arXiv subjects

Giuseppe Leo

Publications and source records attributed to Giuseppe Leo.

30 records · Page 2Linked to original sources

arXiv2015

High-precision spectral tuning of micro and nanophotonic cavities by resonantly enhanced photoelectrochemical etching

We present a simple method to tune optical micro- and nanocavities with picometer precision in the resonant wavelength, corresponding to an effective sub atomic monolayer control of the cavity dimension. This is obtained through resonant photo-electrochemical etching, with in-situ monitoring of the optical spectrum. We employ this technique to spectrally align an ensemble of resonant cavities in a permanent manner, overcoming the dimension variability resulting from current nanofabrication techniques. In a device containing several resonators, each is individually addressed and tuned, with no optical quality factor degradation. The technique is general and opens the way to multiple applications, such as the straightforward fabrication of networks of identical coupled resonators, or the tuning of chip-based cavities to external references.

physics.optics↗

arXiv2015

Integrated AlGaAs source of highly indistinguishable and energy-time entangled photons

The generation of nonclassical states of light in miniature chips is a crucial step towards practical implementations of future quantum technologies. Semiconductor materials are ideal to achieve extremely compact and massively parallel systems and several platforms are currently under development. In this context, spontaneous parametric down conversion in AlGaAs devices combines the advantages of room temperature operation, possibility of electrical injection and emission in the telecom band. Here we report on a chip-based AlGaAs source, producing indistinguishable and energy-time entangled photons with a brightness of $7.2\times10^6$ pairs/s and a signal-to-noise ratio of $141\pm12$. Indistinguishability between the photons is demonstrated via a Hong-Ou-Mandel experiment with a visibility of $89\pm3\%$, while energy-time entanglement is tested via a Franson interferometer leading to a value for the Bell parameter $ S=2.70\pm0.10$.

quant-ph↗

arXiv2015

Origin of optical losses in gallium arsenide disk whispering gallery resonators

Whispering gallery modes in GaAs disk resonators reach half a million of optical quality factor. These high Qs remain still well below the ultimate design limit set by bending losses. Here we investigate the origin of residual optical dissipation in these devices. A Transmission Electron Microscope analysis is combined with an improved Volume Current Method to precisely quantify optical scattering losses by roughness and waviness of the structures, and gauge their importance relative to intrinsic material and radiation losses. The analysis also provides a qualitative description of the surface reconstruction layer, whose optical absorption is then revealed by comparing spectroscopy experiments in air and in different liquids. Other linear and nonlinear optical loss channels in the disks are evaluated likewise. Routes are given to further improve the performances of these miniature GaAs cavities.

physics.optics↗

arXiv2014

Improved optomechanical disk resonator sitting on a pedestal mechanical shield

We experimentally demonstrate the controlled enhancement of the mechanical quality factor Q of GaAs disk optomechanical resonators. Disks vibrating at 1.3 GHz with a mechanical shield integrated in their pedestal show a Q improvement by a factor 10 to 16. The structure is modeled numerically and different modes of vibration are observed, which shed light on the Q enhancement mechanism. An optimized double-disk geometry is presented that promises Q above the million for a large parameter range.

cond-mat.mes-hall↗

arXiv2014

Photoelastic coupling in gallium arsenide optomechanical disk resonators

We analyze the magnitude of the radiation pressure and electrostrictive stresses exerted by light confined inside GaAs semiconductor WGM optomechanical disk resonators, through analytical and numerical means, and find the electrostrictive force to be of prime importance. We investigate the geometric and photoelastic optomechanical coupling resulting respectively from the deformation of the disk boundary and from the strain-induced refractive index changes in the material, for various mechanical modes of the disks. Photoelastic optomechanical coupling is shown to be a predominant coupling mechanism for certain disk dimensions and mechanical modes, leading to total coupling g$_{om}$ and g$_0$ reaching respectively 3 THz/nm and 4 MHz. Finally, we point towards ways to maximize the photoelastic coupling in GaAs disk resonators, and we provide some upper bounds for its value in various geometries.

physics.optics↗

arXiv2013

An electrically injected photon-pair source at room temperature

One of the main challenges for future quantum information technologies is miniaturization and integration of high performance components in a single chip. In this context, electrically driven sources of non-classical states of light have a clear advantage over optically driven ones. Here we demonstrate the first electrically driven semiconductor source of photon pairs working at room temperature and telecom wavelength. The device is based on type-II intracavity Spontaneous Parametric Down-Conversion in an AlGaAs laser diode and generates pairs at 1.57 $μ$m. Time-correlation measurements of the emitted pairs give an internal generation efficiency of $7 \times 10^{-11}$ pairs/injected electron. The capability of our platform to support generation, manipulation and detection of photons opens the way to the demonstration of massively parallel systems for complex quantum operations.

