المؤلفون: Heller, Lukas

المساهمون: University/Department: Universitat Politècnica de Catalunya. Institut de Ciències Fotòniques

مرشدي الرسالة: Riedmatten, Hugues de

المصدر: TDX (Tesis Doctorals en Xarxa)

مصطلحات موضوعية: Àrees temàtiques de la UPC::Física

الوصف: (English) Quantum memories are devices that are able to store photonic quantum states and entanglement. Future quantum networks, which could enhance cybersecurity through quantum key distribution, improve the precision in atomic clock networks, and connect quantum devices over long distances, rely on them. This thesis reports on experiments towards improved quantum memories for quantum repeaters used in long-distance quantum communication. The quantum memory is based on a cloud of laser-cooled Rubidium-87. Thanks to collective interference effects, this system enhances the light-matter interaction compared to that of a single atom. This is exploited to either create long-lived quantum correlations between light and atomic excitations through probabilistic light scattering (DLCZ protocol) or to efficiently absorb an incoming single photon (Raman protocol). In both cases, the excitation is retrieved after a programmable delay as a single photon. An optical cavity around the atoms further enhances the light-matter coupling. In a first experiment, the DLCZ protocol is combined with a photon echo protocol, allowing for the sequential creation of excitations in N distinguishable temporal modes. This is known as temporal multiplexing. Multiplexing improves the rate at which entanglement is created in a network link by a factor N. Here, the cavity is essential to suppress noise originating from the probabilistic scattering of light in the DLCZ protocol. Ten temporal modes are stored while maintaining strong quantum correlations between the scattered photon and the atomic excitation. In a second experiment, a quasi-deterministic single photon is stored in the cloud following the Raman protocol. The photon originates from an ensemble of laser-cooled Rydberg atoms. Strong dipole-dipole interactions prevent the excitation of more than one atom to the Rydberg level, leading to the creation of a single collective Rydberg excitation which is later retrieved as a single photon. A deterministic source, opposed to a probabilistic source, improves the entanglement creation rate as it generates single photons at higher rates. The single photon is stored and faithfully retrieved from the memory while maintaining its single-photon nature. The cavity is not being used in this experiment. In a third experiment, the retrieval efficiency of a stored excitation is increased by cavity-enhancing the read-out process. Highly-efficient memories are important because the entanglement distribution scales strongly with memory efficiency. The intra-cavity efficiency could be improved by a factor 2-3, depending on the protocol, even for a non-optimal cavity setup. Finally, ongoing work towards efficient entanglement between an atomic excitation and a telecom photon is presented, involving a cavity-enhanced DLCZ memory, an atomic dipole trap and quantum frequency conversion (QFC) to the telecom C-band. As the memory operates in the optical domain, where photonic transmission losses are large, QFC will be needed to communicate over large distances. This setup will be used in the future for a hybrid experiment connecting the cold atomic memory to a solid state memory. These investigations target intrinsic limitations of early, proof-of-principle quantum links. They can therefore help to build practical links in the future.

