arXiv subjects

Konstantinos G. Lagoudakis

Publications and source records attributed to Konstantinos G. Lagoudakis.

31 records · Page 2Linked to original sources

arXiv2015

Coherent generation of nonclassical light on chip via detuned photon blockade

The on-chip generation of non-classical states of light is a key-requirement for future optical quantum hardware. In solid-state cavity quantum electrodynamics, such non-classical light can be generated from self-assembled quantum dots strongly coupled to photonic crystal cavities. Their anharmonic strong light-matter interaction results in large optical nonlinearities at the single photon level, where the admission of a single photon into the cavity may enhance (photon-tunnelling) or diminish (photon-blockade) the probability for a second photon to enter the cavity. Here, we demonstrate that detuning the cavity and QD resonances enables the generation of high-purity non-classical light from strongly coupled systems. For specific detunings we show that not only the purity but also the efficiency of single-photon generation increases significantly, making high-quality single-photon generation by photon-blockade possible with current state-of-the-art samples.

cond-mat.mes-hall↗

arXiv2015

Inverse design and demonstration of a compact and broadband on-chip wavelength demultiplexer

Integrated photonic devices are poised to play a key role in a wide variety of applications, ranging from optical interconnects and sensors to quantum computing. However, only a small library of semi-analytically designed devices are currently known. In this paper, we demonstrate the use of an inverse design method that explores the full design space of fabricable devices and allows us to design devices with previously unattainable functionality, higher performance and robustness, and smaller footprints compared to conventional devices. We designed a silicon wavelength demultiplexer that splits $1300~\mathrm{nm}$ and $1550~\mathrm{nm}$ light from an input waveguide into two output waveguides, and fabricated and characterized several devices. The devices display low insertion loss $\left(2 - 4~\mathrm{dB}\right)$, high contrast $\left(12 - 17~\mathrm{dB}\right)$, and wide bandwidths $\left(\sim 100~\mathrm{nm} \right)$. The device footprint is $2.8 \times 2.8 ~\mathrm{μm}$, making this the smallest dielectric wavelength splitter to date.

physics.optics↗

arXiv2014

Visible Photoluminescence from Cubic (3C) Silicon Carbide Microdisks Coupled to High Quality Whispering Gallery Modes

We present the design, fabrication and characterization of cubic (3C) silicon carbide microdisk resonators with high quality factor modes at visible and near infrared wavelengths (600 - 950 nm). Whispering gallery modes with quality factors as high as 2,300 and corresponding mode volumes V ~ 2 (λ/n)^3 are measured using laser scanning confocal microscopy at room temperature. We obtain excellent correspondence between transverse-magnetic (TM) and transverse-electric (TE) polarized resonances simulated using Finite Difference Time Domain (FDTD) method and those observed in experiment. These structures based on ensembles of optically active impurities in 3C-SiC resonators could play an important role in diverse applications of nonlinear and quantum photonics, including low power optical switching and quantum memories.

physics.optics↗

arXiv2014

Inverse design and implementation of a wavelength demultiplexing grating coupler

Nanophotonics has emerged as a powerful tool for manipulating light on chips. Almost all of today's devices, however, have been designed using slow and ineffective brute-force search methods, leading in many cases to limited device performance. In this article, we provide a complete demonstration of our recently proposed inverse design technique, wherein the user specifies design constraints in the form of target fields rather than a dielectric constant profile, and in particular we use this method to demonstrate a new demultiplexing grating. The novel grating, which has not been developed using conventional techniques, accepts a vertical-incident Gaussian beam from a free-space and separates O-band $(1300\mathrm{nm})$ and C-band $(1550\mathrm{nm})$ light into separate waveguides. This inverse design concept is simple and extendable to a broad class of highly compact devices including frequency splitters, mode converters, and spatial mode multiplexers.

physics.optics↗

arXiv2014

Hole Spin Pumping and Re-pumping in a p-type δ-doped InAs Quantum Dot

We have grown high quality p-type δ-doped InAs quantum dots and have demonstrated coherent spin pumping and repumping of a hole spin in a positively charged quantum dot by means of a single-laser driving scheme under a high magnetic field in the Voigt configuration. Modeling of our system shows excellent qualitative agreement with the experimental findings and further explores the performance of the single-laser scheme for spin pumping and re-pumping.

quant-ph↗

arXiv2014

Non-classical higher-order photon correlations with a quantum dot strongly coupled to a photonic-crystal nanocavity

We use the third- and fourth-order autocorrelation functions $g^{(3)}(τ_1,τ_2)$ and $g^{(4)}(τ_1,τ_2, τ_3)$ to detect the non-classical character of the light transmitted through a photonic-crystal nanocavity containing a strongly-coupled quantum dot probed with a train of coherent light pulses. We contrast the value of $g^{(3)}(0, 0)$ with the conventionally used $g^{(2)}(0)$ and demonstrate that in addition to being necessary for detecting two-photon states emitted by a low-intensity source, $g^{(3)}$ provides a more clear indication of the non-classical character of a light source. We also present preliminary data that demonstrates bunching in the fourth-order autocorrelation function $g^{(4)}(τ_1,τ_2, τ_3)$ as the first step toward detecting three-photon states.

