arXiv subjects

Elena del Valle

Publications and source records attributed to Elena del Valle.

At least 19 recordsLinked to original sources

arXiv2025

Deterministic Control of Photon-Number Probabilities via Phase-Controlled Quantum Interference

Deterministically tailoring optical Fock states beyond the single-photon level is crucial for boson sampling, loss-tolerant photonic qubits, and quantum-enhanced sensing, however has yet remained elusive. Here, we report an all-linear-optical protocol that converts a resonantly driven single-photon emitter into a deterministic generator of vacuum--single-photon--two-photon states. A phase-stabilized, path-unbalanced Mach-Zehnder interferometer combines vacuum--single-photon interference and Hong-Ou-Mandel effect, providing two knobs to shape photon-number probabilities. By tuning these knobs, we observe a dynamic transition from antibunching to strong bunching in correlation measurements. A fully quantum-mechanical, discrete time-bin model maps these results onto the tailored photon statistics. The same framework predicts that two indistinguishable emitters would extend the accessible space to deterministic NOON states and single-photon filtering. This protocol relying on linear optics and available single-photon sources provides a scalable, chip-compatible, and platform-independent route to on-demand and deterministic few-photon resources for quantum metrology, photonic computing, as well as long-distance quantum networks.

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arXiv2024

Correlations in Circular Quantum Cascades

We introduce a one-way, one-quantum cascade, whereby a single excitation proceeds one-directionwise in a ladder of energy levels. This makes a variation from more famous two-way cascades where the excitation can go up and down following its excitation or relaxation in the ladder. We provide closed-form solutions for two-photon correlation functions between any transitions in such circular cascades. We discuss how the rich correlations that result from what appears to be an extremely simple implementation, are essentially those which have been obtained from complex architectures relying on strongly-correlated, many-body physics or cavity QED effects, and might constitute the liquid phase of the new family of time materials.

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arXiv2024

Unlocking multiphoton emission from a single-photon source through mean-field engineering

Single-photon emission from a two-level system offers promising perspectives for the development of quantum technologies, where multiphotons are generally regarded as accidental, undesired and should be suppressed. In quantum mechanics, however, multiphoton emission can turn out to be even more fundamental and interesting than the single-photon emission, since in a coherently driven system, the multiphoton suppression arises from quantum interferences between virtual multiphoton fluctuations and the mean field in a Poisson superposition of all number states. Here, we demonstrate how one can control the multiphoton dynamics of a two-level system by disrupting these quantum interferences through a precise and independent homodyne control of the mean field. We show that, counterintuitively, quantum fluctuations always play a major qualitative role, even and in fact especially, when their quantitative contribution is vanishing as compared to that of the mean field. Our findings provide new insights into the paradoxical character of quantum mechanics and open pathways for mean-field engineering as a tool for precision multiphoton control.

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arXiv2024

Two photons everywhere

We discuss two-photon physics, taking for illustration the particular but topical case of resonance fluorescence. We show that the basic concepts of interferences and correlations provide at the two-photon level an independent and drastically different picture than at the one-photon level, with landscapes of correlations that reveal various processes by spanning over all the possible frequencies at which the system can emit. Such landscapes typically present lines of photon bunching and circles of antibunching. The theoretical edifice to account for these features rests on two pillars: i) a theory of frequency-resolved photon correlations and ii) admixing classical and quantum fields. While experimental efforts have been to date concentrated on correlations between spectral peaks, strong correlations exist between photons emitted away from the peaks, which are accessible only through multiphoton observables. These could be exploited for both fundamental understanding of quantum-optical processes as well as applications by harnessing these unsuspected resources.

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arXiv2023

Photon liquefaction in time

We provide a mechanism to imprint local temporal correlations in photon streams which have the same character as spatial correlations in liquids. Usual single-photon emitters correspond, in this picture, to a (temporal) gas while uncorrelated light is the ideal gas. We argue that good single-photon sources are those that exhibit such temporal liquid features, i.e., with a plateau for their short-time correlations (as opposed to a linear dependence) and oscillations at later times, which is a direct manifestation of photon time-ordering. We obtain general, closed-form analytical expressions for the second-order coherence function of a broad family of "liquid light" which can be arbitrarily correlated, though never completely crystallized.

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arXiv2022

Two-photon emission in detuned resonance fluorescence

We discuss two-photon correlations from the side peaks that are formed when a two-level system emitter is driven coherently, with a detuning between the driving source and the emitter (quasi-resonance fluorescence). We do so in the context of the theories of frequency-resolved photon correlations and homodyning, showing that their combination leads to a neat picture compatible with perturbative two-photon scattering that was popular in the early days of quantum electrodynamics. This should help to control, enhance and open new regimes of multiphoton emission. We also propose a way to evidence the quantum coherent nature of the process from photoluminescence only, through the observation of a collapse of the symmetry of the lineshape accompanied by a surge of its intensity of emission. We discuss several of our results in the light of recent experimental works.

