Periodic Reporting for period 4 - Atto-Zepto (Ultrasensitive Nano-Optomechanical Sensors)
Période du rapport: 2024-03-01 au 2024-08-31
By enabling the conversion of forces into measurable displacements, mechanical oscillators have always played a central role in experimental physics. Recent developments in the PI group demonstrated the possibility to realize ultrasensitive and vectorial force field sensing by using suspended SiC nanowires and optical readout of their transverse vibrations. Astonishing sensitivities were obtained at room and dilution temperatures, at the Atto- Zepto-newton level, for which the electron-electron interaction becomes detectable at 100µm.
The goal of the project was to push forward those ultrasensitive nano-optomechanical force sensors, to realize even more challenging explorations of novel fundamental interactions at the quantum-classical interface. We aim at developing universal advanced sensing protocols to explore the vectorial structure of fundamental optical, electrostatic or magnetic interactions, and investigate Casimir force fields above nanostructured surfaces, in geometries where it was recently predicted to become repulsive. The second research axis was the one of cavity nano-optomechanics: inserting the ultrasensitive nanowire in a high finesse optical microcavity enhances the light-nanowire interaction up to the point where a single cavity photon can displace the nanowire by more than its zero point quantum fluctuations. We investigated this so-called ultrastrong optomechanical coupling regime, allowing to explore novel regimes in cavity optomechanics, where optical non-linearities at the single photon level become accessible. The last research direction was dedicated to the exploration of hybrid qubit-mechanical systems, in which the nanowire vibrations were magnetically coupled to the spin of a single Nitrogen Vacancy defect in diamond or to an embedded quantum dot, which propose a route towards the creation and observation of non-classical mechanical states.
The goal of the project was to push forward those ultrasensitive nano-optomechanical force sensors, to realize even more challenging explorations of novel fundamental interactions at the quantum-classical interface. We aim at developing universal advanced sensing protocols to explore the vectorial structure of fundamental optical, electrostatic or magnetic interactions, and investigate Casimir force fields above nanostructured surfaces, in geometries where it was recently predicted to become repulsive. The second research axis was the one of cavity nano-optomechanics: inserting the ultrasensitive nanowire in a high finesse optical microcavity enhances the light-nanowire interaction up to the point where a single cavity photon can displace the nanowire by more than its zero point quantum fluctuations. We investigated this so-called ultrastrong optomechanical coupling regime, allowing to explore novel regimes in cavity optomechanics, where optical non-linearities at the single photon level become accessible. The last research direction was dedicated to the exploration of hybrid qubit-mechanical systems, in which the nanowire vibrations were magnetically coupled to the spin of a single Nitrogen Vacancy defect in diamond or to an embedded quantum dot, which propose a route towards the creation and observation of non-classical mechanical states.
Since the project's start, we developed advanced force sensing protocols and a prototype where the vibrations of a suspended nanowire are optically readout while piezo-scanned above a sample. This allows 2D force field gradient measurements in quasi-real-time. We combined real-time calibration, stabilization loops, and live analysis of driven trajectories via phase lock or multi-frequency excitation.
We first applied the ultrasensitive force sensing of suspended silicon carbide nanowires to explore force fields above metallic nano-structures. This enabled real-time surface exploration and quantitative agreement between force and field gradient measurements. At short distances, electrostatic and Casimir forces dominate, which can be tuned with bias voltages. We mapped topography and residual electrostatic fields, compensating them with a multi-electrode scheme. We confirmed Casimir force repulsion above a sub-micron trench, matching theoretical predictions.
In two nano-optomechanical experiments, we used suspended nanowires in microcavities to increase optomechanical interaction. By scanning the nanowire within the cavity, we mapped the 2D optomechanical interaction, demonstrating sensitivity to intracavity photon number variations. This opens new possibilities in cavity optomechanics, where a single photon can displace an oscillator more than its zero-point fluctuations.
We observed an unexpected interaction when optical and electrostatic fields combined. Laser wavelength near the nanowire semiconductor gap generated electron-hole pairs that, under an electrostatic field, created Coulomb forces, moving the nanowire. A vertical electric field modified charge density at the nanowire's tip, offering a non-contact method to study charge transport. This mechanism, investigated with pump-probe techniques, enables charge state imaging and controls electrostatic effects on Casimir measurements.
We developed a cryogenic platform using a dilution fridge to operate the nanowires, with interferometric fiber objectives enabling motion readout at 32 mK. In this setup, we achieved a force sensitivity of 40zN in 1s and a 1fN/m sensitivity to force gradients. We also explored heat conduction and photothermal effects in the nanowires, providing a promising low-noise environment.
Collaborating with semiconductor experts, we investigated hybrid qubit-mechanical systems combining quantum dots in micromechanical oscillators. The oscillator's vibration modulated the quantum dot's optical resonance, and resonant pumping revealed the hybrid interaction's signature for the first time.
We first applied the ultrasensitive force sensing of suspended silicon carbide nanowires to explore force fields above metallic nano-structures. This enabled real-time surface exploration and quantitative agreement between force and field gradient measurements. At short distances, electrostatic and Casimir forces dominate, which can be tuned with bias voltages. We mapped topography and residual electrostatic fields, compensating them with a multi-electrode scheme. We confirmed Casimir force repulsion above a sub-micron trench, matching theoretical predictions.
