



01817nas a2200181   4500008004100000245006100041210006100102260001400163520125300177100003201430700001901462700002201481700002201503700002001525700002801545700002501573856003701598       2024                        eng d00aEstimation of Hamiltonian parameters from thermal states0 aEstimation of Hamiltonian parameters from thermal states  c1/18/20243 a<p>We upper- and lower-bound the optimal precision with which one can estimate an unknown Hamiltonian parameter via measurements of Gibbs thermal states with a known temperature. The bounds depend on the uncertainty in the Hamiltonian term that contains the parameter and on the term&#39;s degree of noncommutativity with the full Hamiltonian: higher uncertainty and commuting operators lead to better precision. We apply the bounds to show that there exist entangled thermal states such that the parameter can be estimated with an error that decreases faster than 1/n&minus;&minus;&radic;, beating the standard quantum limit. This result governs Hamiltonians where an unknown scalar parameter (e.g. a component of a magnetic field) is coupled locally and identically to n qubit sensors. In the high-temperature regime, our bounds allow for pinpointing the optimal estimation error, up to a constant prefactor. Our bounds generalize to joint estimations of multiple parameters. In this setting, we recover the high-temperature sample scaling derived previously via techniques based on quantum state discrimination and coding theory. In an application, we show that noncommuting conserved quantities hinder the estimation of chemical potentials.</p>1 aGarcía-Pintos, Luis, Pedro1 aBharti, Kishor1 aBringewatt, Jacob1 aDehghani, Hossein1 aEhrenberg, Adam1 aHalpern, Nicole, Yunger1 aGorshkov, Alexey, V.  uhttps://arxiv.org/abs/2401.1034301255nas a2200169   4500008004100000245007000041210006900111260001400180300000800194490000600202520075000208100002500958700001300983700003200996700002001028856003701048       2021                        eng d00aEnergy storage and coherence in closed and open quantum batteries0 aEnergy storage and coherence in closed and open quantum batterie  c7/15/2021  a5050 v53 a<p>We study the role of coherence in closed and open quantum batteries. We obtain upper bounds to the work performed or energy exchanged by both closed and open quantum batteries in terms of coherence. Specifically, we show that the energy storage can be bounded by the Hilbert-Schmidt coherence of the density matrix in the spectral basis of the unitary operator that encodes the evolution of the battery. We also show that an analogous bound can be obtained in terms of the battery&#39;s Hamiltonian coherence in the basis of the unitary operator by evaluating their commutator. We apply these bounds to a 4-state quantum system and the anisotropic XY Ising model in the closed system case, and the Spin-Boson model in the open case.&nbsp;</p>1 aCaravelli, Francesco1 aYan, Bin1 aGarcía-Pintos, Luis, Pedro1 aHamma, Alioscia  uhttps://arxiv.org/abs/2012.15026