arXiv subjects

Laure Mercier de Lépinay

Publications and source records attributed to Laure Mercier de Lépinay.

At least 19 recordsLinked to original sources

arXiv2026

Bismuth-substituted Lutetium Iron Garnet Films with Giant Visible-Range Magneto-Optical Sensitivity

Magneto-optical materials are indispensable across modern physics, serving as the foundation for precision magnetic sensing, nonreciprocal photonics, and optical isolation technologies. The continual pursuit of materials with high Verdet constants has driven the development of garnet-based compounds exhibiting giant magneto-optical sensitivity. In this work, we report the growth and comprehensive magneto-optical characterization of bismuth-substituted lutetium iron garnet (LuBiIG), a material that combines the large spin-orbit coupling of bismuth with the lattice stability of lutetium iron garnet. LuBiIG films with thicknesses between 85-220nm were grown by pulsed laser deposition and characterized at room temperature over the 500-820nm wavelength range. The films exhibit an exceptionally high Verdet constant of up to -1.37e8 degree/meter/Tesla, peaking in the visible spectral range near 520nm. These results position LuBiIG as a highly sensitive magneto-optical material suitable for advanced cryogenic detection and hybrid quantum applications.

cond-mat.mtrl-sci↗

arXiv2026

Measurement of the Casimir force between superconductors

The Casimir force follows from quantum fluctuations of the electromagnetic field and yields a nonlinear attractive force between closely spaced conductive objects. Measuring the Casimir force in superconducting materials on either side of the transition should allow to isolate the specific contribution of low frequencies to the Casimir effect. There is significant interest in this contribution as it is suspected to be involved in an unexplained discrepancy between predictions and measurements of the Casimir force between normal metals. Here, we observe a force acting on a superconducting drum resonator integrated in a microwave optomechanical cavity through the nonlinear dynamics this force imparts to the resonator. The measured dynamics points to an extremely intense force found to be compatible in magnitude with the Casimir force for the range of vacuum separations that can be expected in this device, and incompatible with estimates of other known sources of nonlinearity. This nonlinearity is intense enough that, with a modified design, this device type should operate in the single-phonon nonlinear regime. Accessing this regime has been a long-standing goal that would greatly facilitate quantum operations of mechanical resonators.

cond-mat.mes-hall↗

arXiv2026

Pump-Threshold-Free Frequency Comb via Cavity Floquet Engineering

Frequency combs have revolutionized communication, metrology, and spectroscopy. Considerable efforts have been devoted to developing integrated combs, primarily leveraging Pockels or Kerr nonlinearities. Here, we demonstrate an alternative frequency comb generated via cavity Floquet engineering. By periodically modulating the cavity resonance frequency through a driven mechanical oscillator, a Floquet cavity with multiple equally spaced frequency components is created. These sidebands exhibit nearest-neighbor coupling and are phase-locked to the external modulation drive. A pump tone interacts with the pre-modulated cavity to generate the output frequency comb, which we implement in an on-chip microwave cavity optomechanical system. This approach operates independently of a pumping threshold and is insensitive to pump detuning. Consequently, it enables comb generation under far-sideband pumping with nanowatt-scale total power consumption, providing an ultra-low-power platform for integrated frequency comb synthesis.

quant-ph↗

arXiv2026

Simulating the electrostatic patch force in experimental geometries

Potential patches are responsible for a force between closely-spaced objects that forms a parasitic contribution to sensitive force measurements. Existing analytical models cannot account for the patch force in the 3D geometries of real experiments. Here, we present a finite-element method model to evaluate the impact of patches in geometries with roughness, edges, and curvature. First, we test our model against the plate-plate and sphere-plate geometries, for which the exact solutions are known. Then, we apply it to more complicated geometries for which analytical solution are challenging, and finally we extend it to handle AFM-measured rough surfaces. Patch textures are generated as a Voronoi diagram representing crystalline grains, or may be imported from potentials measured in Kelvin Probe Force Microscopy experiments. This work provides a reliable estimation of the parasitic contribution from random potential patches in realistic experimental geometries, which may be of relevance to Casimir force measurements or gravitational wave interferometers.

