arXiv subjects

Roberto de J. León-Montiel

Publications and source records attributed to Roberto de J. León-Montiel.

At least 37 records · Page 2Linked to original sources

arXiv2021

Entangled Two-Photon Absorption Spectroscopy with Varying Pump Wavelength

In virtual-state spectroscopy, information about the energy-level structure of an arbitrary sample is retrieved by Fourier transforming sets of measured two-photon absorption probabilities of entangled photon pairs where the degree of entanglement and the delay time between the photons have been varied. This works well for simple systems but quickly becomes rather difficult when many intermediate states are involved. We propose and discuss an extension of entangled two-photon absorption spectroscopy that solves this problem by means of repeated measurements at different pump wavelengths. Specifically, we demonstrate that our extension works well for a variety of realistic experimental setups.

quant-ph↗

arXiv2021

Noise-Assisted Discord-Like Correlations in Light-Harvesting Photosynthetic Complexes

Transport phenomena in photosynthetic systems have attracted a great deal of attention due to their potential role in devising novel photovoltaic materials. In particular, energy transport in light-harvesting complexes is considered quite efficient due to the balance between coherent quantum evolution and decoherence, a phenomenon coined Environment-Assisted Quantum Transport (ENAQT). Although this effect has been extensively studied, its behavior is typically described in terms of the decoherence's strength, namely weak, moderate or strong. Here, we study the ENAQT in terms of quantum correlations that go beyond entanglement. Using a subsystem of the Fenna-Matthews-Olson complex, we find that discord-like correlations maximize when the subsystem's transport efficiency increases, while the entanglement between sites vanishes. Our results suggest that quantum discord is a manifestation of the ENAQT and highlight the importance of beyond-entanglement correlations in photosynthetic energy transport processes.

quant-ph↗

arXiv2021

Observation of the Modification of Quantum Statistics of Plasmonic Systems

For almost two decades, it has been believed that the quantum statistical properties of bosons are preserved in plasmonic systems. This idea has been stimulated by experimental work reporting the possibility of preserving nonclassical correlations in light-matter interactions mediated by scattering among photons and plasmons. Furthermore, it has been assumed that similar dynamics underlies the conservation of the quantum fluctuations that define the nature of light sources. Here, we demonstrate that quantum statistics are not always preserved in plasmonic systems and report the first observation of their modification. Moreover, we show that multiparticle scattering effects induced by confined optical near fields can lead to the modification of the excitation mode of plasmonic systems. These observations are validated through the quantum theory of optical coherence for single- and multi-mode plasmonic systems. Our findings constitute a new paradigm in the understanding of the quantum properties of plasmonic systems and unveil new paths to perform exquisite control of quantum multiparticle systems.

quant-ph↗

arXiv2021

Quantum transport in non-Markovian dynamically-disordered photonic lattices

We theoretically show that the dynamics of a driven quantum harmonic oscillator subject to non-dissipative noise is formally equivalent to the single-particle dynamics propagating through an experimentally feasible dynamically-disordered photonic network. Using this correspondence, we find that noise assisted energy transport occurs in this network and, if the noise is Markovian or delta-correlated, we can obtain an analytical solution for the maximum amount of transferred energy between all network's sites at a fixed propagation distance. Beyond the Markovian limit, we further consider two different types of non-Markovian noise and show that it is possible to have efficient energy transport for larger values of the dephasing rate.

quant-ph↗

arXiv2021

Experimental study on the effects of photon-pair temporal correlations in entangled two-photon absorption

Entangled two-photon absorption (ETPA) has recently become a topic of lively debate, mainly due to the apparent inconsistencies in the experimentally-reported ETPA cross sections of organic molecules. In this work, we provide a thorough experimental study of ETPA in the organic molecules Rhodamine B (RhB) and Zinc Tetraphenylporphirin (ZnTPP). The goal of this contribution is twofold: on one hand, it seeks to reproduce the results of previous experimental reports and, on the other, it aims to determine the effects of different temporal correlations -- introduced as a controllable time-delay between the photons to be absorbed -- on the strength of the ETPA signal. In our experiment, the samples are excited by entangled pairs produced by type-I SPDC, with a spectral distribution centered at 810 nm. Surprisingly, and contrary to what was expected, the time delay did not produce in our experiments any systematic change in the cross-sections when monitoring the ETPA signal using a transmission measurement scheme. As a plausible cause of this unexpected result, we argue that the photon-pair flux, typically-used in these experiments, is not sufficient to promote the two-photon absorption process in these molecules. This suggests that the actual absorption cross-section values are lower than those previously reported, and therefore do not lead to a measurable ETPA effect for the transmission method.

