arXiv subjects

Nicholas Rivera

Publications and source records attributed to Nicholas Rivera.

At least 37 records · Page 2Linked to original sources

arXiv2023

Biasing the quantum vacuum to control macroscopic probability distributions

One of the most important insights of quantum field theory is that electromagnetic fields must fluctuate. Even in the vacuum state, the electric and magnetic fields have a nonzero variance, leading to ubiquitous effects such as spontaneous emission, the Lamb shift, the Casimir effect, and more. These "vacuum fluctuations" have also been harnessed as a source of perfect randomness, for example to generate perfectly random photonic bits. Despite these achievements, many potential applications of quantum randomness in fields such as probabilistic computing rely on controllable probability distributions, which have not yet been realized on photonic platforms. In this work, we show that the injection of vacuum-level "bias" fields into a multi-stable optical system enables a controllable source of "biased" quantum randomness. We demonstrate this concept in an optical parametric oscillator (OPO). Ordinarily, an OPO initiated from the ground state develops a signal field in one of two degenerate phase states (0 and $π$) with equal probability. By injecting bias pulses which contain less than one photon on average, we control the probabilities associated with the two output states, leading to the first controllable photonic probabilistic bit (p-bit). We shed light on the physics behind this process, showing quantitative agreement between theory and experiment. Finally, we demonstrate the potential of our approach for sensing sub-photon level fields by showing that our system is sensitive to the temporal shape of bias field pulses far below the single photon level. Our results suggest a new platform for the study of stochastic quantum dynamics in nonlinear driven-dissipative systems, and point toward possible applications in ultrafast photonic probabilistic computing, as well as the sensing of extremely weak fields.

quant-ph↗

arXiv2023

Universal and ultrafast quantum computation based on free-electron-polariton blockade

Cavity quantum electrodynamics (QED), wherein a quantum emitter is coupled to electromagnetic cavity modes, is a powerful platform for implementing quantum sensors, memories, and networks. However, due to the fundamental tradeoff between gate fidelity and execution time, as well as limited scalability, the use of cavity-QED for quantum computation was overtaken by other architectures. Here, we introduce a new element into cavity-QED - a free charged particle, acting as a flying qubit. Using free electrons as a specific example, we demonstrate that our approach enables ultrafast, deterministic and universal discrete-variable quantum computation in a cavity-QED-based architecture, with potentially improved scalability. Our proposal hinges on a novel excitation blockade mechanism in a resonant interaction between a free-electron and a cavity polariton. This nonlinear interaction is faster by several orders of magnitude with respect to current photon-based cavity-QED gates, enjoys wide tunability and can demonstrate fidelities close to unity. Furthermore, our scheme is ubiquitous to any cavity nonlinearity, either due to light-matter coupling as in the Jaynes-Cummings model or due to photon-photon interactions as in a Kerr-type many-body system. In addition to promising advancements in cavity-QED quantum computation, our approach paves the way towards ultrafast and deterministic generation of highly-entangled photonic graph states and is applicable to other quantum technologies involving cavity-QED.

quant-ph↗

arXiv2022

Optical properties of dispersive time-dependent materials

Time-varying optical materials have attracted recent interest for their potential to enable frequency conversion, nonreciprocal physics, photonic time-crystals, and more. However, the description of time-varying materials has been primarily limited to regimes where material resonances (i.e., dispersion) can be neglected. In this work, we describe how the optics of these dispersive time-varying materials emerges from microscopic quantum mechanical models of time-driven systems. Our results are based on a framework for describing the optics of dispersive time-varying materials through quantum mechanical linear response theory. Importantly, we clarify how response functions for time-varying materials are connected to energy transfer. We provide three examples of our framework applied to systems which can be used to model a wide variety of experiments: few level models that can describe atoms, spins, or superconducting qubits, oscillator models which can describe the strong response of polar insulators, and strongly driven atom models which can describe the highly nonperturbative optical response of materials undergoing high harmonic generation. We anticipate that our results will be broadly applicable to electromagnetic phenomena in strongly time-varying systems.

physics.optics↗

arXiv2022

Creating large Fock states and massively squeezed states in optics using systems with nonlinear bound states in the continuum

