arXiv subjects

A. Harouri

Publications and source records attributed to A. Harouri.

At least 19 recordsLinked to original sources

arXiv2024

A deterministic and efficient source of frequency-polarization hyper-encoded photonic qubits

The frequency or color of photons is an attractive degree of freedom to encode and distribute the quantum information over long distances. However, the generation of frequency-encoded photonic qubits has so far relied on probabilistic non-linear single-photon sources and inefficient gates. Here, we demonstrate the deterministic generation of photonic qubits hyper-encoded in frequency and polarization based on a semiconductor quantum dot in a cavity. We exploit the double dipole structure of a neutral exciton and demonstrate the generation of any quantum superposition in amplitude and phase, controlled by the polarization of the pump laser pulse. The source generates frequency-polarization single-photon qubits at a rate of 4 MHz corresponding to a generation probability at the first lens of 28 $\pm$ 2%, with a photon number purity > 98%. The photons show an indistinguishability > 91% for each dipole and 88% for a balanced quantum superposition of both. The density matrix of the hyper-encoded photonic state is measured by time-resolved polarization tomography, evidencing a fidelity to the target state of 94 $\pm$ 8% and concurrence of 77 $\pm$ 2%, here limited by frequency overlap in our device. Our approach brings the advantages of quantum dot sources to the field of quantum information processing based on frequency encoding.

quant-ph↗

arXiv2024

Interference of ultrahigh frequency acoustic phonons from distant quasi-continuous sources

The generation of propagating acoustic waves is essential for telecommunication applications, quantum technologies, and sensing. Up to now, the electrical generation has been at the core of most implementations, but is technologically limited to a few gigahertz. Overcoming this frequency limit holds the prospect of faster modulators, quantum acoustics at higher working temperatures, nanoacoustic sensing from smaller volumes. Alternatively, the optical excitation of acoustic resonators has unlocked frequencies up to 1 THz, but in most cases, the acoustic energy cannot be efficiently extracted from the resonator into a propagating wave. Here, we demonstrate a quasi-continuous and coherent source of 20 GHz acoustic phonons, based on a ridge waveguide, structured in the vertical direction as a high-Q acousto-optic resonator. The high frequency phonons propagate up to 20 $\mu$m away from the source, with a decay rate of $\sim$1.14 dB/$\mu$m. We demonstrate the coherence between acoustic phonons generated from two distant sources through spatio-temporal interference. This concept could be scaled up to a larger number of sources, which enable a new generation of optically programmed, reconfigurable nanoacoustic devices and applications.

cond-mat.mes-hall↗

arXiv2024

Quantum interferences and gates with emitter-based coherent photon sources

Quantum emitters such as quantum dots, defects in diamond or in silicon have emerged as efficient single photon sources that are progressively exploited in quantum technologies. In 2019, it was shown that the emitted single photon states often include coherence with the vacuum component. Here we investigate how such photon-number coherence alters quantum interference experiments that are routinely implemented both for characterising or exploiting the generated photons. We show that it strongly modifies intensity correlation measurements in a Hong-Ou-Mandel experiment and leads to errors in indistinguishability estimations. It also results in additional entanglement when performing partial measurements. We illustrate the impact on quantum protocols by evidencing modifications in heralding efficiency and fidelity of two-qubit gates.

quant-ph↗

arXiv2022

High-rate entanglement between a semiconductor spin and indistinguishable photons

Photonic graph states, quantum light states where multiple photons are mutually entangled, are key resources for optical quantum technologies. They are notably at the core of error-corrected measurement-based optical quantum computing and all-optical quantum networks. In the discrete variable framework, these applications require high efficiency generation of cluster-states whose nodes are indistinguishable photons. Such photonic cluster states can be generated with heralded single photon sources and probabilistic quantum gates, yet with challenging efficiency and scalability. Spin-photon entanglement has been proposed to deterministically generate linear cluster states. First demonstrations have been obtained with semiconductor spins achieving high photon indistinguishablity, and most recently with atomic systems at high collection efficiency and record length. Here we report on the efficient generation of three partite cluster states made of one semiconductor spin and two indistinguishable photons. We harness a semiconductor quantum dot inserted in an optical cavity for efficient photon collection and electrically controlled for high indistinguishability. We demonstrate two and three particle entanglement with fidelities of 80 % and 63 % respectively, with photon indistinguishability of 88%. The spin-photon and spin-photon-photon entanglement rates exceed by three and two orders of magnitude respectively the previous state of the art. Our system and experimental scheme, a monolithic solid-state device controlled with a resource efficient simple experimental configuration, are very promising for future scalable applications.

