arXiv subjects

Roberta Ramponi

Publications and source records attributed to Roberta Ramponi.

At least 19 recordsLinked to original sources

arXiv2025

Enhanced quantum magnetometry with a laser-written integrated photonic diamond chip

An ensemble of negatively charged nitrogen-vacancy centers in diamond can act as a precise quantum sensor even under ambient conditions. In particular, to optimize thier sensitivity, it is crucial to increase the number of spins sampled and maximize their coupling to the detection system, without degrading their spin properties. In this paper, we demonstrate enhanced quantum magnetometry via a high-quality buried laser-written waveguide in diamond with a 4.5 ppm density of nitrogen-vacancy centers. We show that the waveguide-coupled nitrogen-vacancy centers exhibit comparable spin coherence properties as that of nitrogen-vacancy centers in pristine diamond using time-domain optically detected magnetic resonance spectroscopy. Waveguide-enhanced magnetic field sensing is demonstrated in a fiber-coupled integrated photonic chip, where probing an increased volume of high-density spins results in 63 pT$.$Hz $^{-1/2}$ of DC-magnetic field sensitivity and 20 pT$.$Hz $^{-1/2}$ of AC magnetic field sensitivity. This on-chip sensor realizes at least an order of magnitude improvement in sensitivity compared to the conventional confocal detection setup, paving the way for microscale sensing with nitrogen-vacancy ensembles.

quant-ph↗

arXiv2024

Vector Magnetometry Using Shallow Implanted NV Centers in Diamond with Waveguide-Assisted Dipole Excitation and Readout

On-chip magnetic field sensing with Nitrogen-Vacancy (NV) centers in diamond requires scalable integration of 3D waveguides into diamond substrates. Here, we develop a sensing array device with an ensemble of shallow implanted NV centers integrated with arrays of laser-written waveguides for excitation and readout of NV signals. Our approach enables an easy-to-operate on-chip magnetometer with a pixel size proportional to the Gaussian mode area of each waveguide. The performed continuous wave optically detected magnetic resonance on each waveguide gives an average dc-sensitivity value of $195 \pm 3 {nT}/\sqrt{Hz}$, which can be improved with lock-in-detection or pulsed-microwave sequences. We apply a magnetic field to separate the four NV crystallographic orientations of the magnetic resonance and then utilize a DC current through a straight wire antenna close to the waveguide to prove the sensor capabilities of our device. We reconstruct the complete vector magnetic field in the NV crystal frame using three different NV crystallographic orientations. By knowing the polarization axis of the waveguide mode, we project the magnetic field vector into the lab frame.

quant-ph↗

arXiv2024

Laser-written waveguide-integrated coherent spins in diamond

Quantum emitters, such as the negatively charged nitrogen-vacancy center in diamond, are attractive for quantum technologies such as nano-sensing, quantum information processing, and as a non-classical light source. However, it is still challenging to position individual emitters in photonic structures whilst preserving the spin coherence properties of the defect. In this paper, we investigate single and ensemble waveguide-integrated nitrogen-vacancy centers in diamond fabricated by femtosecond laser writing followed by thermal annealing. Their spin coherence properties are systematically investigated and are shown to be comparable to native nitrogen-vacancy centers in diamond. This method paves the way for the fabrication of coherent spins integrated within photonic devices.

quant-ph↗

arXiv2024

Determining Strain Components in a Diamond Waveguide from Zero-Field ODMR Spectra of NV$^{-}$ Center Ensembles

The negatively charged nitrogen-vacancy (NV$^{-}$) center in diamond has shown great potential in nanoscale sensing and quantum information processing due to its rich spin physics. An efficient coupling with light, providing strong luminescence, is crucial for realizing these applications. Laser-written waveguides in diamond promote NV$^{-}$ creation and improve their coupling to light but, at the same time, induce strain in the crystal. The induced strain contributes to light guiding but also affects the energy levels of NV$^{-}$ centers. We probe NV$^{-}$ spin states experimentally with the commonly used continuous-wave zero-field optically detected magnetic resonance (ODMR). In our waveguides, the ODMR spectra are shifted, split, and consistently asymmetric, which we attribute to the impact of local strain. To understand these features, we model ensemble ODMR signals in the presence of strain. By fitting the model results to the experimentally collected ODMR data, we determine the strain tensor components at different positions, thus determining the strain profile across the waveguide. This shows that zero-field ODMR spectroscopy can be used as a strain imaging tool. The resulting strain within the waveguide is dominated by a compressive axial component transverse to the waveguide structure, with a smaller contribution from vertical and shear strain components.

