Application

@article{nokey,

title = {Multiparameter quantum metrology and mode entanglement with spatially split nonclassical spin ensembles},

author = {Fadel, M. and Yadin, B. and Mao, Y. and Byrnes, T. and Gessner, M.},

url = {https://iopscience.iop.org/article/10.1088/1367-2630/ace1a0},

doi = {10.1088/1367-2630/ace1a0},

year  = {2025},

date = {2025-07-12},

urldate = {2025-07-12},

journal = {New Journal of Physics },

volume = {25},

issue = {7},

abstract = {We identify the multiparameter sensitivity of entangled spin states, such as spin-squeezed and Dicke states that are spatially distributed into several addressable spatial modes. Analytical expressions for the spin-squeezing matrix of families of states that are accessible by current atomic experiments reveal the quantum gain in multiparameter metrology, as well as the optimal strategies to maximize the sensitivity gain for the estimation of any linear combination of parameters. We further study the mode entanglement of these states by deriving a witness for genuine k-partite mode entanglement from the spin-squeezing matrix. Our results highlight the advantage of mode entanglement for distributed sensing, and outline optimal protocols for multiparameter estimation with nonclassical spatially-distributed spin ensembles. We illustrate our findings with the design of a protocol for gradient sensing with a Bose–Einstein condensate in an entangled spin state in two modes.},

keywords = {ICFO-4.16},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Sublattice scars and beyond in two-dimensional 𝑈⁡(1) quantum link lattice gauge theories},

author = {Sau, I. and Stornati, P. and Banerjee, D. and Sen, A. },

url = {https://journals.aps.org/prd/abstract/10.1103/PhysRevD.109.034519},

doi = {doi.org/10.1103/PhysRevD.109.034519},

year  = {2024},

date = {2024-02-27},

urldate = {2024-02-27},

journal = {Physical Review Research},

volume = {109},

number = {34519},

issue = {3},

abstract = {In this article, we elucidate the structure and properties of a class of anomalous high‑energy states of matter‑free U(1) quantum link gauge theory Hamiltonians using numerical and analytical methods. Such anomalous states, known as quantum many‑body scars in the literature, have generated a lot of interest due to their athermal nature.



Our starting Hamiltonian is H = Oₖᵢₙ + λ Oₚₒₜ, where λ is a real‑valued coupling, and Oₖᵢₙ (off‑diagonal) and Oₚₒₜ (diagonal) are summed local operators in the electric flux basis acting on the elementary plaquette □.



The spectrum of the model in its spin‑½ representation on Lₓ × Lᵧ lattices reveals the existence of sublattice scars |ψₛ⟩, which satisfy Oₚₒₜ,□ |ψₛ⟩ = |ψₛ⟩ on one sublattice and Oₚₒₜ,□ |ψₛ⟩ = 0 on the other, while being simultaneous zero modes or nonzero integer‑valued eigenstates of Oₖᵢₙ. We demonstrate a “triangle relation” connecting the sublattice scars with nonzero integer eigenvalues of Oₖᵢₙ to particular scars with Oₖᵢₙ = 0 eigenvalues.



A fraction of the sublattice scars admit a simple description in terms of emergent short singlets, on which we place analytic bounds. We further construct a long‑ranged parent Hamiltonian for which all sublattice scars in the null space of Oₖᵢₙ become unique ground states and elucidate some properties of its spectrum. In particular, zero‑energy states of this parent Hamiltonian turn out to be exact scars of another U(1) quantum link model with a staggered short‑ranged diagonal term.},

keywords = {ICFO-4.16},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Frustrated magnets without geometrical frustration in bosonic flux ladders},

author = {Barbiero, L. and Cabedo, J. and Lewenstein, M. and Tarruell, L. and Celi, A.},

url = {https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.5.L042008},

doi = {doi.org/10.1103/PhysRevResearch.5.L042008},

year  = {2023},

date = {2023-10-06},

volume = {5},

issue = {4},

pages = {42008},

abstract = {We propose a scheme to realize a frustrated Bose-Hubbard model with ultracold atoms in an optical lattice that comprises the frustrated spin-1/2 quantum 𝑋𝑋 model. Our approach is based on a square ladder of magnetic flux ∼𝜋 with one real and one synthetic spin dimension. Although this system does not have geometrical frustration, we show that at low energies it maps into an effective triangular ladder with staggered fluxes for specific values of the synthetic tunneling. We numerically investigate its rich phase diagram and show that it contains bond-ordered-wave and chiral superfluid phases. Our scheme gives access to minimal instances of frustrated magnets without the need for real geometrical frustration, in a setup of minimal experimental complexity.},

keywords = {ICFO-4.16},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Quantum-enhanced multiparameter estimation and compressed sensing of a field},

author = {Baamara, Y. and Gessner, M. and Sinatra, A. },

url = {https://scipost.org/10.21468/SciPostPhys.14.3.050},

doi = {10.21468/SciPostPhys.14.3.050},

year  = {2023},

date = {2023-03-27},

journal = {SciPost Physics},

volume = {14},

issue = {3},

pages = {50},

abstract = {We show that a significant quantum gain corresponding to squeezed or over-squeezed spin states can be obtained in multiparameter estimation by measuring the Hadamard coefficients of a 1D or 2D signal. The physical platform we consider consists of two-level atoms in an optical lattice in a squeezed-Mott configuration, or more generally by correlated spins distributed in spatially separated modes. Our protocol requires the possibility to locally flip the spins, but relies on collective measurements. We give examples of applications to scalar or vector field mapping and compressed sensing.},

keywords = {ICFO-4.16},

pubstate = {published},

tppubtype = {article}

}