arXiv subjects

Daniel Z. Rossatto

Publications and source records attributed to Daniel Z. Rossatto.

14 recordsLinked to original sources

arXiv2026

Quantum Limits to Linewidth Narrowing in Single- and Few-Atom Cavity Electromagnetically Induced Transparency

Electromagnetically induced transparency (EIT) in cavities can narrow the transmission resonance below the empty-cavity linewidth. We investigate the limits of this narrowing from a single emitter to the few-atom regime. Using a Lindblad master equation for $N_{at}$ identical three-level atoms coupled to a cavity mode, driven by coherent probe and control fields, we compute the full width at half maximum (FWHM) of the transparency feature. In the strictly low-excitation limit, we derive an analytical cubic polynomial that captures the narrowing and recovers the known linear-response scaling. For finite probe powers, the achievable linewidth faces a quantum bound on the minimum achievable linewidth. Contrasting our model with a semiclassical approximation, we show this limitation arises from the unavoidable excitation of higher-order multiphoton states. Their intrinsically larger decay rates destroy the ideal single-excitation EIT dark state. Increasing $N_{at}$ enhances collective cooperativity, creating a multiphoton blockade that suppresses these detrimental excitations and yields a stepwise reduction of the minimum FWHM. Our results provide analytical boundaries for cavity-EIT linewidth control, guiding the optimization of narrowband filters and highly coherent light-matter interfaces.

quant-ph↗

arXiv2026

Quantum phase estimation for nondestructive monitoring and Wigner tomography of bosonic fields

Quantum phase estimation is usually introduced as an algorithmic primitive for extracting eigenphases of unitary operators. Here we show that, when implemented through a dispersive light-matter interaction, it can also be used as a nondestructive measurement tool for bosonic fields. We consider a bosonic mode coupled to a multi-qubit register and calibrate the photon-number dependent phase shifts so that the register performs a number-resolved quantum phase estimation readout. Repeating this readout during dissipative evolution enables nondestructive monitoring of photon-number dynamics. We then show that the same readout can be converted into a Wigner tomography reconstruction by applying phase-space displacements before the quantum phase estimation block. Numerical reconstructions for Fock, coherent, and even/odd Schrödinger cat states show the expected nonclassical phase-space structures and near-unity Wigner overlap fidelities. The protocol provides a unified route to nondestructive monitoring and state tomography of bosonic fields, with direct relevance for bosonic-state characterization, calibration, and control in superconducting quantum architectures.

quant-ph↗

arXiv2026

Preparation of Large Fock States in Resonators with High Probability

Large Fock states are important resources for bosonic quantum information and quantum-enhanced metrology, but preparing them with high probability at large excitation numbers remains challenging, as deterministic methods become increasingly control-intensive, while measurement-based approaches typically suffer from low heralding probabilities. Here we propose a protocol that combines quantum nondemolition photon-number encoding with quantum amplitude amplification to enable high-probability heralded generation of large Fock states. Starting from a cavity mode prepared in a coherent state, Quantum Phase Estimation encodes photon-number information into a multi-qubit register, while Quantum Amplitude Amplification boosts the probability of a desired target outcome before measurement. The scheme has an immediate implementation in dispersive circuit-QED, but can be analogously adapted to other bosonic platforms with QND photon-number readout, such as cavity-QED. With a register of up to eight qubits, near-deterministic preparation of Fock states with hundreds of excitations is possible. We also show that the protocol can serve as the first stage of an extension toward generating a two-mode NOON state via a conditional beam-splitter operation.

quant-ph↗

arXiv2026

Quantum Resonator as a Directional Quantum Emitter

Single-photon sources are essential for testing fundamental physics and for the development of quantum technologies. In this work a single-photon source is investigated, based on a two-photon Jaynes-Cummings system, where the resonator works as the quantum emitter rather than the two-level system. This role reversal provides certain advantages, such as robustness against losses from the two-level system (e.g., dephasing), as it remains in its ground state throughout the entire dynamics. This provides higher efficiency, purity, and indistinguishability compared to sources based on the usual Jaynes-Cummings model under the same parameter conditions in both models. Another advantage of this system is the possibility of direct conversion of a coherent excitation pulse with one photon on average to a single-photon pulse with efficiency, purity, and indistinguishability above $90\%$. Since the entire excitation pulse is consumed in the generation of a single photon, the system also minimizes energy waste. The potential for implementing the two-photon JC model across different platforms expands the possibilities for controlled single-photon generation in applications in quantum information processing and computation.

quant-ph↗

arXiv2026

Building Block For Universal Continuous Variables Computation In Superconducting Devices

