Quantum Quench Accelerometer Achieves Enhanced Sensitivity Via Nanoparticle Dynamics

Scientists have developed a novel nano-accelerometer that harnesses the principles of quantum mechanics to dramatically improve its sensitivity. M. Kamba, S. Otabe, and K. Funo, alongside T. Sagawa and K. Aikawa, detail in their research how manipulating the trapping potential of a levitated nanoparticle , specifically through a technique called ‘quantum quenching’ , minimises positional uncertainty and consequently enhances the device’s ability to detect minute accelerations. This breakthrough, achieved by exploring the dynamics following rapid quenching, brings the accelerometer’s performance closer to the theoretical limit dictated by the Fisher information, potentially paving the way for highly sensitive inertial sensors with applications ranging from precision navigation to fundamental physics investigations.

Aikawa, detail in their research how manipulating the trapping potential of a levitated nanoparticle, specifically through a technique called ‘quantum quenching’, minimises positional uncertainty and consequently enhances the device’s ability to detect minute accelerations.

Rapid Quenching Boosts Nanoparticle Accelerometer Sensitivity by improving

This breakthrough establishes a pathway towards quantum inertial sensing, sensitised by exploiting these quench dynamics. The study centres on a single nanoparticle levitated in a vacuum, functioning as an isolated nanomechanical oscillator operating within the quantum regime. This unique system allows for the observation and manipulation of motion at a quantum level, making it ideal for investigating nonequilibrium quantum thermodynamics on a single-particle scale. The researchers focused on manipulating uncertainties in position and momentum through nonequilibrium dynamics initiated by an abrupt modification of the potential, effectively enabling quantum squeezing.

Levitated objects have long been indispensable in inertial sensing, and nano- and micro-particles levitated in vacuum represent a promising candidate for next-generation accelerometers. Conventional accelerometers detect acceleration-induced displacement of mechanical oscillators, and the same principle applies to levitated particles. However, the high oscillation frequency, typically around 100kHz, of optically levitated nanoparticles makes detecting the resulting displacement, δ = aω−2, exceptionally challenging. Previous gravimetry demonstrations have largely relied on micron-sized particles with lower oscillation frequencies, below 100Hz, while sensing electric forces with charged nanoparticles has also seen success. Maintaining a constant ω renders the nanoparticle’s motion insensitive to acceleration, but quenching ω by a factor of approximately 40 initiates nonequilibrium dynamics governed by the applied acceleration. Analysis of both mean position and position uncertainty reveals an optimal quenching and observation scheme, with rapid quenching inducing substantial oscillations in position uncertainty, crucial for achieving minimized measurement fluctuation and high sensitivity, as predicted by quantum squeezing.

Nanoparticle Rotation and Radio-Frequency Calibration are crucial

Researchers achieved this by spinning the nanoparticle around the z-axis at approximately 8GHz using circularly polarized light introduced into the trapping laser, detuning the polarization by 1.5° from linear polarization to maintain rotation. To calibrate position, the team employed a radio-frequency technique, applying controlled frequency modulation to the trapping laser to induce known displacements at the nanoparticle’s location and subsequently determining the proportionality between detector voltage and particle displacement. The work meticulously characterized the nanoparticle’s dynamics following the potential quench, modelling it using the Langevin equation. Initial conditions were established assuming a thermal state with a mean phonon number of 1.25, estimated from time-of-flight measurements, defining the initial first and second moments of position and momentum.

For times greater than zero, the dynamics were governed by a Hamiltonian at a new frequency, with the first moments following a classical driven oscillator solution. The covariance matrix, crucial for quantifying uncertainty, evolved via a symplectic rotation dependent on the new frequency, yielding closed-form expressions for variances and covariances. Scientists derived the Quantum Fisher Information (QFI) to quantify the ultimate limit of sensitivity, expressing it as a function of time and experimental parameters. Evaluating the QFI at time T1/2, half an oscillation period in the weak trap, the team obtained a value of (4.96±0.35)×105 s4/m2, demonstrating the potential for high-precision inertial sensing.

To simulate particle dynamics, the research group solved the quantum Langevin equation, accounting for a time-dependent trap frequency proportional to laser intensity, acceleration, damping, and random forces. The laser intensity was modelled using a combination of linear and exponential functions, with fitting parameters determined from observed intensity variations. The study further refined the simulation by incorporating an intensity-dependent displacement of the optical potential minimum, ensuring accurate reproduction of the observed dynamics with short quenching times. Researchers numerically integrated moment equations governing the mean and covariance of the particle’s position and momentum, using initial conditions derived from the time-of-flight measurements. Finally, the team modelled the experimental readout, the envelope of oscillation in the high-frequency trap, by fitting a sum of two Gaussians to the histogram of absolute displacements, extracting the mean and standard deviation to characterize the displacement distribution.

Quench dynamics enhance nanoparticle accelerometer sensitivity by increasing

These results demonstrate a pathway towards inertial sensing enhanced by exploiting quench dynamics. Experiments revealed that manipulating the trapping potential of a levitated nanoparticle allows for precise control over its quantum mechanical behaviour. The team measured the nanoparticle’s motion after abruptly changing the trapping potential, finding that a rapid quench minimises positional uncertainty. This reduction in uncertainty is crucial, as it directly impacts the accelerometer’s sensitivity. The breakthrough delivers a sensitivity approaching the quantum Fisher information limit, indicating a fundamental constraint on measurement precision.

Scientists recorded that the oscillation frequency of the optically levitated nanoparticle was approximately 250kHz, a value suitable for ground-state cooling. Measurements confirm the nanoparticle’s radius to be 145nm with a mass of 2.9x 10−17kg, providing precise characterisation of the system. The team demonstrated that quenching the oscillation frequency by a factor of approximately 40 triggers nonequilibrium dynamics governed by the applied acceleration. Tests prove that by carefully controlling the quenching process and observation timing, the measurement fluctuation can be minimised, achieving a high sensitivity.

Analysis of both the mean position and position uncertainty during the quench revealed an optimum scheme for sensing acceleration. The observed substantial oscillations in position uncertainty are similar to those crucial for quantum squeezing, enabling the selection of an instance for minimal measurement fluctuation. Furthermore, the research indicates that background gas collisions currently limit the sensitivity, suggesting avenues for future improvement through enhanced vacuum conditions.

Faster Trapping Enhances Nanoscale Sensitivity in molecular detection

The findings reveal that precise control of measurement time, considering these nonequilibrium dynamics, is crucial for achieving optimal long-term sensitivity, beyond simply maximizing signal strength. Experiments confirmed the origin of these dynamics stems from the projection of gravity along the measurement direction. Although the achieved sensitivity is promising, the authors acknowledge that long-term measurement stability is currently limited by slow drifts within the experimental setup. Future work could focus on further improving sensitivity by employing even shallower quenching potentials and reducing background gas pressure.