Periodic Reporting for period 3 - Q-ROOT (Quantum optomechanics at ROOm Temperature)
Reporting period: 2021-09-01 to 2023-02-28
Optomechanics is the field of physics that investigates the reciprocal interactions between electromagnetic and mechanical degrees of freedom. Originally emerged in the context of the study of fundamental processes in ultra-sensitive interferometric measurements applied to the detection of gravitational waves, optomechancis research has started to rapidly grow by the end of the 1990's , with the emergence of new materials and technologies enabling strong, quantum interactions between laser light and macroscopic mechanical motion, notably setting the outlook for preparing solid state devices in non-classical quantum states of vibration. The field has made considerable progress over the past 10 years, with outstanding demonstrations such as cooling mechanical devices in their groundstate using lasers, generating non-classical state of light and demonstrating remote quantum entanglement amongst macroscopic systems. These advance have come along a dramatic increase of the sensitivity of optomechanical systems towards external physical phenomena, which may strongly impact industry as a new generation of unprecedentedly sensitive, versatile transducers.
These outstanding performances however require cryogenic operation in order to suppress the vibrations resulting from the thermal agitation, which are usually covering quantum effects. This represent a strong limitation to potential, sustainable and environment-friendly applications of these technologies, since powering cryogenic coolers is highly energy demanding.
In the project "Quantum Optomechanics at Room Temperature" (Q-ROOT), the aim is to provide the first solid state optomechanical platform operating in the quantum regime, and at room temperature. The concept relies on coupling a carbon nanotube resonator to the whispering gallery mode of an optically perfect silica microsphere. The classical noise in both these systems is so low, that the dynamics of their coupling is expected to be dominated by quantum effect, even at room temperature. Amongst objectives, we intend to demonstrate the quantumness of this interaction, as well as the possibility to achieve non-classical operation, that are unavailable to system obeying to the laws of classical physics.
These outstanding performances however require cryogenic operation in order to suppress the vibrations resulting from the thermal agitation, which are usually covering quantum effects. This represent a strong limitation to potential, sustainable and environment-friendly applications of these technologies, since powering cryogenic coolers is highly energy demanding.
In the project "Quantum Optomechanics at Room Temperature" (Q-ROOT), the aim is to provide the first solid state optomechanical platform operating in the quantum regime, and at room temperature. The concept relies on coupling a carbon nanotube resonator to the whispering gallery mode of an optically perfect silica microsphere. The classical noise in both these systems is so low, that the dynamics of their coupling is expected to be dominated by quantum effect, even at room temperature. Amongst objectives, we intend to demonstrate the quantumness of this interaction, as well as the possibility to achieve non-classical operation, that are unavailable to system obeying to the laws of classical physics.
One of the prominent challenges of this project is to fabricate the nanomechanical resonator, that is a carbon nanotube cantilever, as a large part of the expected quantum sensitivity performances arises from it. Additionally, despite many attempts, the vibration of carbon nanotube resonators could not be optomechanically detected, which essentially arises from their very tiny size, in the nanometre range (that is 10 millionth of the size of a human hair), making it very difficult to couple to a laser.
For this reason, the project has readily started with developing entirely new, cutting edge nanofabrication techniques, whose purpose is to decorate the carbon nanotube with an optical aggregate which appears much "brighter" in response to a laser beam. The principle of this method relies on the so-called Focused Electron Beam Induced Deposition (FEBID), which consists in aggregating atomic or molecular precursors at the focus of an electron beam.Directing the electron beam at the tip of the carbon nanotube therefore yield to the sought result, in principle. The carbon nanotube however is very tiny, which requires a level of control on the process which had never been reached priori to this project: Indeed, the mass of the optical scatterer shall be small compared to that of the carbon nanotube, which is on the order of the attogram, that is about a hundred thousandth of a billionth of the mass of a single fly. To address this challenge, we have developed a method enabling to detect the mass of the carbon nanotube using the same electron beam as that utilized to grow the optical aggregate. This method is so precise, that we are able to control the deposition process with an accuracy of just a few tens of atoms. We also started tests intending to grow various functions on our nanotubes, including magnetic and dielectric particles.
Because they are so sensitive, the vibrations of this kind of resonators may be strongly affected by the measurement, either using an electron or a laser beam. In fact, the sensitivity is such that it was long expected that their oscillation behaviour would not follow the usual laws of thermodynamics. We have performed a series of experiments in order to address these outstanding questions, and have be able to provide the first experimental evidence of the role of momentum and thermal energy exchange between the measurement probe (electron or laser beam) and the the carbon nanotube. We also confirmed that the very large thermal vibrations of carbon nanotubes set them in a state that strongly differ from larger scale solid state resonators.
For this reason, the project has readily started with developing entirely new, cutting edge nanofabrication techniques, whose purpose is to decorate the carbon nanotube with an optical aggregate which appears much "brighter" in response to a laser beam. The principle of this method relies on the so-called Focused Electron Beam Induced Deposition (FEBID), which consists in aggregating atomic or molecular precursors at the focus of an electron beam.Directing the electron beam at the tip of the carbon nanotube therefore yield to the sought result, in principle. The carbon nanotube however is very tiny, which requires a level of control on the process which had never been reached priori to this project: Indeed, the mass of the optical scatterer shall be small compared to that of the carbon nanotube, which is on the order of the attogram, that is about a hundred thousandth of a billionth of the mass of a single fly. To address this challenge, we have developed a method enabling to detect the mass of the carbon nanotube using the same electron beam as that utilized to grow the optical aggregate. This method is so precise, that we are able to control the deposition process with an accuracy of just a few tens of atoms. We also started tests intending to grow various functions on our nanotubes, including magnetic and dielectric particles.
Because they are so sensitive, the vibrations of this kind of resonators may be strongly affected by the measurement, either using an electron or a laser beam. In fact, the sensitivity is such that it was long expected that their oscillation behaviour would not follow the usual laws of thermodynamics. We have performed a series of experiments in order to address these outstanding questions, and have be able to provide the first experimental evidence of the role of momentum and thermal energy exchange between the measurement probe (electron or laser beam) and the the carbon nanotube. We also confirmed that the very large thermal vibrations of carbon nanotubes set them in a state that strongly differ from larger scale solid state resonators.
These results bring both new technology (nanofabrication, ultrasensitive nanomechanical measurement techniques) and scientific knowlege (nano-optomechanics, nanomechanical noise dynamics) to the fields of optomechanics, nanomechanics and nanofabrications. These results are lying at the top of the early expectation of this project, and appear very promising in the perspective of implementing the next steps, that is coupling the nanomechanical devices to optical resonators. It is so far expected that strongl, quantum sensitive coupling of carbon nanotube resonators to ultra-high finesse microspheres will be achieved by the end of the project.