Continuous variable (CV) quantum computation offers an alternative to qubit-based computing by exploiting the infinite-dimensional Hilbert space of bosonic modes. Despite recent progress, superconducting platforms have yet to demonstrate a scalable architecture capable of universal computation. Here, we design and numerically simulate a two-layer superconducting architecture that implements all five interactions of the universal CV gate set (rotation, displacement, squeezing, Kerr, and beam splitter) within experimentally accessible regimes. To this end, we employ a DC-SQUID as the bosonic mode, a fluxonium qubit to mediate nonlinear interactions, and two ancillary qubits that enable Gaussian and multi-mode operations. By tuning fluxes and frequencies, we achieve high fidelities ($\geq 98\%$) across all gates within state-of-the-art parameter ranges. The modular nature of the design allows straightforward scaling, establishing a feasible pathway toward high-fidelity, universal CV quantum computation based on superconducting circuits.

quant-ph↗

arXiv2025

Beam splitter for dark and bright states of light

Beam splitters are indispensable elements in optical and photonic systems, and are therefore employed in both classical and quantum technologies. Depending on the intended application, these devices can divide incident light according to its power, polarization state, or wavelength. In this work, we theoretically present a novel type of beam splitter capable of separating a light beam into its two-mode bright and dark components. We propose a prototype based on an optical cross-cavity system resonantly coupled to a $Λ$-type three-level atom. The dark component of the incoming light is transmitted because the antisymmetric collective mode of the cavity setup is decoupled from the atom. Meanwhile, in a high-cooperativity regime, the bright component is reflected due to Autler-Townes splitting, which arises from the strong coupling between the atom and the symmetric collective mode of the cavity setup. Although the device requires only a two-level atom to operate, using a three-level atom allows the device to be turned on or off by controlling the atomic ground state. Our results pave the way for new applications of beam splitters that leverage the collective properties of light. Manipulating and exploiting this additional degree of freedom can advance the field of quantum optics and contribute to the development of quantum technologies.

quant-ph↗

arXiv2025

High Efficiency Storage of Quasi-Classical and Quantum States in Coupled Resonators

We propose an optical model in which both quantum and quasi-classical states can be ideally stored using coupled resonators. The protocol is based on a time-dependent coupling between two cavities, carefully modulated to allow the complete transfer of an external propagating field from one cavity to another. The system maintains high storage efficiency (above $99.99\%$) even when error sources are introduced (up to $5\%$) in the coupling, such as amplitude deviation or a time delay between field propagation and coupling control. Furthermore, this procedure can be extended to store entangled states by considering either a pair of systems or bimodal cavities. Due to its high efficiency, this model may find application in current quantum technologies, such as quantum memories and quantum batteries, which rely on efficient quantum state storage.

quant-ph↗

arXiv2024

Universal quantum computation using atoms in cross-cavity systems

Quantum gates are the building blocks of quantum circuits, which in turn are the cornerstones of quantum information processing. In this work, we theoretically investigate a single-step implementation of both a universal two- (CNOT) and three-qubit (quantum Fredkin) gates in a cross-cavity setup coupled to a $Λ$-type three-level atom. Within a high-cooperativity regime, the system exhibits an atomic-state-dependent $π$-phase gate involving the two-mode single-photon bright and dark states of the input light pulses. This allows for the controlled manipulation of light states by the atom and vice versa. Our results indicate these quantum gates can be implemented with high probability of success using the state-of-the-art parameters, either for the weak- or strong-coupling regime, where the quantum interference is due to an electromagnetically-induced-transparency-like phenomenon and the Autler-Townes splitting, respectively. This work not only paves the way for implementing quantum gates in a single step using simple resources, thus avoiding the need to chain basic gates together in a circuit, but it also endorses the potential of cross-cavity systems for realizing universal quantum computation.

quant-ph↗

arXiv2021

Estimating the degree of non-Markovianity using machine learning

In the last years, the application of machine learning methods has become increasingly relevant in different fields of physics. One of the most significant subjects in the theory of open quantum systems is the study of the characterization of non-Markovian memory effects that emerge dynamically throughout the time evolution of open systems as they interact with their surrounding environment. Here we consider two well-established quantifiers of the degree of memory effects, namely, the trace distance and the entanglement-based measures of non-Markovianity. We demonstrate that using machine learning techniques, in particular, support vector machine algorithms, it is possible to estimate the degree of non-Markovianity in two paradigmatic open system models with high precision. Our approach can be experimentally feasible to estimate the degree of non-Markovianity, since it requires a single or at most two rounds of state tomography.

quant-ph↗

arXiv2021

Superposition of two-mode squeezed states for quantum information processing and quantum sensing

