Quantum

Quantum 10, 2134 (2026). https://doi.org/10.22331/q-2026-06-12-2134 Building upon $\textit{Wan, Zhong (2025)}$ [ 5 ] we present a few methods on how to simulate the non-Clifford $d=5$ magic state cultivation circuits[ 4 ] with a sum of $\approx 8$ Clifford ZX-diagrams on average, at $0.1\%$ noise. Compared to a magic cat state stabiliser decomposition of all $53$ non-Clifford spiders ($6{,}377{,}…

Quantum 10, 2133 (2026). https://doi.org/10.22331/q-2026-06-12-2133 Recent advances in analog and digital quantum-simulation platforms have enabled exploration of the spectrum of entanglement Hamiltonians via variational algorithms. In this work we analyze the convergence properties of the variationally obtained solutions and compare them to numerically exact calculations in quantum critical syst…

Quantum 10, 2132 (2026). https://doi.org/10.22331/q-2026-06-12-2132 Quantum linear optics without post-selection is not powerful enough to produce any quantum state from a given input state. This limits its utility since some applications require entangled resources that are difficult to prepare. Thus, a deeper understanding of linear optical state preparation is needed. In this work, we give a r…

Quantum 10, 2131 (2026). https://doi.org/10.22331/q-2026-06-11-2131 Device-independent quantum information is attracting significant attention, particularly for its applications in information security. This interest arises because the security of device-independent protocols relies solely on the observed outcomes of spatially separated measurements and the validity of quantum physics. Sequential…

Quantum 10, 2130 (2026). https://doi.org/10.22331/q-2026-06-08-2130 We analyze the task of estimating a multi-parameter unitary belonging to the $SU(2)$ or $SU(1,1)$ groups, in a two-bosonic-mode scenario and investigate the scaling of the precision in terms of the total particle number. For the $SU(2)$ case, the total particle number is conserved by the evolution and we discuss optimal states in…

Quantum 10, 2129 (2026). https://doi.org/10.22331/q-2026-06-08-2129 Recent work highlighted the importance of higher-order correlations in quantum dynamics for a deeper understanding of quantum chaos and thermalization. The full Eigenstate Thermalization Hypothesis, the framework encompassing correlations, can be formalized using the language of Free Probability theory. In this context, chaotic d…

Quantum 10, 2128 (2026). https://doi.org/10.22331/q-2026-06-08-2128 Entanglement witnesses (EWs) are a collection of observables that can characterize separable states and, experimentally, estimating EWs can verify entangled states. In this work, we show that a fixed measurement setting on a multipartite entangled state, which we introduce as a network state for the purpose, can estimate EWs. Nam…

Quantum 10, 2127 (2026). https://doi.org/10.22331/q-2026-06-08-2127 Classical shadows provide a versatile framework for estimating many properties of quantum states from repeated, randomly chosen measurements without requiring full quantum state tomography. When prior information is available, such as knowledge of symmetries of states and operators, this knowledge can be exploited to significantl…

Quantum 10, 2126 (2026). https://doi.org/10.22331/q-2026-06-08-2126 The study of quantum reference frames has received renewed interest over the last years, leading to the parallel development of non-equivalent frameworks by different communities. We clarify the differences between these frameworks. At the mathematical level, they mainly differ in the kind of symmetry (either weak or strong) empl…

Quantum 10, 2125 (2026). https://doi.org/10.22331/q-2026-06-02-2125 We construct a local decoder for the 2D toric code using ideas from the hierarchical classical cellular automata of Tsirelson and Gács. Our decoder is a circuit of strictly local quantum operations preserving a logical state for exponential time in the presence of circuit-level noise without the need for non-local classical compu…

Quantum 10, 2124 (2026). https://doi.org/10.22331/q-2026-06-01-2124 We present a new simulation-secure quantum oblivious transfer (QOT) protocol based on one-way functions in the plain model. With a focus on practical implementation, our protocol surpasses prior works in efficiency, promising feasible experimental realization. We address potential experimental errors and their correction, offerin…

Quantum 10, 2123 (2026). https://doi.org/10.22331/q-2026-06-01-2123 We investigate quantum cellular automata (QCA) on one-dimensional spin systems defined over a subalgebra of the full local operator algebra – the symmetric subalgebra under a finite Abelian group symmetry $G$. For systems where each site carries a regular representation of $G$, we establish a complete classification of such subal…

Quantum 10, 2122 (2026). https://doi.org/10.22331/q-2026-06-01-2122 This paper explores the sensitivity gains afforded by spin-squeezed states in atom interferometry, in particular using Bragg diffraction. We introduce a generalised input-output formalism that accurately describes realistic, non-unitary interferometers, including losses due to velocity selectivity and scattering into undesired mo…

Quantum 10, 2121 (2026). https://doi.org/10.22331/q-2026-05-29-2121 A rigorous characterization of the information content of any highest-spin three-fermion wave function is presented. It is based upon a formal decomposition of the wave function into a finite set of fixed invariants, called shapes, whose sole purpose is to satisfy the Pauli principle, and a variable part, constituting the bosonic…

Quantum 10, 2120 (2026). https://doi.org/10.22331/q-2026-05-29-2120 Haar random states are fundamental objects in quantum information theory and quantum computing. We study the density matrix resulting from sampling $t$ copies of a $d$-dimensional quantum state according to the Haar measure on the orthogonal group. In particular, we analytically compute its spectral decomposition. This allows us …

Quantum 10, 2119 (2026). https://doi.org/10.22331/q-2026-05-29-2119 Dynamical Lie algebras (DLAs) have emerged as a valuable tool in the study of parameterized quantum circuits, helping to characterize both their expressiveness and trainability. In particular, the absence or presence of barren plateaus (BPs) – flat regions in parameter space that prevent the efficient training of variational quan…

Quantum 10, 2118 (2026). https://doi.org/10.22331/q-2026-05-29-2118 We propose an efficient classical algorithm to estimate the Neural Tangent Kernel (NTK) associated with a broad class of quantum neural networks. These networks consist of arbitrary unitary operators belonging to the Clifford group interleaved with parametric gates given by the time evolution generated by an arbitrary Hamiltonian…

Quantum 10, 2117 (2026). https://doi.org/10.22331/q-2026-05-29-2117 The availability of certain entangled resource states (catalyst states) can enhance the rate of converting several less entangled states into fewer highly entangled states in a process known as catalytic entanglement concentration (EC). Here, we extend catalytic EC from pure states to mixed states and numerically benchmark it aga…

Quantum 10, 2116 (2026). https://doi.org/10.22331/q-2026-05-26-2116 The Frauchiger–Renner paradox derives an inconsistency when quantum theory is used to describe the use of itself, by means of a scenario where agents model other agents quantumly and reason about each other's knowledge. We observe that logical contextuality (à la Hardy) is the key ingredient of the FR paradox, and we provide a st…

Quantum 10, 2115 (2026). https://doi.org/10.22331/q-2026-05-22-2115 In classical information theory, the Doeblin coefficient of a classical channel provides an efficiently computable upper bound on the total-variation contraction coefficient of the channel, leading to what is known as a strong data-processing inequality. Here, we investigate quantum Doeblin coefficients as a generalization of the…