arXiv subjects

F. Goldfarb

Publications and source records attributed to F. Goldfarb.

At least 19 recordsLinked to original sources

arXiv2024

Long-range interactions revealed by collective spin noise spectra in atomic vapors

We report anomalous features in the spin noise spectroscopy (SNS) of a thin cell of a dense vapor of alkali atoms. At high densities and close to resonance, we observe a dramatic broadening of the spin noise spectra as well as an unexpected extra low-frequency noise component. With the help of a two-body model and simulations, we show that these features are the hallmark of a strong, long-range dipole-dipole interaction within the ensemble. The additional low-frequency noise reveals the correlated evolution of pair of atoms beyond the impact approximation. In this regime, we demonstrate that spin noise can no longer be obtained from one-body dynamics, opening the way for the characterization of many-body spin noise, atomic entanglement or higher order spin correlators in atomic vapors using SNS.

quant-ph↗

arXiv2024

Anomalous high-density spin noise in a strongly interacting atomic vapor

Spin noise spectroscopy (SNS) has become a mainstream approach to probe the dynamics of a spin ensemble in and out of equilibrium. Current models describing spin noise in interacting samples are based on an effective single particle dynamics in a bath. Here, we report the observation of a strong interaction regime which significantly affects the spin dynamics. Performing SNS in a dense Rubidium vapor, we observe anomalous distortions of the usual spin noise spectra, which we attribute to resonant dipole-dipole interaction within the ensemble. As the density of the vapor increases, we observe a dramatic broadening of the usual resonances and the emergence of an unexpected extra low-frequency noise component. We use a simple microscopic two-body numerical model to reproduce and discuss these observations. Our results suggests that the spectra cannot be described by usual models of single-atom dynamics and arise from the evolution of interacting pair of atoms. This work opens the way to the study of many-body spin noise or higher order correlators in atomic vapors using SNS.

quant-ph↗

arXiv2023

Creation and dynamics of spin fluctuations in a noisy magnetic field

We theoretically and numerically investigate the spin fluctuations induced in a thermal atomic ensemble by an external fluctuating uniaxial magnetic field, in the context of a standard spin noise spectroscopy (SNS) experiment. We show that additional spin noise is excited, which dramatically depends on the magnetic noise variance and bandwidth, as well as on the power of the probe light and its polarization direction. We develop an analytical perturbative model proving that this spin noise first emerges from the residual optical pumping in the medium, which is then converted into spin fluctuations by the magnetic noise and eventually detected using SNS. The system studied is a spin-1 system, which thus shows both Faraday rotation and ellipticity noises induced by the random magnetic fluctuations. The analytical model gives results in perfect agreement with the numerical simulations, with potential applications in future experimental characterization of stray field properties and their influence on spin dynamics.

quant-ph↗

arXiv2022

Birefringence and dichroism effects in the spin noise spectra of a spin-1 system

We perform spin noise spectroscopy experiments in metastable helium atoms at room temperature, with a probe light whose frequency is blue detuned from the D0 line. Both circular birefringence fluctuations (Faraday noise) and linear birefringence fluctuations (ellipticity noise) are explored theoretically and experimentally. In particular, it is shown that in both cases but for different optical detunings, two noise resonances are isolated at the Larmor frequency and at twice the Larmor frequency with a behaviour, which strongly depends on the orientation of the probe field polarization. The simple structure of metastable helium allows us to probe, model and explain the changes in the behavior of these peaks in terms of circular and linear dichroisms and birefringences as well as in terms of spin oscillation modes.

quant-ph↗

arXiv2017

Coherent Population Oscillation-Based Light Storage

We theoretically study the propagation and storage of a classical field in a $Λ$-type atomic medium using coherent population oscillations (CPOs). We show that the propagation eigenmodes strongly relate to the different CPO modes of the system. Light storage in such modes is discussed by introducing a "populariton" quantity, a mixture of populations and field, by analogy to the dark state polariton used in the context of electromagnetically induced transparency light storage protocol. As experimentally shown, this memory relies on populations and is then - by contrast with usual Raman coherence optical storage protocols - robust to dephasing effects.

quant-ph↗

arXiv2016

Nonvolatile optical memory via recoil-induced resonance in a pure two-level system

