Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:1602.00299 · Physical review. B./Physical review. B

Protected ground states in short chains of coupled spins in circuit quantum electrodynamics

Adam Callison, Eytan Grosfeld, Eran Ginossar

Published Aug 15, 2017• 2 citations
arXivHTMLPDF

Abstract

The two degenerate ground states of the anisotropic Heisenberg ($XY$) spin model of a chain of qubits (pseudospins) can encode quantum information, but their degree of protection against local perturbations is known to be only partial. We examine the properties of the system in the presence of nonlocal spin-spin interactions, possibly emerging from the quantum electrodynamics of the device. We find a phase distinct from the $XY$ phase admitting two ground states which are highly protected against all local field perturbations, persisting across a range of parameters. In the context of the $XY$ chain we discuss how the coupling between two ground states can be used to observe signatures of topological edge states in a small controlled chain of superconducting transmon qubits.

DOI
10.1103/physrevb.96.085121

Related papers

Preparing 100-qubit symmetry-protected topological order on a digital quantum computer

George Pennington, Kevin C. Smith, James R. Garrison +3 more

Symmetry-protected topological (SPT) phases extend the Landau paradigm of quantum matter by admitting distinct symmetry-preserving phases that lack any local order parameter. Demonstrating these phases at scale on programmable quantum processors is a key milestone in using quantum hardware to probe emergent many-body phenomena, yet it is impeded by the circuit depth normally required to capture non-trivial entanglement. Here we use a tensor network based approximate quantum compiling (AQC) protocol to construct shallow quantum circuits (18-39 CNOT depth), which prepare 100-site ground states of the spin-1/2 bond-alternating Heisenberg chain in both SPT phases, to 97.9-99.0% fidelity. Upon executing the circuits on IBM quantum hardware, the resulting states exhibit all defining signatures of SPT order including non-local string order for strings of up to length 20, characteristic degeneracies in the entanglement spectrum and clear evidence of symmetry-protected edge modes. The simultaneous observation of these independent diagnostics establishes current quantum computers as versatile platforms for large-scale studies of symmetry-protected quantum matter. More broadly, our results establish a practical foundation for probing non-equilibrium quench dynamics of such systems in regimes that challenge classical computational methods.

quant-pharXiv:2603.06325•npj Quantum Information•Mar 9, 2026•0 citations

Signatures of topological quantum phase transitions in driven and dissipative qubit arrays

Yuli Dong, Titus Neupert, R. Chitra +1 more

We study photonic signatures of symmetry broken and topological phases in a driven, dissipative circuit QED realization of spin-1/2 chains. Specifically, we consider the transverse-field XY model and a dual model with three-spin interactions. The former has a ferromagnetic and a paramagnetic phase, while the latter features, in addition, a symmetry protected topological phase. Using the method of third quantization, we calculate the nonequilibrium steady state of the open spin chains for arbitrary system sizes and temperatures. We find that the bilocal correlation function of the spins at both ends of the chain provides a sensitive measure for both symmetry-breaking and topological phase transitions of the systems, but no universal means to distinguish between the two types of transitions. Both models have equivalent representations in terms of free Majorana fermions, which host zero, one and two topological Majorana end modes in the paramagnetic, ferromagnetic, and symmetry protected topological phases, respectively. The correlation function we study retains its bilocal character in the fermionic representation, so that our results are equally applicable to the fermionic models in their own right. We propose a photonic realization of the dissipative transverse-field XY model in a tunable setup, where an array of superconducting transmon qubits is coupled at both ends to a photonic microwave circuit.

arXiv:1604.04770•Physical review. B./Physical review. B•Jul 25, 2016•3 citations

Topological signatures of magnetic phase transitions with Majorana fermions through local observables and quantum information