quant-ph↗

arXiv2022

Experimental analysis of energy transfers between a quantum emitter and light fields

Energy transfer between quantum systems can either be achieved through an effective unitary interaction or through the generation of entanglement. This observation defines two types of energy exchange: unitary and correlation energy. Here we propose and implement experimental protocols to access these energy transfers in interactions between a quantum emitter and light fields. Upon spontaneous emission, we measure the unitary energy transfer from the emitter to the optical field and show that it never exceeds half of the total energy and is reduced when introducing decoherence. We then study the interference of the emitted field and a laser field at a beam splitter and show that the energy transfers quantitatively depend on the quantum purity of the emitted field.

quant-ph↗

arXiv2021

Optically defined cavities in driven-dissipative photonic lattices

The engineering of localised modes in photonic structures is one of the main targets of modern photonics. An efficient strategy to design these modes is to use the interplay of constructive and destructive interference in periodic photonic lattices. This mechanism is at the origin of defect modes in photonic bandgaps, bound states in the continuum and compact localised states in flat bands. Here we show that in lattices of lossy resonators, the addition of external optical drives with controlled phase enlarges the possibilities of manipulating interference effects and allows designing novel types of localised modes. Using a honeycomb lattice of coupled micropillars resonantly driven with several laser spots at energies within its photonic bands we demonstrate the localisation of light in at-will geometries down to a single site. These localised modes can be seen as fully reconfigurable optical cavities with the potentiality of enhancing nonlinear effects and of controlling light-matter interactions with single site resolution.

physics.optics↗

arXiv2021

Three-dimensional electrical control of the excitonic fine structure for a quantum dot in a cavity

The excitonic fine structure plays a key role for the quantum light generated by semiconductor quantum dots, both for entangled photon pairs and single photons. Controlling the excitonic fine structure has been demonstrated using electric, magnetic, or strain fields, but not for quantum dots in optical cavities, a key requirement to obtain high source efficiency and near-unity photon indistinguishability. Here, we demonstrate the control of the fine structure splitting for quantum dots embedded in micropillar cavities. We propose a scheme based on remote electrical contacts connected to the pillar cavity through narrow ridges. Numerical simulations show that such a geometry allows for a three-dimensional control of the electrical field. We experimentally demonstrate tuning and reproducible canceling of the fine structure, a crucial step for the reproducibility of quantum light source technology.

quant-ph↗

arXiv2021

Bright Polarized Single-Photon Source Based on a Linear Dipole

Semiconductor quantum dots in cavities are promising single-photon sources. Here, we present a path to deterministic operation, by harnessing the intrinsic linear dipole in a neutral quantum dot via phonon-assisted excitation. This enables emission of fully polarized single photons, with a measured degree of linear polarization up to 0.994 $\pm$ 0.007, and high population inversion -- 85\% as high as resonant excitation. We demonstrate a single-photon source with a polarized first lens brightness of 0.50 $\pm $ 0.01, a single-photon purity of 0.954 $\pm$ 0.001 and single-photon indistinguishability of 0.909 $\pm$ 0.004.

quant-ph↗

arXiv2021

Chiral emission induced by optical Zeeman effect in polariton micropillars

The low sensitivity of photons to external magnetic fields is one of the major challenges for the engineering of photonic lattices with broken time-reversal symmetry. Here we show that time-reversal symmetry can be broken for microcavity polaritons in the absence of any external magnetic field thanks to polarization dependent polariton interactions. Circularly polarized excitation of carriers in a micropillar induces a Zeeman-like energy splitting between polaritons of opposite polarizations. In combination with optical spin-orbit coupling inherent to semiconductor microstructures, the interaction induced Zeeman splitting results in emission of vortical beams with a well-defined chirality. Our experimental findings can be extended to lattices of coupled micropillars opening the possibility of controling optically the topological properties of polariton Chern insulators.