الوصف (مترجم): (Català) Les memòries quàntiques són dispositius capaços d'emmagatzemar estats quàntics fotònics i entrellaçament. Les xarxes quàntiques futures, que podrien millorar la ciberseguretat mitjançant la distribució de claus quàntiques, millorar la precisió de les xarxes de rellotge atòmic i connectar dispositius quàntics a llargues distàncies, depenen d'elles. Aquesta tesi presenta experiments cap a memòries quàntiques millorades per a la comunicació quàntica a llarga distància. La memòria quàntica es basa en un núvol de Rubidi-87 refrigerat per làser. Gràcies als efectes d'interferència col·lectiva, la interacció llum-matèria d'aquest sistema es millora en comparació amb la d'un sol àtom. Això s'aprofita per crear correlacions quàntiques de llarga duració entre la llum i les excitacions atòmiques mitjançant la dispersió probabilística de la llum (protocol DLCZ) o per absorbir de manera eficient un fotó únic entrant (protocol Raman). En ambdós casos, l'excitació es recupera després d'un retard programable com un fotó únic. Una cavitat òptica al voltant dels àtoms millora encara més l'acoblament llum-matèria. En un primer experiment, el protocol DLCZ es va combinar amb un protocol d'eco de fotons per permetre la creació i la recuperació distingible de N excitacions atòmiques que es van crear seqüencialment en el mateix mode espacial. Això es coneix com a multiplexació temporal. La multiplexació millorarà la velocitat a la qual es crea l'entrellaçament en una xarxa per un factor N. Aquí, la cavitat era essencial per suprimir el soroll provinent de la dispersió probabilística de la llum al protocol DLCZ. Es van emmagatzemar 10 modes temporals mantenint fortes correlacions quàntiques entre el fotó dispers i l'excitació atòmica. En un segon experiment, es va emmagatzemar un fotó únic quasi determinista al núvol seguint el protocol Raman. El fotó es va originar a partir d'un conjunt d'àtoms de Rydberg refrigerats per làser. Les fortes interaccions dipol-dipol impedeixen l'excitació de més d'un àtom al nivell de Rydberg, donant lloc a la creació d'una única excitació col·lectiva de Rydberg que després es recupera com un sol fotó. Una font determinista, oposada a una font probabilística, millora la velocitat de creació d'entrellaçament ja que genera fotons únics a velocitats més altes. Vam demostrar que el fotó únic es podia emmagatzemar i recuperar fidelment de la memòria mantenint la seva naturalesa de fotó únic. La cavitat no es va utilitzar aquí. En un tercer experiment, l'eficiència de recuperació d'una excitació emmagatzemada es va augmentar mitjançant un procés de lectura millorat per una cavitat. Les memòries altament eficients són importants, ja que la distribució de l'entrellaçament escala fortament amb l'eficiència de la memòria. L'eficiència intra-cavitat es va millorar en un factor 2-3, depenent del protocol, fins i tot per a una configuració de cavitat no òptima. Finalment, es presenta el treball en curs cap a l'entrellaçament eficient entre una excitació atòmica i un fotó de telecomunicacions, que inclou una memòria DLCZ millorada per cavitat, una trampa de dipols atòmics i conversió de freqüència quàntica (QFC) a la banda C de telecomunicacions. Com que la memòria opera en el domini òptic, on les pèrdues de transmissió fotònica són grans, caldrà QFC per comunicar-se a grans distàncies. Aquesta configuració s'utilitzarà en el futur per a un experiment híbrid que connecti la memòria atòmica freda amb una memòria d'estat sòlid. En aquestes investigacions ens centrem en les limitacions intrínseques de les primeres proves de principi de connexions quàntiques.Per tant, podrien ajudar a construir connexions pràctics en el futur.
(Español) Las memorias cuánticas son dispositivos capaces de almacenar estados cuánticos de la luz. De ellas dependen las futuras redes cuánticas, que podrían mejorar la ciberseguridad mediante la distribución de claves cuánticas, aumentar la precisión de las redes de relojes atómicos y conectar dispositivos cuánticos a larga distancia. En esta tesis se presentan experimentos para mejorar las memorias cuánticas utilizadas en repetidores cuánticos que permitirán la comunicación cuántica a larga distancia. Aquella memoria cuántica se basa en una nube de Rubidio-87 refrigerada por láser. Gracias a los efectos de interferencia colectiva, la interacción luz-materia de este sistema es mayor que la de un solo átomo. Esto se aprovecha para crear correlaciones cuánticas duraderas entre la luz y las excitaciones atómicas mediante la dispersión probabilística de la luz (protocolo DLCZ) o para absorber eficazmente un solo fotón entrante (protocolo Raman). En ambos casos, tras la excitación se recupera un fotón único después de un retardo programable. Una cavidad óptica alrededor de los átomos mejora aún más el acoplamiento luz-materia. En un primer experimento, el protocolo DLCZ se combinó con un protocolo de eco de fotones que permite crear excitaciones atómicas secuencialmente en N modos temporales distinguibles. Esto se conoce como multiplexación temporal. La multiplexación mejorará la velocidad a la que se crea entrelazamiento en una red en un factor N. En este caso, la cavidad era esencial para suprimir el ruido originado por la dispersión probabilística de la luz en el protocolo DLCZ. Se almacenaron 10 modos temporales mientras se mantenían fuertes correlaciones cuánticas entre el fotón dispersado y la excitación atómica collectiva. En un segundo experimento, se almacenó en la nube un único fotón cuasi-determinista siguiendo el protocolo Raman. El fotón procedía de un conjunto de átomos Rydberg refrigerados por láser. Las fuertes interacciones dipolo-dipolo impiden la excitación de más de un átomo al nivel de Rydberg, lo que conduce a la creación de una única excitación colectiva de Rydberg que posteriormente se recupera como un único fotón. Una fuente determinista, en contraposición a una fuente probabilística, mejora la velocidad de creación de entrelazamiento, ya que genera fotones únicos a tasas más altas. Demostramos que el fotón único podía almacenarse y recuperarse fidedignamente de la memoria manteniendo su naturaleza de fotón único. En este experimento no se utilizó la cavidad. En un tercer experimento, se aumentó la eficiencia de recuperación de una excitación almacenada, mejorando el proceso de lectura mediante la cavidad. Las memorias de alta eficiencia son importantes, ya que la distribución del entrelazamiento depende en gran medida de la eficiencia de la memoria. La eficiencia intracavitaria se mejoró en un factor 2-3, dependiendo del protocolo, incluso para una configuración de cavidad no óptima. Por último, se presentan los trabajos en curso para lograr un entrelazamiento eficiente entre una excitación atómica y un fotón en el rango de las telecomunicaciones, que implican una memoria DLCZ mejorada por cavidad, una trampa dipolar atómica y conversión de frecuencia cuántica (QFC) a la banda C de telecomunicación. Como la memoria funciona en el dominio óptico, donde las pérdidas de transmisión fotónica son grandes, se necesitará QFC para comunicarse a grandes distancias. Esta configuración se utilizará en el futuro para un experimento híbrido que conecte la memoria atómica fría con una memoria de estado sólido. Estas investigaciones se centran en las limitaciones intrínsecas de los primeros enlaces cuánticos, que se han realizados a escala de laboratorio. Por tanto, podrían ayudar a construir enlaces prácticos en el futuro.
DOCTORAT EN FOTÒNICA (Pla 2013)