Karyn Le Hur, Fan Yang, Magali Korolev

The one-dimensional (1D) $J_1-J_2$ quantum spin model can be viewed as a strong-coupling analogue of the Schrieffer-Su-Heeger model with two inequivalent alternating Ising couplings along the wire, associated to the physics of resonating valence bonds. Similar to the quantum Ising model, which differently presents a long-range N\' eel ordered phase, this model also maps onto a p-wave superconducting wire which shows a topological phase transition with the emergence of low-energy Majorana fermions. We show how signatures of the topological phase transition for the p-wave superconducting wire, i.e. a half Skyrmion, are revealed through local (short-range) spin observables and their derivatives related to the capacitance of the pairing fermion model. Then, we present an edge correspondence through the edge spin susceptibility in the $J_1-J_2$ model revealing that the topological phase transition is a metal of Majorana fermions. We justify that the spin magnetization at an edge at very small transverse magnetic field is a good marker of the topological invariant and of Majorana zero modes. We identify a correspondence between the quantum information of resonating valence bonds and the charge fluctuations in a p-wave superconductor through our method "the bipartite fluctuations". Physical properties of this 1D model are in fact robust when including additional interactions, which is optimistic for practical applications e.g. in quantum circuits.

arXiv:2506.11731•Physical review. B./Physical review. B•Feb 10, 2026•1 citation

Gapless symmetry-protected topological phase of quantum antiferromagnets on anisotropic triangular strip

Yuichiro Hidaka, Shunsuke C. Furuya, Atsushi Ueda +1 more

We study a three-leg spin-1/2 ladder with geometrically frustrated interleg interactions. We call this model an anisotropic triangular-strip (ATS) model. We numerically and field-theoretically show that its ground state belongs to a gapless symmetry-protected topological (SPT) phase. The numerical approach is based on density-matrix renormalization group analyses of the entanglement entropy and the entanglement spectrum. Whereas the entanglement entropy exhibits a critical behavior, the entanglement spectrum is nontrivially degenerate. These entanglement properties imply that the ground state is a gapless topological phase. We investigate the ATS model using a quantum field theory to support the numerical findings. When the frustrated interchain interaction is deemed a perturbation acting on the three spin chains, the frustrated interchain interaction almost isolates the second chain from the other two chains. However, at the same time, the second chain mediates a ferromagnetic interaction between the first and third chains. Therefore, the ground state of the ATS model is a gapless Tomonaga-Luttinger liquid weakly coupled to a spin-1 Haldane chain with irrelevant interactions. Last but not least, we show that the gapless SPT phase of the ATS model is a symmetry-protected critical phase. We point out that the symmetry protection of criticality is essential in characterization of the gapless SPT phase.

arXiv:2205.15525•Physical review. B./Physical review. B•Oct 28, 2022•15 citations

Robustness of topological edge states in alternating spin chains against environment

Alexander Sattler, Maria Daghofer

Both the Haldane spin-$1$ chain and dimerized chains of spin-$1/2$ exhibit topologically protected edge states that are robust against specific perturbations. Recently, such spin chains have been specifically assembled on surfaces and we investigate here the robustness of these edge states against coupling to the surface. Since no physical system can be considered perfectly isolated, it is crucial to examine whether topological robustness is maintained in the presence of environmental coupling. We apply exact diagonalization to a Lindblad master equation that couples an alternating Heisenberg spin chain based on spins $1/2$ to a surface via various jump operators. The robustness of topological states is assessed via the time evolution of quantities such as the ground-state degeneracy, correlation function, entropy, and magnetization of edge states. We investigate chains built from dimers with antiferromagnetic and ferromagnetic intra-dimer coupling, which resemble Su-Schrieffer-Heeger and the Haldane models, resp., and assess the impact of $z$-axis anisotropy and longer-ranged couplings. Generally, we find that signatures of topological properties are more robust in Su-Schrieffer-Heeger-like chains than in Haldane-like chains.

