Discrete-time quantum walks in synthetic dimensions
Pith reviewed 2026-05-10 17:18 UTC · model grok-4.3
The pith
Generalized displacement operators on Fock-state lattices from Lie algebras generate discrete-time quantum walks with state-dependent tunneling in synthetic state space.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
We introduce discrete-time quantum walks on Fock-state lattices. For each Lie algebra one associates both a phase space and a Fock-state lattice; by relating these spaces and applying generalized displacement operators we construct the discrete unitary operator that generates the walk. In this framework the displacement operators replace the usual nearest-neighbor shifts and lead to state-dependent tunneling on the lattice. Several examples demonstrate ballistic spreading, coin-walker entanglement, symmetry-induced interference patterns, and, for different algebraic structures, anomalous super-ballistic spreading as well as localization effects.
What carries the argument
Generalized displacement operators acting on Fock-state lattices associated with Lie algebras, which replace fixed nearest-neighbor shifts and produce state-dependent tunneling.
Load-bearing premise
Fock-state lattices derived from Lie algebras supply a usable correspondence to phase space that directly yields a walk-generating unitary from generalized displacement operators.
What would settle it
Numerical simulation or optical experiment that applies the constructed unitary for a chosen Lie algebra and checks whether the walker spreads ballistically, becomes localized, or exhibits the predicted interference pattern on the Fock-state lattice.
Figures
read the original abstract
In this work we introduce discrete-time quantum walks in state space, more precisely on Fock-state lattices. Fock-state lattices provide a natural and clean setting for implementing lattice models, particularly in quantum optical systems. Thus, contrary to the common setting where the walker resides in real space or phase space, here the walk takes place in a synthetic space. We present a general formalism based on Lie algebras and their properties. For each Lie algebra one can associate both a phase space and a Fock-state lattice, and by understanding how these spaces are related, together with the action of generalized displacement operators, we construct the discrete unitary operator that generates the walk. In this framework the displacement operators replace the usual nearest-neighbor shifts and lead to state-dependent tunneling on the lattice. By considering several examples we demonstrate ballistic spreading and other characteristic features of discrete-time quantum walks, such as coin-walker entanglement and symmetry-induced interference patterns. We also show that different algebraic structures can give rise to qualitatively different dynamics, including anomalous behavior such as super-ballistic spreading as well as localization effects.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript introduces discrete-time quantum walks on Fock-state lattices in synthetic dimensions. Using a Lie-algebra-based formalism, the authors relate phase space and Fock-state lattices and construct a discrete unitary operator via generalized displacement operators that replace nearest-neighbor shifts, resulting in state-dependent tunneling. Through several examples, they demonstrate characteristic DTQW behaviors such as ballistic spreading, coin-walker entanglement, and symmetry-induced interference, as well as anomalous dynamics including super-ballistic spreading and localization effects depending on the algebraic structure.
Significance. If the construction holds, this work offers a systematic way to realize quantum walks in quantum optical systems via synthetic Fock-state lattices. The Lie-algebra approach enables algebra-dependent dynamics without free parameters, which could facilitate new quantum simulation protocols and studies of interference and entanglement in non-standard geometries. The framework builds on standard displacement operators and lattice relations, providing a clean theoretical route to tunable walk behaviors.
major comments (2)
- [§3] §3 (Formalism): the central construction of the walk-generating unitary via generalized displacement operators on the Fock lattice is plausible from the phase-space relation, but an explicit step-by-step verification that the operator remains unitary for arbitrary Lie-algebra generators (beyond the abstract statement) is needed to confirm the claim for all presented cases.
- [§4.2] §4.2 (su(1,1) example): the reported super-ballistic spreading is a key anomalous feature, yet the manuscript does not provide a quantitative metric (e.g., variance scaling exponent with error bars from numerics) or direct comparison against the standard DTQW ballistic case to substantiate the distinction.
minor comments (3)
- [Abstract] Abstract: the phrasing 'state space, more precisely on Fock-state lattices' is slightly redundant; a single clear definition of the synthetic space would improve readability.
- [Figure 2] Figure 2: the interference pattern plots lack axis labels for the coin degree of freedom and a scale bar for probability density, making it hard to compare entanglement growth across algebras.
- [§2] Notation: the symbol for the generalized displacement operator is introduced without an explicit definition in terms of the Lie-algebra generators; adding this in the first use would aid clarity.
