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B. Piętka

Publications and source records attributed to B. Piętka.

15 recordsLinked to original sources

Quantum and classical processing with photonic quantum machine learning

Artificial intelligence and machine learning have been widely adopted both in the industry and in everyday life, but at the cost of high compute demands. Recent studies show that implementing machine learning in physical systems in the deep quantum regime could not only lead to faster information processing, but also to perform tasks that are out of reach for classical systems. Here, we report a quantum reservoir processing device capable of performing both quantum and classical machine learning tasks. The implementation is realized with a programmable silicon chip excited with single photons, a highly scalable and adaptable photonics technology. We successfully implement a variety of quantum tasks, including quantum state tomography and measurement of entanglement via negativity. Moreover, we implement a method of mitigation of experimental imperfections which results in a significant improvement in accuracy in comparison to the same system operating in the classical regime. Our results demonstrate a method to overcome a crucial bottleneck of quantum technologies by providing a practical way of probing quantum states.

quant-ph

Emission enhanced exciton-polariton condensates with optical feedback

Optical feedback is a well-known method of controlling laser dynamics, which has been widely studied in photonic systems to induce complex behaviors such as chaos or enhanced coherence. However, its application to systems in the strong light-matter coupling regime remains unexplored. In this work, we introduce a delayed optical feedback loop into a nonresonantly pumped polariton condensate. By feeding part of the emission back into the cavity to seed the next condensate, we observe a strong increase in the output intensity, up to 110%. We explain this effect using a classical rate equation model for the condensate coupled to excitonic reservoirs. Our results evidence that polariton condensates can respond strongly to optical feedback, congruent with well known polariton amplification techniques using resonant pump-probe setups. Our method opens new possibilities for using polariton feedback to connect multiple condensates and can be an essential step toward neuromorphic computing based on recurrent signaling in photonic systems.

physics.optics

Electrical switching of a chiral lasing from polariton condensate in a Rashba-Dresselhaus regime

Efficient optical classical and quantum information processing imposes on light novel requirements: chirality with low threshold non-linearities. In this work we demonstrate a chiral lasing from an optical modes due to emerging photonic Rashba-Dresselhaus spin-orbit coupling (SOC). For this purpose we developed a new electrically tunable device based on an optical cavity filled with birefringent liquid crystal (LC) and perovskite crystals. Our novel method for the growth of single crystals of CsPbBr$_3$ inorganic perovskite in polymer templates allows us to reach a strong light-matter coupling regime between perovskite excitons and cavity modes, and induce polariton condensation. The sensitivity of the LC to external electric fields lets us to tune the condensate energy in situ and induce synthetic SOC. This shapes the condensate between a single linearly polarized or two circularly polarized separated in momentum, emitting coherent light. The difference in the condensation thresholds between the two SOC regimes can be used to switch on and off the chiral condensate emission with a voltage.

physics.optics

Spin polarization of exciton-polariton condensate in a photonic synthetic effective magnetic field

We investigate the spin polarization of localized exciton-polariton condensates. We demonstrate the presence of an effective magnetic field leading to the formation of elliptically polarized condensates. We show that this synthetic field has an entirely photonic origin, which we believe is unique for the CdTe-based microcavities. Moreover, the degree of spin polarization of localized polariton condensates in samples with magnetic ions depends on the excitation power or polarization of the non-resonant excitation laser. In an external magnetic field, the semimagnetic condensate spontaneously builds up strong spin polarization. Based on the magnetic field behavior of the condensate in the presence of magnetic ions, we apply a model that allows us to estimate the polariton-polariton interaction strength in a CdTe-system to approx. 0.8 $μ\text{eV}\!\cdot\!μ\text{m}^2$.

cond-mat.mes-hall

Electrically tunable Berry curvature and strong light-matter coupling in birefringent perovskite microcavities at room temperature

The field of spinoptronics is underpinned by good control over photonic spin-orbit coupling in devices that possess strong optical nonlinearities. Such devices might hold the key to a new era of optoelectronics where momentum and polarization degrees-of-freedom of light are interwoven and interfaced with electronics. However, manipulating photons through electrical means is a daunting task given their charge neutrality and requires complex electro-optic modulation of their medium. In this work, we present electrically tunable microcavity exciton-polariton resonances in a Rashba-Dresselhaus spin-orbit coupling field at room temperature. We show that a combination of different spin orbit coupling fields and the reduced cavity symmetry leads to tunable formation of Berry curvature, the hallmark of quantum geometrical effects. For this, we have implemented a novel architecture of a hybrid photonic structure with a two-dimensional perovskite layer incorporated into a microcavity filled with nematic liquid crystal. Our work interfaces spinoptronic devices with electronics by combining electrical control over both the strong light-matter coupling conditions and artificial gauge fields.

