An Optomechanical Coin Flip: Wavelength-Modulated, Erbium-Powered Rotations in a Levitated System

Abstract

Optical levitation of nano-scale systems offers a pathway to highly sensitive rotation measurements, which are critical for advancing gyroscopic technologies. While prior studies have primarily focused on controlling rotational degrees of freedom of optically levitated particles via modulation of optical power, polarization, and ambient pressure, here we demonstrate wavelength-controlled rotation of the "coin-flip" mode in optically levitated NaYF hexagonal prisms doped with erbium by modulating the wavelength of a secondary pump beam. By switching the pump light wavelength, we precisely modulate the particle's rotation rate in a binary fashion, encoding the ASCII message "hello" in its rotational frequency. Finally, we observe long-term bimodal periodic dynamics in the rotational motion of a levitated prism that are suggestive of a Dzhanibekov (or tennis-racket)-like effect.

Figures (12)

• Figure 1: A: Conceptual figure of an optically levitated hexagon receiving a bitwise binary control signal in the form of red- and blue-detuned (with respect to the trapping light) pumping laser, which causes the hexagon to rotate faster or slower depending on the wavelength of the control signal. Blue causes the hexagon to rotate faster while red either causes less change or causes it to slow down depending on the background pressure of the system. B: The frequency domain data of the free rotational motion of an optically levitated hexagon when being pumped with red-detuned and blue-detuned light at 2mbar pressure. This data is zoomed in to the region of interest of the highest amplitude peak in the Fourier spectrum of the optically levitated test mass's motion. Here low power indicts 0.1mW of pump power and high indicates 31mW of pump power. C: Hello world sequence generated by changing the wavelength of the applied pump beam (blue pump = 1, red pump = 0). Encoded ASCII sequence is sufficiently resilient to long term drifts to encode a 40-bit message in wavelength space, which is then read out in the mechanical motion of the particle. D: Waterfall plot of a single ASCII character from the 'hello' sequence ('H') in its constituent bits. Note that the levitated hexagon used in B is a diferent one than that used for C and D.
• Figure 2: A: Angular momentum injection mechanisms. (left) In the first mechanism the momentum of injected blue-detuned photons is turned directly into rotational angular momentum by the photons being absorbed by the erbium ions embedded in the NaYF crystal matrix - the photons literally push the optically levitated hexagon to spin faster. (right) In the second mechanism, the blue-detuned photons are turned into rotational angular momentum by being absorbed by the erbium ions embedded in the NaYF crystal matrix as heat. The hotter surface temperature of the levitated hexagon then pushes incident background gas particles away faster than they impacted (the hot surface rocket effect), thus leading to a faster total free body spin rate. B: Experimental setup:0.5 of 1560 counterpropagating trapping light (provided by NKT C15 laser) is split in fiber and fed to the trapping site at a beam waist of 12.5, red detuned (1565) and blue detuned (1528) light (provided by a separate Pure Photonics PPCL laser) is fed to the trapping site along one arm of the counterpropagating fibers and thus trapping light. The power of the pump beam incident on the levitated hexagon can be varied across a range of 0.1mW to 50mW. C: The effect of the detuned photons on the spin rate as a function of pressure is explored experimentally over one order of magnitude, for two different wavelengths. For each pressure and wavelength, the frequency difference from 31mW to 0.1mW of pump power is shown.
• Figure 3: A: Erbium energy diagram and green emissions. B: Green erbium photoluminescence measured at different pump wavelengths. C Integrated intensity of the green erbium emission plotted against the pump wavelength. D Digitized and replotted literature absorption spectrum of 5% erbium doped -NaYF Ivaturi2013. E: Optically levitated in free space just below the slide, 5% erbium doped -NaYF illuminated with 1560nm trap light emitting green light with sufficient intensity to image with a long exposure ($\sim$60). F: Undoped optically levitated -NaYF suspended in free space immediately below the launch slide. Contrast and brightness of the images is digitally enhanced.
• Figure 4: Tennis racket effect like flips delineated in a long term dataseries for a levitated mass. A conceptual example of a possible orientation of the hexagon during the experiment is presented.
• Figure 5: Comparison: A: spinning and non tennis racketing levitated hexagon, B: spinning and tennis racketing levitated hexagon, C: non spinning levitated hexagon translating in bound vibrations/librations in the standing wave. The vertical interruptions in C are due to intermittent failures in the data system over long time scales and do not represent particle loss.