Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Quantum states of light can enable sensing configurations with sensitivities beyond the shot-noise limit (SNL). In order to better take advantage of available quantum resources and obtain the maximum possible sensitivity, it is necessary to determine fundamental sensitivity limits for different possible configurations for a given sensing system. Here, due to their wide applicability, we focus on optical resonance sensors, which detect a change in a parameter of interest through a resonance shift. We compare their fundamental sensitivity limits set by the quantum Cramér-Rao bound (QCRB) based on the estimation of changes in transmission or phase of a probing bright two-mode squeezed state (bTMSS) of light. We show that the fundamental sensitivity results from an interplay between the QCRB and the transfer function of the system. As a result, for a resonance sensor with a Lorentzian lineshape a phase-based scheme outperforms a transmission-based one for most of the parameter space; however, this is not the case for lineshapes with steeper slopes, such as higher order Butterworth lineshapes. Furthermore, such an interplay results in conditions under which the phase-based scheme provides a higher sensitivity but a smaller degree of quantum enhancement than the transmission-based scheme. We also study the effect of losses external to the sensor on the degree of quantum enhancement and show that for certain conditions, probing with a classical state can provide a higher sensitivity than probing with a bTMSS. Finally, we discuss detection schemes, namely optimized intensity-difference and optimized homodyne detection, that can achieve the fundamental sensitivity limits even in the presence of external losses.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Sources of broadband quantum correlated photons present a valuable resource for quantum metrology, sensing, and communication. Here, we report the generation of spectrally broadband correlated photons from frequency nondegenerate spontaneous parametric down-conversion in a custom-designed lithium niobate superlattice. The superlattice induces a nonlinear interference between the pump, signal and idler, resulting in an experimentally observed comb-like emission spanning 0.060 <jats:italic>μ</jats:italic>m and 1.4 <jats:italic>μ</jats:italic>m of spectral bandwidth at 0.647 <jats:italic>μ</jats:italic>m and 3.0 <jats:italic>μ</jats:italic>m wavelengths, respectively. While this broad mid-infrared bandwidth is attractive to quantum metrology and sensing due to the enablement of fast spectral multiplexing for data acquisition, the comb-like structure, achieved without an input frequency comb, offers targeted frequencies for quantum communication applications. In addition to useful technological applications, our concept offers an interesting analogy between optical diffraction in quantum and classical optics.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Modern comagnetometry is—in absolute energy units—the most sensitive experimental technique for measuring the energy splitting between quantum states, with certain implementations measuring the nuclear spin-up/spin-down splitting at the 10<jats:sup>−26</jats:sup> eV level. By measuring and subtracting the leading magnetic effects on the spins, comagnetometry can be used to study non-standard-model spin interactions. New physics scenarios that comagnetometers can probe include EDMs, violations of Lorentz invariance, Goldstone bosons from new high-energy symmetries, spin-dependent and CP-violating long-range forces, and axionic dark matter. We describe the many implementations that have been developed and optimized for these applications, and consider the prospects for improvements in the technique. Based purely on existing technology, there is room for several orders of magnitude in further improvement in statistical sensitivity. We also evaluate sources of systematic error and instability that may limit attainable improvements.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The QCD axion is a particle postulated to exist since the 1970s to explain the strong-CP problem in particle physics. It could also account for all of the observed dark matter in the Universe. The axion resonant interaction detection experiment (ARIADNE) intends to detect the QCD axion by sensing the fictitious ‘magnetic field’ created by its coupling to spin. Short-range axion-mediated interactions can occur between a sample of laser-polarized <jats:sup>3</jats:sup>He nuclear spins and an unpolarized source-mass sprocket. The experiment must be sensitive to magnetic fields below the 10<jats:sup>−19</jats:sup> T level to achieve its design sensitivity, necessitating tight control of the experiment’s magnetic environment. We describe a method for controlling three aspects of that environment which would otherwise limit the experimental sensitivity. Firstly, a system of superconducting magnetic shielding is described to screen ordinary magnetic noise from the sample volume at the 10<jats:sup>8</jats:sup> level, which should be sufficient to reduce the contribution of Johnson noise in the sprocket-shaped source mass, expected to be at the 10<jats:sup>−12</jats:sup> T<jats:inline-formula> <jats:tex-math><?CDATA $/\sqrt{\mathrm{H}\mathrm{z}}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mo>/</mml:mo> <mml:msqrt> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi mathvariant="normal">z</mml:mi> </mml:mrow> </mml:msqrt> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="qstabf1ccieqn1.gif" xlink:type="simple" /> </jats:inline-formula> level, to below the threshold for signal detection. Secondly, a method for reducing magnetic field gradients within the sample up to 10<jats:sup>2</jats:sup> times is described, using a simple and cost-effective design geometry. Thirdly, a novel coil design is introduced which allows the generation of fields similar to those produced by Helmholtz coils in regions directly abutting superconducting boundaries. This method allows the nuclear Larmor frequency of the sample to be tuned to match the axion field modulation frequency set by the sprocket rotation. Finally, we experimentally investigate the magnetic shielding factor of sputtered thin-film superconducting niobium on quartz substrates for various geometries and film thicknesses relevant for the ARIADNE axion experiment using SQUID magnetometry. The methods may be generally useful for magnetic field control near superconducting boundaries in other experiments where similar considerations apply.</jats:p>