Tunable Generation of Spatial Entanglement in Nonlinear Waveguide Arrays.

Harnessing high-dimensional entangled states of light presents a frontier for advancing quantum information technologies, from fundamental tests of quantum mechanics to enhanced computation and communication protocols. In this context, the spatial degree of freedom stands out as particularly suited for on-chip integration. But while traditional demonstrations produce and manipulate path-entangled states sequentially with discrete optical elements, continuously coupled nonlinear waveguide systems offer a promising alternative where photons can be generated and interfere along the entire propagation length, unveiling novel capabilities within a reduced footprint.

Approaching Maximal Precision of Hong-Ou-Mandel Interferometry with Nonperfect Visibility.

In quantum mechanics, the precision achieved in parameter estimation using a quantum state as a probe is determined by the measurement strategy employed. The quantum limit of precision is bounded by a value set by the state and its dynamics. Theoretical results have revealed that in interference measurements with two possible outcomes, this limit can be reached under ideal conditions of perfect visibility and zero losses.

Author Correction: Scalable high-precision tuning of photonic resonators by resonant cavity-enhanced photoelectrochemical etching.

The original version of this Article omitted the fourth author, Sara Ducci from Matériaux et Phénomènes Quantiques, Université Paris Diderot, CNRS UMR 7162, Sorbonne Paris-Cité, 10 rue Alice Domon et Léonie Duquet, Paris 75013, France. This mistake has been corrected in both the HTML and PDF versions of the Article.

Semiconductor devices for entangled photon pair generation: a review.

Entanglement is one of the most fascinating properties of quantum mechanical systems; when two particles are entangled the measurement of the properties of one of the two allows the properties of the other to be instantaneously known, whatever the distance separating them. In parallel with fundamental research on the foundations of quantum mechanics performed on complex experimental set-ups, we assist today with bourgeoning of quantum information technologies bound to exploit entanglement for a large variety of applications such as secure communications, metrology and computation. Among the different physical systems under investigation, those involving photonic components are likely to play a central role and in this context semiconductor materials exhibit a huge potential in terms of integration of several quantum components in miniature chips.

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.

High-frequency nano-optomechanical disk resonators in liquids.

Nano- and micromechanical resonators are the subject of research that aims to develop ultrasensitive mass sensors for spectrometry, chemical analysis and biomedical diagnosis. Unfortunately, their merits generally diminish in liquids because of an increased dissipation. The development of faster and lighter miniaturized devices would enable improved performances, provided the dissipation was controlled and novel techniques were available to drive and readout their minute displacement.

AlGaAs guided-wave second-harmonic generation at 2.23 μm from a quantum cascade laser.

We demonstrate the frequency doubling of a quantum cascade laser in a multilayered, partially oxidized GaAs/AlOx waveguide. Using the waveguide width to fulfill the phase-matching condition, the second harmonic is generated in the wavelength range between 2.2 and 2.

Second-harmonic generation in AlGaAs microdisks in the telecom range.

We report on second-harmonic generation in whispering-gallery-mode AlGaAs microcavities suspended on a GaAs pedestal. Frequency doubling of a 1.58 μm pump is observed with 7×10(-4)   W(-1) conversion efficiency.

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 stress 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 gom and g(0) reaching respectively 3 THz/nm and 4 MHz.

Electrically injected photon-pair source at room temperature.

One of the main challenges for future quantum information technologies is the miniaturization and integration of high performance components in a single chip. In this context, electrically driven sources of nonclassical 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 wavelengths.

Direct measurement of the biphoton Wigner function through two-photon interference.

The Hong-Ou-Mandel (HOM) experiment was a benchmark in quantum optics, evidencing the non-classical nature of photon pairs, later generalized to quantum systems with either bosonic or fermionic statistics. We show that a simple modification in the well-known and widely used HOM experiment provides the direct measurement of the Wigner function. We apply our results to one of the most reliable quantum systems, consisting of biphotons generated by parametric down conversion.

Tunable quantum dot parametric source.

We report on the modeling of an electrically pumped nonlinear source for spontaneous parametric down-conversion in an AlGaAs single-sided Bragg waveguide. Laser emission from InAs quantum dots embedded in the waveguide core is designed to excite a Bragg pump mode at 950 nm. This mode is phase matched with two cross-polarized total-internal-reflection fundamental signal and idler modes around 1900 nm.

AlGaAs microdisk cavities for second-harmonic generation.

We report on the design, the fabrication, and the optical characterization of AlGaAs microdisks suspended on a GaAs pedestal, conceived for second-harmonic generation with a pump in the third telecom window. We discuss the results concerning the linear characterization of whispering gallery modes at fundamental and second-harmonic wavelengths, an essential step prior to the investigation of quasi-phase-matched processes in this type of microcavity.

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

We demonstrate the direct generation of polarization-entangled photon pairs at room temperature and telecom wavelength in an 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.

Optical instability and self-pulsing in silicon nitride whispering gallery resonators.

We report time domain observations of optical instability in high Q silicon nitride whispering gallery disk resonators. At low laser power the transmitted optical power through the disk looks chaotic. At higher power, the optical output settles into a stable self-pulsing regime with periodicity ranging from hundreds of milliseconds to hundreds of seconds.

Tuning of a nonlinear THz emitter.

We numerically study a passive THz source based on difference frequency generation between modes sustained by cylindrical AlGaAs microcavities. We show that ring-like structures are advantageous in that they provide additional degrees of freedom for tuning the nonlinear process and for maximizing the nonlinear overlap integral and conversion efficiency.

Nearly-degenerate three-wave mixing at 1.55 μm in oxidized AlGaAs waveguides.

We report on continuous-wave sum and difference frequency generation in selectively oxidized AlGaAs waveguides designed for degenerate spontaneous parametric down-conversion at 1.55 μm. Sum frequency generation with two pumps around this wavelength is observed with a conversion efficiency η = 1080%W-1cm-2.

Large second-harmonic generation at 1.55 μmin oxidized AlGaAs waveguides.

We report on CW second-harmonic generation in selectively oxidized AlGaAs multilayer waveguides. Frequency doubling of a 1.55 μm pump is observed with 2.

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 subwavelength scale interaction volume. We observe a giant optomechanical coupling rate up to 100 GHz/nm involving picogram mass mechanical modes with a frequency between 100 MHz and 1 GHz.

Two-photon interference with a semiconductor integrated source at room temperature.

We experimentally demonstrate an integrated semiconductor ridge microcavity source of counterpropagating twin photons at room temperature in the telecom range. Based on type II parametric down conversion with a counterpropagating phase-matching, pump photons generate photon pairs with an efficiency of about 10(-11) and a spectral linewidth of 0.3 nm for a 1 mm long sample.

Semiconductor waveguide source of counterpropagating twin photons.

We experimentally demonstrate an integrated semiconductor source of counterpropagating twin photons in the telecom range. A pump beam impinging on top of an AlGaAs waveguide generates parametrically two counterpropagating, orthogonally polarized signal/idler guided modes. A 2 mm long waveguide emits at room temperature one average photon pair per pump pulse, with a spectral linewidth of 0.

Tailoring the profile and interactions of optical localized structures.

We experimentally demonstrate the broad tunability of the main features of optical localized structures (LS's) in a nonlinear interferometer. By discussing how a single LS depends on the system spatial frequency bandwidth, we show that a modification of its tail leads to the possibility of tuning the interactions between LS pairs, and thus the equilibrium distances at which LS bound states form. This is in agreement with a general theoretical model describing weak interactions of LS in nonlinear dissipative systems.