arXiv subjects

Irina Novikova

Publications and source records attributed to Irina Novikova.

At least 55 records · Page 3Linked to original sources

arXiv2015

Effect of atomic diffusion on the Raman-Ramsey CPT resonances

We experimentally investigated the characteristics of two-photon transmission resonances in Rb vapor cells with different amount of buffer gas under the conditions of steady-state coherent population trapping (CPT) and pulsed Raman-Ramsey (RR-) CPT interrogation scheme. We particularly focused on the influence of the Rb atoms diffusing in and out of the laser beam. We showed that this effect modifies the shape of both CPT and Raman-Ramsey resonances, as well as their projected performance for CPT clock applications. In particular we found that at moderate buffer gas pressures RR-CPT did not improved the projected atomic clock stability compare to the regular steady-state CPT resonance.

physics.atom-ph↗

arXiv2014

Distinguishing nonlinear processes in atomic media via orbital angular momentum transfer

We suggest a technique based on the transfer of topological charge from applied laser radiation to directional and coherent optical fields generated in ladder-type excited atomic media to identify the major processes responsible for their appearance. As an illustration, in Rb vapours we analyse transverse intensity and phase profiles of the forward-directed collimated blue and near-IR light using self-interference and astigmatic transformation techniques when either or both of two resonant laser beams carry orbital angular momentum. Our observations unambiguously demonstrate that emission at 1.37 μm is the result of a parametric four-wave mixing process involving only one of the two applied laser fields.

quant-ph↗

arXiv2014

Excess optical quantum noise in atomic sensors

Enhanced nonlinear optical response of a coherent atomic medium is the basis for many atomic sensors, and their performance is ultimately limited by the quantum fluctuations of the optical read-out. Here we demonstrate that off-resonant interactions can significantly modify the quantum noise of the optical field, even when their effect on the mean signal is negligible. We illustrate this concept by using an atomic magnetometer based on the nonlinear Faraday effect: the rotation of the light polarization is mainly determined by the resonant light-induced spin alignment, which alone does not change the photon statistics of the optical probe. Yet, we found that the minimum noise of output polarization rotation measurements is above the expected shot noise limit. This excess quantum noise is due to off-resonant coupling and grows with atomic density. We also show that the detection scheme can be modified to reduce the measured quantum noise (even below the shot-noise limit) but only at the expense of the reduced rotational sensitivity. These results show the existence of previously unnoticed factors in fundamental limitations in atomic magnetometry and could have impacts in many other atom-light based precision measurements.

quant-ph↗

arXiv2014

Four-wave mixing in a ring cavity

We investigate a four-wave mixing process in an N interaction scheme in Rb vapor placed inside a low-finesse ring cavity. We observe strong amplification and generation of a probe signal, circulating in the cavity, in the presence of two strong optical pump fields. We study the variations in probe field gain and dispersion as functions of experimental parameters with an eye on potential application of such a system for enhanced rotation measurements. A density-matrix calculation is performed to model the system, and the theoretical results are compared to those of the experiment.

physics.atom-ph↗

arXiv2014

Propagation of a squeezed optical field in a medium with superluminal group velocity

We investigated the propagation of a squeezed optical field, generated via the polarization self-rotation (PSR) effect, with a sinusoidally-modulated degree of squeezing through an atomic medium with anomalous dispersion. We observed the advancement of the signal propagating through a resonant Rb vapor compared to the reference signal, propagating in air. The measured advancement time grew linearly with atomic density, reaching a maximum of $11 \pm 1~μ$s, which corresponded to a negative group velocity of $v_g\approx - 7,000~$m/s. We also confirmed that the increasing advancement was accompanied by a reduction of output squeezing levels due to optical losses, in good agreement with theoretical predictions.

physics.optics↗

arXiv2013

Generating squeezed vacuum field with non-zero orbital angular momentum with atomic ensembles

We demonstrated that by using a pump field with non-zero orbital angular momentum (OAM) in the polarization self-rotation squeezing process it is possible to generate a squeezed vacuum optical field with the matching OAM. We found a similar level of maximum quantum noise reduction for a first-order Laguerre-Gaussian pump beam and a regular Gaussian pump beam, even though the optimal operational conditions differed in these two cases. Also, we investigated the effect of self-defocusing on the level of the vacuum squeezing by simultaneously monitoring the minimum quantum noise level and the output beam transverse profile at various pump laser powers and atomic densities, and found no direct correlations between the increased beam size and the degree of measured squeezing.

