Francesco Pagliano

Spontaneous emission control of single quantum dots by electromechanical tuning of a photonic crystal cavity

We demonstrate the control of the spontaneous emission rate of single InAs quantum dots embedded in a double-membrane photonic crystal cavity by the electromechanical tuning of the cavity resonance. Controlling the separation between the two membranes with an electrostatic field, we obtain the real-time spectral alignment of the cavity mode to the excitonic line and we observe an enhancement of the spontaneous emission rate at resonance. The cavity has been tuned over 13 nm without shifting the exciton energies. A spontaneous emission enhancement of ≈4.5 has been achieved with a coupling efficiency of the dot to the mode β≈92%.

Efficient coupling of single photons to ridge-waveguide photonic integrated circuits

We demonstrate the efficient coupling of single photons emitted by single quantum dots (QDs) in a photonic crystal cavity (PhCC) to a ridge waveguide (RWG). Using a single-step lithographic process with an optimized tapering, up to 70% coupling efficiency between the photonic crystal waveguide and the RWG was achieved. The emission enhancement of single QDs inside an in-line PhCC coupled via the RWG to a single-mode fiber was observed. Single-photon funneling rates around 3.5 MHz from a single QD into the RWG were obtained. This result is a step toward the realization of a fully functional quantum photonic integrated circuit.

Fully tuneable, Purcell-enhanced solid-state quantum emitters

We report the full energy control over a semiconductor cavity-emitter system, consisting of single Stark-tunable quantum dots embedded in mechanically reconfigurable photonic crystal membranes. A reversible wavelength tuning of the emitter over 7.5 nm as well as an 8.5 nm mode shift are realized on the same device. Harnessing these two electrical tuning mechanisms, a single exciton transition is brought on resonance with the cavity mode at several wavelengths, demonstrating a ten-fold enhancement of its spontaneous emission. These results open the way to bring several cavity-enhanced emitters mutually into resonance and therefore represent a key step towards scalable quantum photonic circuits featuring multiple sources of indistinguishable single photons.

Deep-subwavelength imaging of both electric and magnetic localized optical fields by plasmonic campanile nanoantenna

Tailoring the electromagnetic field at the nanoscale has led to artificial materials exhibiting fascinating optical properties unavailable in naturally occurring substances. Besides having fundamental implications for classical and quantum optics, nanoscale metamaterials provide a platform for developing disruptive novel technologies, in which a combination of both the electric and magnetic radiation field components at optical frequencies is relevant to engineer the light-matter interaction. Thus, an experimental investigation of the spatial distribution of the photonic states at the nanoscale for both field components is of crucial importance. Here we experimentally demonstrate a concomitant deep-subwavelength near-field imaging of the electric and magnetic intensities of the optical modes localized in a photonic crystal nanocavity. We take advantage of the “campanile tip”, a plasmonic near-field probe that efficiently combines broadband field enhancement with strong far-field to near-field coupling. By exploiting the electric and magnetic polarizability components of the campanile tip along with the perturbation imaging method, we are able to map in a single measurement both the electric and magnetic localized near-field distributions.

Integrated nano-opto-electro-mechanical sensor for spectrometry and nanometrology

Spectrometry is widely used for the characterization of materials, tissues, and gases, and the need for size and cost scaling is driving the development of mini and microspectrometers. While nanophotonic devices provide narrowband filtering that can be used for spectrometry, their practical application has been hampered by the difficulty of integrating tuning and read-out structures. Here, a nano-opto-electro-mechanical system is presented where the three functionalities of transduction, actuation, and detection are integrated, resulting in a high-resolution spectrometer with a micrometer-scale footprint. The system consists of an electromechanically tunable double-membrane photonic crystal cavity with an integrated quantum dot photodiode. Using this structure, we demonstrate a resonance modulation spectroscopy technique that provides subpicometer wavelength resolution. We show its application in the measurement of narrow gas absorption lines and in the interrogation of fiber Bragg gratings. We also explore its operation as displacement-to-photocurrent transducer, demonstrating optomechanical displacement sensing with integrated photocurrent read-out.Fully integratable spectrometers have trade-offs between size and resolution. Here, the authors present a nano-opto-electro-mechanical system where the functionalities of transduction, actuation and detection are fully integrated, resulting in an ultra-compact high-resolution spectrometer with a micrometer-scale footprint.