cond-mat.mes-hall↗

arXiv2021

On-chip single-photon subtraction by individual silicon vacancy centers in a laser-written diamond waveguide

Modifying light fields at single-photon level is a key challenge for upcoming quantum technologies and can be realized in a scalable manner through integrated quantum photonics. Laser-written diamond photonics offers three-dimensional fabrication capabilities and large mode-field diameters matched to fiber optic technology, though limiting the cooperativity at the single-emitter level. To realize large cooperativities, we combine excitation of single shallow-implanted silicon vacancy centers via large numerical aperture optics with detection assisted by laser-written type-II waveguides. We demonstrate single-emitter extinction measurements with a cooperativity of 0.153 and a beta factor of 13% yielding 15.3% as lower bound for the quantum efficiency of a single emitter. The transmission of resonant photons reveals single-photon subtraction from a quasi-coherent field resulting in super-Poissonian light statistics. Our architecture enables single quantum level light field engineering in an integrated design which can be fabricated in three dimensions and with a natural connectivity to optical fiber arrays.

quant-ph↗

arXiv2020

An integrated magnetometry platform with stackable waveguide-assisted detection channels for sensing arrays

The negatively-charged NV$^-$-center in diamond has shown great success in nanoscale, high-sensitivity magnetometry. Efficient fluorescence detection is crucial for improving the sensitivity. Furthermore, integrated devices enable practicable sensors. Here, we present a novel architecture which allows us to create NV$^-$-centers a few nanometers below the diamond surface, and at the same time in the mode field maximum of femtosecond-laser-written type-II waveguides. We experimentally verify the coupling efficiency, showcase the detection of magnetic resonance signals through the waveguides and perform first proof-of-principle experiments in magnetic field and temperature sensing. The sensing task can be operated via the waveguide without direct light illumination through the sample, which marks an important step for magnetometry in biological systems which are fragile to light. In the future, our approach will enable the development of two-dimensional sensing arrays facilitating spatially and temporally correlated magnetometry.

physics.optics↗

arXiv2020

Laser-Inscribed Diamond Waveguide Resonantly Coupled to Diamond Microsphere

An all-diamond photonic circuit was implemented by integrating a diamond microsphere with a femtosecond-laser-written bulk diamond waveguide. The near surface waveguide was fabricated by exploiting the Type II fabrication method to achieve stress-induced waveguiding. Transverse electrically and transverse magnetically polarized light from a tunable laser operating in the near-infrared region was injected into the diamond waveguide, which when coupled to the diamond microsphere showed whispering-gallery modes with a spacing of 0.33 nm and high-quality factors of 105. By carefully engineering these high-quality factor resonances, and further exploiting the properties of existing nitrogen-vacancy centers in diamond microspheres and diamond waveguides in such configurations, it should be possible to realize filtering, sensing and nonlinear optical applications in integrated diamond photonics.

physics.optics↗

arXiv2020

Quantum micro-nano devices fabricated in diamond by femtosecond laser and ion irradiation

Diamond has attracted great interest as a quantum technology platform thanks to its optically active nitrogen vacancy center (NV). The NV's ground state spin can be read out optically exhibiting long spin coherence times of about 1 ms even at ambient temperatures. In addition, the energy levels of the NV are sensitive to external fields. These properties make NVs attractive as a scalable platform for efficient nanoscale resolution sensing based on electron spins and for quantum information systems. Diamond photonics enhances optical interaction with NVs, beneficial for both quantum sensing and information. Diamond is also compelling for microfluidic applications due to its outstanding biocompatibility, with sensing functionality provided by NVs. However, it remains a significant challenge to fabricate photonics, NVs and microfluidics in diamond. In this Report, an overview is provided of ion irradiation and femtosecond laser writing, two promising fabrication methods for diamond based quantum technological devices. The unique capabilities of both techniques are described, and the most important fabrication results of color center, optical waveguide and microfluidics in diamond are reported, with an emphasis on integrated devices aiming towards high performance quantum sensors and quantum information systems of tomorrow

physics.optics↗

arXiv2018

Femtosecond laser written diamond waveguides - a step towards integrated photonics in the far infrared