arXiv:2505.22420•May 28, 2025•0 citations

Heisenberg-Kitaev Interactions for Topologically Protected Spintronic Qubits

Revista, Zen, PHYSICS, 10

The pursuit of fault-tolerant quantum computing necessitates qubit architectures that are inherently robust against environmental decoherence and operational errors. Spintronic qubits, leveraging the spin degree of freedom of electrons, offer a promising platform due to their long coherence times and compatibility with solid-state systems. However, even spintronic qubits remain susceptible to local noise. This paper explores the profound potential of Heisenberg-Kitaev interactions to confer topological protection upon spintronic qubits. By engineering materials and systems that exhibit these anisotropic, bond-directional interactions, it is theoretically possible to realize exotic quantum spin liquid states hosting non-Abelian anyons, such as Majorana zero modes. Encoding quantum information in the nonlocal properties of these anyons would render qubits immune to local perturbations, dramatically extending coherence times and simplifying error correction protocols. We provide a comprehensive review of the theoretical underpinnings of the Kitaev and Heisenberg-Kitaev models, survey candidate materials where such interactions are prevalent, and propose conceptual designs for topologically protected spintronic qubits. This work uniquely consolidates the theoretical framework of Heisenberg-Kitaev interactions with the practical demands of spintronic qubit design, offering a systematic conceptual pathway for their topological protection and predicting their robust characteristics. We further discuss the methodologies for theoretical modeling, the expected characteristics of such qubits, and the significant experimental challenges that must be overcome for their practical realization. This work highlights Heisenberg-Kitaev interactions as a crucial pathway towards the development of truly fault-tolerant and scalable quantum computing technologies.

