arXiv subjects

Pau Gomez

Publications and source records attributed to Pau Gomez.

7 recordsLinked to original sources

arXiv2022

Single-domain Bose condensate magnetometer achieves energy resolution per bandwidth below $\hbar$

We present a magnetic sensor with energy resolution per bandwidth $E_R < \hbar$. We show how a $^{87}\mathrm{Rb}$ single domain spinor Bose-Einstein condensate, detected by non-destructive Faraday-rotation probing, achieves single shot dc magnetic sensitivity of $72(8)~\mathrm{fT}$ measuring a volume $V= 1091(30)~μ\mathrm{m}^3$ for $3.5~\mathrm{s}$, and thus $E_R = 0.075(16)~\hbar$. We measure experimentally the condensate volume, spin coherence time, and readout noise, and use phase-space methods, backed by 3+1D mean-field simulations, to compute the spin noise. Contributions to the spin noise include one-body and three-body losses and shearing of the projection noise distribution, due to competition of ferromagnetic contact interactions and quadratic Zeeman shifts. Nonetheless, the fully-coherent nature of the single-domain, ultracold two-body interactions allows the system to escape the coherence vs.~density trade-off that imposes an energy resolution limit on traditional spin-precession sensors. We predict that other Bose-condensed alkalis, especially the antiferromagnetic $^{23}\mathrm{Na}$, can further improve the energy resolution of this method.

cond-mat.quant-gas↗

arXiv2021

Cavity-enhanced polarization rotation measurements for low-disturbance probing of atoms

We propose and demonstrate cavity-enhanced polarization-rotation measurement as a means to detect magnetic effects in transparent media with greater sensitivity at equal optical disturbance to the medium. Using the Jones calculus, we compute the effective polarization rotation effect in a Fabry-Perot cavity containing a magnetic medium, including losses due to enclosure windows or other sources. The results show that when measuring polarization rotation, collecting the transmitted light has advantages in simplicity and linearity relative to collecting the reflected light. We demonstrate the technique by measuring Faraday rotation in a $^{87}$Rb atomic ensemble in the single-pass and cavity-enhanced geometries, and observe enhancement in good agreement with the theoretical predictions. We also demonstrate shot-noise-limited operation of the enhanced rotation scheme in the small-angle regime.

physics.atom-ph↗

arXiv2020

Bose-Einstein Condensate Comagnetometer

We describe a comagnetometer employing the $f=1$ and $f=2$ ground state hyperfine manifolds of a $^{87}$Rb spinor Bose-Einstein condensate as co-located magnetometers. The hyperfine manifolds feature nearly opposite gyromagnetic ratios and thus the sum of their precession angles is only weakly coupled to external magnetic fields, while being highly sensitive to any effect that rotates both manifolds in the same way. The $f=1$ and $f=2$ transverse magnetizations and azimuth angles are independently measured by non-destructive Faraday rotation probing, and we demonstrate a $44.0(8)\text{dB}$ common-mode rejection in good agreement with theory. We show how spin-dependent interactions can be used to inhibit $2\rightarrow 1$ hyperfine relaxing collisions, extending to $\sim 1\text{s}$ the transverse spin lifetime of the $f=1,2$ mixtures. The technique could be used in high sensitivity searches for new physics on sub-millimeter length scales, precision studies of ultra-cold collision physics, and angle-resolved studies of quantum spin dynamics.

physics.atom-ph↗

arXiv2019

Narrowband photon pairs with independent frequency tuning for quantum light-matter interactions

We describe a cavity-enhanced spontaneous parametric down-conversion (CE-SPDC) source for narrowband photon pairs with filters such that over 97% of the correlated photons are in a single mode of 4.3(4) MHz bandwidth. Type-II phase matching, a tuneable-birefringence resonator, MHz-resolution pump tuning, and tuneable Fabry-Perot filters are used to achieve independent signal and idler tuning. We map the CE-SPDC spectrum using difference frequency generation to precisely locate the emission clusters, and demonstrate CE-SPDC driven atomic spectroscopy. The generated photon pairs efficiently interact with neutral rubidium, a well-developed system for quantum networking and quantum simulation. The techniques are readily extensible to other material systems.

quant-ph↗

arXiv2019

Interferometric measurement of interhyperfine scattering lengths in $^{87}$Rb

We present interferometeric measurements of the $f=1$ to $f=2$ inter-hyperfine scattering lengths in a single-domain spinor Bose-Einstein condensate of $^{87}$Rb. The inter-hyperfine interaction leads to a strong and state-dependent modification of the spin-mixing dynamics with respect to a non-interacting description. We employ hyperfine-specific Faraday-rotation probing to reveal the evolution of the transverse magnetization in each hyperfine manifold for different state preparations, and a comagnetometer strategy to cancel laboratory magnetic noise. The method allows precise determination of inter-hyperfine scattering length differences, calibrated to intra-hyperfine scattering length differences. We report $(a_{3}^{(12)}-a_{2}^{(12)})/(a_{2}^{(1)}-a_{0}^{(1)})=-1.27(15)$ and $(a_{1}^{(12)}-a_{2}^{(12)})/(a_{2}^{(1)}-a_{0}^{(1)})=-1.31(13)$, limited by atom number uncertainty. With achievable control of atom number, we estimate precisions of $ \approx 0.3\%$ should be possible with this technique.

physics.atom-ph↗

arXiv2017

Multi-second magnetic coherence in a single domain spinor Bose-Einstein condensate

We describe a compact, robust and versatile system for studying magnetic dynamics in a spinor Bose-Einstein condensate. Condensates of 87 Rb are produced by all-optical evaporation in a 1560 nm optical dipole trap, using a non-standard loading sequence that employs an auxiliary 1529 nm beam for partial compensation of the strong differential light shift induced by the dipole trap itself. We use near-resonance Faraday rotation probing to non-destructively track the condensate magnetization, and demonstrate few-Larmor-cycle tracking with no detectable degradation of the spin polarization. In the ferromagnetic F = 1 ground state, we observe magnetic T1 and T2$^*$ coherence times limited only by the several-second residence time of the atoms in the trap.

cond-mat.quant-gas↗

arXiv2017

Strong light shifts from near-resonant and polychromatic fields: comparison of Floquet theory and experiment

We present a non-perturbative numerical technique for calculating strong light shifts in atoms under the influence of multiple optical fields with arbitrary polarization. We confirm our technique experimentally by performing spectroscopy of a cloud of cold $^{87}$Rb atoms subjected to $\sim$ kW/cm$^2$ intensities of light at 1560.492 nm simultaneous with 1529.269 nm or 1529.282 nm. In these conditions the excited state resonances at 1529.26 nm and 1529.36 nm induce strong level mixing and the shifts are highly nonlinear. By absorption spectroscopy, we observe that the induced shifts of the 5P3/2 hyperfine Zeeman sublevels agree well with our theoretical predictions.. We propose the application of our theory and experiment to accurate measurements of excited-state electric-dipole matrix elements.

physics.atom-ph↗