The quantization of the electromagnetic field leads directly to the existence of quantum mechanical states, called Fock states, with an exact integer number of photons. Despite these fundamental states being long-understood, and despite their many potential applications, generating them is largely an open problem. For example, at optical frequencies, it is challenging to deterministically generate Fock states of order two and beyond. Here, we predict the existence of a new effect in nonlinear optics, which enables the deterministic generation of large Fock states at arbitrary frequencies. The effect, which we call an n-photon bound state in the continuum, is one in which a photonic resonance (such as a cavity mode) becomes lossless when a precise number of photons n is inside the resonance. Based on analytical theory and numerical simulations, we show that these bound states enable a remarkable phenomenon in which a coherent state of light, when injected into a system supporting this bound state, can spontaneously evolve into a Fock state of a controllable photon number. This effect is also directly applicable for creating (highly) squeezed states of light, whose photon number fluctuations are (far) below the value expected from classical physics (i.e., shot noise). We suggest several examples of systems to experimentally realize the effects predicted here in nonlinear nanophotonic systems, showing examples of generating both optical Fock states with large n (n > 10), as well as more macroscopic photonic states with very large squeezing, with over 90% less noise (10 dB) than the classical value associated with shot noise.

quant-ph↗

arXiv2022

High harmonic generation driven by quantum light

High harmonic generation (HHG) is an extreme nonlinear process where intense pulses of light drive matter to emit high harmonics of the driving frequency, reaching the extreme ultraviolet (XUV) and x-ray spectral ranges. So far, the HHG process was always generated by intense laser pulses that are well described as a classical electromagnetic field. Advances in the generation of intense squeezed light motivate us to revisit the fundamentals of HHG and ask how the photon statistics of light may alter this process, and more generally alter the field of extreme nonlinear optics. The role of photon statistics in non-perturbative interactions of intense light with matter has remained unexplored in both experiments and theory. Here we show that the defining spectral characteristics of HHG, such as the plateau and cutoff, are sensitive to the photon statistics of the driving light. While coherent (classical) and Fock light states induce the established HHG cutoff law, thermal and squeezed states substantially surpass it, extending the cutoff compared to classical light of the same intensity. Hence, shaping the photon statistics of light enables producing far higher harmonics in HHG. We develop the theory of extreme nonlinear optics driven by squeezed light, and more generally by arbitrary quantum states of light. Our work introduces quantum optical concepts to strong-field physics as new degrees of freedom in the creation and control of HHG, and finally shows that experiments in this field are feasible. Looking forward, HHG driven by quantum light creates quantum states of XUV and X-rays, enabling applications of quantum optics in new spectral regimes.

physics.optics↗

arXiv2022

Light emission from strongly driven many-body systems

Strongly driven systems of emitters offer an attractive source of light over broad spectral ranges up to the X-ray region. A key limitation of these systems is that the light they emit is for the most part classical. We challenge this paradigm by building a quantum-optical theory of strongly driven many-body systems, showing that the presence of correlations among the emitters creates emission of nonclassical many-photon states of light. We consider the example of high-harmonic generation (HHG), by which a strongly driven system emits photons at integer multiples of the drive frequency. In the conventional case of uncorrelated emitters, the harmonics are in an almost perfectly multi-mode coherent state lacking any correlation between harmonics. By contrast, a correlation of the emitters prior to the strong drive is converted onto nonclassical features of the output light, including doubly-peaked photon statistics, ring-shaped Wigner functions, and quantum correlations between harmonics. We propose schemes for implementing these concepts, creating the correlations between emitters via an interaction between them or their joint interaction with the background electromagnetic field (as in superradiance). By tuning the time at which these processes are interrupted by the strong drive, one can control the amount of correlations between the emitters, and correspondingly the deviation of the emitted light from a classical state. Our work paves the way towards the engineering of novel many-photon states of light over a broadband spectrum of frequencies, and suggests HHG as a diagnostic tool for characterizing correlations in many-body systems with attosecond temporal resolution.

quant-ph↗

arXiv2022

Double-superradiant cathodoluminescence

There exist two families of superradiance phenomena: relying on correlated emission by an ensemble of atoms or by free electrons. Here we investigate emission from an ensemble of atoms driven by coherently shaped electrons. This interaction creates superradiance emerging from both the atoms' and the electrons' coherence - with emission intensity that scales quadratically in both the number of atoms and number of electrons. This phenomenon enables electrons to become novel probes of quantum correlations in matter, with high temporal and spatial resolution.

quant-ph↗

arXiv2022

Quantum Electrodynamical Metamaterials

Recent experiments have revealed ultrastrong coupling between light and matter as a promising avenue for modifying material properties, such as electrical transport, chemical reaction rates, and even superconductivity. Here, we explore (ultra)strong coupling as a means for manipulating the optical response of metamaterials based on ensembles of constituent units individually in the ultrastrong coupling regime. We develop a framework based on linear response for quantum electrodynamical systems to study how light-matter coupling affects the optical response. We begin by applying this framework to find the optical response of a two-level emitter coupled to a single cavity mode, which could be seen as a "meta-atom" of a metamaterial built from repeated units of this system. We find optical behaviors ranging from that of a simple two-level system (Lorentz-oscillator) to effectively transparent, as the coupling goes from the weak to deep strong coupling regimes. We explore a one-dimensional chain of these meta-atoms, demonstrating the tunability of its optical behavior. Our scheme may ultimately provide a framework for designing new metamaterials with low-loss, highly-confined modes, as well as tunable (single-photon) nonlinearities.

