arXiv subjects

Maxime Joos

Publications and source records attributed to Maxime Joos.

12 recordsLinked to original sources

arXiv2024

Role of Oxygen in Laser Induced Contamination at Diamond-Vacuum Interfaces

Many modern-day quantum science experiments rely on high-fidelity measurement of fluorescent signals emitted by the quantum system under study. A pernicious issue encountered when such experiments are conducted near a material interface in vacuum is "laser-induced contamination" (LIC): the gradual accretion of fluorescent contaminants on the surface where a laser is focused. Fluorescence from these contaminants can entirely drown out any signal from e.g. optically-probed color centers in the solid-state. Crucially, while LIC appears often in this context, it has not been systematically studied. In this work, we probe the onset and growth rate of LIC for a diamond nitrogen-vacancy center experiment in vacuum, and we correlate the contamination-induced fluorescence intensities to micron-scale physical build-up of contaminant on the diamond surface. Drawing upon similar phenomena previously studied in the space optics community, we use photo-catalyzed oxidation of contaminants as a mitigation strategy. We vary the residual oxygen pressure over 9 orders of magnitude and find that LIC growth is inhibited at near-atmospheric oxygen partial pressures, but the growth rate at lower oxygen pressure is non-monotonic. Finally, we discuss a model for the observed dependence of LIC growth rate on oxygen content and propose methods to extend in situ mitigation of LIC to a wider range of operating pressures.

quant-ph↗

arXiv2023

Long-lived coherences in strongly interacting spin ensembles

Periodic driving has emerged as a powerful tool to control, engineer, and characterize many-body quantum systems. However, the required pulse sequences are often complex, long, or require the ability to control the individual degrees of freedom. In this work, we study how a simple Carr-Purcell Meiboom-Gill (CPMG)-like pulse sequence can be leveraged to enhance the coherence of a large ensemble of spin qubits and serve as an important characterization tool. We implement the periodic drive on an ensemble of dense nitrogen-vacancy (NV) centers in diamond and examine the effect of pulse rotation offset as a control parameter on the dynamics. We use a single diamond sample prepared with several spots of varying NV density, which, in turn, varies the NV-NV dipolar interaction strength. Counter-intuitively, we find that rotation offsets deviating from the ideal π-pulse in the CPMG sequence (often classified as pulse errors) play a critical role in preserving coherence even at nominally zero rotation offset. The cause of the coherence preservation is an emergent effective field that scales linearly with the magnitude of the rotation offset. In addition to extending coherence, we compare the rotation offset dependence of coherence to numerical simulations to measure the disorder and dipolar contributions to the Hamiltonian to quantitatively extract the densities of the constituent spin species within the diamond.

quant-ph↗

arXiv2022

Probing many-body dynamics in a two dimensional dipolar spin ensemble

The most direct approach for characterizing the quantum dynamics of a strongly-interacting system is to measure the time-evolution of its full many-body state. Despite the conceptual simplicity of this approach, it quickly becomes intractable as the system size grows. An alternate framework is to think of the many-body dynamics as generating noise, which can be measured by the decoherence of a probe qubit. Our work centers on the following question: What can the decoherence dynamics of such a probe tell us about the many-body system? In particular, we utilize optically addressable probe spins to experimentally characterize both static and dynamical properties of strongly-interacting magnetic dipoles. Our experimental platform consists of two types of spin defects in diamond: nitrogen-vacancy (NV) color centers (probe spins) and substitutional nitrogen impurities (many-body system). We demonstrate that signatures of the many-body system's dimensionality, dynamics, and disorder are naturally encoded in the functional form of the NV's decoherence profile. Leveraging these insights, we directly characterize the two-dimensional nature of a nitrogen delta-doped diamond sample. In addition, we explore two distinct facets of the many-body dynamics: First, we address a persistent debate about the microscopic nature of spin dynamics in strongly-interacting dipolar systems. Second, we demonstrate direct control over the correlation time of the many-body system. Finally, we demonstrate polarization exchange between NV and P1 centers, opening the door to quantum sensing and simulation using two-dimensional spin-polarized ensembles.

quant-ph↗

arXiv2022

Reporter-spin-assisted T1 relaxometry

A single spin quantum sensor can quantitatively detect and image fluctuating electromagnetic fields via their effect on the sensor spin's relaxation time, thus revealing important information about the target solid-state or molecular structures. However, the sensitivity and spatial resolution of spin relaxometry are often limited by the distance between the sensor and target. Here, we propose an alternative approach that leverages an auxiliary reporter spin in conjunction with a single spin sensor, a diamond nitrogen vacancy (NV) center. We show that this approach can realize a 10^4 measurement speed improvement for realistic working conditions and we experimentally verify the proposed method using a single shallow NV center. Our work opens up a broad path of inquiry into a range of possible spin systems that can serve as relaxation sensors without the need for optical initialization and readout capabilities.

quant-ph↗

arXiv2021

Protecting qubit coherence by spectrally engineered driving of the spin environment

Modern quantum technologies rely crucially on techniques to mitigate quantum decoherence; these techniques can be either passive, achieved for example via materials engineering, or active, typically achieved via pulsed monochromatic driving fields applied to the qubit. Using a solid-state defect spin coupled to a microwave-driven spin bath, we experimentally demonstrate a decoherence mitigation method based on spectral engineering of the environmental noise with a polychromatic drive waveform, and show that it outperforms monochromatic techniques. Results are in agreement with quantitative modeling, and open the path to active decoherence protection using custom-designed waveforms applied to the environment rather than the qubit.