cond-mat.mes-hall↗

arXiv2014

Second harmonic generation in GaAs photonic crystal cavities in (111)B and (001) crystal orientations

We demonstrate second harmonic generation in photonic crystal cavities in (001) and (111)B oriented GaAs. The fundamental resonance is at 1800 nm, leading to second harmonic below the GaAs bandgap. Below-bandgap operation minimizes absorption of the second harmonic and two photon absorption of the pump. Photonic crystal cavities were fabricated in both orientations at various in-plane rotations of the GaAs substrate. The rotation dependence and farfield patterns of the second harmonic match simulation. We observe similar maximum efficiencies of 1.2 %/W in (001) and (111)B oriented GaAs.

physics.optics↗

arXiv2014

Photo-oxidative tuning of individual and coupled GaAs photonic crystal cavities

We demonstrate a new photo-induced oxidation technique for tuning GaAs photonic crystal cavities using a $390~\mathrm{nm}$ pulsed laser with an average power of $10~\mathrm{μW}$. The laser oxidizes a small $\left(\sim 500~\mathrm{nm}\right)$ diameter spot, reducing the local index of refraction and blueshifting the cavity. The tuning progress can be actively monitored in real time. We also demonstrate tuning an individual cavity within a pair of proximity-coupled cavities, showing that this method can be used to correct undesired frequency shifts caused by fabrication imperfections in cavity arrays.

physics.optics↗

arXiv2013

Deterministically Charged Quantum Dots in Photonic Crystal Nanoresonators for Efficient Spin-Photon Interfaces

We demonstrate a novel method for deterministic charging of InAs quantum dots embedded in photonic crystal nanoresonators using a unique vertical p-n-i-n junction within the photonic crystal membrane. Charging is confirmed by the observation of Zeeman splitting for magnetic fields applied in the Voigt configuration. Spectrally resolved photoluminescence measurements are complemented by polarization resolved studies that show the precise structure of the Zeeman quadruplet. Integration of quantum dots in nanoresonators strongly enhances far-field collection efficiency and paves the way for the exploitation of enhanced spin-photon interactions for fabrication of efficient quantum nodes in a scalable solid state platform.

cond-mat.mes-hall↗

arXiv2013

Coupling an electron spin in a semiconductor quantum dot to an optical nano-cavity

We propose a scheme to efficiently couple a single quantum dot electron spin to an optical nano-cavity, which enables us to simultaneously benefit from a cavity as an efficient photonic interface, as well as to perform high fidelity (nearly 100%) spin initialization and manipulation achievable in bulk semiconductors. Moreover, the presence of the cavity speeds up the spin initialization process beyond GHz.

quant-ph↗

arXiv2012

Spontaneous symmetry breaking in a polariton and photon laser

We report on the simultaneous observation of spontaneous symmetry breaking and long-range spatial coherence both in the strong and the weak-coupling regime in a semiconductor microcavity. Under pulsed excitation, the formation of a stochastic order parameter is observed in polariton and photon lasing regimes. Single-shot measurements of the Stokes vector of the emission exhibit the buildup of stochastic polarization. Below threshold, the polarization noise does not exceed 10%, while above threshold we observe a total polarization of up to 50% after each excitation pulse, while the polarization averaged over the ensemble of pulses remains nearly zero. In both polariton and photon lasing regimes, the stochastic polarization buildup is accompanied by the buildup of spatial coherence. We find that the Landau criterion of spontaneous symmetry breaking and Penrose-Onsager criterion of long-range order for Bose-Einstein condensation are met in both polariton and photon lasing regimes.

cond-mat.mes-hall↗

arXiv2010

Selective photoexcitation of exciton-polariton vortices

We resonantly excite exciton-polariton states confined in cylindrical traps. Using a homodyne detection setup, we are able to image the phase and amplitude of the confined polariton states. We evidence the excitation of vortex states, carrying an integer angular orbital momentum m, analogous to the transverse TEM01* "donut" mode of cylindrically symmetric optical resonators. Tuning the excitation conditions allows us to select the charge of the vortex. In this way, the injection of singly charged (m = 1 & m = -1) and doubly charged (m = 2) polariton vortices is shown. This work demonstrates the potential of in-plane confinement coupled with selective excitation for the topological tailoring of polariton wavefunctions.

cond-mat.quant-gas↗

arXiv2007

Superconducting nanowire photon number resolving detector at telecom wavelength

The optical-to-electrical conversion, which is the basis of optical detectors, can be linear or nonlinear. When high sensitivities are needed single-photon detectors (SPDs) are used, which operate in a strongly nonlinear mode, their response being independent of the photon number. Nevertheless, photon-number resolving (PNR) detectors are needed, particularly in quantum optics, where n-photon states are routinely produced. In quantum communication, the PNR functionality is key to many protocols for establishing, swapping and measuring entanglement, and can be used to detect photon-number-splitting attacks. A linear detector with single-photon sensitivity can also be used for measuring a temporal waveform at extremely low light levels, e.g. in long-distance optical communications, fluorescence spectroscopy, optical time-domain reflectometry. We demonstrate here a PNR detector based on parallel superconducting nanowires and capable of counting up to 4 photons at telecommunication wavelengths, with ultralow dark count rate and high counting frequency.

physics.optics↗