Coherent states bridge the gap between quantum and classical physics, but their overcomplete and nonorthogonal nature makes it difficult to identify the minimal discrete set needed to reconstruct quantum information. Finite spin-coherent tomography and discrete coherent-state operator bases are known, but here we address the more specific rank-resolved problem of preserving the canonical contravariant-symbol representation. We show that the canonical finite coherent-state formula reconstructs every operator in the rank-$S$ sector exactly if and only if the sampling points form a spherical $(2J+S)$-design. We call the associated configurations spin-coherent quantum designs. We further give a fully explicit positive-weight Gauss-Legendre construction that avoids the need for an equal-weight spherical design. Together, these results establish a unified framework for reading out physical observables from a handful of measurement samples, playing for spin systems the role that the so-called von Neumann lattice plays for canonical coherent states. Finally, we derive practical protocols for estimating moments of spin operators from these constructions, with direct applications to polarimetry, magnetometry, and quantum state tomography.
How a quantum state responds to small parameter changes is central to quantum criticality, state distinguishability, and metrological sensitivity. Pauli-string statistics provide a natural many-body representation of quantum states, but it is not evident how much of their local quantum geometry is retained by the corresponding classical probability distribution. We show that, for any smooth family of pure $N$-qubit states, the classical Fisher matrix of the complete labeled Pauli distribution is exactly twice the quantum Fisher information matrix (QFIM). The Pauli spectrum is therefore locally metric-complete, while scalar R\'enyi functionals retain only compressed information about its parameter-dependent motion. The same distribution has a direct physical realization: pairwise Bell measurements between corresponding sites of a state and its complex conjugate sample the Pauli spectrum and attain the full QFIM of the conjugate-pair state with a fixed transversal readout. For generic mixed states, physical Bell statistics separate from Hilbert--Schmidt-normalized squared Pauli coordinates, and we derive an exact positive decomposition of the resulting Bell-information gap. These results identify the labeled Pauli spectrum as a common statistical structure underlying many-body response, nonstabilizerness, and multiparameter quantum geometry.
This work introduces a unified measure, the magic R\'enyi entropy (MRE), to quantify computational resources in spins, bosons, and fermions on an equal footing and shows that the MRE is a resource monotone under stabilizer and Gaussian protocols involving measurements and feedforward operations.
Recent work introduced Interval Quantum Mechanics (IQM), a finite-precision framework in which physical information is represented by sets of possible states rather than exact states. We extend this approach to algebraic quantum field theory (AQFT) by introducing Interval Algebraic Quantum Field Theory (IAQFT), whose basic objects are quantum parcels: weak* open convex regions of state space encoding finite-precision information obtained from finitely many local observations. We develop parcel reduction and measurement update, establish finite-dimensional information-contraction results, and formulate locality through compatible parcel nets. Major structural features of AQFT are recast in parcel-theoretic terms, including the Reeh--Schlieder property, Haag's theorem, modular theory, the KMS condition, and the Unruh effect. We show that spacelike vacuum correlations and strict Bell violations persist under finite precision, and that lattice approximations are compatible with the parcel framework. Finally, we recover the Murray--von Neumann classification of factors together with the trace and projection equivalence in Type~$\mathrm{II}_1$ factors from the geometry of limiting parcels. IAQFT thus provides a unified finite-precision formulation of the operational, modular, and operator-algebraic structures of relativistic quantum theory.
Quantum computation has traditionally been formulated by postulating abstract information carriers and subsequently identifying physical systems that realize them. We adopt the opposite viewpoint and ask what computational structure is supplied by a fundamental relativistic quantum system itself. Focusing on the simplest nontrivial massive spin carrier, spin-1/2, we show that its relativistic description supplies a native four-dimensional information carrier through the Dirac equation. The resulting Dirac information carrier possesses an intrinsic positive- and negative-energy decomposition that induces a physics-constrained computational structure comprising sector-preserving and sector-coupling quantum logic. Restricting the relativistic computational structure to the positive-energy sector and taking the nonrelativistic regime recovers the familiar Pauli qubit description. We distinguish mathematical unitary transformations from physically admissible gates and show how charge-conjugation structure, charge superselection, and associated reference-frame resources can constrain quantum logic beyond the sector-preserving structure. Finally, under appropriate physical assumptions, we establish the conditions under which this structure supports full single-carrier controllability. Our work establishes the Dirac information carrier as the massive spin-1/2 instance of a broader programme in which computational structures are derived from the relativistic representation carried by the underlying physical system.
Quantum state tomography provides complete information about a quantum state, but its measurement cost generally grows exponentially with system size. In many-particle quantum simulators, this challenge is further compounded by the limited accessibility of local measurements and controls. Here we develop a tomography protocol for permutation-invariant fermionic many-body states with U(1) particle-number symmetry. We show that any such state is completely determined by the distribution of the total particle number and the occupation of a single collective mode within each particle-number sector, both of which are accessible in current ultracold-atom experiments. The number of required observables scales only linearly with the system size. More generally, the protocol reconstructs the permutation-symmetrized component of arbitrary U(1)-symmetric fermionic states, which can still encode nontrivial many-body and state-level structure beyond conventional few-body observables. We demonstrate this protocol in interacting non-Gaussian states of the complex Sachdev-Ye-Kitaev model and in free-fermion chains across a Lifshitz transition. This framework opens a route toward information-theoretic characterization of strongly correlated itinerant quantum matter in experimentally realistic fermionic quantum simulators.
Quantum algorithms are intrinsically two-boundary processes: an input state is prepared, and an output state or subspace is selected as the computational answer. We formulate this observation as a coherent Quantum Schr\"odinger Bridge (QSB), a pure-state Hamiltonian counterpart of Schr\"odinger bridge theory in which the endpoint constraint is imposed on state vectors and the transport cost is the quadratic control action. In this setting Aharonov's two-state vector becomes the natural optimal-control pair: a forward state from the input and a backward state from the target. Pontryagin's principle then yields a universal optimal Hamiltonian whose weak value is purely imaginary in the geodesic gauge. Thus weak values are not an auxiliary interpretation; they are the local response functions that quantify the drift of the pre-selected state toward the post-selected boundary. Applying this framework to unstructured search, periodicity finding, and matrix arithmetic, we reconstruct Grover's algorithm, the quantum Fourier transform underlying Shor's algorithm, and quantum singular value transformation (QSVT). The usual circuit components -- oracles, diffusion reflections, controlled phases, and signal-processing rotations -- emerge as Lie-algebraic syntheses of the optimal weak-value drift. This perspective unifies distinct algorithmic paradigms into a single geometric principle: algorithm design is the problem of choosing computational boundary conditions and realizing the corresponding optimal flow.