Taofiq Paraiso - Academia.edu (original) (raw)
Papers by Taofiq Paraiso
CLEO 2023
Here we demonstrate a hybrid integrated quantum key distribution chip which combines through edge... more Here we demonstrate a hybrid integrated quantum key distribution chip which combines through edge-coupling an ultra-low-loss SiN interferometer with a high-speed InP phase modulator. This novel devices produces record chip-to-chip secure key rates.
npj Quantum Information, 2019
Quantum key distribution (QKD) has convincingly been proven compatible with real life application... more Quantum key distribution (QKD) has convincingly been proven compatible with real life applications. Its wide-scale deployment in optical networks will benefit from an optical platform that allows miniature devices capable of encoding the necessarily complex signals at high rates and with low power consumption. While photonic integration is the ideal route toward miniaturisation, an efficient route to high-speed encoding of the quantum phase states on chip is still missing. Consequently, current devices rely on bulky and high power demanding phase modulation elements which hinder the sought-after scalability and energy efficiency. Here we exploit a novel approach to high-speed phase encoding and demonstrate a compact, scalable and power efficient integrated quantum transmitter. We encode cryptographic keys on-demand in high repetition rate pulse streams using injection-locking with deterministic phase control at the seed laser. We demonstrate record secure-key-rates under multi-proto...
Advanced Quantum Technologies, 2021
Quantum communications is the art of exchanging and manipulating information beyond the capabilit... more Quantum communications is the art of exchanging and manipulating information beyond the capabilities of our conventional technologies using the laws of quantum mechanics. With applications ranging from quantum computing to cryptographic systems with information-theoretic security, there is strong incentive to introduce quantum communications into many areas of our society. However, an important challenge is to develop viable technologies meeting the stringent requirements of low noise and high coherence for quantum state encoding, of high bit rate and low power for the integration with classical communication networks and of scalable and low-cost production for a practical wide-deployment. This tutorial presents recent advances in laser modulation technologies that have enabled the development of efficient and versatile light sources for quantum communications, with a particular focus on quantum key distribution (QKD). Such approaches have been successfully used to demonstrate several QKD protocols with state-of-the-art performance. The applications and experimental results are reviewed and interpreted in the light of a complete theoretical background, allowing the reader to model and simulate such sources.
Quantum Technology: Driving Commercialisation of an Enabling Science III
Quantum Technologies 2022
Quantum Computing, Communication, and Simulation II, 2022
Optical Interconnects XXII, 2022
We present the optical and mechanical design of a mechanically compliant quasi-two-dimensional ph... more We present the optical and mechanical design of a mechanically compliant quasi-two-dimensional photonic crystal cavity formed from thin-film silicon in which a pair of linear nanoscale slots are used to create two coupled high-Q optical resonances. The optical cavity supermodes, whose frequencies are designed to lie in the 1500 nm wavelength band, are shown to interact strongly with mechanical resonances of the structure whose frequencies range from a few MHz to a few GHz. Depending upon the symmetry of the mechanical modes and the symmetry of the slot sizes, we show that the optomechanical coupling between the optical supermodes can be either linear or quadratic in the mechanical displacement amplitude. Tuning of the nanoscale slot size is also shown to adjust the magnitude and sign of the cavity supermode splitting 2J, enabling near-resonant motional scattering between the two optical supermodes and greatly enhancing the x^2-coupling strength. Specifically, for the fundamental fle...
We demonstrate on-chip quantum random number generation at high data rates using the random phase... more We demonstrate on-chip quantum random number generation at high data rates using the random phases of gain-switched laser pulses. Interference of the gain-switched pulses produced by two independent semiconductor lasers is performed on a photonic integrated circuit (PIC) and the resulting pulse train is received and processed in real-time using homebuilt capture electronics consisting a field programmable gate array (FPGA) and a 10-bit digitizer. Random numbers with low correlation coefficient are shown for pulse clock rates of 1 GHz and data rates of 8 Gbps. The random numbers are also shown to successfully pass all tests within the National Institute for Standards and Technology (NIST) test suite. The system provides genuine random numbers in a compact platform that can be readily integrated into existing quantum cryptographic technology.
