Every matter-based qubit platform—superconducting circuits, trapped ions, nitrogen- vacancy centres—exhibits decoherence in excess of what the standard two-level error model predicts from known noise sources. In superconducting qubits, two-level system (TLS) defect coupling accounts for 30–50% of the dephasing budget with debated mi- croscopic origin. In trapped ions, anomalous motional heating exceeds Johnson noise predictions by two to six orders of magnitude. In NV centres, residual pure dephasing persists after the nuclear spin bath and all identified sources are eliminated. These phenomena are platform-specific in detail but share a common structural feature: they all involve coupling of the qubit’s spin-projection state to spatial or motional degrees of freedom that the two-level model does not describe. Photonic qubits, by contrast, exhibit none of these anomalies. We propose that this asymmetry has a topological origin. A recent classifica- tion of electromagnetic field configurations into open (Class O, massless) and closed (Class C, massive) Poynting topologies [1] implies that massive particles carry internal structure—chirality, spatial mode geometry, Beltrami eigenstate classification—beyond their spin projection. Photons do not. The anomalous decoherence channels observed in every matter-based platform, and absent in every photonic platform, are the envi- ronmental coupling to this internal topological structure that the standard qubit model omits. This is not a small correction: the topological channels account for 5–50% of the observed decoherence, depending on the platform, and their platform-specific coupling fractions are consistent with known spin-to-spatial-mode coupling mechanisms at each scale.
Recent progress with microfabricated quantum devices has revealed that an ubiquitous source of noise originates in tunneling material defects that give rise to a sparse bath of parasitic two-level systems (TLSs). For superconducting qubits, TLSs residing on electrode surfaces and in tunnel junctions account for a major part of decoherence and thus pose a serious roadblock to the realization of solid-state quantum processors. Here, we utilize a superconducting qubit to explore the quantum state evolution of coherently operated TLSs in order to shed new light on their individual properties and environmental interactions. We identify a frequency-dependence of TLS energy relaxation rates that can be explained by a coupling to phononic modes rather than by anticipated mutual TLS interactions. Most investigated TLSs are found to be free of pure dephasing at their energy degeneracy points, around which their Ramsey and spin-echo dephasing rates scale linearly and quadratically with asymmetry energy, respectively. We provide an explanation based on the standard tunneling model, and identify interaction with incoherent low-frequency (thermal) TLSs as the major mechanism of the pure dephasing in coherent high-frequency TLS.
Recent progress with microfabricated quantum devices has revealed that an ubiquitous source of noise originates in tunneling material defects that give rise to a sparse bath of parasitic two-level systems (TLSs). For superconducting qubits, TLSs residing on electrode surfaces and in tunnel junctions account for a major part of decoherence and thus pose a serious roadblock to the realization of solid-state quantum processors. Here, we utilize a superconducting qubit to explore the quantum state evolution of coherently operated TLSs in order to shed new light on their individual properties and environmental interactions. We identify a frequency-dependence of TLS energy relaxation rates that can be explained by a coupling to phononic modes rather than by anticipated mutual TLS interactions. Most investigated TLSs are found to be free of pure dephasing at their energy degeneracy points, around which their Ramsey and spin-echo dephasing rates scale linearly and quadratically with asymmetry energy, respectively. We provide an explanation based on the standard tunneling model, and identify interaction with incoherent low-frequency (thermal) TLSs as the major mechanism of the pure dephasing in coherent high-frequency TLS.