We investigate superpositions of two-mode squeezed states (TMSSs), which have potential applications to quantum information processing and quantum sensing. Firstly we study some properties of these nonclassical states such as the statistics of each mode and the degree of entanglement between the two modes, which can be higher than that of a TMSS with the same degree of squeezing. The states we consider can be prepared by inducing two-mode Jaynes-Cummings and anti-Jaynes-Cummings interactions in a system of two modes and a spin-$\tfrac{1}{2}$ particle, for instance in the trapped ion domain, as described here. We show that when two harmonic oscillators are prepared in a superposition of two TMSSs, each reduced single-mode state can be advantageously employed to sense arbitrary displacements of the mode in phase space. The Wigner function of this reduced state exhibits a symmetrical peak centered at the phase-space origin, which has the convenient peculiarity of getting narrower in both quadratures simultaneously as the average photon number increases. This narrow peakcan be used as the pointer of our quantum sensor, with its position in phase space indicating the displacement undergone by the oscillator.

quant-ph↗

arXiv2019

Multiphoton Jaynes-Cummings Model: Arbitrary Rotations in Fock Space and Quantum Filters

The multiphoton Jaynes-Cummings model is investigated and applications in quantum information science are explored. Considering the strong atom-field coupling regime and an $N$-photon interaction, a nonlinear driving field can perform an arbitrary rotation in the Fock space of the cavity mode involving the vacuum and an $M$-Fock state, with $M<N$. Besides, driving the cavity mode with a linear coherent field (superposition of many Fock states), only the cavity states within the Fock subspace {$|0\rangle,|1\rangle,..., |N-1\rangle$} can be populated, i.e., we show how to implement a Fock state filter, or quantum scissor, that restricts the dynamics of a given bosonic mode to a limited Hilbert space. Such a device can be employed as a generator of finite-dimensional quantum-optical states and also as a quantum-optical intensity limiter, allowing as a special case the deterministic generation of single-photon pulses. On the other hand, our system also provides a very rich physics in the weak atom-field coupling regime, multiphoton electromagnetically-induced-transparency-like phenomena, inducing a narrow (controllable) reflectivity window for nonlinear probe fields. These results are useful for applications in quantum information processing and also motivate further investigations, e.g., the use of an $N$-photon Jaynes-Cummings system as a qudit with harmonic spectrum and the exploration of multiphoton quantum interference.

quant-ph↗

arXiv2017

Heralded entangling quantum gate via cavity-assisted photon scattering

We theoretically investigate the generation of heralded entanglement between two identical atoms via cavity-assisted photon scattering in two different configurations, namely either both atoms confined in the same cavity or trapped into locally separated ones. Our protocols are given by a very simple and elegant single-step process, whose key mechanism is a controlled-phase-flip gate implemented by impinging a single photon on single-sided cavities. In particular, when the atoms are localized in remote cavities, we introduce a single-step parallel quantum circuit instead of the serial process extensively adopted in the literature. We also show that such parallel circuit can be straightforwardly applied to entangle two macroscopic clouds of atoms. Both protocols proposed here predict a high entanglement degree with a success probability close to the unity for the state-of-the-art parameters. Among other applications, our proposal and its extension to multiple atom-cavity systems step toward a suitable route for quantum networking, in particular for quantum state transfer, quantum teleportation and nonlocal quantum memory.

quant-ph↗

arXiv2016

Spectral Classification of Coupling Regimes in the Quantum Rabi Model

The quantum Rabi model is in the scientific spotlight due to the recent theoretical and experimental progress. Nevertheless, a full-fledged classification of its coupling regimes remains as a relevant open question. We propose a spectral classification dividing the coupling regimes into three regions based on the validity of perturbative criteria on the quantum Rabi model, which allows us the use of exactly solvable effective Hamiltonians. These coupling regimes are i) the perturbative ultrastrong coupling regime which comprises the Jaynes-Cummings model, ii) a region where non-perturbative ultrastrong and non-perturbative deep strong coupling regimes coexist, and iii) the perturbative deep strong coupling regime. We show that this spectral classification depends not only on the ratio between the coupling strength and the natural frequencies of the unperturbed parts, but also on the energy to which the system can access. These regimes additionally discriminate the completely different behaviors of several static physical properties, namely the total number of excitations, the photon statistics of the field, and the cavity-qubit entanglement. Finally, we explain the dynamical properties which are traditionally associated to the deep strong coupling regime, such as the collapses and revivals of the state population, in the frame of the proposed spectral classification.

quant-ph↗

arXiv2013

Probing the degree of non-Markovianity for independent and common environments

We study the non-Markovianity of the dynamics of open quantum systems focusing on the cases of independent and common environmental interactions. We investigate the degree of non-Markovianity quantified by two distinct measures proposed by Luo, Fu and Song (LFS) and Breuer, Laine and Pillo (BLP). We show that the amount of non-Markovianity, for a single and a pair of qubits, depends on the quantum process, the proposed measure and whether the environmental interaction is collective or independent. In particular, we demonstrate that while the degree of non-Markovianity generally increases with the number of the qubits in the system for independent environments, the same behavior is not always observed for common environments. In the latter case, our analysis suggests that the amount of non-Markovianity could increase or decrease depending on the properties of the considered quantum process.

quant-ph↗