Simulated Author's Rebuttal
We are grateful to the referee for the thorough review and the recommendation for minor revision. The comments are helpful and we will revise the manuscript accordingly to address them.
read point-by-point responses
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Referee: [§3] §3 (Formalism): the central construction of the walk-generating unitary via generalized displacement operators on the Fock lattice is plausible from the phase-space relation, but an explicit step-by-step verification that the operator remains unitary for arbitrary Lie-algebra generators (beyond the abstract statement) is needed to confirm the claim for all presented cases.
Authors: We thank the referee for this observation. The unitarity of the walk operator is indeed central to our construction. Although it follows from the unitarity of the generalized displacement operators and the properties of the Lie algebra representations, we agree that an explicit verification would be beneficial. In the revised manuscript, we will add a detailed step-by-step proof in §3 demonstrating that the operator U satisfies U†U = I for arbitrary generators, and we will explicitly verify this for the su(2), su(1,1), and other cases presented. revision: yes
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Referee: [§4.2] §4.2 (su(1,1) example): the reported super-ballistic spreading is a key anomalous feature, yet the manuscript does not provide a quantitative metric (e.g., variance scaling exponent with error bars from numerics) or direct comparison against the standard DTQW ballistic case to substantiate the distinction.
Authors: We appreciate the referee's suggestion to strengthen the evidence for the anomalous dynamics. In the revised version, we will include a quantitative analysis of the spreading in the su(1,1) case. Specifically, we will report the variance scaling exponent obtained from numerical simulations, including error bars from fits, and provide a direct comparison with the standard ballistic spreading (where variance scales as t²) to clearly highlight the super-ballistic behavior. revision: yes
Circularity Check
No significant circularity detected
full rationale
The paper constructs the discrete unitary walk operator on Fock-state lattices by relating Lie-algebra phase spaces to the lattices and replacing nearest-neighbor shifts with generalized displacement operators. This relies on standard Lie algebra properties and relations between phase space and Fock lattices, without reducing the central result to fitted parameters, self-referential definitions, or load-bearing self-citations. The derivation is self-contained against external benchmarks of Lie algebra theory and produces the reported features (ballistic spreading, entanglement, interference) as direct consequences of the construction.
Axiom & Free-Parameter Ledger
axioms (1)
- domain assumption Lie algebras possess associated phase spaces and Fock-state lattices whose relation permits construction of a discrete unitary walk operator from generalized displacement operators
Reference graph
Works this paper leans on
-
[1]
This operator is also suitable for Grover’s search algorithm, and is only one of many possible ones. We initialize the coin in state|s⟩ and the walker in the symmetric coherent state (53) with βi = 1/ √ 3, which ensures a symmetric walk. Figure 4(a) shows the distributionP(n 1, n2, n3) after five steps. For the chosen parameters (N= 120,β= 0.2) the walker...
-
[2]
Y. Aharonov, L. Davidovich, and N. Zagury, Quantum random walks, Physical Review A48, 1687 (1993)
work page 1993
-
[3]
Kempe, Quantum random walks: an introductory overview, Contemporary Physics44, 307 (2003)
J. Kempe, Quantum random walks: an introductory overview, Contemporary Physics44, 307 (2003)
work page 2003
-
[4]
S. E. Venegas-Andraca, Quantum walks: a comprehen- sive review, Quantum Information Processing11, 1015 (2012)
work page 2012
- [5]
-
[6]
A. M. Childs, R. Cleve, E. Deotto, E. Farhi, S. Gutmann, and D. A. Spielman, Exponential algorithmic speedup by a quantum walk, inProceedings of the thirty-fifth annual ACM symposium on Theory of computing(2003) pp. 59– 68