We report on the storage of light via the phenomenon of recoil-induced resonance in a pure two- level system of cold cesium atoms. We use a strong coupling beam and a weak probe beam to couple different external momentum states of the cesium atom via two-photon Raman interaction which leads to the storage of the optical information of the probe beam. We have also measured the probe transmission spectrum, as well as the light storage spectrum which reveals very narrow subnatural resonance features showing absorption and gain. We have demonstrated that this memory presents the unique property of being insensitive to the reading process, which does not destroy the stored information leading to a memory lifetime limited only by the atomic thermal motion.

quant-ph↗

arXiv2016

Phase-sensitive amplification via coherent population oscillations in metastable helium at room temperature

We report our experimental results on phase-sensitive amplification (PSA) in non-degenerate signal-idler configuration using ultra-narrow coherent population oscillations in metastable helium at room temperature. We achieved a high PSA gain of nearly 7 with a bandwidth of 200 kHz, by using the system at resonance in a single-pass scheme. Further, the measured minimum gain is close to the ideal value, showing that we have a pure PSA. This is also confirmed from our phase-to-phase transfer curves measurements, illustrating that we have a nearly perfect squeezer, which is interesting for a variety of applications.

quant-ph↗

arXiv2014

Light storage in a room temperature atomic vapor based on coherent population oscillations

We report the experimental observation of Coherent Population Oscillation (CPO) based light storage in an atomic vapor cell at room temperature. Using the ultranarrow CPO between the ground levels of a $Λ$ system selected by polarization in metastable $^4$He, such a light storage is experimentally shown to be phase preserving. As it does not involve any atomic coherences it has the advantage of being robust to dephasing effects such as small magnetic field inhomogeneities. The storage time is limited by the population lifetime of the ground states of the $Λ$ system.

physics.atom-ph↗

arXiv2014

Light storage via coherent population oscillation in a thermal cesium vapor

We report on the storage of light via the phenomenon of Coherent Population Oscillation (CPO) in an atomic cesium vapor at room temperature. In the experiment the optical information of a probe field is stored in the CPO of two ground states of a Lambda three-level system formed by the Zeeman sublevels of the hyperfine transition F = 3 - F' = 2 of cesium D2 line. We show directly that this CPO based memory is very insensitive to stray magnetic field inhomogeneities and presents a lifetime which is mainly limited only by atomic motion. A theoretical simulation of the measured spectra was also developed and is in very good agreement with the experiment.

quant-ph↗

arXiv2014

Observation and measurement of an extra phase shift created by optically detuned light storage in metastable helium

Electromagnetically induced transparency (EIT) in metastable helium at room temperature is experimentally shown to exhibit light storage capabilities for intermediate values of the detuning between the coupling and probe beams and the center of the atomic Doppler profiles. An additional phase shift is shown to be imposed to the retrieved pulse of light when the EIT protocol is performed at non-zero optical detunings. The value of this phase shift is measured for different optical detunings between 0 and 2 GHz, and its origin is discussed.

quant-ph↗

arXiv2013

Symplectic approach to the amplification process in a nonlinear fiber

We analyze the amplification processes occurring in a nonlinear fiber, either driven with one or two pumps. After determining the solution for the signal and idler fields resulting from these amplification processes, we analyze the physical transformations that these fields undergo. To this aim, we use a Bloch-Messiah decomposition for the symplectic transformation governing the fields evolution. Although conceptually equivalent to other works in this area [McKinstrie and Karlsson, Opt. Expr. 21, 1374 (2013)], this analysis is intended to be particularly simple, gathering results spread in the literature, which is useful for guiding practical implementations. Furthermore, we present a study of the correlations of the signal-idler fields at the amplifier output. We show that these fields are correlated, study their correlations as a function of the pump power, and stress the impact of these correlations on the amplifier noise figure. Finally, we address the effect of losses. We determine whether it is advantageous to consider a link consisting in an amplifying non-linear fiber, followed by a standard fiber based lossy transmission line, or whether the two elements should be reversed, by comparing the respective noise figures.