cond-mat.mes-hall↗

arXiv2024

Optomechanics driven by noisy and narrowband fields

We report a study of a cavity optomechanical system driven by narrow-band electromagnetic fields, which are applied either in the form of uncorrelated noise, or as a more structured spectrum. The bandwidth of the driving spectra is smaller than the mechanical resonant frequency, and thus we can describe the resulting physics using concepts familiar from regular cavity optomechanics in the resolved-sideband limit. With a blue-detuned noise driving, the noise-induced interaction leads to anti-damping of the mechanical oscillator, and a self-oscillation threshold at an average noise power that is comparable to that of a coherent driving tone. This process can be seen as noise-induced dynamical amplification of mechanical motion. However, when the noise bandwidth is reduced down to the order of the mechanical damping, we discover a large shift of the power threshold of self-oscillation. This is due to the oscillator adiabatically following the instantaneous noise profile. In addition to blue-detuned noise driving, we investigate narrow-band driving consisting of two coherent drive tones nearby in frequency. Also in these cases, we observe deviations from a naive optomechanical description relying only on the tones' frequencies and powers.

quant-ph↗

arXiv2024

Progress toward detection of individual TLS in nanomechanical resonators

The low temperature properties of amorphous solids are usually explained in terms of atomic-scale tunneling two level systems (TLS). For almost 20 years, individual TLS have been probed in insulating layers of superconducting quantum circuits. Detecting individual TLS in mechanical systems has been proposed but not definitively demonstrated. We describe an optomechanical system that is appropriate for this goal and describe our progress toward achieving it. In particular, we show that the expected coupling between the mechanical mode and a resonant TLS is strong enough for high visibility of a TLS given the linewidth of the mechanical mode. Furthermore, the electronic noise level of our measurement system is low enough and the anomalous force noise observed in other nanomechanical devices is absent.

cond-mat.mes-hall↗

arXiv2023

Ground-state cooling of a mechanical oscillator by heating

Dissipation and the accompanying fluctuations are often seen as detrimental for quantum systems, since they are associated with fast relaxation and loss of phase coherence. However, it has been proposed that a pure state can be prepared if external noise induces suitable downwards transitions, while exciting transitions are blocked. We demonstrate such a refrigeration mechanism in a cavity optomechanical system, where we prepare a mechanical oscillator in its ground state by injecting strong electromagnetic noise at frequencies around the red mechanical sideband of the cavity. The optimum cooling is reached with a noise bandwidth smaller than, but on the order of the cavity decay rate. At higher bandwidths, cooling is less efficient. In the opposite regime where the noise bandwidth becomes comparable to the mechanical damping rate, damping follows the noise amplitude adiabatically, and the cooling is also suppressed.

quant-ph↗

arXiv2022

Cavity nano-optomechanics with suspended subwavelength-sized nanowires

In the field of cavity nano-optomechanics, the nanoresonator-in-the-middle approach consists in inserting a sub-wavelength sized deformable resonator, here a nanowire, in the small mode volume of a fiber microcavity. Internal resonances in the nanowire enhance the light nanowire interaction which provide giant coupling strengthes -- sufficient to enter the single photon regime of cavity optomechanics -- at the condition to precisely position the nanowire within the cavity field. Here we expose a theoretical description that combines an analytical formulation of the Mie-scattering of the intracavity light by the nanowire and an input-output formalism describing the dynamics of the intracavity optical eigenmodes. We investigate both facets of the optomechanical interaction describing the position dependent parametric and dissipative optomechanical coupling strengths, as well as the optomechanical force field experienced by the nanowire. We find a quantitative agreement with recent experimental realization. We discuss the specific phenomenology of the optomechanical interaction which acquires a vectorial character since the nanowire can identically vibrate along both transverse directions: the optomechanical force field presents a non-zero rotational, while anomalous positive cavity shifts are expected. Taking advantage of the large Kerr-like non linearity, this work opens perspectives in the field of quantum optics with nanoresonator with for instance broadband squeezing of the outgoing cavity fields close to the single photon level.