physics.optics

Annihilation of exceptional points from different Dirac valleys in a 2D photonic system

Topological physics relies on the existence of Hamiltonian's eigenstate singularities carrying a topological charge, such as quantum vortices, Dirac points, Weyl points and -- in non-Hermitian systems -- exceptional points (EPs), lines or surfaces. They appear only in pairs connected by a Fermi arc and are related to a Hermitian singularity, such as a Dirac point. The annihilation of 2D Dirac points carrying opposite charges has been experimentally reported. It remained elusive for Weyl points and second order EPs terminating different Fermi arcs. Here, we observe the annihilation of second order EPs issued from different Dirac points forming distinct valleys. We study a liquid crystal microcavity with voltage-controlled birefringence and TE-TM photonic spin-orbit-coupling. Two neighboring modes can be described by a two-band Hermitian Hamiltonian showing two topological phases with either two same-sign or four opposite-sign Dirac points (valleys). Non-Hermiticity is provided by polarization-dependent losses, which split Dirac points into pairs of EPs, connected by Fermi arcs. We measure their topological charges and control their displacement in reciprocal space by increasing the non-Hermiticity degree. EPs of opposite charges from different valleys meet and annihilate, connecting in a closed line the different Fermi arcs. This non-Hermitian topological transition occurs only when the Hermitian part of the Hamiltonian is topologically trivial (with four valleys), but is distinct from the Hermitian transition. Our results offer new perspectives of versatile manipulation of EPs, opening the new field of non-Hermitian valley-physics.

cond-mat.mes-hall

Leaky Integrate-and-Fire Mechanism in Exciton-Polariton Condensates for Photonic Spiking Neurons

This paper introduces a new approach to neuromorphic photonics in which microcavities exhibiting strong exciton-photon interaction may serve as building blocks of optical spiking neurons. The experimental results demonstrate the intrinsic property of exciton-polaritons to resemble the Leaky Integrate-and-Fire spiking mechanism. It is shown that exciton-polariton microcavities when non-resonantly pumped with a pulsed laser exhibit leaky-integration due to relaxation of the excitonic reservoir, threshold-and-fire mechanism due to transition to Bose-Einstein condensate, and resetting due to stimulated emission of photons. These effects, evidenced in photoluminescence characteristics, arise within sub-ns timescales. The presented approach provides means for energy-efficient ultrafast processing of spike-like laser pulses at the level below 1 pJ/spike.

physics.optics

Energy-efficient neural network inference with microcavity exciton-polaritons

We propose all-optical neural networks characterized by very high energy efficiency and performance density of inference. We argue that the use of microcavity exciton-polaritons allows to take advantage of the properties of both photons and electrons in a seamless manner. This results in strong optical nonlinearity without the use of optoelectronic conversion. We propose a design of a realistic neural network and estimate energy cost to be at the level of attojoules per bit, also when including the optoelectronic conversion at the input and output of the network, several orders of magnitude below state-of-the-art hardware implementations. We propose two kinds of nonlinear binarized nodes based either on optical phase shifts and interferometry or on polariton spin rotations.

physics.optics

Observation of second order meron polarisation textures in optical microcavities

Multicomponent Bose-Einstein condensates, quantum Hall systems, and chiral magnetic materials display twists and knots in the continuous symmetries of their order parameter, known as Skyrmions. Originally discovered as solutions to the nonlinear sigma model in quantum field theory, these vectorial excitations are quantified by a topological winding number dictating their interactions and global properties of the host system. Here, we report the first experimental observation of a stable individual second order meron, and antimeron, appearing in an electromagnetic field. These complex textures are realised by confining light into a liquid-crystal filled cavity which, through its anisotropic refractive index, provides an adjustable artificial photonic gauge field which couples the cavity photons motion to its polarisation resulting in formation of these fundamental vectorial vortex states of light. Our observations take a step towards bringing topologically robust room-temperature optical vector textures into the field of photonic information processing and storage.