physics.optics↗

arXiv2022

Free-electron-light interactions in nanophotonics

When impinging on optical structures or passing in their vicinity, free electrons can spontaneously emit electromagnetic radiation, a phenomenon generally known as cathodoluminescence. Free-electron radiation comes in many guises: Cherenkov, transition, and Smith-Purcell radiation, but also electron scintillation, commonly referred to as incoherent cathodoluminescence. While those effects have been at the heart of many fundamental discoveries and technological developments in high-energy physics in the past century, their recent demonstration in photonic and nanophotonic systems has attracted a lot of attention. Those developments arose from predictions that exploit nanophotonics for novel radiation regimes, now becoming accessible thanks to advances in nanofabrication. In general, the proper design of nanophotonic structures can enable shaping, control, and enhancement of free-electron radiation, for any of the above-mentioned effects. Free-electron radiation in nanophotonics opens the way to promising applications, such as widely-tunable integrated light sources from x-ray to THz frequencies, miniaturized particle accelerators, and highly sensitive high-energy particle detectors. Here, we review the emerging field of free-electron radiation in nanophotonics. We first present a general, unified framework to describe free-electron light-matter interaction in arbitrary nanophotonic systems. We then show how this framework sheds light on the physical underpinnings of many methods in the field used to control and enhance free-electron radiation. Namely, the framework points to the central role played by the photonic eigenmodes in controlling the output properties of free-electron radiation (e.g., frequency, directionality, and polarization). [... see full abstract in paper]

physics.optics↗

arXiv2022

Creation of Optical Cat and GKP States Using Shaped Free Electrons

Cat states and Gottesman-Kitaev-Preskill (GKP) states play a key role in quantum computation and communication with continuous variables. The creation of such states relies on strong nonlinear light-matter interactions, which are widely available in microwave frequencies as in circuit quantum electrodynamics platforms. However, strong nonlinearities are hard to come by in optical frequencies, severely limiting the use of continuous variable quantum information in the optical range. Here we propose using the strong interactions of free electrons with light as a source for optical cat and GKP states. The strong interactions can be realized by phase-matching of free electrons with photonic structures such as optical waveguides and photonic crystals. Our approach enables the generation of optical GKP states with above 10 dB squeezing and fidelities above 90% at post-selection probability of 10%, even reaching >30% using an initially squeezed vacuum state. Furthermore, the free-electron interaction allows for conditional rotations on the photonic state, enabling to entangle a pair of GKP states into a GKP Bell state. Since electrons can interact resonantly with light across the electromagnetic spectrum, our approach may be used for the generation of cat and GKP states over the entire electromagnetic spectrum, from radio-waves to X-rays.

quant-ph↗

arXiv2022

Ultrafast Electron Microscopy of Nanoscale Charge Dynamics in Semiconductors

The ultrafast dynamics of charge carriers in solids plays a pivotal role in emerging optoelectronics, photonics, energy harvesting, and quantum technology applications. However, the investigation and direct visualization of such non-equilibrium transport phenomena remains as a long-standing challenge, owing to the nanometer-femtosecond spatio-temporal scales at which the charge carriers evolve. Here, we propose and demonstrate a novel interaction mechanism enabling nanoscale imaging of the femtosecond dynamics of charge carriers in solids. This imaging modality, which we name charge dynamics electron microscopy (CDEM), exploits the strong interaction between terahertz (THz) electromagnetic near fields produced by the moving charges and synchronized free-electron pulses in an ultrafast scanning transmission electron microscope. The measured free-electron energy at different spatio-temporal coordinates allows us to directly retrieve the THz near-field amplitude and phase, from which we reconstruct movies of the generated charges by comparison with microscopic theory. The introduced CDEM technique thus allows us to investigate previously inaccessible spatio-temporal regimes of charge dynamics in solids, for example revealing new insight into the photo-Dember effect, showing oscillations of photo-generated electron-hole distributions inside a semiconductor. Our work lays the foundation for exploring a wide range of previously inaccessible charge-transport phenomena in condensed matter using ultrafast electron microscopy.

