@unpublished{kollar2026hiddensymmetryoperatorsasymmetric,

title = {The hidden symmetry operators of the asymmetric quantum Rabi model and its two-photon and two-mode variants in closed form},

author = {M. Kollar and A. Dutta},

url = {https://arxiv.org/abs/2611.12859},

doi = {10.48550/arXiv.2611.12859},

year  = {2026},

date = {2026-11-09},

urldate = {2026-11-09},

abstract = {The asymmetric quantum Rabi model, a two-level system with splitting Δ and bias ϵ coupled with strength g to a boson mode, has level crossings when ϵ is an integer multiple N of the mode frequency. They are due to a hidden symmetry operator J, for which no general formula has been available. Here we obtain J in closed form for every N. We find that J is given by the parity of the symmetric model times the continuant (ordered tridiagonal determinant) of N first-order operators, which are the Hamiltonians at the intermediate biases N−1,N−3,…,1−N minus a common number operator. The symmetry is thus a staircase of N bias steps that closes on the mirror image of the model precisely at integer bias. The proof uses induction on two commutation relations. The same relations hold in the asymmetric two-photon and two-mode models, written with the generators of su(1,1), so that the same continuant gives their symmetry operators for every order, previously known only for the lowest ones. We also relate the closed formula for J to the known recursion relations for its coefficients and give their terms of lowest order in Δ explicitly.},

note = {arXiv: 2611.12859 

datadoi: 10.5281/zenodo.24079060},

keywords = {},

pubstate = {published},

tppubtype = {unpublished}

}

@unpublished{littlehalesInsituAzimuthalSample2026,

title = {In-situ azimuthal sample rotation within a horizontal-field cryomagnet for small-angle neutron scattering},

author = {M. T. Littlehales and A. Bauer and M. Bartkowiak and M. Zolliker and J. S. White and C. Pfleiderer},

url = {https://arxiv.org/abs/2611.05159},

doi = {10.48550/arXiv.2611.05159},

year  = {2026},

date = {2026-11-03},

urldate = {2026-11-01},

publisher = {arXiv},

abstract = {We present an in-situ azimuthal rotation stage for small-angle neutron scattering measurements. The stage provides an azimuthal rotation range of 315∘ about the stage normal. At the reference sample-stick orientation, the stage normal is parallel to the incident neutron beam, so that the sample rotates in the plane perpendicular to the beam. Combined with a sample stick rotation about a second, orthogonal axis, the stage provides control of the magnetic-field direction relative to the crystal axes, while the field remains fixed in the laboratory frame. For a 5 mm diameter incident beam, sample-stick rotations of approximately ±315∘ are accessible with negligible additional attenuation from the holder. The commercial rotator is specified for operation between 1 and 373 K and in magnetic fields up to 35 T, making the stage nominally compatible with the full temperature (1.8 to 320 K) and field (0 to 6.8 T) ranges of the used cryomagnet. As a working example, we characterize its performance on a spherical single crystal of MnSi between 20 and 35 K and in fields up to 183 mT, observing local sample heating during operation of ∼20 mK per 5∘ step. We illustrate the design considerations behind the holder construction, with specific notes for mounting spherical samples, and discuss the resulting performance and limitations.},

note = {arXiv:2611.05159},

keywords = {},

pubstate = {published},

tppubtype = {unpublished}

}

@unpublished{dutta2026universalgaugestructurephoton,

title = {A universal gauge structure in the photon content of light-matter systems},

author = {A. Dutta and M. Kollar},

url = {https://arxiv.org/abs/2610.40446},

doi = {10.48550/arXiv.2610.40446},

year  = {2026},

date = {2026-10-29},

urldate = {2026-10-01},

abstract = {After truncating the matter Hilbert space of a single-mode light-matter model, gauge transformations leave the spectrum invariant whereas the ground-state photon number is gauge dependent, hence, its meaning remains disputed. We show that this gauge dependence obeys an exact algebraic law whenever the gauge transformation acts as a displacement of the field coupled to a matter operator G. Namely, the ground-state photon number is a quadratic polynomial in the gauge parameter λ, ⟨a†a⟩λ = ⟨a†a⟩0 + Cλ + Qλ2. Here the coefficients are the correlator C=⟨Gp⟩ of G and the field momentum p, and Q=⟨G2⟩. Its minimum over all gauges is naturally gauge-invariant, and for the quantum Rabi model it is determined by the ground-state energy alone. We show that it is strictly positive for the quantum Rabi and Dicke models with level splitting, so that a residual photon content survives in every gauge. At weak coupling the gauge of minimal photon number is the Jaynes-Cummings gauge, and for the Dicke model it remains so at all couplings in the thermodynamic limit.},

note = {arXiv: 2610.40446},

keywords = {},

pubstate = {published},

tppubtype = {unpublished}

}