work page 2003
-
[7]
A. M. Childs and J. Goldstone, Spatial search by quan- tum walk, Physical Review A—Atomic, Molecular, and Optical Physics70, 022314 (2004)
work page 2004
-
[8]
A. M. Childs, Universal computation by quantum walk, Physical review letters102, 180501 (2009)
work page 2009
-
[9]
N. B. Lovett, S. Cooper, M. Everitt, M. Trevers, and V. Kendon, Universal quantum computation us- ing the discrete-time quantum walk, Physical Review A—Atomic, Molecular, and Optical Physics81, 042330 (2010)
work page 2010
- [10]
-
[11]
M. B. Plenio and S. F. Huelga, Dephasing-assisted trans- port: quantum networks and biomolecules, New Journal of Physics10, 113019 (2008)
work page 2008
-
[12]
J. Wang and K. Manouchehri,Physical implementation of quantum walks, Vol. 10 (Springer, 2013)
work page 2013
-
[13]
T. Kitagawa, M. S. Rudner, E. Berg, and E. Demler, Ex- ploring topological phases with quantum walks, Physical Review A—Atomic, Molecular, and Optical Physics82, 033429 (2010)
work page 2010
- [14]
-
[15]
X. Wang, L. Xiao, X. Qiu, K. Wang, W. Yi, and P. Xue, Detecting topological invariants and revealing topologi- cal phase transitions in discrete-time photonic quantum walks, Physical Review A98, 013835 (2018)
work page 2018
-
[16]
M. Mohseni, P. Rebentrost, S. Lloyd, and A. Aspuru- Guzik, Environment-assisted quantum walks in pho- tosynthetic energy transfer, The Journal of chemical physics129(2008)
work page 2008
-
[17]
G. S. Engel, T. R. Calhoun, E. L. Read, T.-K. Ahn, T. Manˇ cal, Y.-C. Cheng, R. E. Blankenship, and G. R. Fleming, Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems, Nature 446, 782 (2007)
work page 2007
-
[18]
S. D. Berry and J. B. Wang, Two-particle quantum walks: Entanglement and graph isomorphism testing, Physical Review A—Atomic, Molecular, and Optical Physics83, 042317 (2011)
work page 2011
-
[19]
B. L. Douglas and J. B. Wang, A classical approach to the graph isomorphism problem using quantum walks, Journal of Physics A: Mathematical and Theoretical41, 075303 (2008)
work page 2008
-
[20]
T. Chen, X. Zhang, and X. Zhang, Quantum sensing of noises in one and two dimensional quantum walks, Sci- entific Reports7, 4962 (2017)
work page 2017
-
[21]
M. Annabestani, M. Hassani, D. Tamascelli, and M. G. Paris, Multiparameter quantum metrology with discrete- time quantum walks, Physical Review A105, 062411 (2022)
work page 2022
-
[22]
A. M. Childs, On the relationship between continuous- and discrete-time quantum walk, Communications in Mathematical Physics294, 581 (2010)
work page 2010
-
[23]
H. B. Perets, Y. Lahini, F. Pozzi, M. Sorel, R. Moran- dotti, and Y. Silberberg, Realization of quantum walks with negligible decoherence in waveguide lattices, Physi- cal review letters100, 170506 (2008)
work page 2008
-
[24]
H. Schmitz, R. Matjeschk, C. Schneider, J. Glueckert, M. Enderlein, T. Huber, and T. Schaetz, Quantum walk of a trapped ion in phase space, Physical review letters 103, 090504 (2009)
work page 2009
-
[25]
F. Z¨ ahringer, G. Kirchmair, R. Gerritsma, E. Solano, R. Blatt, and C. F. Roos, Realization of a quantum walk with one and two trapped ions, Physical review letters 104, 100503 (2010)
work page 2010
-
[26]
C. Huerta Alderete, S. Singh, N. H. Nguyen, D. Zhu, R. Balu, C. Monroe, C. Chandrashekar, and N. M. Linke, Quantum walks and dirac cellular automata on a pro- grammable trapped-ion quantum computer, Nature com- munications11, 3720 (2020)
work page 2020
-
[27]
A. Peruzzo, M. Lobino, J. C. Matthews, N. Matsuda, A. Politi, K. Poulios, X.-Q. Zhou, Y. Lahini, N. Ismail, K. W¨ orhoff,et al., Quantum walks of correlated photons, Science329, 1500 (2010)
work page 2010
- [28]
-
[29]
K. Poulios, R. Keil, D. Fry, J. D. Meinecke, J. C. Matthews, A. Politi, M. Lobino, M. Gr¨ afe, M. Heinrich, S. Nolte,et al., Quantum walks of correlated photon pairs in two-dimensional waveguide arrays, Physical review let- ters112, 143604 (2014)
work page 2014
-
[30]