وصف الملف: application/pdf

الوصول الحر: http://hdl.handle.net/10803/690315Test

المؤلفون: Müller, Lukas, Woike, Lukas

مصطلحات موضوعية: Mathematics - Quantum Algebra, Mathematical Physics, Mathematics - Algebraic Topology

الوصف: In this short note, we classify linear categorified open topological field theories in dimension two by pivotal Grothendieck-Verdier categories. In combination with recently developed string-net techniques, this leads to a new description of the spaces of conformal blocks of Drinfeld centers $Z(\mathcal{C})$ of pivotal finite tensor categories $\mathcal{C}$ in terms of the modular envelope of the cyclic associative operad. If $\mathcal{C}$ is unimodular, we prove that the space of conformal blocks inherits the structure of a module over the algebra of class functions of $\mathcal{C}$ for every free boundary component. As a further application, we prove that the sewing along a boundary circle for the modular functor for $Z(\mathcal{C})$ can be decomposed into a sewing procedure along an interval and the application of the partial trace. Finally, we construct mapping class group representations from Grothendieck-Verdier categories that are not necessarily rigid and make precise how these generalize existing constructions.
Comment: 14 pages, some diagrams

الوصول الحر: http://arxiv.org/abs/2406.11605Test

المؤلفون: Adam, Lukáš, Čermák, Vojtěch, Papafitsoros, Kostas, Picek, Lukas

مصطلحات موضوعية: Computer Science - Computer Vision and Pattern Recognition

الوصف: We introduce a new wildlife re-identification dataset WildlifeReID-10k with more than 214k images of 10k individual animals. It is a collection of 30 existing wildlife re-identification datasets with additional processing steps. WildlifeReID-10k contains animals as diverse as marine turtles, primates, birds, African herbivores, marine mammals and domestic animals. Due to the ubiquity of similar images in datasets, we argue that the standard (random) splits into training and testing sets are inadequate for wildlife re-identification and propose a new similarity-aware split based on the similarity of extracted features. To promote fair method comparison, we include similarity-aware splits both for closed-set and open-set settings, use MegaDescriptor - a foundational model for wildlife re-identification - for baseline performance and host a leaderboard with the best results. We publicly publish the dataset and the codes used to create it in the wildlife-datasets library, making WildlifeReID-10k both highly curated and easy to use.