Optomechanical crystals [1] are periodic dielectric and elastic materials in which a strong coupl... more Optomechanical crystals [1] are periodic dielectric and elastic materials in which a strong coupling between optical and acoustic waves exists via radiation pressure. Thin film optomechanical crystals, for instance, can be formed in the device layer of wafers such as silicon-on-insulator (SOI), enabling large scale integration of photonic and phononic circuits using conventional microfabrication techniques. In addition to classical photon-phonon microwave signal processing, such circuits have been proposed for quantum information processing tasks as well as a means for realizing synthetic quantum many-body systems [2,3]. Such coupled optomechanical (OM) systems require flexible building blocks that are able to compensate for errors and non-idealities in the fabrication process. In particular, the coupling of arrays of mechanical modes remains difficult due to the current lack of effective techniques for tuning of the mechanics. Here we propose, design, and optimize a suspended silic...
The practical combination of quantum cryptography and classical communications will require conve... more The practical combination of quantum cryptography and classical communications will require convergence of their technologies. In this pivotal time where both fields are transitioning towards photonic integrated architectures, it is essential to develop devices that fully leverage their hardware compatibilities, while still addressing the key issues of cost reduction, miniaturization and infrastructure energetic footprint, essential for future high- bandwidth, low-latency networks. Here, we address these issues by developing an on-chip transmitter consisting of just 3 building blocks but capable of transmitting both quantum encrypted photons and classical multi-level modulation signals. By combining optical injection locking and direct phase modulation we are able to encode pulse trains with multiple levels of differential phase, without the need of high-speed electro-optic modulators and their associated power footprint. We generate return-to-zero differential phase shift keying si...
Optics Express, 2016
We present a silicon optomechanical nanobeam design with a dynamically tunable acoustic mode at 1... more We present a silicon optomechanical nanobeam design with a dynamically tunable acoustic mode at 10.2 GHz. The resonance frequency can be shifted by 90 kHz/V 2 with an on-chip capacitor that was optimized to exert forces up to 1 µN at 10 V operation voltage. Optical resonance frequencies around 190 THz with Q factors up to 2.2 × 10 6 place the structure in the well-resolved sideband regime with vacuum optomechanical coupling rates up to g0/2π = 353 kHz. Tuning can be used, for instance, to overcome variation in the device-to-device acoustic resonance frequency due to fabrication errors, paving the way for optomechanical circuits consisting of arrays of optomechanical cavities.
Superlattices and Microstructures, 2010
We present the optical tomography of the probability density of microcavity polaritons, confined ... more We present the optical tomography of the probability density of microcavity polaritons, confined in three dimensions by cylindrical traps of various sizes. Collecting the photoluminescence emitted by the quasimodes under continuous nonresonant laser excitation, we reconstruct a three dimensional mapping of the photoluminescence, from which we can extract the spatial distribution of the confined states at any energy. We discuss the impact of the confinement shape and size on the probability density patterns.
Physical Review B, 2009
We experimentally investigate the relaxation of spatially confined microcavity polaritons. We mea... more We experimentally investigate the relaxation of spatially confined microcavity polaritons. We measure the time-and energy-resolved photoluminescence under resonant excitation and in the low-density regime. In this way, we have access to the time evolution of the energy distribution of the polariton population. We show that, when one confined level is resonantly excited, after an initial transient, the population of the confined levels is thermally distributed. The reported efficiency of the relaxation process strongly depends on the confinement size. These experimental findings are well reproduced by a theoretical model accounting for the coupling between the confined states and a bath of acoustic phonons. Our results thus suggest that the phonon-mediated relaxation mechanisms are enhanced in the presence of spatial confinement.