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arXiv2021

Loss of Antibunching

We describe some of the main external mechanisms that lead to a loss of antibunching, i.e., that spoil the character of a given quantum light to deliver its photons separated the ones from the others. Namely, we consider contamination by noise, a time jitter in the photon detection and the effect of frequency filtering (or detection with finite bandwidth). The emission from a two-level system under both incoherent and coherent driving is taken as a particular case of special interest. The coherent case is further separated into its vanishing (Heitler) and high (Mollow) driving regimes. We provide analytical solutions which, in the case of filtering, unveil an unsuspected structure in the transitions from perfect antibunching to thermal (incoherent case) or uncorrelated (coherent case) emission. The experimental observations of these basic and fundamental transitions would provide another compelling evidence of the correctness and importance of the theory of frequency-resolved photon correlations.

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arXiv2020

Tuning photon statistics with coherent fields

Photon correlations, as measured by Glauber's $n$-th order coherence functions $g^{(n)}$, are highly sought to be minimized and/or maximized. In systems that are coherently driven, so-called blockades can give rise to strong correlations according to two scenarios based on level-repulsion (conventional blockade) or interferences (unconventional blockade). Here we show how these two approaches relate to the admixing of a coherent state with a quantum state such as a squeezed state for the simplest and most recurrent case. The emission from a variety of systems, such as resonance fluorescence, the Jaynes-Cummings model or microcavity polaritons, as a few examples of a large family of quantum optical sources, are shown to be particular cases of such admixtures, that can further be doctored-up externally by adding an amplitude- and phase-controlled coherent field with the effect of tuning the photon statistics from exactly zero to infinity. We show how such an understanding also allows to classify photon statistics throughout platforms according to conventional and unconventional features, with the effect of optimizing the correlations and with possible spectroscopic applications. In particular, we show how configurations that can realize simultaneously conventional and unconventional antibunching bring the best of both worlds: huge antibunching (unconventional) with large populations and being robust to dephasing (conventional).

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arXiv2020

The Origin of Antibunching in Resonance Fluorescence

Epitaxial quantum dots have emerged as one of the best single-photon sources, not only for applications in photonic quantum technologies but also for testing fundamental properties of quantum optics. One intriguing observation in this area is the scattering of photons with subnatural linewidth from a two-level system under resonant continuous wave excitation. In particular, an open question is whether these subnatural linewidth photons exhibit simultaneously antibunching as an evidence of single-photon emission. Here, we demonstrate that this simultaneous observation of subnatural linewidth and antibunching is not possible with simple resonant excitation. First, we independently confirm single-photon character and subnatural linewidth by demonstrating antibunching in a Hanbury Brown and Twiss type setup and using high-resolution spectroscopy, respectively. However, when filtering the coherently scattered photons with filter bandwidths on the order of the homogeneous linewidth of the excited state of the two-level system, the antibunching dip vanishes in the correlation measurement. Our experimental work is consistent with recent theoretical findings, that explain antibunching from photon-interferences between the coherent scattering and a weak incoherent signal in a skewed squeezed state.

cond-mat.mes-hall↗

arXiv2018

Joint subnatural-linewidth and single-photon emission from resonance fluorescence

Resonance fluorescence---the light emitted when exciting resonantly a two-level system---is a popular quantum source as it seems to inherit its spectral properties from the driving laser and its statistical properties from the two-level system, thus providing a subnatural-linewidth single-photon source. However, these two qualities do not actually coexist in resonance fluorescence, since an optical target detecting these antibunched photons will either be spectrally broad itself and not benefit from the spectrally narrow source, or match spectrally with the source but in this case the antibunching will be spoiled. We first explain this failure through a decomposition of the field-emission and how this gets affected by frequency resolution. We then show how to restore the sought joint subnatural linewidth and antibunched properties, by interfering the resonance fluorescence output with a coherent beam. We finally discuss how the signal that is eventually generated in this way features a new type of quantum correlations, with a plateau of antibunching which suppresses much more strongly close photon pairs. This introduces a new concept of perfect single-photon source.

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arXiv2018

Impact of detuning and dephasing on a laser-corrected subnatural-linewidth single-photon source

The elastic scattering peak of a resonantly driven two-level system has been argued to provide narrow-linewidth antibunched photons. Although independent measurements of spectral width on the one hand and antibunching on the other hand do seem to show that this is the case, a joint measurement reveals that only one or the other of these attributes can be realised in the direct emission. We discuss a scheme which interferes the emission with a laser to produce simultaneously single photons of subnatural linewidth. In particular, we consider the effect of dephasing and of the detuning between the driving laser and/or the detector with the emitter. We find that also in presence of dephasing, our scheme brings considerable improvement as compared to the standard scheme.