quant-ph↗

arXiv2020

Reconfigurable Network for Quantum Transport Simulation

In 1981, Richard Feynman discussed the possibility of performing quantum mechanical simulations of nature. Ever since, there has been an enormous interest in using quantum mechanical systems, known as quantum simulators, to mimic specific physical systems. Hitherto, these controllable systems have been implemented on different platforms that rely on trapped atoms, superconducting circuits and photonic arrays. Unfortunately, these platforms do not seem to satisfy, at once, all desirable features of an universal simulator, namely long-lived coherence, full control of system parameters, low losses, and scalability. Here, we overcome these challenges and demonstrate robust simulation of quantum transport phenomena using a state-of-art reconfigurable electronic network. To test the robustness and precise control of our platform, we explore the ballistic propagation of a single-excitation wavefunction in an ordered lattice, and its localization due to disorder. We implement the Su-Schrieffer-Heeger model to directly observe the emergence of topologically-protected one-dimensional edge states. Furthermore, we present the realization of the so-called perfect transport protocol, a key milestone for the development of scalable quantum computing and communication. Finally, we show the first simulation of the exciton dynamics in the B800 ring of the purple bacteria LH2 complex. The high fidelity of our simulations together with the low decoherence of our device make it a robust, versatile and promising platform for the simulation of quantum transport phenomena.

quant-ph↗

arXiv2020

Multi-Photon Synthetic Lattices in Multi-Port Waveguide Arrays: Synthetic Atoms and Fock Graphs

Activating transitions between internal states of physical systems has emerged as an appealing approach to create lattices and complex networks. In such a scheme, the internal states or modes of a physical system are regarded as lattice sites or network nodes in an abstract space whose dimensionality may exceed the systems' apparent (geometric) dimensionality. This introduces the notion of synthetic dimensions, thus providing entirely novel pathways for fundamental research and applications. Here, we analytically show that the propagation of multi-photon states through multi-port waveguide arrays gives rise to synthetic dimensions where a single waveguide system generates a multitude of synthetic lattices. Since these synthetic lattices exist in photon-number space, we introduce the concept of pseudo-energy and demonstrate its utility for studying multi-photon interference processes. Specifically, the spectrum of the associated pseudo-energy operator generates a unique ordering of the relevant states. Together with generalized pseudo-energy ladder operators, this allows for representing the dynamics of multi-photon states by way of pseudo-energy term diagrams that are associated with a synthetic atom. As a result, the pseudo-energy representation leads to concise analytical expressions for the eigensystem of $N$ photons propagating through $M$ nearest-neighbor coupled waveguides. In the regime where $N>2$ and $M>2$, non-local coupling in Fock space gives rise to hitherto unknown all-optical dark states which display intriguing non-trivial dynamics.

quant-ph↗

arXiv2020

Topological Protection in non-Hermitian Haldane Honeycomb Lattices

Topological phenomena in non-Hermitian systems have recently become a subject of great interest in the photonics and condensed-matter communities. In particular, the possibility of observing topologically-protected edge states in non-Hermitian lattices has sparked an intensive search for systems where this kind of states are sustained. Here, we present the first study on the emergence of topological edge states in two-dimensional Haldane lattices exhibiting balanced gain and loss. In line with recent studies on other Chern insulator models, we show that edge states can be observed in the so-called broken $\mathcal{P}\mathcal{T}$-symmetric phase, that is, when the spectrum of the gain-loss-balanced system's Hamiltonian is not entirely real. More importantly, we find that such topologically protected edge states emerge irrespective of the lattice boundaries, namely zigzag, bearded or armchair.

cond-mat.mes-hall↗

arXiv2020

Experimental realization of the classical Dicke model

We report the experimental implementation of the Dicke model in the semiclassical approximation, which describes a large number of two-level atoms interacting with a single-mode electromagnetic field in a perfectly reflecting cavity. This is managed by making use of two non-linearly coupled active, synthetic LC circuits, implemented by means of analog electrical components. The simplicity and versatility of our platform allows us not only to experimentally explore the coexistence of regular and chaotic trajectories in the Dicke model but also to directly observe the so-called ground-state and excited-state ``quantum'' phase transitions. In this analysis, the trajectories in phase space, Lyapunov exponents and the recently introduced Out-of-Time-Order-Correlator (OTOC) are used to identify the different operating regimes of our electronic device. Exhaustive numerical simulations are performed to show the quantitative and qualitative agreement between theory and experiment.