physics.optics

Exciton-polaritons in multilayer WSe$_2$ in a planar microcavity

Due to high binding energy and oscillator strength, excitons in thin flakes of transition metal dichalcogenides constitute a perfect foundation for realizing a strongly coupled light-matter system. In this paper we investigate mono- and few-layer WSe$_2$ flakes encapsulated in hexagonal boron nitride and incorporated into a planar dielectric cavity. We use an open cavity design which provides tunability of the cavity mode energy by as much as 150 meV. We observe a strong coupling regime between the cavity photons and the neutral excitons in direct-bandgap monolayer WSe$_2$, as well as in few-layer WSe$_2$ flakes exhibiting indirect bandgap. We discuss the dependence of the exciton's oscillator strength and resonance linewidth on the number of layers and predict the exciton-photon coupling strength.

cond-mat.mes-hall

Giant spin Meissner effect in a non-equilibrium exciton-polariton gas

The suppression of Zeeman energy splitting due to spin-dependent interactions within a Bose-Einstein condensate (the spin Meissner effect) was predicted to occur up to a certain value of magnetic field strength. We report a clear observation of this effect in semimagnetic microcavities which exhibit the giant Zeeman energy splitting between two spin-polarised polariton states as high as 2 meV, and demonstrate that partial suppression of energy difference occurs already in the uncondensed phase in a striking similarity to the up-critical superconductors in the fluctuation dominated regime. These observations are explained quantitatively by a kinetic model accounting for both the condensed and uncondensed polaritons and taking into account the non-equilibrium character of the system.

cond-mat.quant-gas

Valley polarization of exciton-polaritons in monolayer WSe2 in a tunable microcavity

Monolayer transition metal dichalcogenides, known for exhibiting strong excitonic resonances, constitute a very interesting and versatile platform for investigation of light-matter interactions. In this work we report on a strong coupling regime between excitons in monolayer WSe2 and photons confined in an open, voltage-tunable dielectric microcavity. The tunability of our system allows us to extend the exciton-polariton state over a wide energy range and, in particular, to bring the excitonic component of the lower polariton mode into resonance with other excitonic transitions in monolayer WSe2. With selective excitation of spin-polarized exciton-polaritons we demonstrate the valley polarization when the polaritons from the lower branch come into resonance with a bright trion state in monolayer WSe2 and valley depolarization when they are in resonance with a dark trion state.

cond-mat.mes-hall

Effect of magnetic field on the lasing threshold of a semimagnetic polariton condensate

We evidence magnetic field triggered polariton lasing in a microcavity containing semimagnetic quantum wells. This effect is associated with a decrease of the polariton lasing threshold power in magnetic field. The observed magnetic field dependence of the threshold power systematically exhibits a minimum which only weakly depends on the zero-field photon-exciton detuning. These results are interpreted as a consequence of the polariton giant Zeeman splitting which in magnetic field: leads to a decrease of the number of accessible states in the lowest polariton branch by a factor of two, and substantially changes the photon-exciton detuning.

cond-mat.mes-hall

Doubly dressed bosons - exciton-polaritons in a strong terahertz field

We demonstrate the existence of a novel quasiparticle: an exciton in a semiconductor doubly dressed with two photons of different wavelengths: near infrared cavity photon and terahertz (THz) photon, with the THz coupling strength approaching the ultra-strong coupling regime. This quasiparticle is composed of three different bosons, being a mixture of a matter-light quasiparticle. Our observations are confirmed by a detailed theoretical analysis, treating quantum mechanically all three bosonic fields. The doubly dressed quasiparticles retain the bosonic nature of their constituents, but their internal quantum structure strongly depends on the intensity of the applied terahertz field.

cond-mat.quant-gas

Angular dependence of giant Zeeman effect for semi-magnetic cavity polaritons

The observation of spin-related phenomena of microcavity polaritons has been limited due to weak Zeeman effect of non-magnetic semiconductors. We demonstrate that the incorporation of magnetic ions into quantum wells placed in a non-magnetic microcavity results in enhanced effects of magnetic field on exciton-polaritons. We show that in such a structure the Zeeman splitting of exciton-polaritons strongly depends on the photon - exciton detuning and polariton wavevector. Our experimental data are explained by a model where the impact of magnetic field on the lower polariton state is directly inherited from the excitonic component, and the coupling strength to cavity photon is modified by external magnetic field.

cond-mat.mes-hall