quant-ph↗

arXiv2012

Ultranarrow CPO resonance in a Λ-type atomic system

It is well known that ultranarrow electromagnetically induced transparency (EIT) resonances can be observed in atomic gases at room temperature. We report here the experimental observation of another type of ultranarrow resonances, as narrow as the EIT ones, in a Λ-system selected by light polarization in metastable 4He at room temperature. It is shown to be due to coherent population oscillations in an open two-level system (TLS). For perpendicular linearly polarized coupling and probe beams, this system can be considered as two coupled open TLSs, in which the ground state populations exhibit anti-phase oscillations. We also predict theoretically that in case of two parallel polarizations, the system would behave like a closed TLS, and the narrow resonance associated with these oscillations would disappear.

physics.atom-ph↗

arXiv2012

Anomalous ring-down effects and breakdown of the decay rate concept in optical cavities with negative group delay

Propagation of light pulses through negative group velocity media is known to give rise to a number of paradoxical situations that seem to violate causality. The solution of these paradoxes has triggered the investigation of a number of interesting and unexpected features of light propagation. Here we report a combined theoretical and experimental study of the ring-down oscillations in optical cavities filled with a medium with such a strongly negative frequency dispersion to give a negative round-trip group delay time. We theoretically anticipate that causality imposes the existence of additional resonance peaks in the cavity transmission, resulting in a non-exponential decay of the cavity field and in a breakdown of the cavity decay rate concept. Our predictions are validated by simulations and by an experiment using a room-temperature gas of metastable helium atoms in the detuned electromagnetically induced transparency regime as the cavity medium.

quant-ph↗

arXiv2011

Observation of noise phase locking in a single-frequency VECSEL

We present an experimental observation of phase locking effects in the intensity noise spectrum of a semiconductor laser. These noise correlations are created in the medium by coherent carrier-population oscillations induced by the beatnote between the lasing and non-lasing modes of the laser. This phase locking leads to a modification of the intensity noise profile at around the cavity free-spectral-range value. The noise correlations are evidenced by varying the relative phase shift between the laser mode and the non-lasing adjacent side modes.

physics.optics↗

arXiv2011

Interacting double dark resonances in a hot atomic vapor of helium

We experimentally and theoretically study two different tripod configurations using metastable helium ($^4$He*), with the probe field polarization perpendicular and parallel to the quantization axis, defined by an applied weak magnetic field. In the first case, the two dark resonances interact incoherently and merge together into a single EIT peak with increasing coupling power. In the second case, we observe destructive interference between the two dark resonances inducing an extra absorption peak at the line center.

quant-ph↗

arXiv2010

Observation of slow light in the noise spectrum of a vertical external cavity surface emitting laser

The role of coherent population oscillations is evidenced in the noise spectrum of an ultra-low noise lasers. This effect is isolated in the intensity noise spectrum of an optimized single-frequency vertical external cavity surface emitting laser. The coherent population oscillations induced by the lasing mode manifest themselves through their associated dispersion that leads to slow light effects probed by the spontaneous emission present in the non-lasing side modes.

physics.optics↗

arXiv2009

Observation of Electromagnetically Induced Transparency and Slow Light in the Dark State - Bright State Basis of CPT

Electromagnetically induced transparency (EIT) is observed in a three-level system composed of an excited state and two coherent superpositions of the two ground-state levels. This peculiar ground state basis is composed of the so-called bright and dark states of the same atomic system in a standard coherent population trapping configuration. The characteristics of EIT, namely, width of the transmission window and reduced group velocity of light, in this unusual basis, are theoretically and experimentally investigated and are shown to be essentially identical to those of standard EIT in the same system.

quant-ph↗

arXiv2009

Realistic theory of electromagnetically-induced transparency and slow light in a hot vapor of atoms undergoing collisions

We present a realistic theoretical treatment of a three-level $Λ$ system in a hot atomic vapor interacting with a coupling and a probe field of arbitrary strengths, leading to electromagnetically-induced transparency and slow light under the two-photon resonance condition. We take into account all the relevant decoherence processes including col5Blisions. Velocity-changing collisions (VCCs) are modeled in the strong collision limit effectively, which helps in achieving optical pumping by the coupling beam across the entire Doppler profile. The steady-state expressions for the atomic density-matrix elements are numerically evaluated to yield the experimentally measured response characteristics. The predictions, taking into account a dynamic rate of influx of atoms in the two lower levels of the $Λ$, are in excellent agreement with the reported experimental results for $^4$He*. The role played by the VCC parameter is seen to be distinct from that by the transit time or Raman coherence decay rate.

quant-ph↗