quant-ph↗

arXiv2012

All-atomic generation and noise-quadrature filtering of squeezed vacuum in hot Rb vapor

With our all-atomic squeezing and filtering setup, we demonstrate control over the noise amplitudes and manipulation of the frequency-dependent squeezing angle of a squeezed vacuum quantum state by passing it through an atomic medium with electromagnetically induced transparency (EIT). We generate low sideband frequency squeezed vacuum using the polarization self-rotation effect in a hot Rb vapor cell, and input it into a second atomic vapor subject to EIT conditions. We use the frequency-dependent absorption of the EIT window to demonstrate an example of squeeze amplitude attenuation and squeeze angle rotation of the quantum noise quadratures of the squeezed probe. These studies have implications for quantum memory and storage as well as gravitational wave interferometric detectors.

quant-ph↗

arXiv2012

Controllable steep dispersion with gain in a four-level N-scheme with four-wave mixing

We present a theoretical analysis of the propagation of light pulses through a medium of four-level atoms, with two strong pump fields and a weak signal field in an N-scheme arrangement. We show that the generation of four-wave mixing has a profound effect on the signal field group velocity and absorption, allowing the signal field propagation to be tuned from superluminal to slow light regimes with amplification.

physics.atom-ph↗

arXiv2012

All-atomic source of squeezed vacuum with full pulse-shape control

We report on the generation of pulses of a low-frequency squeezed vacuum with noise suppression >2 dB below the standard quantum limit in a hot resonant 87 Rb vapor with polarization self-rotation. We demonstrate the possibility to precisely control the temporal profile of the squeezed noise quadrature by applying a calibrated longitudinal magnetic field, without degrading the maximum amount of squeezing.

quant-ph↗

arXiv2011

Observation of second-order hyper-Raman generation in LiNbO3 whispering-gallery mode disk resonators

In this manuscript we report experimental demonstration of nonlinear frequency conversion at several optical frequencies in a whispering-gallery mode resonator (WGMR). Due to the enhancement of nonlinear interactions inside a WGMR, interaction of a 1064 nm pump field with a LiNbO3 disk produced a weak, but measurable non-phase matched 532 nm second harmonic field at room temperature (>100C below the phase-matching temperature), for pump powers of a few tens of mW. For higher pump powers, we observed the generation of four additional fields at 545 nm, 559 nm, 573 nm, and 587 nm. The relative spectral shift between two consecutive fields corresponds to a 455 cm^-1 vibrational mode in LiNbO3 crystal. Our preliminary analysis indicates that these fields are the result of a multi-phonon hyper-Raman scattering, in which two photons of the pump field are converted into one photon of a higher-frequency field and one or several optical phonons.

physics.optics↗

arXiv2011

Optical vortex filtering for the detection of Electromagnetically Induced Transparency

We report the realization of an optical filter based on an optical vortex mask designed to exclusively detect a weak coherent laser field in the presence of much stronger spatially-overlapping field. We demonstrate the performance of such an optical vortex filter to eliminate the strong control field and detect only a weak optical field's transmission under the conditions of electromagnetically induced transparency. The attractive feature of such filter is its insensitivity to optical field frequencies and polarizations, which makes it applicable for a wide range of coherent processes.

physics.optics↗

arXiv2011

Light storage in an optically thick atomic ensemble under conditions of electromagnetically induced transparency and four-wave mixing

We study the modification of a traditional electromagnetically induced transparency (EIT) stored light technique that includes both EIT and four-wave mixing (FWM) in an ensemble of hot Rb atoms. The standard treatment of light storage involves the coherent and reversible mapping of one photonic mode onto a collective spin coherence. It has been shown that unwanted, competing processes such as four-wave mixing are enhanced by EIT and can significantly modify the signal optical pulse propagation. We present theoretical and experimental evidence to indicate that while a Stokes field is indeed detected upon retrieval of the signal field, any information originally encoded in a seeded Stokes field is not independently preserved during the storage process. We present a simple model that describes the propagation dynamics of the fields and the impact of FWM on the spin wave.

quant-ph↗

arXiv2010

Measurements of vector magnetic field using multiple electromagnetically induced transparency resonances in Rb vapor