الوصول الحر: http://arxiv.org/abs/2406.09211Test

المؤلفون: Amiriparian, Shahin, Christ, Lukas, Kathan, Alexander, Gerczuk, Maurice, Müller, Niklas, Klug, Steffen, Stappen, Lukas, König, Andreas, Cambria, Erik, Schuller, Björn, Eulitz, Simone

مصطلحات موضوعية: Computer Science - Artificial Intelligence, Computer Science - Computation and Language, 68T10, I.2

الوصف: The Multimodal Sentiment Analysis Challenge (MuSe) 2024 addresses two contemporary multimodal affect and sentiment analysis problems: In the Social Perception Sub-Challenge (MuSe-Perception), participants will predict 16 different social attributes of individuals such as assertiveness, dominance, likability, and sincerity based on the provided audio-visual data. The Cross-Cultural Humor Detection Sub-Challenge (MuSe-Humor) dataset expands upon the Passau Spontaneous Football Coach Humor (Passau-SFCH) dataset, focusing on the detection of spontaneous humor in a cross-lingual and cross-cultural setting. The main objective of MuSe 2024 is to unite a broad audience from various research domains, including multimodal sentiment analysis, audio-visual affective computing, continuous signal processing, and natural language processing. By fostering collaboration and exchange among experts in these fields, the MuSe 2024 endeavors to advance the understanding and application of sentiment analysis and affective computing across multiple modalities. This baseline paper provides details on each sub-challenge and its corresponding dataset, extracted features from each data modality, and discusses challenge baselines. For our baseline system, we make use of a range of Transformers and expert-designed features and train Gated Recurrent Unit (GRU)-Recurrent Neural Network (RNN) models on them, resulting in a competitive baseline system. On the unseen test datasets of the respective sub-challenges, it achieves a mean Pearson's Correlation Coefficient ($\rho$) of 0.3573 for MuSe-Perception and an Area Under the Curve (AUC) value of 0.8682 for MuSe-Humor.

الوصول الحر: http://arxiv.org/abs/2406.07753Test

المؤلفون: Scherzer, Johannes, Lackner, Lukas, Han, Bo, Polovnikov, Borislav, Husel, Lukas, Göser, Jonas, Li, Zhijie, Drawer, Jens-Christian, Esmann, Martin, Bennenhei, Christoph, Eilenberger, Falk, Watanabe, Kenji, Taniguchi, Takashi, Baimuratov, Anvar S., Schneider, Christian, Högele, Alexander

مصطلحات موضوعية: Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science, Condensed Matter - Strongly Correlated Electrons

الوصف: We demonstrate evidence of correlated magnetism for exciton-polaritons in a MoSe$_{2}$/WS$_{2}$ moir\'e heterostructure with near-parallel alignment subject to electron doping. In our experiments, interactions between electrons and moir\'e excitons are controlled electrostatically by field-effect doping, and the polaritonic regime of strong light-matter coupling is established in an open cryogenic microcavity. Remarkably, at filling fractions around one electron per moir\'e cell, we observe drastic and nonlinear enhancement of the effective polariton Land\'e factor as a hallmark of correlated magnetism, which is cavity-controlled via resonance tuning of light and matter polariton constituents. Our work establishes moir\'e van der Waals heterostructures as an outstanding platform for studies of correlated phenomena in the presence of strong light-matter coupling and many-body phases of lattice-ordered excitons, charges and spins.

الوصول الحر: http://arxiv.org/abs/2405.12698Test

المؤلفون: Albers, Tony, Hille, Lukas, Müller-Bender, David, Radons, Günter

مصطلحات موضوعية: Nonlinear Sciences - Chaotic Dynamics

الوصف: We demonstrate that standard delay systems with a linear instantaneous and a delayed nonlinear term show weak chaos, asymptotically subdiffusive behavior, and weak ergodicity breaking if the nonlinearity is chosen from a specific class of functions. In the limit of large constant delay times, anomalous behavior may not be observable due to exponentially large crossover times. A periodic modulation of the delay causes a strong reduction of the effective dimension of the chaotic phases, leads to hitherto unknown types of solutions, and the occurrence of anomalous diffusion already at short times. The observed anomalous behavior is caused by non-hyperbolic fixed points in function space.
Comment: 7 pages, 5 figures

الوصول الحر: http://arxiv.org/abs/2407.09449Test

المؤلفون: Fischer, Lukas, Menzel, Andreas M.