cond-mat.mes-hall↗

arXiv2021

Photon-number entanglement generated by sequential excitation of a two-level atom

Entanglement and spontaneous emission are fundamental quantum phenomena that drive many applications of quantum physics. During the spontaneous emission of light from an excited two-level atom, the atom briefly becomes entangled with the photonic field. Here, we show that this natural process can be used to produce photon-number entangled states of light distributed in time. By exciting a quantum dot -- an artificial two-level atom -- with two sequential $\pi$ pulses, we generate a photon-number Bell state. We characterise this state using time-resolved intensity and phase correlation measurements. Furthermore, we theoretically show that applying longer sequences of pulses to a two-level atom can produce a series of multi-temporal mode entangled states with properties intrinsically related to the Fibonacci sequence. Our results on photon-number entanglement can be further exploited to generate new states of quantum light with applications in quantum technologies.

quant-ph↗

arXiv2021

Direct observation of photonic Landau levels and helical edge states in strained honeycomb lattices

We report the realization of a synthetic magnetic field for photons and polaritons in a honeycomb lattice of coupled semiconductor micropillars. A strong synthetic field is induced in both the s and p orbital bands by engineering a uniaxial hopping gradient in the lattice, giving rise to the formation of Landau levels at the Dirac points. We provide direct evidence of the sublattice symmetry breaking of the lowest-order Landau level wavefunction, a distinctive feature of synthetic magnetic fields. Our realization implements helical edge states in the gap between n=0 and n=1 Landau levels, experimentally demonstrating a novel way of engineering propagating edge states in photonic lattices. In light of recent advances in the enhancement of polariton-polariton nonlinearities, the Landau levels reported here are promising for the study of the interplay between pseudomagnetism and interactions in a photonic system.

cond-mat.mes-hall↗

arXiv2021

Topological gap solitons in a 1D non-Hermitian lattice

Nonlinear topological photonics is an emerging field aiming at extending the fascinating properties of topological states to the realm where interactions between the system constituents cannot be neglected. Interactions can indeed trigger topological phase transitions, induce symmetry protection and robustness properties for the many-body system. Moreover when coupling to the environment via drive and dissipation is also considered, novel collective phenomena are expected to emerge. Here, we report the nonlinear response of a polariton lattice implementing a non-Hermitian version of the Su-Schrieffer-Heeger model. We trigger the formation of solitons in the topological gap of the band structure, and show that these solitons demonstrate robust nonlinear properties with respect to defects, because of the underlying sub-lattice symmetry. Leveraging on the system non-Hermiticity, we engineer the drive phase pattern and unveil bulk solitons that have no counterpart in conservative systems. They are localized on a single sub-lattice with a spatial profile alike a topological edge state. Our results demonstrate a tool to stabilize the nonlinear response of driven dissipative topological systems, which may constitute a powerful resource for nonlinear topological photonics.

cond-mat.mes-hall↗

arXiv2020

Semi-Dirac Transport and Anisotropic Localization in Polariton Honeycomb Lattices

Compression dramatically changes the transport and localization properties of graphene. This is intimately related to the change of symmetry of the Dirac cone when the particle hopping is different along different directions of the lattice. In particular, for a critical compression, a semi-Dirac cone is formed with massless and massive dispersions along perpendicular directions. Here we show direct evidence of the highly anisotropic transport of polaritons in a honeycomb lattice of coupled micropillars implementing a semi-Dirac cone. If we optically induce a vacancy-like defect in the lattice, we observe an anisotropically localized polariton distribution in a single sublattice, a consequence of the semi-Dirac dispersion. Our work opens up new horizons for the study of transport and localization in lattices with chiral symmetry and exotic Dirac dispersions.

cond-mat.mes-hall↗

arXiv2020

Fiber-integrated microcavities for efficient generation of coherent acoustic phonons