Physical Review B, 2006
We demonstrate the spatial confinement of electronic excitations in a solid state system, within ... more We demonstrate the spatial confinement of electronic excitations in a solid state system, within novel artificial structures that can be designed having arbitrary dimensionality and shape. The excitations under study are exciton-polaritons in a planar semiconductor microcavity. They are confined within a micron-sized region through lateral trapping of their photon component. Striking signatures of confined states of lower and upper polaritons are found in angle-resolved light emission spectra, where a discrete energy spectrum and broad angular patterns are present. A theoretical model supports unambiguously our observations.
physica status solidi (c), 2008
We performed studies on microcavity polaritons trapped along the three dimensions of space, under... more We performed studies on microcavity polaritons trapped along the three dimensions of space, under resonant excitation on a confined lower polariton state. We observed various nonlinear behaviors as a function of the pump power, without any apparent loss of the strong-coupling. That may be understood as effects of Coulomb interaction. Indications of bistable behaviors in the system are observed and discussed. G. Nardin et al.: Resonant nonlinear studies of trapped 0D-microcavity polaritons
Nature Communications, 2013
Non-linear interactions in coherent gases are not only at the origin of bright and dark solitons ... more Non-linear interactions in coherent gases are not only at the origin of bright and dark solitons and superfluids; they also give rise to phenomena such as multistability, which hold great promise for the development of advanced photonic and spintronic devices. In particular, spinor multistability in strongly coupled semiconductor microcavities shows that the spin of hundreds of exciton-polaritons can be coherently controlled, opening the route to spin-optronic devices such as ultrafast spin memories, gates or even neuronal communication schemes. Here we demonstrate that switching between the stable spin states of a driven polariton gas can be controlled by ultrafast optical pulses. Although such a long-lived spin memory necessarily relies on strong and anisotropic spinor interactions within the coherent polariton gas, we also highlight the crucial role of non-linear losses and formation of a non-radiative particle reservoir for ultrafast spin switching.
Applied Physics Letters, 2009
Applied Physics Letters, 2017
Reference EPFL-CONF-171966View record in Web of Science Record created on 2011-12-16, modified on... more Reference EPFL-CONF-171966View record in Web of Science Record created on 2011-12-16, modified on 2017-12-03
CLEO 2023
Here we demonstrate a hybrid integrated quantum key distribution chip which combines through edge... more Here we demonstrate a hybrid integrated quantum key distribution chip which combines through edge-coupling an ultra-low-loss SiN interferometer with a high-speed InP phase modulator. This novel devices produces record chip-to-chip secure key rates.
npj Quantum Information, 2019
Quantum key distribution (QKD) has convincingly been proven compatible with real life application... more Quantum key distribution (QKD) has convincingly been proven compatible with real life applications. Its wide-scale deployment in optical networks will benefit from an optical platform that allows miniature devices capable of encoding the necessarily complex signals at high rates and with low power consumption. While photonic integration is the ideal route toward miniaturisation, an efficient route to high-speed encoding of the quantum phase states on chip is still missing. Consequently, current devices rely on bulky and high power demanding phase modulation elements which hinder the sought-after scalability and energy efficiency. Here we exploit a novel approach to high-speed phase encoding and demonstrate a compact, scalable and power efficient integrated quantum transmitter. We encode cryptographic keys on-demand in high repetition rate pulse streams using injection-locking with deterministic phase control at the seed laser. We demonstrate record secure-key-rates under multi-proto...
Advanced Quantum Technologies, 2021
Quantum communications is the art of exchanging and manipulating information beyond the capabilit... more Quantum communications is the art of exchanging and manipulating information beyond the capabilities of our conventional technologies using the laws of quantum mechanics. With applications ranging from quantum computing to cryptographic systems with information-theoretic security, there is strong incentive to introduce quantum communications into many areas of our society. However, an important challenge is to develop viable technologies meeting the stringent requirements of low noise and high coherence for quantum state encoding, of high bit rate and low power for the integration with classical communication networks and of scalable and low-cost production for a practical wide-deployment. This tutorial presents recent advances in laser modulation technologies that have enabled the development of efficient and versatile light sources for quantum communications, with a particular focus on quantum key distribution (QKD). Such approaches have been successfully used to demonstrate several QKD protocols with state-of-the-art performance. The applications and experimental results are reviewed and interpreted in the light of a complete theoretical background, allowing the reader to model and simulate such sources.
