Measuring kinetic energy changes in the mesoscale with low acquisition rates

We describe a new technique to estimate the mean square velocity of a Brownian particle from time series of the position of the particle sampled at frequencies several orders of magnitude smaller than the momentum relaxation frequency. We apply our technique to determine the mean square velocity of single optically trapped polystyrene microspheres immersed in water. The velocity is increased applying a noisy electric field that mimics a higher kinetic temperature. Therefore, we are able to measure the average kinetic energy change in isothermal and non-isothermal quasistatic processes. Moreover, we show that the dependence of the mean square time-averaged velocity on the sampling frequency can be used to quantify properties of the electrophoretic mobility of a charged colloid. Our method could be applied to detect temperature gradients in inhomogeneous media and to characterize the complete thermodynamics of microscopic heat engines.Comment: 9 pages, 5 figure

Overdamped dynamics of a Brownian particle levitated in a Paul trap

We study the dynamics of the center of mass of a Brownian particle levitated in a Paul trap. We focus on the overdamped regime in the context of levitodynamics, comparing theory with our numerical simulations and experimental data from a nanoparticle in a Paul trap. We provide an exact analytical solution to the stochastic equation of motion, expressions for the standard deviation of the motion, and thermalization times by using the WKB method under two different limits. Finally, we prove the power spectral density of the motion can be approximated by that of an Ornstein-Uhlenbeck process and use the found expression to calibrate the motion of a trapped particle

Adiabatic processes realized with a trapped Brownian particle

We experimentally realize quasistatic adiabatic processes using a single optically-trapped micro- sphere immersed in water whose effective temperature is controlled by an external random electric field. A full energetic characterization of adiabatic processes that preserve either the position dis- tribution or the full phase space volume is presented. We show that only in the latter case the exchanged heat and the change in the entropy of the particle vanish when averaging over many repetitions. We provide analytical expressions for the distributions of the fluctuating heat and en- tropy, which we verify experimentally. We show that the heat distribution is asymmetric for any non-isothermal quasistatic process. Moreover, the shape of the distribution of the system entropy change in the adiabatic processes depends significantly on the number of degrees of freedom that are considered for the calculation of system entropy

Electrothermoplasmonic flow in gold nanoparticles suspensions: nonlinear dependence of flow velocity on aggregate concentration

Efficient mixing and pumping of liquids at the microscale is a technology that is still to be optimized. The combination of an AC electric field with a small temperature gradient leads to a strong electrothermal flow that can be used for multiple purposes. Combining simulations and experiments, an analysis of the performance of electrothermal flow is provided when the temperature gradient is generated by illuminating plasmonic nanoparticles in suspension with a near-resonance laser. Fluid flow is measured by tracking the velocity of fluorescent tracer microparticles in suspension as a function of the electric field, laser power, and concentration of plasmonic particles. Among other results, a non-linear relationship is found between the velocity of the fluid and particle concentration, which is justified in terms of multiple scattering-absorption events, involving aggregates of nanoparticles, that lead to enhanced absorption when the concentration is raised. Simulations provide a description of the phenomenon that is compatible with experiments and constitute a way to understand and estimate the absorption and scattering cross-sections of both dispersed particles and/or aggregates. A comparison of experiments and simulations suggests that there is some aggregation of the gold nanoparticles by forming clusters of about 2–7 particles, but no information about their structure can be obtained without further theoretical and experimental developments. This nonlinear behavior could be useful to get very high ETP velocities by inducing some controlled aggregation of the particles.This research has been supported by Consejería de Universidad, Investigación e Innovación de la Junta de Andalucía and FEDER, “Una manera de hacer Europa”/Projects P18-FR-3583 and FQM-410-UGR18, Ministerio de Ciencia, Innovación y Universidades through Project EQC2018-004693-P, and Grant PID2021-127427NB-I00/ MCIN/AEI/10.13039/501100011033/FEDER,UE. Funding for open access charge: Universidad de Málaga/CBUA

The TRAPSENSOR facility: an open-ring 7 tesla Penning trap for laserbased precision experiments