Coherent phonon generation by optical pump-probe experiments has enabled the study of acoustic properties at the nanoscale in planar heterostructures, plasmonic resonators, micropillars and nanowires. Focalizing both pump and probe on the same spot of the sample is a critical part of pump-probe experiments. This is particularly relevant in the case of small objects. The main practical challenges for the actual implementation of this technique are: stability of the spatio-temporal overlap, reproducibility of the focalization and optical mode matching conditions. In this work, we solve these three challenges for the case of planar and micropillar optophononic cavities. We integrate the studied samples to single mode fibers lifting the need for focusing optics to excite and detect coherent acoustic phonons. The resulting excellent reflectivity contrast of at least 66% achieved in our samples allows us to observe stable coherent phonon signals over at least a full day and signals at extremely low excitation powers of 1uW. The monolithic sample structure is transportable and could provide a means to perform reproducible plug-and-play experiments.

physics.optics↗

arXiv2020

Measuring topological invariants in polaritonic graphene

Topological materials rely on engineering global properties of their bulk energy bands called topological invariants. These invariants, usually defined over the entire Brillouin zone, are related to the existence of protected edge states. However, for an important class of Hamiltonians corresponding to 2D lattices with time-reversal and chiral symmetry (e.g. graphene), the existence of edge states is linked to invariants that are not defined over the full 2D Brillouin zone, but on reduced 1D sub-spaces. Here, we demonstrate a novel scheme based on a combined real- and momentum-space measurement to directly access these 1D topological invariants in lattices of semiconductor microcavities confining exciton-polaritons. We extract these invariants in arrays emulating the physics of regular and critically compressed graphene sucht that Dirac cones have merged. Our scheme provides a direct evidence of the bulk-edge correspondence in these systems, and opens the door to the exploration of more complex topological effects, for example involving disorder and interactions.

cond-mat.mes-hall↗

arXiv2020

Hong-Ou-Mandel Interference with Imperfect Single Photon Sources

Hong-Ou-Mandel interference is a cornerstone of optical quantum technologies. We explore both theoretically and experimentally how the nature of unwanted multi-photon components of single photon sources affect the interference visibility. We apply our approach to quantum dot single photon sources in order to access the mean wavepacket overlap of the single-photon component - an important metric to understand the limitations of current sources. We find that the impact of multi-photon events has thus far been underestimated, and that the effect of pure dephasing is even milder than previously expected.

quant-ph↗

arXiv2020

Deterministic assembly of a charged quantum dot-micropillar cavity device

Developing future quantum communication may rely on the ability to engineer cavity-mediated interactions between photons and solid-state artificial atoms, in a deterministic way. Here, we report a set of technological and experimental developments for the deterministic coupling between the optical mode of a micropillar cavity and a quantum dot trion transition. We first identify a charged transition through in-plane magnetic field spectroscopy, and then tune the optical cavity mode to its energy via in-situ lithography. In addition, we design an asymmetric tunneling barrier to allow the optical trapping of the charge, assisted by a quasi-resonant pumping scheme, in order to control its occupation probability. We evaluate the generation of a positively-charged quantum dot through second order auto-correlation measurements of its resonance fluorescence, and the quality of light-matter interaction for these spin-photon interfaces is assessed by measuring the performance of the device as a single-photon source.

quant-ph↗

arXiv2020

Sequential generation of linear cluster states from a single photon emitter

Light states composed of multiple entangled photons - such as cluster states - are essential for developing and scaling-up quantum computing networks. Photonic cluster states with discrete variables can be obtained from single-photon sources and entangling gates, but so far this has only been done with probabilistic sources constrained to intrinsically-low efficiencies, and an increasing hardware overhead. Here, we report the resource-efficient generation of polarization-encoded, individually-addressable, photons in linear cluster states occupying a single spatial mode. We employ a single entangling-gate in a fiber loop configuration to sequentially entangle an ever-growing stream of photons originating from the currently most efficient single-photon source technology - a semiconductor quantum dot. With this apparatus, we demonstrate the generation of linear cluster states up to four photons in a single-mode fiber. The reported architecture can be programmed to generate linear-cluster states of any number of photons with record scaling ratios, potentially enabling practical implementation of photonic quantum computing schemes.

quant-ph↗