quant-ph↗

arXiv2022

Fast feedback control of mechanical motion using circuit optomechanics

Measurement-based control, utilizing an active feedback loop, is a standard tool in technology. Feedback control is also emerging as a useful and fundamental tool in quantum technology and in related fundamental studies, where it can be used to prepare and stabilize pure quantum states in various quantum systems. Feedback-cooling of center-of-mass micromechanical oscillators, which typically exhibit a high thermal noise far above the quantum regime has been particularly actively studied and has recently been shown to allow for ground-state cooling using optical measurements. Here, we realize measurement-based feedback operations in an electromechanical system, cooling the mechanical thermal noise down to 3 quanta, limited by added amplifier noise. Counter-intuitively, we also obtain significant cooling when the system is pumped at the blue optomechanical sideband, where the system is unstable without feedback.

quant-ph↗

arXiv2022

Quantum backaction evading measurements of a silicon nitride membrane resonator

Quantum backaction disturbs the measurement of the position of a mechanical oscillator by introducing additional fluctuations. In a quantum backaction measurement technique, the backaction can be evaded, although at the cost of losing part of the information. In this work, we carry out such a quantum backaction measurement using a large 0.5 mm diameter silicon nitride membrane oscillator with 707 kHz frequency, via a microwave cavity readout. The measurement shows that quantum backaction noise can be evaded in the quadrature measurement of the motion of a large object.

quant-ph↗

arXiv2021

Quantum-mechanics free subsystem with mechanical oscillators

Quantum mechanics sets a limit for the precision of continuous measurement of the position of an oscillator. Here we show how it is possible to measure an oscillator without quantum backaction of the measurement by constructing one effective oscillator from two physical oscillators. We realize such a quantum-mechanics free subsystem using two micromechanical oscillators, and show the measurements of two collective quadratures while evading the quantum backaction by $8$ decibels on both of them, obtaining a total noise within a factor two of the full quantum limit. This facilitates detection of weak forces and the generation and measurement of nonclassical motional states of the oscillators. Moreover, we directly verify the quantum entanglement of the two oscillators by measuring the Duan quantity $1.4$ decibels below the separability bound.

quant-ph↗

arXiv2021

Inducing micromechanical motion by optical excitation of a single quantum dot

Hybrid quantum optomechanical systems offer an interface between a single two-level system and a macroscopical mechanical degree of freedom. In this work, we build a hybrid system made of a vibrating microwire coupled to a single semiconductor quantum dot (QD) via material strain. It was shown a few years ago, that the QD excitonic transition energy can thus be modulated by the microwire motion. We demonstrate here the reverse effect, whereby the wire is set in motion by the resonant drive of a single QD exciton with a laser modulated at the mechanical frequency. The resulting driving force is found to be almost 3 orders of magnitude larger than radiation pressure. From a fundamental aspect, this state dependent force offers a convenient strategy to map the QD quantum state onto a mechanical degree of freedom.

cond-mat.mes-hall↗

arXiv2021

Microwave single-tone optomechanics in the classical regime

We report on the quantitative experimental illustration of elementary optomechanics within the classical regime. All measurements are performed in a commercial dilution refrigerator on a mesoscopic drumhead aluminium resonator strongly coupled to a microwave cavity, using only strict single-tone schemes. Sideband asymmetry is reported using in-cavity microwave pumping, along with noise squashing and back-action effects. Results presented in this paper are analysed within the simple classical electric circuit theory, emphasizing the analogous nature of classical features with respect to their usual quantum description. The agreement with theory is obtained with no fitting parameters. Besides, based on those results a simple method is proposed for the accurate measurement of the ratio between microwave internal losses and external coupling.

cond-mat.mes-hall↗

arXiv2020

Ultrasensitive nano-optomechanical force sensor at dilution temperatures

Cooling down nanomechanical force probes is a generic strategy to enhance their sensitivities through the concomitant reduction of their thermal noise and mechanical damping rates. However, heat conduction mechanisms become less efficient at low temperatures, which renders difficult to ensure and verify their proper thermalization. To operate with minimally perturbing measurements, we implement optomechanical readout techniques operating in the photon counting regime to probe the dynamics of suspended silicon carbide nanowires in a dilution refrigerator. Readout of their vibrations is realized with sub-picowatt optical powers, in a regime where less than one photon is collected per oscillation period. We demonstrate their thermalization down to $32\pm2$ mK and report on record sensitivities for scanning probe force sensors, at the $40\,\rm zN/Hz^{1/2}$ level, with a sensitivity to lateral force field gradients in the fN/m range. This work opens the road toward nanomechanical vectorial imaging of faint forces at dilution temperatures, at minimal excitation levels.

