arXiv subjects

A. Cidrim

Publications and source records attributed to A. Cidrim.

13 recordsLinked to original sources

arXiv2025

Postselected Entangled States by Photon Detection

Postselection is a non-deterministic mechanism to entangle subsystems, often used in weakly-excited systems. We here show how highly-excited ensembles of two-level emitters can be entangled by photon detection. A collective spin is formed, characterized by a squeezing parameter detected by far-field measurements. While decoherence is detrimental to this conditional entanglement, successive photon detections act as a purification process and restores the spin squeezing. Our work opens up new avenues for the generation of postselected entanglement in open quantum systems.

quant-ph↗

arXiv2025

Unraveling Dicke Superradiant Decay with Separable Coherent Spin States

We show that idealized Dicke superradiant decay from a fully inverted state can at all times be described by a positive statistical mixture of coherent spin states (CSS). Since CSS are separable, this implies that no entanglement is involved in Dicke decay. Based on this result, we introduce a new numerical quantum trajectory approach leading to low-entanglement unravelings. This opens up new possibilities for employing matrix product state (MPS) techniques for large-scale numerical simulations with collective decay processes.

quant-ph↗

arXiv2024

Light Statistics from Large Ensembles of Independent Two-level Emitters: Classical or Non-classical?

We investigate the photon statistics of an ensemble of coherently driven non-interacting two-level atoms in the weak driving regime. As it turns out, the system displays unique emission characteristics that are strongly in contrast to the emission of classical oscillating dipoles. By deriving the second-order autocorrelation function, we show that extraordinary two-photon correlations are obtained, ranging from strong antibunching to superbunching. These features are enhanced by disorder in the emitter positions, and the control parameter is the number of excitations in the system. We observe the appearance of bunching and antibunching when the light is scattered by the atoms predominantly coherently, i.e., mimicking classical Rayleigh scattering, whereas thermal photon statistics is obtained when the light is scattered via spontaneous decay, a well-known quantum effect. The underlying mechanism is the interplay between coherent scattering, which exhibits spatial fluctuations due to interference, and dissipation in the form of isotropic spontaneous decay.

quant-ph↗

arXiv2024

Coherent Control of Photon Correlations in Trapped Ion Crystals

While the spontaneous emission from independent emitters provides spatially uncorrelated photons - a typical manifestation of quantum randomness, the interference of the coherent scattering leads to a well-defined intensity pattern - a feature described by linear optics. We here demonstrate experimentally how the interplay between the two mechanisms in large systems of quantum emitters leads to spatial variations of photon correlations. The implementation with trapped ion crystals in free space allows us to observe the anti-correlation between photon rates and variance of the photon number distributions in chains of up to 18 ions. For smaller crystals of four ions, the transition from a sub-Poissonian to a super-Poissonian variance of the photon number in the scattered light is reported. For higher numbers of scatterers, the photon statistics still display a strong deviation from the fully incoherent scattering case. Our results illustrate how the interference of coherent scattering, combined with spontaneous emission, provides a control mechanism for the light statistics.

quant-ph↗

arXiv2022

Universal dynamics of a turbulent superfluid Bose gas

We study the emergence of universal scaling in the time-evolving momentum distribution of a harmonically trapped three-dimensional Bose-Einstein condensate, parametrically driven to a turbulent state. We demonstrate that the out-of-equilibrium dynamics post excitation is described by a single function due to nearby non-thermal fixed points. The observed behavior connects the dynamics of a quantum turbulent state to several far-from-equilibrium phenomena. We present a controllable protocol to explore universality in such systems, obtaining scaling exponents that can serve as reference for future theoretical investigations. Our experimental results thus offer a promising route to investigate the complex dynamics of the quantum turbulent regime under a novel perspective.

cond-mat.quant-gas↗

arXiv2021

Soliton trains after interaction quenches in Bose mixtures

We investigate the quench dynamics of a two-component Bose mixture and study the onset of modulational instability, which leads the system far from equilibrium. Analogous to the single-component counterpart, this phenomenon results in the creation of trains of bright solitons. We provide an analytical estimate of the number of solitons at long times after the quench for each of the two components based on the most unstable mode of the Bogoliubov spectrum, which agrees well with our simulations for quenches to the weak attractive regime when the two components possess equal intraspecies interactions and loss rates. We also explain the significantly different soliton dynamics in a realistic experimental homonuclear potassium mixture in terms of different intraspecies interaction and loss rates. We investigate the quench dynamics of the particle number of each component estimating the characteristic time for the appearance of modulational instability for a variety of interaction strengths and loss rates. Finally, we evaluate the influence of the beyond-mean-field contribution, which is crucial for the ground-state properties of the mixture, in the quench dynamics for both the evolution of the particle number and the radial width of the mixture. In particular, even for quenches to strongly attractive effective interactions, we do not observe the dynamical formation of solitonic droplets.