A first demonstration and complete characterization of mid-infrared waveguides in diamond are reported in detail. Waveguides were designed for 2.4 um and 8.6 um waveguiding, with their group velocity dispersion was analyzed using femtosecond pulses at 2.4 um wavelength propagated through the waveguide and the bulk substrate. The total dispersion was found to be dominated by the bulk material rather than the waveguide, and was on the range of 275 fs2/mm, demonstrating that femtosecond laser written modifications in diamond introduce negligible perturbations to the intrinsic material.

physics.optics↗

arXiv2018

Femtosecond laser inscription of nonlinear photonic circuits in Gallium Lanthanum Sulphide glass

We report on femtosecond laser writing of single mode optical waveguides in chalcogenide Gallium Lanthanum Sulphide (GLS) glass. A multiscan fabrication process was employed to create waveguides with symmetric single mode guidance and low insertion losses at 800 nm wavelength, compatible with Ti:Sapphire ultrafast lasers. {\mu}Raman and X-Ray microanalysis were used to elucidate the origin of the laser-induced refractive index change in GLS. Nonlinear refractive index measurements of the waveguides were performed by finding the optical switching parameters of a directional coupler, demonstrating that the nonlinear properties were preserved, evidencing that GLS is a promising platform for laser-written integrated nonlinear photonics.

physics.optics↗

arXiv2018

One-dimensional disordered photonic structures with two or more materials

Here we would like to discuss the light transmission modulation by periodic and disordered one dimensional (1D) photonic structures. In particular, we will present some theoretical and experimental findings highlighting the peculiar optical properties of: i) 1D periodic and disordered photonic structures made with two or more materials; ii) 1D photonic structures in which the homogeneity or the aggregation of the high refractive index layers is controlled. We will focus also on the fabrication aspects of these structures.

physics.optics↗

arXiv2017

First FAMU observation of muon transfer from mu-p atoms to higher-Z elements

The FAMU experiment aims to accurately measure the hyperfine splitting of the ground state of the muonic hydrogen atom. A measurement of the transfer rate of muons from hydrogen to heavier gases is necessary for this purpose. In June 2014, within a preliminary experiment, a pressurized gas-target was exposed to the pulsed low-energy muon beam at the RIKEN RAL muon facility (Rutherford Appleton Laboratory, UK). The main goal of the test was the characterization of both the noise induced by the pulsed beam and the X-ray detectors. The apparatus, to some extent rudimental, has served admirably to this task. Technical results have been published that prove the validity of the choices made and pave the way for the next steps. This paper presents the results of physical relevance of measurements of the muon transfer rate to carbon dioxide, oxygen, and argon from non-thermalized excited mu-p atoms. The analysis methodology and the approach to the systematics errors are useful for the subsequent study of the transfer rate as function of the kinetic energy of the mu-p currently under way.

physics.atom-ph↗

arXiv2016

Diamond photonics platform enabled by femtosecond laser writing

We demonstrate the first buried optical waveguides in diamond using focused femtosecond laser pulses. The properties of nitrogen vacancy centers are preserved in the waveguides, making them promising for diamond-based magnetometers or quantum information systems.

physics.optics↗

arXiv2016

Learning an unknown transformation via a genetic approach

Recent developments in integrated photonics technology are opening the way to the fabrication of complex linear optical interferometers. The application of this platform is ubiquitous in quantum information science, from quantum simulation to quantum metrology, including the quest for quantum supremacy via the boson sampling problem. Within these contexts, the capability to learn efficiently the unitary operation of the implemented interferometers becomes a crucial requirement. In this letter we develop a reconstruction algorithm based on a genetic approach, which can be adopted as a tool to characterize an unknown linear optical network. We report an experimental test of the described method by performing the reconstruction of a 7-mode interferometer implemented via the femtosecond laser writing technique. Further applications of genetic approaches can be found in other contexts, such as quantum metrology or learning unknown general Hamiltonian evolutions.