quant-ph↗

arXiv2013

Direct high-resolution characterization of quantum correlations via classical measurements

Quantum optics plays a central role in the study of fundamental concepts in quantum mechanics, and in the development of new technological applications. Typical experiments employ non-classical light, such as entangled photons, generated by parametric processes. The standard characterization of the sources by quantum tomography, which relies on detecting the pairs themselves and thus requires single photon detectors, limits both measurement speed and accuracy. Here we show that the spectral characterization of the quantum correlations generated by two-photon sources can be directly performed classically with an unprecedented spectral resolution. This streamlined technique has the potential to speed up design and testing of massively parallel integrated sources by providing a fast and reliable quality control procedure. Adapting our method to explore other degrees of freedom would allow the complete characterization of biphoton states generated by parametric processes.

quant-ph↗

arXiv2013

Bell states generation on a III-V semiconductor chip at room temperature

We demonstrate the generation of polarization-entangled photon pairs at room temperature and telecom wavelength in a AlGaAs semiconductor waveguide. The source is based on spontaneous parametric down conversion with a counterpropagating phase-matching scheme. The quality of the two-photon state is assessed by the reconstruction of the density matrix giving a raw fidelity to a Bell state of 0.83; a theoretical model, taking into account the experimental parameters, provides ways to understand and control the amount of entanglement. Its compatibility with electrical injection, together with the high versatility of the generated two-photon state, make this source an attractive candidate for completely integrated quantum photonics devices.

quant-ph↗

arXiv2013

Ultrahigh Q-Frequency product for optomechanical disk resonators with a mechanical shield

We report on optomechanical GaAs disk resonators with ultrahigh quality factor - frequency product Qf. Disks standing on a simple pedestal exhibit GHz breathing modes attaining a Qf of 10^13 measured under vacuum at cryogenic temperature. Clamping losses are found to be the dominant source of dissipation in this configuration. A new type of disk resonator integrating a shield within the pedestal is then proposed and its working principles and performances investigated by numerical simulations. For dimensions compatible with fabrication constraints, the clamping-loss-limited Q reaches 10^7-10^9 corresponding to Qf of 10^16-10^18. This shielded pedestal approach applies to any heterostructure presenting an acoustic mismatch.

cond-mat.mes-hall↗

arXiv2011

Wavelength-sized GaAs optomechanical resonators with GHz frequency

We report on wavelength-sized GaAs optomechanical disk resonators showing ultra-strong optomechanical interaction. We observe optical transduction of a disk mechanical breathing mode with 1.4 GHz frequency and effective mass of ~ 2 pg. The measured vacuum optomechanical coupling rate reaches 0.8 MHz, with a related differential optomechanical coupling factor of 485 GHz/nm. The disk Brownian motion is optically resolved with a sensitivity of 10-17 m/{\sqrt}Hz at room temperature and pressure.

physics.optics↗

arXiv2010

High frequency GaAs nano-optomechanical disk resonator

Optomechanical coupling between a mechanical oscillator and light trapped in a cavity increases when the coupling takes place in a reduced volume. Here we demonstrate a GaAs semiconductor optomechanical disk system where both optical and mechanical energy can be confined in a sub-micron scale interaction volume. We observe giant optomechanical coupling rate up to 100 GHz/nm involving picogram mass mechanical modes with frequency between 100 MHz and 1 GHz. The mechanical modes are singled-out measuring their dispersion as a function of disk geometry. Their Brownian motion is optically resolved with a sensitivity of 10^(-17)m/sqrt(Hz) at room temperature and pressure, approaching the quantum limit imprecision.

physics.optics↗

arXiv2010

Ultra-low loss single-mode silica tapers manufactured by a microheater

Using a ceramic thermoelectric heater, we show highly reproducible fabrication of single-mode sub-wavelength silica tapers with ultra-low loss level. The reproducibility of the process is studied statistically, leading to an average taper transmission of 94%. The best tapers have a transmission superior to 99%, above common level reached by other fabrication methods. The taper profile is inspected along its length and closely follows the exponential profile predicted by the model of Birks and Li. This high degree of control over the taper shape allows a detailed analysis of the transition to the single-mode regime during tapering. As an application of this fabrication method, we present a micro-looped taper probe for evanescent coupling experiments requiring fine spatial selectivity.

physics.optics↗