cond-mat.quant-gas↗

arXiv2021

Dipole-dipole frequency shifts in multilevel atoms

Dipole-dipole interactions lead to frequency shifts that are expected to limit the performance of next-generation atomic clocks. In this work, we compute dipolar frequency shifts accounting for the intrinsic atomic multilevel structure in standard Ramsey spectroscopy. When interrogating the transitions featuring the smallest Clebsch-Gordan coefficients, we find that a simplified two-level treatment becomes inappropriate, even in the presence of large Zeeman shifts. For these cases, we show a net suppression of dipolar frequency shifts and the emergence of dominant non-classical effects for experimentally relevant parameters. Our findings are pertinent to current generations of optical lattice and optical tweezer clocks, opening a way to further increase their current accuracy, and thus their potential to probe fundamental and many-body physics.

cond-mat.quant-gas↗

arXiv2020

Quantum turbulence in Bose-Einstein condensates: present status and new challenges ahead

The field of quantum turbulence is related to the manifestation of turbulence in quantum fluids, such as liquid helium and ultracold gases. The concept of turbulence in quantum systems was conceived more than 70 years ago by Onsager and Feynman, but the study of turbulent ultracold gases is very recent. Although it is a young field, it already provides new approaches to the problem of turbulence. We review the advances and present status, of both theory and experiments, concerning atomic Bose-Einstein condensates (BECs). We present the difficulties of characterizing turbulence in trapped BECs, if compared to classical turbulence or turbulence in liquid helium. We summarize the challenges ahead, mostly related to the understanding of fundamental properties of quantum turbulence, including what is being done to investigate them.

cond-mat.quant-gas↗

arXiv2020

Photon blockade with ground-state neutral atoms

We show that induced dipole-dipole interactions allow for photon blockade in subwavelength ensembles of two-level, ground-state neutral atoms. Our protocol relies on the energy shift of the single-excitation, superradiant state of $N$ atoms, which can be engineered to yield an effective two-level system. A coherent pump induces Rabi oscillation between the ground state and a collective bright state, with at most a single excitation shared among all atoms. The possibility of using clock transitions that are long-lived and relatively robust against stray fields, alongside new prospects on experiments with subwavelength lattices, makes our proposal a promising alternative for quantum information protocols.

cond-mat.quant-gas↗

arXiv2017

Vinen turbulence via the decay of multicharged vortices in trapped atomic Bose-Einstein condensates

We investigate a procedure to generate turbulence in a trapped Bose-Einstein condensate which takes advantage of the decay of multicharged vortices. We show that the resulting singly-charged vortices twist around each other, intertwined in the shape of helical Kelvin waves, which collide and undergo vortex reconnections, creating a disordered vortex state. By examining the velocity statistics, the energy spectrum, the correlation functions and the temporal decay, and comparing these properties with the properties of ordinary turbulence and observations in superfluid helium, we conclude that this disordered vortex state can be identified with the `Vinen' regime of turbulence which has been discovered in the context of superfluid helium.

cond-mat.quant-gas↗

arXiv2016

Twisted unwinding of multi-charged quantum vortex and generation of turbulence in atomic Bose-Einstein condensates

We report the observation of the twisted decay of quadruply charged vortices in an atomic Bose-Einstein condensate. Supporting numerical simulations show that the singly-charged vortices, which result from the decay of a multi-charged vortex, twist around intertwined in the shape of helical Kelvin waves. Finally, we propose to apply this effect to generate an almost isotropic state of turbulence which we characterize in terms of the velocity statistics.

cond-mat.quant-gas↗

arXiv2015

Controlled polarization of two-dimensional quantum turbulence in atomic Bose-Einstein condensates

We propose a scheme for generating two-dimensional turbulence in harmonically trapped atomic condensates with the novelty of controlling the polarization (net rotation) of the turbulence. Our scheme is based on an initial giant (multicharged) vortex which induces a large-scale circular flow. Two thin obstacles, created by blue-detuned laser beams, speed up the decay of the giant vortex into many singly-quantized vortices of the same circulation; at the same time, vortex-antivortex pairs are created by the decaying circular flow past the obstacles. Rotation of the obstacles against the circular flow controls the relative proportion of positive and negative vortices, from the limit of strongly anisotropic turbulence (almost all vortices having the same sign) to that of isotropic turbulence (equal number of vortices and antivortices). Using the new scheme, we numerically study quantum turbulence and report on its decay as a function of the polarization.

cond-mat.quant-gas↗

arXiv2014

Internal Decoherence of a Gaussian Wave Packet in a Harmonic Potential

We have studied the quantum dissipative problem of a Gaussian wave packet under the influence of a harmonic potential. A phenomenological approach to dissipation is adopted in the light of the well-known model in which the environment is composed of a bath of non-interacting harmonic oscillators. As one of the effects of the coupling to the bath is the evolution of an initially pure wave packet into a statistical mixture, we estimate the characteristic time elapsed for this to occur for different regimes of temperature, damping, and also different initial states.

quant-ph↗