Nano-opto-electro-mechanical switch based on a four-waveguide directional coupler

Optical switches connect optical circuits, and route optical signals in networks. Nano-electromechanical systems can in principle enable compact and power-effective switches that can be integrated in photonic circuits. We proposed an optical switch based on four coupled waveguides arranged in three-dimensional configuration. The switching operation is controlled by a cantilever displacement of only 55 nm. Simulations show that our proposed device requires a low switching voltage down to 3V and can operate at frequencies in the MHz range. Our results also pave the way towards novel optical components that electromechanically manipulate light in both the horizontal and the vertical direction in photonic circuits.

Electrically driven quantum light emission in electromechanically tuneable photonic crystal cavities

A single quantum dot deterministically coupled to a photonic crystal environment constitutes an indispensable elementary unit to both generate and manipulate single-photons in next-generation quantum photonic circuits. To date, the scaling of the number of these quantum nodes on a fully integrated chip has been prevented by the use of optical pumping strategies that require a bulky off-chip laser along with the lack of methods to control the energies of nano-cavities and emitters. Here, we concurrently overcome these limitations by demonstrating electrical injection of single excitonic lines within a nano-electro-mechanically tuneable photonic crystal cavity. When an electrically driven dot line is brought into resonance with a photonic crystal mode, its emission rate is enhanced. Anti-bunching experiments reveal the quantum nature of these on-demand sources emitting in the telecom range. These results represent an important step forward in the realization of integrated quantum optics experiments featurin...

Fully-tunable, purcell-enhanced on-chip quantum emitters

We report the all-electrical control over cavity-emitter systems, consisting in Stark-tunable quantum dots embedded in mechanically reconfigurable photonic crystal membranes. Purcell-effect from a single dot is demonstrated at distinct wavelengths.

Generalized Fano lineshapes reveal exceptional points in photonic molecules

The optical behavior of coupled systems, in which the breaking of parity and time-reversal symmetry occurs, is drawing increasing attention to address the physics of the exceptional point singularity, i.e., when the real and imaginary parts of the normal-mode eigenfrequencies coincide. At this stage, fascinating phenomena are predicted, including electromagnetic-induced transparency and phase transitions. To experimentally observe the exceptional points, the near-field coupling to waveguide proposed so far was proved to work only in peculiar cases. Here, we extend the interference detection scheme, which lies at the heart of the Fano lineshape, by introducing generalized Fano lineshapes as a signature of the exceptional point occurrence in resonant-scattering experiments. We investigate photonic molecules and necklace states in disordered media by means of a near-field hyperspectral mapping. Generalized Fano profiles in material science could extend the characterization of composite nanoresonators, semiconductor nanostructures, and plasmonic and metamaterial devices.Fano lineshapes are found in many photonic systems where discrete and extended spectra interfere. Here, the authors extend this description and introduce generalized Fano lineshapes to describe the results from hyperspectral mapping around an exceptional point in a coupled-cavity system.

Quantum photonic integrated circuits based on tunable dots and tunable cavities

Quantum photonic integrated circuits hold great potential as a novel class of semiconductor technologies that exploit the evolution of a quantum state of light to manipulate information. Quantum dots encapsulated in photonic crystal structures are promising single-photon sources that can be integrated within these circuits. However, the unavoidable energy mismatch between distant cavities and dots, along with the difficulties in coupling to a waveguide network, has hampered the implementation of circuits manipulating single photons simultaneously generated by remote sources. Here we present a waveguide architecture that combines electromechanical actuation and Stark-tuning to reconfigure the state of distinct cavity-emitter nodes on a chip. The Purcell-enhancement from an electrically controlled exciton coupled to a ridge waveguide is reported. Besides, using this platform, we implement an integrated Hanbury-Twiss and Brown experiment with a source and a splitter on the same chip. These results open new avenues to scale the number of indistinguishable single photons produced on-demand by distinct emitters.