D. N. Biggerstaff, R. Heilmann, A. A. Zecevik, M. Gr¨ afe, M. A. Broome, A. Fedrizzi, S. Nolte, A. Szameit, A. G. White, and I. Kassal, Enhancing coherent transport in a photonic network using controllable decoherence, Nature communications7, 11282 (2016)
work page 2016
-
[31]
K. Wang, X. Qiu, L. Xiao, X. Zhan, Z. Bian, W. Yi, and P. Xue, Simulating dynamic quantum phase transitions in photonic quantum walks, Physical review letters122, 020501 (2019)
work page 2019
-
[32]
H. Tang, X.-F. Lin, Z. Feng, J.-Y. Chen, J. Gao, K. Sun, C.-Y. Wang, P.-C. Lai, X.-Y. Xu, Y. Wang,et al., Ex- perimental two-dimensional quantum walk on a photonic chip, Science advances4, eaat3174 (2018)
work page 2018
-
[33]
K. Sengupta, S. Dinesh, K. M. Shafi, S. Asokan, and C. Chandrashekar, Experimental realization of univer- sal quantum gates and a six-qubit entangled state using a photonic quantum walk, Physical Review Applied24, 024012 (2025)
work page 2025
- [34]
- [35]
- [36]
-
[37]
B. C. Sanders, S. D. Bartlett, B. Tregenna, and P. L. Knight, Quantum quincunx in cavity quantum electro- dynamics, Physical Review A67, 042305 (2003)
work page 2003
-
[38]
P. Xue, B. C. Sanders, A. Blais, and K. Lalumi` ere, Quan- tum walks on circles in phase space via superconduct- ing circuit quantum electrodynamics, Physical Review A—Atomic, Molecular, and Optical Physics78, 042334 (2008)
work page 2008
-
[39]
P. Xue, B. C. Sanders, and D. Leibfried, Quantum walk on a line for a trapped ion, Physical review letters103, 183602 (2009)
work page 2009
-
[40]
A. ¨U. Hardal, P. Xue, Y. Shikano, ¨O. E. M¨ ustecaplıo˘ glu, and B. C. Sanders, Discrete-time quantum walk with nitrogen-vacancy centers in diamond coupled to a su- perconducting flux qubit, Physical Review A—Atomic, Molecular, and Optical Physics88, 022303 (2013)
work page 2013
-
[41]
Duan, Quantum walk on the bloch sphere, Physical Review A105, 042215 (2022)
L. Duan, Quantum walk on the bloch sphere, Physical Review A105, 042215 (2022)
work page 2022
-
[42]
Duan, Quantum walk for su (1, 1), Physical Review A 107, 022224 (2023)
L. Duan, Quantum walk for su (1, 1), Physical Review A 107, 022224 (2023)
work page 2023
-
[43]
J. Larson and T. Mavrogordatos,The Jaynes–Cummings model and its descendants: modern research directions (IoP Publishing, 2021)
work page 2021
-
[44]
D.-W. Wang, H. Cai, R.-B. Liu, and M. O. Scully, Meso- scopic superposition states generated by synthetic spin- orbit interaction in fock-state lattices, Physical review letters116, 220502 (2016)
work page 2016
-
[45]
H. Cai and D.-W. Wang, Topological phases of quantized light, National Science Review8, nwaa196 (2021)
work page 2021
-
[46]
P. Saugmann and J. Larson, Fock-state-lattice approach to quantum optics, Physical Review A108, 033721 (2023)
work page 2023
-
[47]
Mumford, Meissner effect in fock space, Physical Re- view A106, 043325 (2022)
J. Mumford, Meissner effect in fock space, Physical Re- view A106, 043325 (2022)
work page 2022
-
[48]
J. Mumford, D. Kamp, and D. O’Dell, Gauge poten- tials and vortices in the fock space of a pair of periodi- cally driven bose-einstein condensates, Physical Review A110, 043310 (2024)
work page 2024
-
[49]
J. Yuan, H. Cai, and D.-W. Wang, Quantum simulation 15 in fock-state lattices, Advances in Physics: X9, 2325611 (2024)
work page 2024
-
[50]
M. Peng, Q. Wei, J. Yuan, D.-W. Wang, M. Yan, H. Cai, and G. Chen, Ideal flat and resolved su (3) landau levels in three dimensions, Physical Review Letters134, 116601 (2025)
work page 2025
- [51]
-
[52]
X. Zhao, Y. Xu, L.-M. Kuang, and J.-Q. Liao, Dark- state engineering in fock-state lattices, Physical Review Research7, 033070 (2025)
work page 2025
-
[53]
J. Deng, H. Dong, C. Zhang, Y. Wu, J. Yuan, X. Zhu, F. Jin, H. Li, Z. Wang, H. Cai,et al., Observing the quantum topology of light, Science378, 966 (2022)
work page 2022
-
[54]
C. Wu, W. Liu, Y. Jia, G. Chen, and F. Chen, Obser- vation of topological pumping of a defect state in a fock photonic lattice, Physical Review A107, 033501 (2023)
work page 2023
-
[55]
