Characterizing two-mode-squeezed light from four-wave mixing in rubidium vapor for quantum sensing and information processing.

We present a study of homodyne measurements of two-mode, vacuum-seeded, quadrature-squeezed light generated by four-wave mixing in warm rubidium vapor. Our results reveal that the vacuum squeezing can extend down to measurement frequencies of less than 1 Hz, and the squeezing bandwidth, similar to the seeded intensity-difference squeezing measured in this system, reaches up to approximately 20 MHz for typical pump parameters. By dividing the squeezing bandwidth into smaller frequency bins, we show that different sideband frequencies represent independent sources of two-mode squeezing. These properties are useful for quantum sensing and quantum information processing applications. We also investigate the impact of group velocity delays on the correlations in the system, which allows us to optimize the useful spectrum.

Oscillatory trajectory of an optical beam propagating in free space.

We describe the experimental observation of nonrectilinear trajectories of a nearly Gaussian light beam propagating in free space, after reflecting from a glass-air interface near critical incidence. The angular-dependent reflection coefficients modulate the incident beam's angular spectrum, shifting the reflected beam from the rectilinear path predicted by geometrical optics. The beam trajectory shows strong dependence on the angle of incidence, changing from rectilinear to oscillatory within 0.07°. Our experimental results are in good agreement with theoretical predictions for the trajectories followed by the intensity peak of the reflected beam.

Direct measurement of the composite Goos-Hänchen shift of an optical beam.

We experimentally study the Goos-Hänchen shift of a focused Gaussian optical beam in the critical region of incidence. We directly measure the beam's shift evaluated from the displacement of the location of the beam's intensity peak and its centroid by a novel image analysis method. We verify that the evaluation method has a dramatic impact on the physics of beam shift phenomena. The influence of wavelength, beam waist, and propagation distance on the beam shift is studied. Our experimental results confirm recent theoretical predictions about the composite Goos-Hänchen shift, including the observation of negative shifts of the beam's intensity peak.

Side-lobe level reduction in bio-inspired optical phased-array antennas.

Phased arrays are expected to play a critical role in visible and infrared wireless systems. Their improved performance compared to single element antennas finds uses in communications, imaging, and sensing. However, fabrication of photonic antennas and their feeding network require long element separation, leading to the appearance of secondary radiation lobes and, consequently, crosstalk and interference. In this work, we experimentally show that by arranging the elements according to the Fermat's spiral, the side lobe level (SLL) can be reduced. This reduction is proved in a CMOS-compatible 8-element array, revealing a SLL decrement of 0.9 dB. Arrays with larger numbers of elements and inter-element spacing are demonstrated through an spatial light modulator (SLM) and an SLL drop of 6.9 dB is measured for a 64-element array. The reduced SLL, consequently, makes the proposed approach a promising candidate for applications in which antenna gain, power loss, or information security are key requirements.

Optical image cloning based on electromagnetic induced absorption.

We investigate, both theoretically and experimentally, optical image cloning via electromagnetic induced absorption (EIA). We demonstrate the transfer of small 2D real images imprinted onto a strong coupling beam to a weak probe beam in a Rb vapor cell. We show through EIA that the coupling beam's image is cloned beyond the usual diffraction, with a potential improvement in spatial resolution of the cloned image by a factor of three in comparison to that of the original coupling beam. Optical cloning through EIA is based on position selective nonlinear absorption, and it does not rely on spatial modulation of the refractive index.

Weak measurement of the composite Goos-Hänchen shift in the critical region.

By using a weak measurement technique, we investigated the interplay between the angular and the lateral Goos-Hänchen shift of a focused He-Ne laser beam for incidence near the critical angle. We verified that this interplay dramatically affects the composite Goos-Hänchen shift of the propagated beam. The experimental results confirm theoretical predictions that recently appeared in the literature.

Electromagnetically-induced phase grating: a coupled-wave theory analysis.

We use a coupled-wave theory analysis to describe an atomic phase grating based on the giant Kerr nonlinearity of an atomic medium under electromagnetically induced transparency. An analytical expression is found for the diffraction efficiency of the grating. Efficiencies greater than 70% are predicted for incidence at the Bragg angle.

Measuring vortex charge with a triangular aperture.

A triangular aperture illuminated with a vortex beam creates a truncated lattice diffraction pattern that identifies the charge of the vortex. In this Letter, we demonstrate the measurement of vortex charge via this approach for vortex beams up to charge ±7. We also demonstrate the use of this technique for measuring femtosecond vortices and noninteger vortices, comparing these results with numerical modeling. It is shown that this technique is simple and reliable, but care must be taken when interpreting the results for the noninteger case.

Electromagnetically induced phase grating.

I propose an electromagnetically induced phase grating based on the giant Kerr nonlinearity of an atomic medium under electromagnetically induced transparency. The atomic phase grating behaves similarly to an ideal sinusoidal phase grating, and it is capable of producing a pi phase excursion across a weak probe beam along with high transmissivity. The grating is created with arbitrarily weak fields, and diffraction efficiencies as high as 30% are predicted.

Photoassociation of sodium in a Bose-Einstein condensate.

We form ultracold Na2 molecules by single-photon photoassociation of a Bose-Einstein condensate, measuring the photoassociation rate, linewidth, and light shift of the J = 1, v = 135 vibrational level of the A1 Sigma (+)(u) molecular state. The photoassociation rate constant increases linearly with intensity, even where it is predicted that many-body effects might limit the rate. Our observations are in good agreement with a two-body theory having no free parameters.