Periodic Reporting for period 3 - Atto-Zepto (Ultrasensitive Nano-Optomechanical Sensors)
Berichtszeitraum: 2022-09-01 bis 2024-02-29
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 is 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 is the one of cavity nano-optomechanics: inserting the ultrasensitive nanowire in a high finesse optical microcavity should enhance 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, and aim at exploring novel regimes in cavity optomechanics, where optical non-linearities at the single photon level become accessible. The last part is dedicated to the exploration of hybrid qubit-mechanical systems, in which nanowire vibrations are magnetically coupled to the spin of a single Nitrogen Vacancy defect in diamond or to a embedded quantum dot.
The goal of the project is 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 is the one of cavity nano-optomechanics: inserting the ultrasensitive nanowire in a high finesse optical microcavity should enhance 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, and aim at exploring novel regimes in cavity optomechanics, where optical non-linearities at the single photon level become accessible. The last part is dedicated to the exploration of hybrid qubit-mechanical systems, in which nanowire vibrations are magnetically coupled to the spin of a single Nitrogen Vacancy defect in diamond or to a embedded quantum dot.
Since the beginning of the project, we have first developed advanced force sensing protocols and a prototype experiment, where the vibrations of a suspended nanowire are optically readout, while the nanowire is piezo scanned above a sample of interest. Those measurement principles allow us to record 2D force field gradients with a quasi-real-time measurement rate. To do so we combined a real-time calibration of the optical measurement channels, multiple stabilization loops, and the recording and live analysis of driven trajectories ensured either via phase lock loops or multi-frequency excitation tones.
The ultrasensitive and vectorial force sensing capacities of suspended silicon carbide nanowires were first used to explore force fields appearing above metallic nano-structures. New sensing protocols allow approaching and exploring surfaces with a real-time measurement rate and provide a quantitative agreement between measurements of forces and force field gradients.
At short distances the nanowire-surface interactions are dominated by electrostatic and proximity Casimir forces whose relative contributions can be tuned by adjusting bias voltages. We mapped the nano-structures' topography by recording force fields quadratic in the bias voltage and imaged the impact of residual electrostatic fields produced by surface imperfections. Their contribution must be properly compensated to correctly measure the proximity forces in those novel geometries, which was done through a multi-electrode compensation scheme. We investigated the Casimir force field above a sub-micron trench and confirmed its laterally repulsive character, in agreement with recent theoretical predictions and numerical simulations.
We also further investigated the light-nanowire interaction in a cavity nano-optomechanical experiment. In canonical optomechanical systems, mechanical vibrations are dynamically encoded on an optical probe field which reciprocally exerts a backaction force. Due to the weak single photon coupling strength achieved with macroscopic oscillators, most of existing experiments were conducted with large photon numbers to achieve sizeable effects, thereby hiding the original optomechanical non-linearity.
To increase the optomechanical interaction, we made use of sub-wavelength-sized ultrasensitive suspended nanowires inserted in the mode volume of a fiber-based microcavity.
By scanning the nanowire within the cavity mode volume and measuring its impact on the cavity mode, we obtained a map the 2D optomechanical interaction. Then, by using the toolbox of nanowire-based force sensing protocols, we explored the optomechanical force field experienced by the nanowire. These measurements allowed to demonstrate the possibility to detect variations of the mean intracavity photon number smaller than unity.
This implementation should also allow to enter the promising regime of cavity optomechanics where a single intracavity photon can displace the oscillator by more than its zero point fluctuations, which will open novel perspectives in the field.
Then, we developed a cryogenic platform to operate the nanowires in a home-made dilution fridge. We developed interferometric fibered objectives allowing to readout the nanowire motion down to noise temperatures of 32 mK at the condition to operate with ultra-low optical fluxes, around 100 fW. The demonstrated force sensitivities reach a record value of 40zN in 1s for a scanning probe, offering a promising environment for the next steps of the project.
We also explored hybrid qubit mechanical systems made of a quantum dot embedded in a micromechanical oscillator in the form of a semi-conducting photonic trumpet. When vibrating, it applied a dynamical strain on the quantum dot which resulted in a parametric modulation of its optical resonance line. We demonstrated that the quantum could put the micromechanical oscillator into motion, a prominent signature of the hybrid interaction.