quant-ph↗

arXiv2016

Path-polarization hyperentangled and cluster states of photons on a chip

Encoding many qubits in different degrees of freedom (DOFs) of single photons is one of the routes towards enlarging the Hilbert space spanned by a photonic quantum state. Hyperentangled photon states (i.e. states showing entanglement in multiple DOFs) have demonstrated significant implications for both fundamental physics tests and quantum communication and computation. Increasing the number of qubits of photonic experiments requires miniaturization and integration of the basic elements and functions to guarantee the set-up stability. This motivates the development of technologies allowing the precise control of different photonic DOFs on a chip. We demonstrate the contextual use of path and polarization qubits propagating within an integrated quantum circuit. We tested the properties of four-qubit linear cluster states built on both DOFs. Our results pave the way towards the full integration on a chip of hybrid multiqubit multiphoton states.

quant-ph↗

arXiv2015

Thermally-Reconfigurable Quantum Photonic Circuits at Telecom Wavelength by Femtosecond Laser Micromachining

The importance of integrated quantum photonics in the telecom band resides on the possibility of interfacing with the optical network infrastructure developed for classical communications. In this framework, femtosecond laser written integrated photonic circuits, already assessed for quantum information experiments in the 800 nm wavelength range, have great potentials. In fact these circuits, written in glass, can be perfectly mode-matched at telecom wavelength to the in/out coupling fibers, which is a key requirement for a low-loss processing node in future quantum optical networks. In addition, for several applications quantum photonic devices will also need to be dynamically reconfigurable. Here we experimentally demonstrate the high performance of femtosecond laser written photonic circuits for quantum experiments in the telecom band and we show the use of thermal shifters, also fabricated by the same femtosecond laser, to accurately tune them. State-of-the-art manipulation of single and two-photon states is demonstrated, with fringe visibilities greater than 95%. This opens the way to the realization of reconfigurable quantum photonic circuits on this technological platform.

quant-ph↗

arXiv2015

Photonic glass-ceramics: consolidated outcomes and prospects

Transparent glass-ceramics are nanocomposite materials which offer specific characteristics of capital importance in photonics. This kind of two-phase materials is constituted by nanocrystals embedded in a glass matrix and the respective composition and volume fractions of crystalline and amorphous phase determine the properties of the glass-ceramic. Among these properties transparency is crucial, in particular when confined structures, such as dielectric optical waveguides and optical fibers, are considered, and the number of papers devoted to this topic is continuously increasing. Another important point is the role of the nanocrystals when activated by luminescent species, as rare earth ions, and their effect on the spectroscopic properties of the glass-ceramic. The presence of the crystalline environment around the rare earth ion allows high absorption and emission cross sections, reduction of the non-radiative relaxation thanks to the lower phonon cutoff energy, and tailoring of the ion-ion interaction by the control of the rare earth ion partition. This last point is crucial and still object of intense experimental and theoretical studies. The composition of the glass matrix also impacts the properties of the rare earth ions located in nanoparticles. Moreover, some kinds of nanocrystals can play as effective rare earth sensitizers. Fabrication, assessment and application of glass-ceramic photonic systems, especially waveguides, deserve an appropriate discussion which is the aim of this paper, focused on luminescent glass-ceramics. In this work, a brief historical review, consolidated results and recent advances in this important scientific and technological area will be presented, and some perspectives will be outlined.

cond-mat.mtrl-sci↗

arXiv2015

Quantum suppression law in a 3-D photonic chip implementing the Fast Fourier Transform

The identification of phenomena able to pinpoint quantum interference is attracting large interest. Indeed, a generalization of the Hong-Ou-Mandel effect valid for any number of photons and optical modes would represent an important leap ahead both from a fundamental perspective and for practical applications, such as certification of photonic quantum devices, whose computational speedup is expected to depend critically on multiparticle interference. Quantum distinctive features have been predicted for many particles injected into multimode interferometers implementing the Fourier transformation in the Fock space. In this work we develop a scalable approach for the implementation of quantum fast Fourier transform using 3-D photonic integrated interferometers, fabricated via femtosecond laser writing technique. We observe the quantum suppression of a large number of output states with 4- and 8-mode optical circuits: the experimental results demonstrate genuine quantum interference between the injected photons, thus offering a powerful tool for diagnostic of photonic platforms.

quant-ph↗