[EN] Two-level system (TLS) defects constitute a major source of noise and decoherence in superconducting qubits, particularly due to microscopic defects located in Josephson junctions and their surrounding materials, limiting coherence times and the performance of quantum information devices. While extensive experimental evidence of TLS-induced noise exists, establishing a microscopic theoretical description that consistently connects quantum defect dynamics, open-system theory, and experimental observations remains an open challenge. The objective of this Master s thesis is to study the impact of TLS defects on superconducting qubits using a fully quantum, open-system framework. Starting from a microscopic Hamiltonian description of a qubit coupled to TLS defects in Josephson junctions, the project aims to derive and analyze a Bloch-Redfield master equation that captures the correlated dynamics between a qubit, a quantum TLS, and a dissipative environment. This approach enables the investigation of coherence decay, population dynamics, and qubit-TLS correlations beyond phenomenological Lindblad models. The work will combine analytical methods with numerical simulations implemented in the Julia programming language. In addition to master-equation techniques, tensor-network methods based on Matrix Product States (MPS) will be employed as a scalable framework to extend the analysis to multiple interacting TLS, allowing the explicit treatment of quantum correlations and non-Markovian effects in many-body defect environments. Simple effective noise models, such as random telegraph noise, will be considered for comparison in order to assess their range of validity relative to microscopic descriptions. The theoretical analysis will be discussed in connection with recent experimental observations in superconducting circuits, particularly those reported in the work of Christopher Eichler and Andreas Wallraff, with the goal of contributing to a unified microscopic understanding of TLS-induced noise in Josephson-junction-based superconducting qubits.
Low-frequency charge noise is a dominant source of decoherence in many solid-state qubit platforms. Conventionally, the noise is modeled as a bath of two-level fluctuators that activate or tunnel between minima in a potential energy landscape. Here, the authors describe measurements of charge noise in a superconducting qubit that suggest an unexpected dependence of the noise on the device scale. The measurements cannot be explained by the two-level fluctuate model. Rather, they are consistent with charge drift.
Decoherence is the operative crisis of quantum computing——every architecture confronts it, and every proposed remedy carries a hidden cost in overhead, gap requirement, or temperature constraint. This paper derives, in full algebraic detail and without unexplained transitions, a holographic decoherence-suppression mechanism rooted in the AdS
3/CFT
2 correspondence, showing that the bulk--boundary geometry of three-dimensional anti-de Sitter space acts as a geometric filter that exponentially screens environmental noise from qubit degrees of freedom encoded in the helical edge modes of topological insulators and in trapped-ion chains. Starting from the chiral Luttinger liquid Hamiltonian of a quantum spin Hall edge, we derive the Virasoro algebra with central charge
c, identify the bosonic density fluctuation
δρ(x,t) as the boundary trace of a bulk dilaton field
ϕ(z,x,t), solve the dilaton equation of motion step by step to obtain the bulk-to-boundary propagator, and couple it to the Lindblad master equation to derive the modified decoherence rate:
γholo=γstdexp(−c2πΔnξl),TstdstdTstdholo=exp(6ξlnξl).. Every intermediate numerical estimate in the paper is anchored to independently measured material parameters: Fermi velocity
vF, bulk gap
Δgap, and coherence length
ξ=ℏvF/Δgap. We derive explicit density--density correlation functions, dynamical structure factors, and out-of-time-order correlators (OTOCs), each carrying logarithmic holographic corrections testable by scanning tunneling microscopy, angle-resolved photoemission spectroscopy (ARPES), and Ramsey interferometry. Gate fidelities exceeding
99.9% are shown to be achievable for Majorana-based qubits when the geometric ratio satisfies
L/ξ≳15withc≥2. Three experimental platforms are analyzed quantitatively:
Bi2Se3 topological insulator edges,
HgTe/CdTe quantum wells, and
171Yb+ trapped-ion chains, with detailed measurement protocols for each.
Decoherence is conventionally regarded as an obstacle to realizing topological quantum phases. This has motivated extensive efforts to suppress noise in candidate topological materials and devices. Here, we show that decoherence can instead induce topological phenomena. We demonstrate this in a lattice system subject to environment-induced dephasing. The noise-averaged dynamics, governed by an interacting quantum master equation, realize a topological phase characterized by a winding number and the non-Hermitian skin effect. The dynamical consequence is striking: the correlated nature of the stochastic noise yields asymmetric diffusion, whose direction is fixed by the winding number and is reversible only through a topological phase transition. This effect is induced purely by interactions, distinguishing it from previous studies of free, effectively single-particle systems. It also disappears upon postselecting measurement outcomes, confirming that it is a genuinely open-system phenomenon with no effective Hamiltonian description. Remarkably, the model remains analytically tractable. Our results establish correlated quantum noise as a route to topology in open many-body systems, beyond free-particle and non-Hermitian Hamiltonian paradigms.