Quantum Technology: Driving Commercialisation of an Enabling Science III
Quantum Technologies 2022
Quantum Computing, Communication, and Simulation II, 2022
Optical Interconnects XXII, 2022
We present the optical and mechanical design of a mechanically compliant quasi-two-dimensional ph... more We present the optical and mechanical design of a mechanically compliant quasi-two-dimensional photonic crystal cavity formed from thin-film silicon in which a pair of linear nanoscale slots are used to create two coupled high-Q optical resonances. The optical cavity supermodes, whose frequencies are designed to lie in the 1500 nm wavelength band, are shown to interact strongly with mechanical resonances of the structure whose frequencies range from a few MHz to a few GHz. Depending upon the symmetry of the mechanical modes and the symmetry of the slot sizes, we show that the optomechanical coupling between the optical supermodes can be either linear or quadratic in the mechanical displacement amplitude. Tuning of the nanoscale slot size is also shown to adjust the magnitude and sign of the cavity supermode splitting 2J, enabling near-resonant motional scattering between the two optical supermodes and greatly enhancing the x^2-coupling strength. Specifically, for the fundamental fle...
We demonstrate on-chip quantum random number generation at high data rates using the random phase... more We demonstrate on-chip quantum random number generation at high data rates using the random phases of gain-switched laser pulses. Interference of the gain-switched pulses produced by two independent semiconductor lasers is performed on a photonic integrated circuit (PIC) and the resulting pulse train is received and processed in real-time using homebuilt capture electronics consisting a field programmable gate array (FPGA) and a 10-bit digitizer. Random numbers with low correlation coefficient are shown for pulse clock rates of 1 GHz and data rates of 8 Gbps. The random numbers are also shown to successfully pass all tests within the National Institute for Standards and Technology (NIST) test suite. The system provides genuine random numbers in a compact platform that can be readily integrated into existing quantum cryptographic technology.
Optomechanical crystals [1] are periodic dielectric and elastic materials in which a strong coupl... more Optomechanical crystals [1] are periodic dielectric and elastic materials in which a strong coupling between optical and acoustic waves exists via radiation pressure. Thin film optomechanical crystals, for instance, can be formed in the device layer of wafers such as silicon-on-insulator (SOI), enabling large scale integration of photonic and phononic circuits using conventional microfabrication techniques. In addition to classical photon-phonon microwave signal processing, such circuits have been proposed for quantum information processing tasks as well as a means for realizing synthetic quantum many-body systems [2,3]. Such coupled optomechanical (OM) systems require flexible building blocks that are able to compensate for errors and non-idealities in the fabrication process. In particular, the coupling of arrays of mechanical modes remains difficult due to the current lack of effective techniques for tuning of the mechanics. Here we propose, design, and optimize a suspended silic...
The practical combination of quantum cryptography and classical communications will require conve... more The practical combination of quantum cryptography and classical communications will require convergence of their technologies. In this pivotal time where both fields are transitioning towards photonic integrated architectures, it is essential to develop devices that fully leverage their hardware compatibilities, while still addressing the key issues of cost reduction, miniaturization and infrastructure energetic footprint, essential for future high- bandwidth, low-latency networks. Here, we address these issues by developing an on-chip transmitter consisting of just 3 building blocks but capable of transmitting both quantum encrypted photons and classical multi-level modulation signals. By combining optical injection locking and direct phase modulation we are able to encode pulse trains with multiple levels of differential phase, without the need of high-speed electro-optic modulators and their associated power footprint. We generate return-to-zero differential phase shift keying si...