•Nov 28, 2025•0 citations
The two degenerate ground states of the anisotropic Heisenberg (XYXYXY) spin model of a chain of qubits (pseudospins) can encode quantum information, but their degree of protection against local perturbations is known to be only partial. We examine the properties of the system in the presence of nonlocal spin-spin interactions, possibly emerging from the quantum electrodynamics of the device. We find a phase distinct from the XYXYXY phase admitting two ground states which are highly protected against all local field perturbations, persisting across a range of parameters. In the context of the XYXYXY chain we discuss how the coupling between two ground states can be used to observe signatures of topological edge states in a small controlled chain of superconducting transmon qubits.
Symmetry-protected topological (SPT) phases extend the Landau paradigm of quantum matter by admitting distinct symmetry-preserving phases that lack any local order parameter. Demonstrating these phases at scale on programmable quantum processors is a key milestone in using quantum hardware to probe emergent many-body phenomena, yet it is impeded by the circuit depth normally required to capture non-trivial entanglement. Here we use a tensor network based approximate quantum compiling (AQC) protocol to construct shallow quantum circuits (18-39 CNOT depth), which prepare 100-site ground states of the spin-1/2 bond-alternating Heisenberg chain in both SPT phases, to 97.9-99.0% fidelity. Upon executing the circuits on IBM quantum hardware, the resulting states exhibit all defining signatures of SPT order including non-local string order for strings of up to length 20, characteristic degeneracies in the entanglement spectrum and clear evidence of symmetry-protected edge modes. The simultaneous observation of these independent diagnostics establishes current quantum computers as versatile platforms for large-scale studies of symmetry-protected quantum matter. More broadly, our results establish a practical foundation for probing non-equilibrium quench dynamics of such systems in regimes that challenge classical computational methods.
We study photonic signatures of symmetry broken and topological phases in a driven, dissipative circuit QED realization of spin-1/2 chains. Specifically, we consider the transverse-field XY model and a dual model with three-spin interactions. The former has a ferromagnetic and a paramagnetic phase, while the latter features, in addition, a symmetry protected topological phase. Using the method of third quantization, we calculate the nonequilibrium steady state of the open spin chains for arbitrary system sizes and temperatures. We find that the bilocal correlation function of the spins at both ends of the chain provides a sensitive measure for both symmetry-breaking and topological phase transitions of the systems, but no universal means to distinguish between the two types of transitions. Both models have equivalent representations in terms of free Majorana fermions, which host zero, one and two topological Majorana end modes in the paramagnetic, ferromagnetic, and symmetry protected topological phases, respectively. The correlation function we study retains its bilocal character in the fermionic representation, so that our results are equally applicable to the fermionic models in their own right. We propose a photonic realization of the dissipative transverse-field XY model in a tunable setup, where an array of superconducting transmon qubits is coupled at both ends to a photonic microwave circuit.
The one-dimensional (1D) J1−J2J_1-J_2J1​−J2​ quantum spin model can be viewed as a strong-coupling analogue of the Schrieffer-Su-Heeger model with two inequivalent alternating Ising couplings along the wire, associated to the physics of resonating valence bonds. Similar to the quantum Ising model, which differently presents a long-range N\' eel ordered phase, this model also maps onto a p-wave superconducting wire which shows a topological phase transition with the emergence of low-energy Majorana fermions. We show how signatures of the topological phase transition for the p-wave superconducting wire, i.e. a half Skyrmion, are revealed through local (short-range) spin observables and their derivatives related to the capacitance of the pairing fermion model. Then, we present an edge correspondence through the edge spin susceptibility in the J1−J2J_1-J_2J1​−J2​ model revealing that the topological phase transition is a metal of Majorana fermions. We justify that the spin magnetization at an edge at very small transverse magnetic field is a good marker of the topological invariant and of Majorana zero modes. We identify a correspondence between the quantum information of resonating valence bonds and the charge fluctuations in a p-wave superconductor through our method "the bipartite fluctuations". Physical properties of this 1D model are in fact robust when including additional interactions, which is optimistic for practical applications e.g. in quantum circuits.
We study a three-leg spin-1/2 ladder with geometrically frustrated interleg interactions. We call this model an anisotropic triangular-strip (ATS) model. We numerically and field-theoretically show that its ground state belongs to a gapless symmetry-protected topological (SPT) phase. The numerical approach is based on density-matrix renormalization group analyses of the entanglement entropy and the entanglement spectrum. Whereas the entanglement entropy exhibits a critical behavior, the entanglement spectrum is nontrivially degenerate. These entanglement properties imply that the ground state is a gapless topological phase. We investigate the ATS model using a quantum field theory to support the numerical findings. When the frustrated interchain interaction is deemed a perturbation acting on the three spin chains, the frustrated interchain interaction almost isolates the second chain from the other two chains. However, at the same time, the second chain mediates a ferromagnetic interaction between the first and third chains. Therefore, the ground state of the ATS model is a gapless Tomonaga-Luttinger liquid weakly coupled to a spin-1 Haldane chain with irrelevant interactions. Last but not least, we show that the gapless SPT phase of the ATS model is a symmetry-protected critical phase. We point out that the symmetry protection of criticality is essential in characterization of the gapless SPT phase.
Both the Haldane spin-111 chain and dimerized chains of spin-1/21/21/2 exhibit topologically protected edge states that are robust against specific perturbations. Recently, such spin chains have been specifically assembled on surfaces and we investigate here the robustness of these edge states against coupling to the surface. Since no physical system can be considered perfectly isolated, it is crucial to examine whether topological robustness is maintained in the presence of environmental coupling. We apply exact diagonalization to a Lindblad master equation that couples an alternating Heisenberg spin chain based on spins 1/21/21/2 to a surface via various jump operators. The robustness of topological states is assessed via the time evolution of quantities such as the ground-state degeneracy, correlation function, entropy, and magnetization of edge states. We investigate chains built from dimers with antiferromagnetic and ferromagnetic intra-dimer coupling, which resemble Su-Schrieffer-Heeger and the Haldane models, resp., and assess the impact of zzz-axis anisotropy and longer-ranged couplings. Generally, we find that signatures of topological properties are more robust in Su-Schrieffer-Heeger-like chains than in Haldane-like chains.
The pursuit of fault-tolerant quantum computing necessitates qubit architectures that are inherently robust against environmental decoherence and operational errors. Spintronic qubits, leveraging the spin degree of freedom of electrons, offer a promising platform due to their long coherence times and compatibility with solid-state systems. However, even spintronic qubits remain susceptible to local noise. This paper explores the profound potential of Heisenberg-Kitaev interactions to confer topological protection upon spintronic qubits. By engineering materials and systems that exhibit these anisotropic, bond-directional interactions, it is theoretically possible to realize exotic quantum spin liquid states hosting non-Abelian anyons, such as Majorana zero modes. Encoding quantum information in the nonlocal properties of these anyons would render qubits immune to local perturbations, dramatically extending coherence times and simplifying error correction protocols. We provide a comprehensive review of the theoretical underpinnings of the Kitaev and Heisenberg-Kitaev models, survey candidate materials where such interactions are prevalent, and propose conceptual designs for topologically protected spintronic qubits. This work uniquely consolidates the theoretical framework of Heisenberg-Kitaev interactions with the practical demands of spintronic qubit design, offering a systematic conceptual pathway for their topological protection and predicting their robust characteristics. We further discuss the methodologies for theoretical modeling, the expected characteristics of such qubits, and the significant experimental challenges that must be overcome for their practical realization. This work highlights Heisenberg-Kitaev interactions as a crucial pathway towards the development of truly fault-tolerant and scalable quantum computing technologies.