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arXiv2018

Photon correlations in both time and frequency

We summarise the main results that follow from our theory of frequency- and time-resolved photon correlations, which provides exact computations in nontrivial systems. We illustrate the theory with original results as interesting cases can be picked up from the endless configurations that abound in any quantum optical system. In particular, we compare our exact results with previous approximations, upgrade correlations to the case of photon bundles as otherwise no clear physical picture emerge, highlight the interest of measuring away from the peaks in rich landscapes of correlations and emphasize the joint time and frequency aspect of our theory.

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arXiv2018

Photon correlations in both time and frequency

While quantum mechanics precludes the perfect knowledge of so-called "conjugate" variables, such as time and frequency, we discuss the importance of compromising to retain a fair knowledge of their combined values. In the case of light, we show how time and frequency photon correlations allow us to identify a new type of photon emission, which can be used to design a new type of quantum source where we can choose the distribution in time and energy of the emitted photons.

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arXiv2017

Frequency-resolved Monte Carlo

We adapt the Quantum Monte Carlo method to the cascaded formalism of quantum optics, allowing us to simulate the emission of photons of known energy. Statistical processing of the photon clicks thus collected agrees with the theory of frequency-resolved photon correlations, extending the range of applications based on correlations of photons of prescribed energy, in particular those of a photon-counting character. We apply the technique to autocorrelations of photon streams from a two-level system under coherent and incoherent pumping, including the Mollow triplet regime where we demonstrate the direct manifestation of leapfrog processes in producing an increased rate of two-photon emission events.

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arXiv2017

Filtering Multiphoton Emission from State-of-the-Art Cavity QED

Engineering multiphoton states is an outstanding challenge with applications in multiple fields, such as quan- tum metrology, quantum lithography or even biological systems. State-of-the-art methods to obtain them rely on post-selection, multi-level systems or Rydberg atomic ensembles. Recently, it was shown that a strongly driven two-level system interacting with a detuned cavity mode can be engineered to continuously emit n-photon states. In the present work, we show that spectral filtering of its emission relaxes considerably the requirements on the system parameters even to the more accessible bad-cavity situation, opening up the possibility of implementing this protocol in a much wider landscape of different platforms. This improvement is based on a key observation: in the imperfect case where only a certain fraction of emission is composed of n-photon states, these have a well defined energy separated from the rest of the signal, which allows to reveal and purify multiphoton emission just by frequency filtering. We demonstrate these results by obtaining analytical expressions for relevant figures of merit of multiphoton emission, such as the n-photon coupling rate between cavity and emitter, the fraction of light emitted as n-photon states, and n-photon emission rates. This allows us to make a systematic study of such figures of merit as a function of the system parameters and demonstrate the viability of the protocol in several relevant types of cavity QED setups, where we take into account the impact of their respective experimental limitations.

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arXiv2017

Entangling one polariton with a photon: effect of interactions on a single-polariton quantum state

Polaritons are quasi-particles originating from the coupling of light with matter that demonstrated quantum phenomena at the many-particle mesoscopic level, such as BEC and superfluidity. A highly sought and long-time missing feature of polaritons is a genuine quantum manifestation of their dynamics at the single-particle level. Although they are conceptually perceived as entangled states and theoretical proposals abound for an explicit manifestation of their single-particle properties, so far their behaviour has remained fully accountable for by classical and mean-field theories. In this Article, we report the first experimental demonstration of a genuinely-quantum manifestation of microcavity polaritons, by swapping, in a two-photon entangled state generated by parametric down-conversion, a photon for a polariton. Furthermore, we show how single polaritons are affected by polariton-polariton interactions in a propaedeutic demonstration of their qualities for quantum information applications.

cond-mat.mes-hall↗

arXiv2017

Photon Correlations from the Mollow Triplet

Photon correlations between the photoluminescence peaks of the Mollow triplet have been known for a long time, and recently hailed as a resource for heralded single-photon sources. Here, we provide the full picture of photon-correlations at all orders (we deal explicitly with up to four photons) and with no restriction to the peculiar frequency windows enclosing the peaks. We show that a rich multi-photon physics lies between the peaks, due to transition involving virtual photons, and thereby much more strongly correlated than those transiting through the dressed states. Specifically, we show that such emissions occur in bundles of photons rather than as successive, albeit correlated, photons. We provide the recipe to frequency-filter the emission of the Mollow triplet to turn it into a versatile and tunable photon source, allowing in principle all scenarios of photon emission, with advantages already at the one-photon level, i.e., providing more strongly correlated heralded single-photon sources than those already known.

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arXiv2016

Criterion for Single Photon Sources

We propose a criterion to classify and compare sources of single photons: the $p$-norm of their $k$th-order photon correlations. While ideally one should use the uniform norm with $p\rightarrow\infty$, in practice, the 3-norm already allows a meaningful comparison and shows the serious limitations of the usual criterion based on the second order correlation $g^{(2)}$ only. We apply this new criterion to a large family of popular single photon sources and show that some of them do not, in fact, qualify for this function. The best sources from our selections consist of a cascade of two-level systems, improving on the otherwise standard low-power resonant excitation of a single two-level system.

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