quant-ph↗

arXiv2020

Photochemical dynamics under incoherent illumination: light harvesting in self-assembled molecular J-aggregates

Transport phenomena in organic, self-assembled molecular J-aggregates have long attracted a great deal of attention due to its potential role in designing novel organic photovoltaic devices. A large number of theoretical and experimental studies have been carried out describing excitonic energy transfer in J-aggregates under the assumption that excitons are induced by a coherent laser-light source or initialized by a localized excitation on a particular chromophore. However, these assumptions may not provide an accurate description to assess the efficiency of J-aggregates, particularly as building blocks of organic solar cells. In natural conditions, J-aggregates would be subjected to an incoherent source of light (as is sunlight), which would illuminate the whole photosynthetic complex rather than a single molecule. In this work, we present the first study of the efficiency of photosynthetic energy transport in self-assembled molecular aggregates under incoherent sunlight illumination. By making use of a minimalistic model of a cyanine dye J-aggregate, we demonstrate that long-range transport efficiency is enhanced when exciting the aggregate with incoherent light. Our results thus support the conclusion that J-aggregates are indeed excellent candidates for devices where efficient long-range incoherently-induced exciton transport is desired, such as in highly efficient organic solar cells.

physics.chem-ph↗

arXiv2019

Exceptional points of any order in a single, lossy, waveguide beamsplitter by photon-number-resolved detection

Exceptional points (EPs) are degeneracies of non-Hermitian operators where, in addition to the eigenvalues, corresponding eigenmodes become degenerate. Classical and quantum photonic systems with EPs have attracted tremendous attention due to their unusual properties, topological features, and an enhanced sensitivity that depends on the order of the EP, i.e. the number of degenerate eigenmodes. Yet, experimentally engineering higher-order EPs in classical or quantum domains remains an open challenge due to the stringent symmetry constraints that are required for the coalescence of multiple eigenmodes. Here we analytically show that the number-resolved dynamics of a single, lossy, waveguide beamsplitter, excited by $N$ indistinguishable photons and post-selected to the $N$-photon subspace, will exhibit an EP of order $N+1$. By using the well-established mapping between a beamsplitter Hamiltonian and the perfect state transfer model in the photon-number space, we analytically obtain the time evolution of a general $N$-photon state, and numerically simulate the system's evolution in the post-selected manifold. Our results pave the way towards realizing robust, arbitrary-order EPs on demand in a single device.

quant-ph↗

arXiv2019

Phase dependent vectorial current control in symmetric noisy optical ratchets

In this work we demonstrate single microparticle transport in a symmetric noisy optical ratchet where each potential is a low power ($<2.5$ mW) three dimensional trap. The optical potentials consist of 20 symmetric optical traps arranged in a one-dimensional lattice produced by a spatial light modulator. The external periodic force of the ratchet system adds to zero over one period (symmetric) and is generated by the motion of a piezo-electric microscope stage. Transport is achieved by adding noise to the potentials by randomly varying the diffracted power into the traps at the same frequency of the external force. We show that the direction and speed of motion (current) is coupled to the phase difference between the noise in the optical potentials and the external periodic force.

physics.optics↗

arXiv2019

Two-particle quantum correlations in stochastically-coupled networks

Quantum walks in dynamically-disordered networks have become an invaluable tool for understanding the physics of open quantum systems. In this work, we introduce a novel approach to describe the dynamics of indistinguishable particles in noisy quantum networks. By making use of stochastic calculus, we derive a master equation for the propagation of two non-interacting correlated particles in tight-binding networks affected by off-diagonal dynamical disorder. We show that the presence of noise in the couplings of a quantum network creates a pure-dephasing-like process that destroys all coherences in the single-particle Hilbert subspace. Remarkably, we find that when two or more correlated particles propagate in the network, coherences accounting for particle indistinguishability are robust against the impact of noise, thus showing that it is possible, in principle, to find specific conditions for which many indistinguishable particles can traverse dynamically-disordered systems without losing their ability to interfere. These results shed light on the role of particle indistinguishability in the preservation of quantum coherence in dynamically-disordered quantum networks.