مصطلحات موضوعية: Condensed Matter - Soft Condensed Matter, Mathematical Physics

الوصف: Calculating by analytical theory the deformation of finite-sized elastic bodies in response to internally applied forces is a challenge. Here, we derive explicit analytical expressions for the amplitudes of modes of surface deformation of a homogeneous, isotropic, linearly elastic sphere. The modes under consideration correspond to overall changes in volume and to relative uniaxial elongation or contraction. Both situations of an elastic sphere embedded under no-slip conditions in a linearly elastic, homogeneous, isotropic, infinitely extended background medium and of a free-standing elastic sphere are considered. For example, our analytical expressions are important as a basis for computational material optimization in the context of spherical soft actuators.
Comment: 29 pages, 0 figures

الوصول الحر: http://arxiv.org/abs/2407.09291Test

المؤلفون: Brantner, Lukas, Taelman, Lenny

مصطلحات موضوعية: Mathematics - Algebraic Geometry, Mathematics - Algebraic Topology, Mathematics - Number Theory, 14J32, 14B12, 14F30, 13D03, 14F35, 18M70

الوصف: We study deformations of Calabi-Yau varieties in characteristic $p$ using techniques from derived algebraic geometry. We prove a mixed characteristic analogue of the Bogomolov-Tian-Todorov theorem (which states that Calabi-Yau varieties in characteristic $0$ are unobstructed), and we show that ordinary Calabi-Yau varieties admit canonical lifts to characteristic $0$, generalising the Serre-Tate theorem on ordinary abelian varieties.
Comment: 77 pages

الوصول الحر: http://arxiv.org/abs/2407.09256Test

المؤلفون: Gräfner, Lukas

مصطلحات موضوعية: Mathematics - Probability

الوصف: In this note we consider the SDE \begin{equation*} \text{d}X_t = b (t, X_t) \text{d} t + \sqrt{2} \text{d} B_t, \label{mainSDE} \end{equation*} in dimension $d \geqslant 2$, where $B$ is a Brownian motion and $b : \mathbb{R}_+ \rightarrow \mathcal{S}' (\mathbb{R}^d ; \mathbb{R}^d)$ is distributional, scaling super-critical and satisfies $\nabla \cdot b \equiv 0$. We partially extend the super-critical weak well-posedness result for energy solutions from [GP24] by allowing a mixture of the regularity regimes treated therein: Outside of environments of a small (and compared to [GP24] ''time-dependent'') set $K \subset \mathbb{R}_+ \times \mathbb{R}^d$, the antisymmetric matrix field $A$ with $b^i = \nabla\cdot A_i$ is assumed to be in a certain supercritical $L^q_T H^{s, p}$-type class that allows a direct link between the PDE and the SDE from a-priori estimates up to the stopping time of visiting $K$. To establish this correspondence, and thus uniqueness, globally in time we then show that $K$ is actually never visited which requires us to impose a relation between the dimension of $K$ and the H\"older regularity of $X$.
Comment: 11 pages

الوصول الحر: http://arxiv.org/abs/2407.09222Test

المؤلفون: Hartung, Lukas, Seubert, Matthias, Welte, Stephan, Distante, Emanuele, Rempe, Gerhard

المصدر: Science 385, 179-183 (2024)

مصطلحات موضوعية: Quantum Physics

الوصف: Quantum computation and quantum communication are expected to provide users with capabilities inaccessible by classical physics. However, scalability to larger systems with many qubits is challenging. One solution is to develop a quantum network consisting of small-scale quantum registers containing computation qubits that are reversibly interfaced to communication qubits. Here we report on a register that uses both optical tweezers and optical lattices to deterministically assemble a two-dimensional array of atoms in an optical cavity. Harnessing a single-atom addressing beam, we stimulate the emission of a photon from each atom and demonstrate multiplexed atom-photon entanglement with a generation-to-detection efficiency approaching 90$\%$. Combined with cavity-mediated quantum logic, our approach provides a possible route to distributed quantum information processing.

الوصول الحر: http://arxiv.org/abs/2407.09109Test