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Conference on Lasers and Electro-Optics

Quantum Enhancement of Optical Measurements using Four-wave Mixing in Rb vapor

Irina V. Novikova, Nikunj Prajapati, Savannah L. Cuozzo, Elisha S. Matekole, Lior Cohen, Jonathan P. Dowling, Eugeniy E. Mikhailov

Published Jan 1, 2020• 0 citations
Publisher

Abstract

Using four-wave mixing in hot Rb vapor, we demonstrate the production of two-mode intensity squeezing between beams with significantly different optical angular momenta and an all-optical polarization-based truncated SU(1,1) interferometer for alloptical quantum-enhanced imaging and sensing.
DOI
10.1364/cleo_qels.2020.fw4c.3

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In this manuscript, we discuss the performance of a recently demonstrated polarization-based truncated SU(1,1) interferometer1 which can potentially generate polarization-entangled twin beams for applications in quantum communications or in quantum metrology as an interferometer with enhanced phase sensitivity. Using the intensity-squeezed twin beams generated via four-wave mixing (FWM) in hot Rubidium vapor, we report the detection of nearly -2 dB of noise reduction below the shot-noise in the joint-quadrature measurements in such interferometer. We also used this setup to confirms the non-classical nature of quantum correlations between the twin beams with an inseparability parameter I = 1:32±0:04 that falls below the classical limit of 2. One of the important advantages of the proposed interferometer is its better rejection of common-mode, technical, and environmental noises due to its intrinsic symmetry, which allows for squeezing and entanglement measurements at wide spectrum of detection frequencies from as low as 200 Hz (limited by 1=f electronic noise) to up to a few MHz (limited by the photodetector gain bandwidth).

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Multi-photon nonlinear processes in atoms have served as important tools for quantum metrology, quantum communications, and quantum sensing. In this thesis, we experimentally address the interplay of various multi-photon Raman processes in hot Rb vapor, with the four-wave mixing (FWM) process being a central theme. FWM is the nonlinear response of a medium to a strong optical pump field inelastically scattering off atomic resonances and resulting in the generation of additional photons in different modes. FWM is a detrimental, but inherent part of electromagnetically induced transparency (EIT) and Raman based quantum memories. However, we were able to weaken the four-photon resonance by utilizing two-photon absorption to remove the additional photons without interfering with the signal beam. We also demonstrate the ability to tailor FWM to generate new photons in a controlled fashion for mode conversion. With this, we showed the conversion of 795 nm light to 420 nm light. While FWM is a source of noise in quantum memories, it can also be used for the generation squeezed twin-beams. Such beams have relative intensity noise reduced below the classical shot noise limit and share mode dependence based on the phase-matching conditions. Using this, we demonstrated that twin-beams can be generated with largely different spatial structure (optical angular momentum) and still share strong correlations, so long as the phase-matching conditions are satisfied. We then constructed and demonstrated the operation of a polarization-based quantum interferometer using squeezed twin-beams and showed that our beams were entangled under the inseparability condition. Using this interferometer, we were also able to achieve squeezing at low detection frequencies, which is necessary for things like quantum imaging and gravitational wave detection. We also demonstrated that squeezed twin-beams can be utilized to enhance the sensitivity of two-photon absorption spectroscopy. This research has touched on many different subjects related to quantum information science and improved upon some of the tools needed for the implementation of such technologies.