In two nano-optomechanical experiments, we used suspended nanowires in microcavities to increase optomechanical interaction. By scanning the nanowire within the cavity, we mapped the 2D optomechanical interaction, demonstrating sensitivity to intracavity photon number variations. This opens new possibilities in cavity optomechanics, where a single photon can displace an oscillator more than its zero-point fluctuations.
We observed an unexpected interaction when optical and electrostatic fields combined. Laser wavelength near the nanowire semiconductor gap generated electron-hole pairs that, under an electrostatic field, created Coulomb forces, moving the nanowire. A vertical electric field modified charge density at the nanowire's tip, offering a non-contact method to study charge transport. This mechanism, investigated with pump-probe techniques, enables charge state imaging and controls electrostatic effects on Casimir measurements.
We developed a cryogenic platform using a dilution fridge to operate the nanowires, with interferometric fiber objectives enabling motion readout at 32 mK. In this setup, we achieved a force sensitivity of 40zN in 1s and a 1fN/m sensitivity to force gradients. We also explored heat conduction and photothermal effects in the nanowires, providing a promising low-noise environment.
Collaborating with semiconductor experts, we investigated hybrid qubit-mechanical systems combining quantum dots in micromechanical oscillators. The oscillator's vibration modulated the quantum dot's optical resonance, and resonant pumping revealed the hybrid interaction's signature for the first time.
Force Field Sensing
We advanced optical readout and force field sensing techniques with nanowires, achieving 2D gradient measurements at ~10 Hz. Through calibration and tracking improvements, we significantly enhanced measurement reliability. Our scanning probe can now sensitively detect optical, electrical, and magnetic fields at very low excitation levels.
Cryogenic Developments
We developed a dilution refrigerator, optical interferometric objectives and photon-counting methods to operate the nanowire probe at ultra-low temperatures. This enabled record sensitivities in force and force gradient detection, opening the road towards condensed matter samples where the physics emerges at low-temperatures.
Nanomechanical Force Probe
By studying nanowire optical, thermal, and electrical properties, we optimized their preparation and internal characterization (e.g. thermal resistance, optical absorption, charge mobility), essential for their role as ultrasensitive probes.
Electrostatic and Casimir Forces
Nanowires were used to map electrostatic forces near nanostructures, revealing contribution from both geometry and contaminants. A compensation method allowed isolation of Casimir force gradients, using protocols based on the simultaneous mapping of force and force gradients, matching theoretical predictions and revealing features like lateral anti-trapping above trenches and holes.
Cavity Nano-Optomechanics
We inserted nanowires into optical microcavities to achieve ultrastrong coupling where a single photon can displace the nanowire beyond their zero-point fluctuations. Using precise positioning and our scanning techniques, we probed the bidirectional optomechanical interaction. Cryogenic follow-ups aim to reach quantum fluctuation-dominated regimes.
Charge-Wave Enhanced Optomechanics
We found that light-induced free carriers in nanowires can enhance light-matter interaction, allowing low-power control via static fields. Using pump-probe techniques, we measured charge transport and used this internal mechanism to modulate forces and optimize light-nanowire interaction.
Hybrid Quantum-Dot Mechanical Systems
We studied quantum dots embedded in “photonic trumpets” where mechanical vibrations are strain coupled with embedded quantum dots. Through resonant optical pumping, we could detect the quantum-dot-induced mechanical actuation.
We advanced optical readout and force field sensing techniques with nanowires, achieving 2D gradient measurements at ~10 Hz. Through calibration and tracking improvements, we significantly enhanced measurement reliability. Our scanning probe can now sensitively detect optical, electrical, and magnetic fields at very low excitation levels.
Cryogenic Developments
We developed a dilution refrigerator, optical interferometric objectives and photon-counting methods to operate the nanowire probe at ultra-low temperatures. This enabled record sensitivities in force and force gradient detection, opening the road towards condensed matter samples where the physics emerges at low-temperatures.
Nanomechanical Force Probe
By studying nanowire optical, thermal, and electrical properties, we optimized their preparation and internal characterization (e.g. thermal resistance, optical absorption, charge mobility), essential for their role as ultrasensitive probes.
Electrostatic and Casimir Forces
Nanowires were used to map electrostatic forces near nanostructures, revealing contribution from both geometry and contaminants. A compensation method allowed isolation of Casimir force gradients, using protocols based on the simultaneous mapping of force and force gradients, matching theoretical predictions and revealing features like lateral anti-trapping above trenches and holes.
Cavity Nano-Optomechanics
We inserted nanowires into optical microcavities to achieve ultrastrong coupling where a single photon can displace the nanowire beyond their zero-point fluctuations. Using precise positioning and our scanning techniques, we probed the bidirectional optomechanical interaction. Cryogenic follow-ups aim to reach quantum fluctuation-dominated regimes.
Charge-Wave Enhanced Optomechanics
We found that light-induced free carriers in nanowires can enhance light-matter interaction, allowing low-power control via static fields. Using pump-probe techniques, we measured charge transport and used this internal mechanism to modulate forces and optimize light-nanowire interaction.
Hybrid Quantum-Dot Mechanical Systems
We studied quantum dots embedded in “photonic trumpets” where mechanical vibrations are strain coupled with embedded quantum dots. Through resonant optical pumping, we could detect the quantum-dot-induced mechanical actuation.