Optics Express, 2016
We present a silicon optomechanical nanobeam design with a dynamically tunable acoustic mode at 1... more We present a silicon optomechanical nanobeam design with a dynamically tunable acoustic mode at 10.2 GHz. The resonance frequency can be shifted by 90 kHz/V 2 with an on-chip capacitor that was optimized to exert forces up to 1 µN at 10 V operation voltage. Optical resonance frequencies around 190 THz with Q factors up to 2.2 × 10 6 place the structure in the well-resolved sideband regime with vacuum optomechanical coupling rates up to g0/2π = 353 kHz. Tuning can be used, for instance, to overcome variation in the device-to-device acoustic resonance frequency due to fabrication errors, paving the way for optomechanical circuits consisting of arrays of optomechanical cavities.
Superlattices and Microstructures, 2010
We present the optical tomography of the probability density of microcavity polaritons, confined ... more We present the optical tomography of the probability density of microcavity polaritons, confined in three dimensions by cylindrical traps of various sizes. Collecting the photoluminescence emitted by the quasimodes under continuous nonresonant laser excitation, we reconstruct a three dimensional mapping of the photoluminescence, from which we can extract the spatial distribution of the confined states at any energy. We discuss the impact of the confinement shape and size on the probability density patterns.
Physical Review B, 2009
We experimentally investigate the relaxation of spatially confined microcavity polaritons. We mea... more We experimentally investigate the relaxation of spatially confined microcavity polaritons. We measure the time-and energy-resolved photoluminescence under resonant excitation and in the low-density regime. In this way, we have access to the time evolution of the energy distribution of the polariton population. We show that, when one confined level is resonantly excited, after an initial transient, the population of the confined levels is thermally distributed. The reported efficiency of the relaxation process strongly depends on the confinement size. These experimental findings are well reproduced by a theoretical model accounting for the coupling between the confined states and a bath of acoustic phonons. Our results thus suggest that the phonon-mediated relaxation mechanisms are enhanced in the presence of spatial confinement.
Physical Review B, 2006
We demonstrate the spatial confinement of electronic excitations in a solid state system, within ... more We demonstrate the spatial confinement of electronic excitations in a solid state system, within novel artificial structures that can be designed having arbitrary dimensionality and shape. The excitations under study are exciton-polaritons in a planar semiconductor microcavity. They are confined within a micron-sized region through lateral trapping of their photon component. Striking signatures of confined states of lower and upper polaritons are found in angle-resolved light emission spectra, where a discrete energy spectrum and broad angular patterns are present. A theoretical model supports unambiguously our observations.
physica status solidi (c), 2008
We performed studies on microcavity polaritons trapped along the three dimensions of space, under... more We performed studies on microcavity polaritons trapped along the three dimensions of space, under resonant excitation on a confined lower polariton state. We observed various nonlinear behaviors as a function of the pump power, without any apparent loss of the strong-coupling. That may be understood as effects of Coulomb interaction. Indications of bistable behaviors in the system are observed and discussed. G. Nardin et al.: Resonant nonlinear studies of trapped 0D-microcavity polaritons
Nature Communications, 2013
Non-linear interactions in coherent gases are not only at the origin of bright and dark solitons ... more Non-linear interactions in coherent gases are not only at the origin of bright and dark solitons and superfluids; they also give rise to phenomena such as multistability, which hold great promise for the development of advanced photonic and spintronic devices. In particular, spinor multistability in strongly coupled semiconductor microcavities shows that the spin of hundreds of exciton-polaritons can be coherently controlled, opening the route to spin-optronic devices such as ultrafast spin memories, gates or even neuronal communication schemes. Here we demonstrate that switching between the stable spin states of a driven polariton gas can be controlled by ultrafast optical pulses. Although such a long-lived spin memory necessarily relies on strong and anisotropic spinor interactions within the coherent polariton gas, we also highlight the crucial role of non-linear losses and formation of a non-radiative particle reservoir for ultrafast spin switching.
Applied Physics Letters, 2009
Applied Physics Letters, 2017
Reference EPFL-CONF-171966View record in Web of Science Record created on 2011-12-16, modified on... more Reference EPFL-CONF-171966View record in Web of Science Record created on 2011-12-16, modified on 2017-12-03