•Mar 22, 2021•0 citations
In this manuscript, we discuss the performance of a recently demonstrated polarization-based truncated SU(1,1) interferometer1 which can potentially generate polarization-entangled twin beams for applications in quantum communications or in quantum metrology as an interferometer with enhanced phase sensitivity. Using the intensity-squeezed twin beams generated via four-wave mixing (FWM) in hot Rubidium vapor, we report the detection of nearly -2 dB of noise reduction below the shot-noise in the joint-quadrature measurements in such interferometer. We also used this setup to confirms the non-classical nature of quantum correlations between the twin beams with an inseparability parameter I = 1:32±0:04 that falls below the classical limit of 2. One of the important advantages of the proposed interferometer is its better rejection of common-mode, technical, and environmental noises due to its intrinsic symmetry, which allows for squeezing and entanglement measurements at wide spectrum of detection frequencies from as low as 200 Hz (limited by 1=f electronic noise) to up to a few MHz (limited by the photodetector gain bandwidth).
Quantum-enhanced precision measurements have emerged as one of the most useful applications of quantum optics. Exploiting quantum states of light and quantum processes, classical measurement limits can be surpassed, leading to improvements in areas including clocks, spectroscopy, magnetometry, and imaging. One measurement where straightforward quantum enhancements are possible is phase sensing with an interferometer. One can inject squeezed vacuum states into the dark port of the beamsplitter in a traditional interferometer to reduce the quantum noise and reach phase sensitivities beyond the shot noise limit. An alternate approach is to replace the beamsplitters of an interferometer with nonlinear parametric amplifiers, which produce nonclassical states of light that can be used to surpass classical performance. This so called SU(1,1) interferometer can theoretically approach sensitivities that scale as 1/n, the Heisenberg limit where n is the interior phase sensing photon number, compared to the shot noise limit of 1/ √ n for a traditional interferometer [1]. I will present our group’s experimental progress in testing a Mach-Zender SU(1,1) interferometer using four-wave mixers (4WMs) in hot Rb atoms as the parametric beamsplitters. The 4WM process generates entangled twin beams which serve as the two arms of the interferometer, and are then recombined in a second 4WM cell, resulting in a phase-sensitive output. We will extend the work done on this interferometer [2, 3] by performing a detailed analysis of the output signal to noise through homodyne measurements, and will attempt to observe the better-than-shot-noise scaling of the sensitivity. We will also consider the various difficulties of this optical interferometer such as the susceptibility to loss and imperfect mode-matching within the interferometer. Our group is also considering an analogous SU(1,1) interferometer in a cold atom system. Collisions in a spinor Bose-Einstein condensate of sodium atoms give rise to a 4WM process that produces spin states of the atoms which are entangled in atom number. These interactions can be controlled to set up an SU(1,1) atom interferometer, where the relevant measurements are now atomic population differences rather than photon intensities. These enhancements can lead to drastic improvements in atomic spin interferometry [3, 4].
We propose and demonstrate a polarization-based truncated SU(1,1) interferometer that outputs the desired optical joint-quadrature of a two-mode squeezed vacuum field and allows its measurements using a single balanced homodyne detector. Using such a setup, we demonstrate up to ≈2dB of quantum noise suppression below the shot-noise limit in intensity-difference and phase-sum joint-quadratures, and confirm entanglement between the two quantum fields. Our proposed technique results in a better balance between the two ports of the detector and, consequently, in better common noise suppression for differential measurements. As a result, we are able to observe flat joint-quadrature squeezing and entanglement at a wide range of detection frequencies: from several MHz (limited by the photodiode gain bandwidth) down to a few hundred Hz (limited by electronic noises).
Multi-photon nonlinear processes in atoms have served as important tools for quantum metrology, quantum communications, and quantum sensing. In this thesis, we experimentally address the interplay of various multi-photon Raman processes in hot Rb vapor, with the four-wave mixing (FWM) process being a central theme. FWM is the nonlinear response of a medium to a strong optical pump field inelastically scattering off atomic resonances and resulting in the generation of additional photons in different modes. FWM is a detrimental, but inherent part of electromagnetically induced transparency (EIT) and Raman based quantum memories. However, we were able to weaken the four-photon resonance by utilizing two-photon absorption to remove the additional photons without interfering with the signal beam. We also demonstrate the ability to tailor FWM to generate new photons in a controlled fashion for mode conversion. With this, we showed the conversion of 795 nm light to 420 nm light. While FWM is a source of noise in quantum memories, it can also be used for the generation squeezed twin-beams. Such beams have relative intensity noise reduced below the classical shot noise limit and share mode dependence based on the phase-matching conditions. Using this, we demonstrated that twin-beams can be generated with largely different spatial structure (optical angular momentum) and still share strong correlations, so long as the phase-matching conditions are satisfied. We then constructed and demonstrated the operation of a polarization-based quantum interferometer using squeezed twin-beams and showed that our beams were entangled under the inseparability condition. Using this interferometer, we were also able to achieve squeezing at low detection frequencies, which is necessary for things like quantum imaging and gravitational wave detection. We also demonstrated that squeezed twin-beams can be utilized to enhance the sensitivity of two-photon absorption spectroscopy. This research has touched on many different subjects related to quantum information science and improved upon some of the tools needed for the implementation of such technologies.