APenning-trap facility for high-precision mass spectrometry based on a novel detection method has been built. This method consists in measuring motional frequencies of singly-charged ions trapped in strong magnetic fields through the fluorescence photons from laser-cooled 40Ca+ ions, to overcome limitations faced in electronic single-ion detection techniques. The key element of this facility is an open-ring Penning trap coupled upstream to a preparation Penning trap similar to those used at Radioactive Ion Beam facilities. Here we present a full characterization of the trap and demonstrate motional frequency measurements of trapped ions stored by applying external radiofrequency fields in resonance with the ions’ eigenmotions, in combination with time-of-flight identification. The infrastructure developed to observe the fluorescence photons from 40Ca+, comprising the 12 laser beams and the optical system to register the image in a high-sensitive CCD sensor, has been proved by taking images of the trapped and cooled 40Ca+ ions. This demonstrates the functionality of the proposed laser-based mass-spectrometry technique, providing a unique platform for precision experiments with implications in different fields of physics.This work was supported by the European Research Council (contract no. 278648-TRAPSENSOR), from the SpanishMINECO/ FEDER (project nos. FPA2012-32076, FPA2015-67694-P, FIS2015-69983-P, UNGR10-1E- 501, UNGR13-1E-1830), Ramón y Cajal Grant RYC-2012-11391, Juan de la Cierva grant IJCI-2015-26091, Centro Nacional de Partículas, Astropartículas y Nuclear CPAN13-TM01, and ‘Sistema Nacional de Garantía Juvenil y del Programa Operativo de Empleo Juvenil’; from the SpanishMECD(PhD grant nos. FPU15-04679 and FPU17/02596); from Junta de Andalucía/FEDER (project no. IE-57131) and ‘Programa de Empleo Juvenil; from Basque Government (PhD grant no. PRE-2015-1-0394) and (project no. IT986-16), and from the University of Granada ‘Plan propio-Programa de Intensificación de la Investigación PP2017-PRI.I-04’. I.A, L.L. and E.S acknowledge also support from projects OpenSuperQ (820363) and QMiCS (820505) of the EUFlagship on Quantum Technologies

Testing a Paul trap through determining the evaporation rate of levitated single semi-volatile organic droplets

Rigorous knowledge of the optical fingerprint of droplets is imperative for the understanding of complex aerosol processes. Here, a Paul trap is operated to store single semi-volatile organic droplets in air. The droplets are illuminated with a green laser and the elastic scattering is collected on a CMOS camera. The setup provides excellent performance in terms of confinement and stability, allowing us to detect size changes of the order of few nanometres. The stability also allows us to measure vapour pressures with remarkable reproducibility. This approach supplies a robust method for the optical interrogation in the sub-micron range.Horizon 2020 Framework Programme 654109 871115 754446IISTA Research CentreUniversidad de Granada C-FQM-410-UGR18Andalusia Regional Government P18-RT-3820Spanish Government CGL2016-81092-R CGL2017-90884-REDT PGC2018-098770-B-I00 RTI2018-097864-BI00Universidad de Granada (Athenea3i

Adiabatic Processes Realized with a Trapped Brownian Particle

The ability to implement adiabatic processes in the mesoscale is of key importance in the study of artificial or biological micro- and nanoengines. Microadiabatic processes have been elusive to experimental implementation due to the difficulty in isolating Brownian particles from their fluctuating environment. Here we report on the experimental realization of a microscopic quasistatic adiabatic process employing a trapped Brownian particle. We circumvent the complete isolation of the Brownian particle by designing a protocol where both characteristic volume and temperature of the system are changed in such a way that the entropy of the system is conserved along the process. We compare the protocols that follow from either the overdamped or underdamped descriptions, demonstrating that the latter is mandatory in order to obtain a vanishing average heat flux to the particle. We provide analytical expressions for the distributions of the fluctuating heat and entropy and verify them experimentally. Our protocols could serve to implement the first microscopic engine that is able to attain the fundamental limit for the efficiency set by Carnot