C. Wang, F.-M. Liu, M.-C. Chen, H. Chen, X.-H. Zhao, C. Ying, Z.-X. Shang, J.-W. Wang, Y.-H. Huo, C.-Z. Peng,et al., Realization of fractional quantum hall state with interacting photons, Science384, 579 (2024)
work page 2024
-
[56]
Y. Wang, Y.-K. Wu, Y. Jiang, M.-L. Cai, B.-W. Li, Q.- X. Mei, B.-X. Qi, Z.-C. Zhou, and L.-M. Duan, Realiz- ing synthetic dimensions and artificial magnetic flux in a trapped-ion quantum simulator, Physical Review Letters 132, 130601 (2024)
work page 2024
-
[57]
J. Yang, Y. Li, Y. Yang, X. Xie, Z. Zhang, J. Yuan, H. Cai, D.-W. Wang, and F. Gao, Realization of all-band- flat photonic lattices, Nature Communications15, 1484 (2024)
work page 2024
- [58]
-
[59]
D. Aharonov, A. Ambainis, J. Kempe, and U. Vazirani, Quantum walks on graphs, inProceedings of the thirty- third annual ACM symposium on Theory of computing (2001) pp. 50–59
work page 2001
-
[60]
C. Moore and A. Russell, Quantum walks on the hy- percube, inInternational Workshop on Randomization and Approximation Techniques in Computer Science (Springer, 2002) pp. 164–178
work page 2002
-
[61]
Kendon, Quantum walks on general graphs, Interna- tional Journal of Quantum Information4, 791 (2006)
V. Kendon, Quantum walks on general graphs, Interna- tional Journal of Quantum Information4, 791 (2006)
work page 2006
- [62]
-
[63]
Georgi,Lie algebras in particle physics: from isospin to unified theories(Taylor & Francis, 2000)
H. Georgi,Lie algebras in particle physics: from isospin to unified theories(Taylor & Francis, 2000)
work page 2000
-
[64]
J. Fuchs and C. Schweigert,Symmetries, Lie algebras and representations: A graduate course for physicists(Cam- bridge University Press, 2003)
work page 2003
-
[65]
D. H. Sattinger and O. L. Weaver,Lie groups and alge- bras with applications to physics, geometry, and mechan- ics(Springer Science & Business Media, 2013)
work page 2013
-
[66]
L. Mandel and E. Wolf,Optical coherence and quantum optics(Cambridge university press, 1995)
work page 1995
-
[67]
P. Ferraro, C. B. Naves, and J. Larson, Algebraic struc- ture of fock-state lattices (2026), arXiv preprint (to be assigned)
work page 2026
-
[68]
A. M. Perelomov, Generalized coherent states and some of their applications, Soviet Physics Uspekhi20, 703 (1977)
work page 1977
-
[69]
G. Abal, R. Siri, A. Romanelli, and R. Donangelo, Quan- tum walk on the line: Entanglement and nonlocal initial conditions, Physical Review A—Atomic, Molecular, and Optical Physics73, 042302 (2006)
work page 2006
-
[70]
M. Brune, S. Haroche, J.-M. Raimond, L. Davidovich, and N. Zagury, Manipulation of photons in a cavity by dispersive atom-field coupling: Quantum-nondemolition measurements and generation of “schr¨ odinger cat”states, Physical Review A45, 5193 (1992)
work page 1992
- [71]
-
[72]
J. R. Klauder and B.-S. Skagerstam,Coherent states: ap- plications in physics and mathematical physics(World scientific, 1985)
work page 1985
-
[73]
Gazeau,Coherent states in quantum physics(Wiley Online Library, 2009)
J.-P. Gazeau,Coherent states in quantum physics(Wiley Online Library, 2009)
work page 2009
-
[74]
A. B. Klimov and S. M. Chumakov,A group-theoretical approach to quantum optics: models of atom-field inter- actions, Vol. 10 (Wiley Online Library, 2009)
work page 2009
- [75]
-
[76]
T. D. Mackay, S. D. Bartlett, L. T. Stephenson, and B. C. Sanders, Quantum walks in higher dimensions, Journal of Physics A: Mathematical and General35, 2745 (2002)
work page 2002
-
[77]
G. Grimmett, S. Janson, and P. F. Scudo, Weak limits for quantum random walks, Physical Review E69, 026119 (2004)
work page 2004
-
[78]
N. Inui, Y. Konishi, and N. Konno, Localization of two-dimensional quantum walks, Physical Review A—Atomic, Molecular, and Optical Physics69, 052323 (2004)
work page 2004
-
[79]
R. Anishetty, M. Mathur, and I. Raychowdhury, Irre- ducible su (3) schwinger bosons, Journal of mathematical physics50(2009)
work page 2009
-
[80]
A. M. Perelomov,Generalized Coherent States and Their Applications, Theoretical and Mathematical Physics (Springer, Berlin, Heidelberg, 1986)
work page 1986
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