quant-ph↗

arXiv2020

Nanofiber based displacement sensor

We report on the realization of a displacement sensor based on an optical nanofiber. A single gold nano-sphere is deposited on top of a nanofiber and the system is placed within a standing wave which serves as a position ruler. Scattered light collected within the guided mode of the fiber gives a direct measure of the nanofiber displacement. We calibrated our device and found a sensitivity up to 1.2~nm/$\sqrt{\text{Hz}}$. A mechanical model based on the Mie scattering theory is then used to evaluate the optically induced force on the nanofiber by an external laser. With our sensing system, we demonstrate that an external force of 1~pN applied at the nanofiber waist can be detected.

physics.optics↗

arXiv2019

Nanophotonic approaches for integrated quantum photonics

Photons for quantum technologies have been identified early on as a very good candidate for carrying quantum information encoded onto them, either by polarization encoding, time encoding or spatial encoding. Quantum cryptography, quantum communications, quantum networks in general and quantum computing are some of the applications targeted by what is now called quantum photonics. Nevertheless, it was pretty clear at an early stage that bulk optics for handling quantum states of light with photons would not be able to deliver what is needed for these technologies. More recently, single photons, entangled photons and quantum optics in general have been coupled to more integrated approaches coming from classical optics in order to meet the requirements of scalability, reliablility and efficiency for quantum technologies. In this article, we develop our recent advances in two different nanophotonic platforms for quantum photonics using elongated optical fibers and integrated glass waveguides made by the so-called ion-exchange technique. We also present our latest results on quantum nanoemitters that we plan to couple and incorporate with our photonics platforms. These nanoemitters are of two kinds: nanocrystals made of perovskites as well as silicon-vacancy defect centers in nanodiamonds. Some of their properties are developed in this work. We will then give the general steps necessary in order to couple these nanoemitters efficiently with our platforms in the near future.

quant-ph↗

arXiv2019

Optical nanofiber interferometer and resonator

We report the fabrication and characterization of photonic structures using tapered optical nanofibers. Thanks to the extension of the evanescent electromagnetic field outside of the nanofiber two types of devices can be built: a ring interferometer and a knot resonator. We propose a general approach to predict the properties of these structures using the linear coupling theory. In addition, we describe a new source of birefringence due to the ovalization of a nanofiber under strong bending, known in mechanical engineering as the Brazier effect.

physics.optics↗

arXiv2019

Full control of polarization in tapered optical nanofibers

We report on a protocol to achieve full control of the polarization in a nanofiber. The protocol relies on studying the light scattered out from a nanofiber by means of two optical systems with $45^\circ$ camera angle difference. By studying the disturbance of the nanofiber on the radiation of embedded scatterers, we propose an explanation for the observed reduced scattering contrast of the nanofiber. Thanks to this approach, we demonstrate an accuracy of the polarization control larger than 95\%.

physics.optics↗

arXiv2018

Imaging light scattered by a subwavelength nanofiber, from near field to far field

We present a direct experimental investigation of the optical field distribution around a suspended tapered optical nanofiber by means of a fluorescent scanning probe. Using a 100 nm diameter fluorescent bead as a probe of the field intensity, we study interferences made by a nanofiber (400 nm diameter) scattering a plane wave (568 nm wavelength). Our scanning fluorescence near-field microscope maps the optical field over 36 $μ$m$^2$, with $λ/ 5$ resolution, from contact with the surface of the nanofiber to a few micrometers away. Comparison between experiments and Mie scattering theory allows us to precisely determine the emitter-nanofiber distance and experimental drifts.

physics.optics↗

arXiv2018

Toward a compact fibered squeezing parametric source

In this work, we investigate three different compact fibered systems generating vacuum squeezing that involve optical cavities limited by the end surface of a fiber and by a curved mirror and containing a thin parametric crystal. These systems have the advantage to couple squeezed states directly to a fiber, allowing the user to benefit from the flexibility of fibers in the use of squeezing. Three types of fibers are investigated: standard single-mode fibers, photonic-crystal large mode area single-mode fibers and short multi-mode fiber taped to a single-mode fiber. The observed squeezing is modest (-0.56 dB, -0.9 dB, -1 dB), but these experiments open the way to miniaturized squeezing devices that could be a very interesting advantage in scaling up quantum systems for quantum processing, opening new perspectives in the domain of integrated quantum optics.

quant-ph↗

arXiv2017

Polarisation control of linear dipole radiation using spin-momentum locking of light

We experimentally demonstrate that a linear dipole is not restricted to emit linearly polarised light, provided it is embedded in the appropriate nanophotonic environment. We observe emission of various elliptical polarisations by a linear dipole including circularly polarised light, without the need for birefringent components. We further show that the emitted state of polarisation can theoretically span the entire Poincare sphere. The experimental demonstration is based on elongated gold nanoparticles (nanorods) deposited on an optical nanofibre and excited by a free-space laser beam. The light directly collected in the guided mode of the nanofibre is analysed in regard to the azimuthal position and orientation of the nanorods, observed by means of scanning electron microscopy. This work constitutes a demonstration of the mapping between purely geometrical degrees of freedom of a light source and all polarisation states and could open the way to new methods for polarisation control of light sources at the nanoscale.

quant-ph↗