Light entanglement holds the potential for quantum telecommunication and quan- tum computing. The goal of the project is to produce a pair of polarization-entangled light fields using Four Wave Mixing (FWM) in hot Rb vapor. In this process interaction of atoms with near-resonant strong control optical field results in strong amplification of a probe optical field and in generation of a quantum correlated conjugate Stokes opti- cal field. The optimum parameters for FWM have been established. Through analysis of the noise, the RF settings allowing for experimental quantum noise to match the shot noise has been confirmed as well. After establishing the shot noise limit, there were many trials to achieve noise lower than the shot noise. To further improve the noise and thus establish the quantum correlation between our fields, we switched from a single laser to a double laser setup. In the future, the quantum correlation between the Stokes field and the probe field will be further improved to allow for the entangled Bell states creation.
Light entanglement holds the potential for quantum telecommunication and quan- tum computing. The goal of the project is to produce a pair of polarization-entangled light fields using Four Wave Mixing (FWM) in hot Rb vapor. In this process interaction of atoms with near-resonant strong control optical field results in strong amplification of a probe optical field and in generation of a quantum correlated conjugate Stokes opti- cal field. The optimum parameters for FWM have been established. Through analysis of the noise, the RF settings allowing for experimental quantum noise to match the shot noise has been confirmed as well. After establishing the shot noise limit, there were many trials to achieve noise lower than the shot noise. To further improve the noise and thus establish the quantum correlation between our fields, we switched from a single laser to a double laser setup. In the future, the quantum correlation between the Stokes field and the probe field will be further improved to allow for the entangled Bell states creation.
The goal of the project is to produce a pair of polarization-entangled light fields using four-wave mixing in hot Rb vapor. In this process, interaction of atoms with near-resonant strong control optical field results in strong amplification of a nearly-collinear probe optical field and in generation of a quantum correlated conjugate Stokes optical field. In order to establish the quantum correlation between the Stokes and probe fields, we have adopted a homodyne detection scheme. If the differential noise between the Stokes and probe fields is below the quantum noise limit, then intensity fluctuation entanglement has been achieved, and it is possible to produce the polarization Bell states.
The goal of the project is to produce a pair of intensity-squeezed light fields using Four-Wave Mixing (FWM) in hot Rubidium vapor. In this process, interaction of atoms with near-resonant strong control optical field results in strong amplification of a weak probe optical field and in generation of a quantum correlated conjugate Stokes optical field. In order to establish the quantum correlation between the Stokes and probe fields, we measured the differential intensity noise between the Stokes and probe fields. If the noise falls below the quantum noise limit, then two-mode intensity squeezing has been achieved, as a first step toward realization of the polarization Bell states. We also examine the conservation of orbital angular momentum (OAM) in the FWM process with OAM-bearing input fields.
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.
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].
Quantum correlations and entanglement shared among multiple quantum modes are important for both fundamental science and the future development of quantum technologies. This development will also require an efficient quantum interface between multimode quantum light sources and atomic ensembles, which makes it necessary to implement multimode quantum light sources that match the atomic transitions. Here, we report on such a source that provides a method for generating quantum correlated beams that can be extended to a large number of modes by using multiple four-wave mixing (FWM) processes in hot rubidium vapor. Experimentally, we show that two cascaded FWM processes produce strong quantum correlations between three bright beams but not between any two of them. In addition, the intensity-difference squeezing is enhanced with the cascaded system to -7.0±0.1 dB from the -5.5±0.1/-4.5±0.1 dB squeezing obtained with only one FWM process. One of the main advantages of our system is that as the number of quantum modes increases, so does the total degree of quantum correlations. The proposed method is also immune to phase instabilities due to its phase insensitive nature, can easily be extended to multiple modes, and has potential applications in the production of multiple quantum correlated images.