cond-mat.mes-hall↗

arXiv2022

Complete condensation of photon noise in nonlinear dissipative systems

Fock states are the most fundamental quantum states of bosonic fields, forming an important basis for understanding their quantum dynamics. As energy and number eigenstates, they have an exactly defined number of quanta, and most faithfully express the particle nature of fields. These properties make them attractive for many applications in metrology, and quantum simulation and information processing. Yet, Fock states are notoriously difficult to generate. The problem is especially acute in optics, where it is difficult to deterministically produce Fock states with more than a single photon, let alone at macroscopic scales. This is in part due to a dearth of mechanisms to produce large Fock states, as well as the deleterious effects of linear dissipation. Here, we introduce a new effect in the physics of nonlinear bosons, arising from the interplay of dissipation and Kerr nonlinearity. In this effect, a nonlinear resonance is dissipationless when it has a particular number of quanta (e.g., photons) inside it, and lossy otherwise. This loss, which results from nonlinear interference, leads to several new quantum statistical effects. For example, it leads to spontaneous condensation of intensity noise, which may enable generation of large Fock and extremely photon-number-squeezed states of light. We also show how this effect has implications for new classes of optoelectronic devices such as lasers, which can stabilize extremely low-noise states in an equilibrium between gain and the nonlinear loss that we introduce. Throughout the text, we present examples of systems that may realize these effects. In one, we show how the nonlinear dissipation could lead to optical Fock states of $n=1000$, while in another, we show how conventional laser architectures could be used to generate macroscopic light ($>10^{12}$ photons) with nearly 95% less noise than the standard quantum limit.

quant-ph↗

arXiv2021

A general framework for scintillation in nanophotonics

Bombardment of materials by high-energy particles (e.g., electrons, nuclei, X- and $γ$-ray photons) often leads to light emission, known generally as scintillation. Scintillation is ubiquitous and enjoys widespread applications in many areas such as medical imaging, X-ray non-destructive inspection, night vision, electron microscopy, and high-energy particle detectors. A large body of research focuses on finding new materials optimized for brighter, faster, and more controlled scintillation. Here, we develop a fundamentally different approach based on integrating nanophotonic structures into scintillators to enhance their emission. To start, we develop a unified and ab initio theory of nanophotonic scintillators that accounts for the key aspects of scintillation: the energy loss by high-energy particles, as well as the light emission by non-equilibrium electrons in arbitrary nanostructured optical systems. This theoretical framework allows us, for the first time, to experimentally demonstrate nearly an order-of-magnitude enhancement of scintillation, in both electron-induced, and X-ray-induced scintillation. Our theory also allows the discovery of structures that could eventually achieve several orders-of-magnitude scintillation enhancement. The framework and results shown here should enable the development of a new class of brighter, faster, and higher-resolution scintillators with tailored and optimized performances - with many potential applications where scintillators are used.

physics.optics↗

arXiv2021

Two photon emission from superluminal and accelerating index perturbations

Sources of photons with controllable quantum properties such as entanglement and squeezing are desired for applications in quantum information, metrology, and sensing. However, fine-grained control over these properties is hard to achieve, especially for two-photon sources. Here, we propose a new mechanism for generating entangled and squeezed photon pairs using superluminal and/or accelerating modulations of the refractive index in a medium. By leveraging time-changing dielectric media, where quantum vacuum fluctuations of the electromagnetic field can be converted into photon pairs, we show that energy- and momentum-conservation in multi-mode systems give rise to frequency and angle correlations of photon pairs which are controlled by the trajectory of the index modulation. These radiation effects are two-photon analogues of Cherenkov and synchrotron radiation by moving charged particles such as free electrons. We find the particularly intriguing result that synchrotron-like radiation into photon pairs exhibits frequency correlations which can enable the realization of a heralded single photon frequency comb. We conclude with a general discussion of experimental viability, showing how solitons, ultrashort pulses, and nonlinear waveguides may enable pathways to realize this two-photon emission mechanism. For completeness, we discuss in the Supplementary Information how these effects, sensitive to the local density of photonic states, can be strongly enhanced using photonic nanostructures. As an example, we show that index modulations propagating near the surface of graphene produce entangled pairs of graphene plasmons with high efficiency, leading to additional experimental opportunities.

