    Charge conjugation is implemented in the enlarged space via the unitary operation V_C.

    “we can deduce that charge conjugation is implemented in the enlarged space via the unitary operation V C ,”
    Quote in the paperSubstantial claim
  • Findingown data

    In the numerical experiment, a Dirac particle splits into a fraction that bounces back and a large antiparticle component that penetrates the barrier.

    “This is shown in Fig. 2(a), where a Dirac particle splits into a fraction of a particle that bounces back, and a large antiparticle component that penetrates the barrier.”
    Quote in the paperSubstantial claim
  • Findingreasoning

    The non-Hermitian Majorana equation for a complex spinor becomes a 3+1-dimensional Dirac equation for a four-component real bispinor under the mapping.

    “Surprisingly, the non-Hermitian Majorana equation for a complex spinor becomes a 3 þ 1-dimensional Dirac equation for a four-component real bispinor,”
    Quote in the paperSubstantial claim
  • Findingcitation

    The application of a state-dependent displacement operation on ion 2 followed by a measurement of σ_z^1 is equivalent to measuring the observable Σ.

    “The application of a state-dependent displacement operation on ion 2, U 2 ¼ exp½Àikð1 y Þ p x =2, generated by resonant blue and red sidebands, followed by a measurement of 1 z , is equivalent to measuring the observable [13]”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [13] source

      Not checked in the free run.

  • May combine two claims. 7
  • Classified as probably not a substantial claim. 3
  • The quote only partly states this claim. 1
  • May combine two claims.

    Findingown data

    Applying charge conjugation changes the sign of the charge and turns a repulsive electric potential into an attractive one, which can be easily penetrated by the antiparticle.

    “In Fig. 2(c) we apply charge conjugation, changing the sign of the charge and turning a repulsive electric potential into an attractive one, which can be easily penetrated by the antiparticle.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingown data

    Applying time reversal after the particle has entered the barrier reverses all momenta and refocuses the wave packet, tracing back exactly its trajectory.

    “In Fig. 2(b) we apply the time-reversal operation after the particle has entered the barrier: All momenta are reversed and the wave packet is refocused, tracing back exactly its trajectory.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingreasoning

    In the limit of large detuning, Eq. (5) is recovered with the momentum operator p_x = iħ(a†-a)/2Δ and the equivalences c = 2Δ and mc^2 = 2ħ^2 r^2/...

    “In the limit of large detuning, we have ) r ffiffiffiffiffiffiffiffiffiffiffi ffi hb y bi p , jha y À aij, and we recover Eq. ( 5) with the momentum operator p x ¼ i@ða y À aÞ=2Á and the equivalences c ¼ 2Á and mc 2 ¼ 2@ 2 r 2 = with Á ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi @=4m 0 p .”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingnone given

    Pseudohelicity Σ = σ_x p_x is conserved in the 1+1-dimensional Majorana dynamics of Eq. (3) but not in the 1+1-dimensional Dirac equation.

    “This quantity is conserved in the 1 þ 1-dimensional Majorana dynamics of Eq. ( 3) but not in the 1 þ 1-dimensional Dirac equation.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingreasoning

    The dynamics of the mapped equation preserves the reality of the bispinor and cannot be reduced to a single 1+1 Dirac particle.

    “Here, the dynamics preserves the reality of the bispinor É and cannot be reduced to a single 1 þ 1 Dirac particle.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Interpretationreasoning

    Complex conjugation of the simulated state becomes a local unitary V_K acting solely on the ancillary space, and is physically implementable for a wave function of arbitrary dimensions.

    “In this manner, the complex conjugation of the simulated state becomes a local unitary V K acting solely on the ancillary space,”
    • Also stated in: § Abstract · plain
      “and thus is physically implementable for a wave function of arbitrary dimensions.”
    Quote in the paperSubstantial claim
  • Probably not a substantial claim: may not pass S4 (based).

    Interpretationnone given

    A situation where an unphysical operation is performed between unitary evolutions is impossible to reproduce seamlessly with classical computers.

    “Such a situation is impossible to reproduce seamlessly with classical computers.”
    Quote in the paperNot a substantial claim
  • Probably not a substantial claim: may not pass S4 (based).