The ultrasensitive and vectorial force sensing capacities of suspended silicon carbide nanowires were first used to explore force fields appearing above metallic nano-structures. New sensing protocols allow approaching and exploring surfaces with a real-time measurement rate and provide a quantitative agreement between measurements of forces and force field gradients.
At short distances the nanowire-surface interactions are dominated by electrostatic and proximity Casimir forces whose relative contributions can be tuned by adjusting bias voltages. We mapped the nano-structures' topography by recording force fields quadratic in the bias voltage and imaged the impact of residual electrostatic fields produced by surface imperfections. Their contribution must be properly compensated to correctly measure the proximity forces in those novel geometries, which was done through a multi-electrode compensation scheme. We investigated the Casimir force field above a sub-micron trench and confirmed its laterally repulsive character, in agreement with recent theoretical predictions and numerical simulations.
We also further investigated the light-nanowire interaction in a cavity nano-optomechanical experiment. In canonical optomechanical systems, mechanical vibrations are dynamically encoded on an optical probe field which reciprocally exerts a backaction force. Due to the weak single photon coupling strength achieved with macroscopic oscillators, most of existing experiments were conducted with large photon numbers to achieve sizeable effects, thereby hiding the original optomechanical non-linearity.
To increase the optomechanical interaction, we made use of sub-wavelength-sized ultrasensitive suspended nanowires inserted in the mode volume of a fiber-based microcavity.
By scanning the nanowire within the cavity mode volume and measuring its impact on the cavity mode, we obtained a map the 2D optomechanical interaction. Then, by using the toolbox of nanowire-based force sensing protocols, we explored the optomechanical force field experienced by the nanowire. These measurements allowed to demonstrate the possibility to detect variations of the mean intracavity photon number smaller than unity.
This implementation should also allow to enter the promising regime of cavity optomechanics where a single intracavity photon can displace the oscillator by more than its zero point fluctuations, which will open novel perspectives in the field.
Then, we developed a cryogenic platform to operate the nanowires in a home-made dilution fridge. We developed interferometric fibered objectives allowing to readout the nanowire motion down to noise temperatures of 32 mK at the condition to operate with ultra-low optical fluxes, around 100 fW. The demonstrated force sensitivities reach a record value of 40zN in 1s for a scanning probe, offering a promising environment for the next steps of the project.
We also explored hybrid qubit mechanical systems made of a quantum dot embedded in a micromechanical oscillator in the form of a semi-conducting photonic trumpet. When vibrating, it applied a dynamical strain on the quantum dot which resulted in a parametric modulation of its optical resonance line. We demonstrated that the quantum could put the micromechanical oscillator into motion, a prominent signature of the hybrid interaction.
In the coming phase of the project, we will first aim at exploring even further the Casimir force measurements in novel geometries and investigate the impact of the nanowire dipensions/material on the measured force field. We will also aim at exploring novel geometries such as chiral nanostructures, so as to explore wether Casimir force field can acquire a rotational character. A magnetic functionalisation of the nanowires will be realized in order to explore magnetic nanostructures.
For what concerns the cavity nano-optomechanical objectives, we will further explore the possibility to use photonic crystals microcavities, which will facilitate its integration in the dilution fridge. The main objective will be to reach the regime where the single photon recoil becomes larger than the thermal noise spreading of the nanowire, which should be achieved at 1 K.
Further exploration in the cryostat will also concern the heat propagation along the nanowire, which is expected to become ballistic at temperatures smaller than 200 mK.
For what concerns the hybrid qubit-mechanical experiments, we will aim at observing the spin-dependent force, and observe the first dynamical spino-mechanical interaction, in analogy with original effects observed in cavity optomechanics.
For what concerns the cavity nano-optomechanical objectives, we will further explore the possibility to use photonic crystals microcavities, which will facilitate its integration in the dilution fridge. The main objective will be to reach the regime where the single photon recoil becomes larger than the thermal noise spreading of the nanowire, which should be achieved at 1 K.
Further exploration in the cryostat will also concern the heat propagation along the nanowire, which is expected to become ballistic at temperatures smaller than 200 mK.
For what concerns the hybrid qubit-mechanical experiments, we will aim at observing the spin-dependent force, and observe the first dynamical spino-mechanical interaction, in analogy with original effects observed in cavity optomechanics.