physics.optics↗

arXiv2021

Casimir light in dispersive nanophotonics

Time-varying optical media, whose dielectric properties are actively modulated in time, introduce a host of novel effects in the classical propagation of light, and are of intense current interest. In the quantum domain, time-dependent media can be used to convert vacuum fluctuations (virtual photons) into pairs of real photons. We refer to these processes broadly as ``dynamical vacuum effects'' (DVEs). Despite interest for their potential applications as sources of quantum light, DVEs are generally very weak, providing many opportunities for enhancement through modern techniques in nanophotonics, such as using media which support excitations such as plasmon and phonon polaritons. Here, we present a theory of DVEs in arbitrary nanostructured, dispersive, and dissipative systems. A key element of our framework is the simultaneous incorporation of time-modulation and ``dispersion'' through time-translation-breaking linear response theory. We propose a highly efficient scheme for generating entangled surface polaritons based on time-modulation of the optical phonon frequency of a polar insulator. We show that the high density of states, especially in hyperbolic polaritonic media, may enable high-efficiency generation of entangled phonon-polariton pairs. More broadly, our theoretical framework enables the study of quantum light-matter interactions in time-varying media, such as spontaneous emission, and energy level shifts.

physics.optics↗

arXiv2020

Super- and subradiance by entangled free particles

When multiple quantum emitters radiate, their emission rate may be enhanced or suppressed due to collective interference in a process known as super- or subradiance. Such processes are well-known to occur also in light emission by free charged particles. To date, all experimental and theoretical studies of super- and subradiance in these systems involved the classical correlations between the emitters. However, dependence on quantum correlations, such as entanglement between different emitting particles, has not been studied. Recent advances in coherent-shaping of free-electron wavefunctions motivate the investigation of such quantum regimes of super- and subradiance. In this Letter, we show how a pair of coincident path-entangled electrons can demonstrate either super- or subradiant light emission, depending on the two-particle wavefunction. By choosing different free-electron Bell-states, the spectrum and emission pattern of the light can be reshaped, in a manner that cannot be accounted for by a classical mixed state. We show these results for light emission in any optical medium, and discuss their generalization to many-body quantum states. Our findings suggest that light emission can be sensitive to the explicit quantum state of the emitting matter wave, and possibly serve as a non-destructive measurement scheme for measuring the quantum state of many-body systems.

quant-ph↗

arXiv2020

Control of quantum electrodynamical processes by shaping electron wavepackets

Fundamental quantum electrodynamical (QED) processes such as spontaneous emission and electron-photon scattering encompass a wealth of phenomena that form one of the cornerstones of modern science and technology. Conventionally, calculations in QED and in other field theories assume that incoming particles are single-momentum states. The possibility that coherent superposition states, i.e. "shaped wavepackets", will alter the result of fundamental scattering processes is thereby neglected, and is instead assumed to sum to an incoherent (statistical) distribution in the incoming momentum. Here, we show that free-electron wave-shaping can be used to engineer quantum interferences that alter the results of scattering processes in QED. Specifically, the interference of two or more pathways in a QED process (such as photon emission) enables precise control over the rate of that process. As an example, we apply our concept to Bremsstrahlung, a ubiquitous phenomenon that occurs, for instance, in X-ray sources for state-of-the-art medical imaging, security scanning, materials analysis, and astrophysics. We show that free electron wave-shaping can be used to tailor both the spatial and the spectral distribution of emitted photons, enhancing their directionality and monochromaticity, and adding more degrees of freedom that make emission processes like Bremsstrahlung more versatile. The ability to tailor the spatiotemporal attributes of photon emission via quantum interference provides a new degree of freedom in shaping radiation across the entire electromagnetic spectrum. More broadly, the ability to tailor general QED processes through the shaping of free electrons opens up new avenues of control in processes ranging from optical excitation processes (e.g., plasmon and phonon emission) in electron microscopy to free electron lasing in the quantum regime.

quant-ph↗

arXiv2020

Shaping Quantum Photonic States Using Free Electrons

It is a long-standing goal to generate robust deterministic states of light with unique quantum properties, such as squeezing, sub-Poissonian statistics and entanglement. It is of interest to consider whether such quantum states of light could be generated by exploiting interactions with free electrons, going beyond their already ubiquitous use in generating classical light. This question is motivated by developments in electron microscopy, which present a new platform for manipulating photons through their interaction with quantum free electrons. Here, we explore the shaping of photon statistics using the quantum interactions of free electrons with photons in optical cavities. We find a variety of quantum states of light that can be generated by a judicious choice of the input light and electron states. For example, we show how shaping an electron into an energy comb can provide an implementation of a photon displacement operation, allowing, for instance, the generation of displaced Fock and displaced squeezed states. We also show how one can generate a desired Fock state by repeated interactions of electrons with a cavity, followed by measurements. We develop the underlying theory of the interaction of both a single and many consecutive electrons with a common cavity mode. Looking forward, by exploiting the degrees of freedom of arbitrary electron-photon quantum states, we may achieve complete control over the statistics and correlations of output photonic states, leading to the generation of novel quantum states of light.

quant-ph↗