    Interpretationnone given

    The conventional approach to implementing an unphysical operation mid-simulation (stop, full quantum tomography, classical operation, re-encoding, and proceeding) would be impossible with classical resources.

    “Clearly, this task would be impossible with classical resources but could be accomplished with a suitable implementation of our proposed ideas.”
    Quote in the paperNot a substantial claim
  • May combine two claims.

    Interpretationcitation

    The mapping works in arbitrary dimensions and can be immediately applied on different experimental setups.

    “The mapping works in arbitrary dimensions and can be immediately applied on different experimental setups.”
    Quote in the paperNot a substantial claim
  • The quote only partly states this claim.

    Interpretationreasoning

    It is possible to tune the numerator and denominator independently to preserve the dispersive regime while exploring the range from ζ≈0 (ultrarelativistic limit) to ζ→∞ (nonrelativistic limit).

    “we see that it is possible to tune the numerator and denominator independently to preserve the dispersive regime, while exploring simultaneously the range from ' 0 (ultrarelativistic limit) to ! 1 (nonrelativistic limit).”
    Quote in the paperSubstantial claim
  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

    Interpretationnone given

    The previous implementation of discrete symmetries is valid both for Majorana and Dirac equations.

    “The previous implementation of discrete symmetries is valid both for Majorana and Dirac equations.”
    Quote in the paperNot a substantial claim
11 of 11

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?

  • Direct laser-written waveguides offer the possibility of implementing complex lattice geometries including the third spatial dimension, and consequently of utilization for investigating systems beyond the standard model, in quantum biophysics, and in quantum artificial life.

    “Special attention is paid to direct laser-written waveguides since they offer the possibility of implementing complex lattice geometries including the third spatial dimension [129, 130], and consequently of utilization for investigating systems beyond the standard model [131], in quantum biophysics [132-134], and in quantum artificial life [135,136].”

    From Integrated photonic quantum walks (2020) · cites this paper as [131]

    Split into 2 atoms — 1 confirmed, 1 partially supported, 0 disputed, 0 misattributed, 0 unverifiable. Expand the claim to see per-atom verdicts.

    Experimental — accuracy not yet measured
  • The spin degrees of freedom can be encoded in long-lived electronic states of the ions.

    “The spin degrees of freedom can be encoded in long-lived electronic states of the ions [5, 6, 12, 14, 19, 32, 39].”

Cites

Flagged first, then by citations

Research works printed but not linked: 2

  1. A. Zee, 2003, Quantum Field Theory in a Nutshell
  2. R. F. Streater, 2000, PCT, Spin and Statistics and All That

Cited by

Sorted by citations

Authors
Casanova, J., Sabín, C., León, J., Egusquiza, I. L., Gerritsma, R., Roos, C. F., García-Ripoll, J. J., & Solano, E.
Affiliations
  • University of the Basque Country (ES)
  • Consejo Superior de Investigaciones Científicas (ES)
  • Austrian Academy of Sciences (AT)
  • Ikerbasque (ES)
Venue
Physical Review X
Published
2011-12-09
Volume
1
Issue
2
ISSN
2160-3308 (ISSN-L)
OpenAlex
W2001928329
Cited by
77
References
20
Citations by year
2025: 1 · 2024: 3 · 2023: 1 · 2022: 3 · 2020: 5 · 2019: 4 · 2018: 7 · 2017: 6 · 2016: 6 · 2015: 10 · 2014: 11 · 2013: 8 · 2012: 10
FWCI
9.13
Type
journal article
Language
en
Open access
Locations
  • Physical Review X (publishedVersion, cc-by)
  • arXiv (Cornell University) (submittedVersion)
  • DIGITAL.CSIC (Spanish National Research Council (CSIC)) (submittedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
  • arXiv (Cornell University)
Funders
  • Eusko Jaurlaritza (IT-559-10, IT-472-10, IT472)
  • Ministerio de Ciencia e Innovación (FIS2009-12773-C02-01)
Topics
  • Physical Sciences › Computer Science › Artificial Intelligence › Quantum Computing Algorithms and Architecture
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Topological Materials and Phenomena
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Quantum many-body systems
Keywords
Majorana equation, quantum simulation, charge conjugation, complex conjugation, time reversal, wave function symmetry, Majorana fermions

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