quant-ph↗

arXiv2019

Temperature-Controlled Entangled-Photon Absorption Spectroscopy

Entangled two-photon absorption spectroscopy (TPA) has been widely recognized as a powerful tool for revealing relevant information about the structure of complex molecular systems. However, to date, the experimental implementation of this technique has remained elusive, mainly because of two major difficulties. First, the need to perform multiple experiments with two-photon states bearing different temporal correlations, which translates in the necessity to have at the experimenter's disposal tens, if not hundreds, of sources of entangled photons. Second, the need to have \emph{a priori} knowledge of the absorbing medium's lowest-lying intermediate energy level. In this work, we put forward a simple experimental scheme that successfully overcomes these two limitations. By making use of a temperature-controlled entangled-photon source, which allows the tuning of the central frequencies of the absorbed photons, we show that the TPA signal, measured as a function of the temperature of the nonlinear crystal that generates the paired photons, and a controllable delay between them, carries all information about the electronic level structure of the absorbing medium, which can be revealed by a simple Fourier transformation.

quant-ph↗

arXiv2018

Endurance of quantum coherence due to particle indistinguishability in noisy quantum networks

Quantum coherence, the physical property underlying fundamental phenomena such as multi-particle interference and entanglement, has emerged as a valuable resource upon which modern technologies are founded. In general, the most prominent adversary of quantum coherence is noise arising from the interaction of the associated dynamical system with its environment. Under certain conditions, however, the existence of noise may drive quantum and classical systems to endure intriguing nontrivial effects. In this vein, here we demonstrate, both theoretically and experimentally, that when two indistinguishable non-interacting particles co-propagate through quantum networks affected by non-dissipative noise, the system always evolves into a steady state in which coherences accounting for particle indistinguishabilty perpetually prevail. Furthermore, we show that the same steady state with surviving quantum coherences is reached even when the initial state exhibits classical correlations.

quant-ph↗

arXiv2018

Observation of slowly decaying eigenmodes without exceptional points in Floquet, dissipative, synthetic circuits

We report the first experimental observation of multiple transitions showing the emergence and disappearance of slowly decaying eigenmodes in a dissipative, Floquet electronic system with synthetic components. Conventional wisdom has it that such transitions occur at exceptional points, and avoided-level-crossing driven phenomena in purely dissipative systems are formerly unexplored. Remarkably, in our system, the slowly decaying eigenmodes emerge without exceptional points. Our experimental setup makes use of an LC oscillator inductively coupled to an RLC oscillator, where the time-periodic (Floquet) inductive coupling and resistive-heating losses can be independently controlled by means of external voltage signals. With a Floquet dissipation, we observe that slowly-decaying eigenmodes emerge at vanishingly small dissipation strength in the weak coupling limit. With a moderate, Floquet coupling, multiple instances of their emergence and disappearance are observed. With an asymmetric dimer model, we show that these transitions, driven by avoided-level-crossing in purely dissipative systems, are generically present in both static and Floquet domains.

physics.class-ph↗

arXiv2018

Two-Photon Absorption Spectroscopy using Intense Phase-Chirped Entangled Beams

We numerically analyze the use of intense entangled twin beams for ultra-sensitive spectroscopic measurements in chemical and biological systems. The examined scheme makes use of intense frequency-modulated (chirped) entangled beams to successfully extract information about the intermediate material states that contribute to the two-photon excitation of an absorbing medium. Robustness of the presented method is examined with respect to the applied intervals of the frequency chirp.

quant-ph↗

arXiv2018

Virtual-State Spectroscopy with Frequency-Tailored Intense Entangled Beams

In this contribution we analyze virtual-state spectroscopy --- a unique tool for extracting information about the virtual states that contribute to the two-photon excitation of an absorbing medium --- as implemented by means of intense entangled beams with tunable spectral correlations. We provide a thorough description of all contributing terms (classical and quantum) in the two-photon absorption signal, as well as the limits imposed by the power of the pump that produces the entangled beams on the observability of the spectral lines of the virtual transitions. We find that virtual-state spectroscopy may be implemented with entangled twin beams carrying up to $10^4$ photon pairs. This implies that, in principle, one might be able to detect two-photon absorption signals up to four orders of magnitude larger than previously reported, thus paving the way towards the first experimental realization of the virtual-state spectroscopy technique.

quant-ph↗