cond-mat.mes-hall↗

arXiv2019

Nonreciprocal transport based on cavity Floquet modes in optomechanics

Directional transport is obtained in various multimode systems by driving multiple, nonreciprocally-interfering interactions between individual bosonic modes. However, systems sustaining the required number of modes become physically complex. In our microwave-optomechanical experiment, we show how to configure nonreciprocal transport between frequency components of a single superconducting cavity coupled to two drumhead oscillators. The frequency components are promoted to Floquet modes and generate the missing dimension to realize an isolator and a directional amplifier. A second cavity left free by this arrangement is used to cool the mechanical oscillators and bring the transduction noise close to the quantum limit. We furthermore uncover a new type of instability specific to nonreciprocal coupling. Our approach is generic and can greatly simplify quantum signal processing and the design of topological lattices from low-dimensional systems.

cond-mat.mes-hall↗

arXiv2019

Cavity nano-optomechanics in the ultrastrong coupling regime with ultrasensitive force sensors

In a canonical optomechanical system, 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 causing a dilution of the original optomechanical non-linearity. Here, we investigate the optomechanical interaction of an ultrasensitive suspended nanowire inserted in a fiber-based microcavity mode. This implementation allows to enter far into the hitherto unexplored ultrastrong optomechanical coupling regime, where one single intracavity photon can displace the oscillator by more than its zero point fluctuations. To fully characterize our system, we implement nanowire-based scanning probe measurements to map the vectorial optomechanical coupling strength, but also to reveal the intracavity optomechanical force field experienced by the nanowire. This work establishes that the single photon cavity optomechanics regime is within experimental reach.

quant-ph↗

arXiv2016

Eigenmode orthogonality breaking and deviation from the fluctuation dissipation relation in rotationally dressed nanomechanical oscillators

The ultimate sensitivities achieved in force or mass sensing are limited by the employed nanomechanical probes thermal noise. Its proper understanding is critical for ultimate operation and any deviation from the underlying fluctuation dissipation theorem should be carefully inspected. Here we investigate an ultrasensitive vectorial force-field sensor, a singly clamped nanowire oscillating along two quasi frequency degenerated transverse directions. Immersing the nanowire in a non-conservative optical force field causes dramatic modifications of its thermal noise and driven dynamics. In regions of strong vorticity, eigenmodes orientations are distorted and lose their initial orthogonality. Thermal noise spectra strongly deviate from the normal mode expansion and presents an anomalous excess of noise violating the fluctuation dissipation theorem. Our model quantitatively accounts for all observations and underlines the role of non-axial response when patching the fluctuation dissipation relation. These results reveal the intriguing properties of thermal fluctuations in multimode nano-optomechanical systems and the subtleties appearing when performing thermal noise thermometry in such systems. They are also valid in any non-symmetrically coupled dual systems.

cond-mat.mes-hall↗

arXiv2016

Universal Vectorial and Ultrasensitive Nanomechanical Force Field Sensor

Miniaturization of force probes into nanomechanical oscillators enables ultrasensitive investigations of forces on dimensions smaller than their characteristic length scale. Meanwhile it also unravels the force field vectorial character and how its topology impacts the measurement. Here we expose an ultrasensitive method to image 2D vectorial force fields by optomechanically following the bidimensional Brownian motion of a singly clamped nanowire. This novel approach relies on angular and spectral tomography of its quasi frequency-degenerated transverse mechanical polarizations: immersing the nanoresonator in a vectorial force field does not only shift its eigenfrequencies but also rotate eigenmodes orientation as a nano-compass. This universal method is employed to map a tunable electrostatic force field whose spatial gradients can even take precedence over the intrinsic nanowire properties. Enabling vectorial force fields imaging with demonstrated sensitivities of attonewton variations over the nanoprobe Brownian trajectory will have strong impact on scientific exploration at the nanoscale.

cond-mat.mes-hall↗