We study intensity distribution of transmission resonances under the conditions of electromagnetically induced transparency (EIT) with lin||lin configuration in 87Rb vapor. We demonstrate that for various orientations of the external magnetic field all seven resolved EIT resonances exhibit maxima or minima at certain directions of the linear polarization of the laser field. This effect can be used for development of a high-precision vector EIT magnetometer.

physics.atom-ph↗

arXiv2009

Coherent population trapping resonances with linearly polarized light for all-optical miniature atomic clocks

We present a joint theoretical and experimental characterization of the coherent population trapping (CPT) resonance excited on the D1 line of 87Rb atoms by bichromatic linearly polarized laser light. We observe high-contrast transmission resonances (up to 25%), which makes this excitation scheme promising for miniature all-optical atomic clock applications. We also demonstrate cancellation of the first-order light shift by proper choice of the frequencies and relative intensities of the two laser field components. Our theoretical predictions are in good agreement with the experimental results.

physics.atom-ph↗

arXiv2009

Performance of a prototype atomic clock based on lin||lin coherent population trapping resonances in Rb atomic vapor

We report on the performance of the first table-top prototype atomic clock based on coherent population trapping (CPT) resonances with parallel linearly polarized optical fields (lin||lin configuration). Our apparatus uses a vertical cavity surface emitting laser (VCSEL) tuned to the D1 line of 87Rb with current modulation at the 87Rb hyperfine frequency. We demonstrate cancellation of the first-order light shift by proper choice of rf modulation power, and further improve our prototype clock stability by optimizing the parameters of the microwave lock loop. Operating in these optimal conditions, we measured a short-term fractional frequency stability (Allan deviation) 2*10^{-11} tau^{-1/2} for observation times 1s<tau< 20s. This value is limited by large VCSEL phase noise and environmental temperature fluctuation. Further improvements in frequency stability should be possible with an apparatus designed as a dedicated lin||lin CPT resonance clock with environmental impacts minimized.

physics.atom-ph↗

arXiv2009

Atomic Clocks and Coherent Population Trapping: Experiments for Undergraduate Laboratories

We demonstrate how to construct and operate a simple and affordable experimental apparatus, appropriate for an undergraduate setting, in order to produce and study coherent effects in atomic vapor and to investigate their applications for metrology. The apparatus consists of a vertical cavity surface emitting diode laser (VCSEL) directly current-modulated using a tunable microwave oscillator to produce multiple optical fields needed for the observation of the coherent population trapping (CPT). This effect allows very accurate measurement of the transition frequency between two ground state hyperfine sublevels (a "clock transition"), that can be used to construct a CPT-based atomic clock.

physics.ed-ph↗

arXiv2009

Vacuum squeezing via polarization self-rotation and excess noise in hot Rb vapors

We present experimental and theoretical analysis of quantum fluctuation in a vacuum field in the presence of orthogonal linearly polarized pump field propagating through a Rb vapor cell. Previously reported theoretical and experimental studies provided somewhat contradictory conclusions regarding the possibility to observe the "squeezed vacuum" -- the reduction of vacuum fluctuations below standard quantum limit -- in this system. Here, using the D1 transitions of Rb in a cell without buffer as as an example, we demonstrate that vacuum squeezing is corrupted by incoherent processes (such as spontaneous emission, elastic scattering, etc.), and its observation is only possible in a specific small region of the experimental parameter space. Numerical simulations, in good agreement with the experiment, demonstrate that the two excited state hyperfine levels play a crucial role in the squeezing and excess noise production. The significant influence of far-detuned atoms on the field fluctuations at low noise frequencies imposes the explicit consideration of the full velocity distribution of the atomic vapor.

quant-ph↗

arXiv2008

Optimal light storage in atomic vapor

We study procedures for the optimization of efficiency of light storage and retrieval based on the dynamic form of electromagnetically induced transparency (EIT) in warm Rb vapor. We present a detailed analysis of two recently demonstrated optimization protocols: a time-reversal-based iteration procedure, which finds the optimal input signal pulse shape for any given control field, and a procedure based on the calculation of an optimal control field for any given signal pulse shape. We verify that the two procedures are consistent with each other, and that they both independently achieve the maximum memory efficiency for any given optical depth. We observe good agreement with theoretical predictions for moderate optical depths (<25), while at higher optical depths the experimental efficiency falls below the theoretically predicted values. We identify possible effects responsible for this reduction in memory efficiency.

quant-ph↗