Generation of 87^{87}Rb-resonant bright two-mode squeezed light with four-wave mixing

Squeezed states of light have found their way into a number of applications in quantum-enhanced metrology due to their reduced noise properties. In order to extend such an enhancement to metrology experiments based on atomic ensembles, an efficient light-atom interaction is required. Thus, there is a particular interest in generating narrow-band squeezed light that is on atomic resonance. This will make it possible not only to enhance the sensitivity of atomic based sensors, but also to deterministically entangle two distant atomic ensembles. We generate bright two-mode squeezed states of light, or twin beams, with a non-degenerate four-wave mixing (FWM) process in hot $^{85}$Rb in a double-lambda configuration. Given the proximity of the energy levels in the D1 line of $^{85}$Rb and $^{87}$Rb, we are able to operate the FWM in $^{85}$Rb in a regime that generates two-mode squeezed states in which both modes are simultaneously on resonance with transitions in the D1 line of $^{87}$Rb, one mode with the $F=2$ to $F'=2$ transition and the other one with the $F=1$ to $F'=1$ transition. For this configuration, we obtain an intensity difference squeezing level of $-3.5$ dB. Moreover, the intensity difference squeezing increases to $-5.4$ dB and $-5.0$ dB when only one of the modes of the squeezed state is resonant with the D1 $F=2$ to $F'=2$ or $F=1$ to $F'=1$ transition of $^{87}$Rb, respectively

Effect of Closely-Spaced Excited States on Electromagnetically Induced Transparency

Electromagnetically induced transparency (EIT) is a well-known phenomenon due in part to its applicability to quantum devices such as quantum memories and quantum gates. EIT is commonly modeled with a three-level lambda system due to the simplicity of the calculations. However, this simplified model does not capture all the physics of EIT experiments with real atoms. We present a theoretical study of the effect of two closely-spaced excited states on EIT and off-resonance Raman transitions. We find that the coherent interaction of the fields with two excited states whose separation is smaller than their Doppler broadened linewidth can enhance the EIT transmission and broaden the width of the EIT peak. However, a shift of the two-photon resonance frequency for systems with transitions of unequal dipole strengths leads to a reduction of the maximum transparency that can be achieved when Doppler broadening is taken into account even under ideal conditions of no decoherence. As a result, complete transparency cannot be achieved in a vapor cell. Only when the separation between the two excited states is of the order of the Doppler width or larger can complete transparency be recovered. In addition, we show that off-resonance Raman absorption is enhanced and its resonance frequency is shifted. Finally, we present experimental EIT measurements on the D1 line of $^{85}$Rb that agree with the theoretical predictions when the interaction of the fields with the four levels is taken into account

Atomic Resonant Single-Mode Squeezed Light from Four-Wave Mixing through Feedforward

Squeezed states of light have received renewed attention due to their applicability to quantum-enhanced sensing. To take full advantage of their reduced noise properties to enhance atomic-based sensors, it is necessary to generate narrowband near or on atomic resonance single-mode squeezed states of light. We have previously generated bright two-mode squeezed states of light, or twin beams, that can be tuned to resonance with the D1 line of $^{87}$Rb with a non-degenerate four-wave mixing (FWM) process in a double-lambda configuration in a $^{85}$Rb vapor cell. Here we report on the use of feedforward to transfer the amplitude quantum correlations present in the twin beams to a single beam for the generation of single-mode amplitude squeezed light. With this technique we obtain a single-mode squeezed state with a squeezing level of $-2.9\pm0.1$ dB when it is tuned off-resonance and a level of $-2.0\pm 0.1$ dB when it is tuned on resonance with the D1 $F=2$ to $F'=2$ transition of $^{87}$Rb

Generation and Control of Atomic Resonant Squeezed Light

Quantum metrology is a new emerging technology studying of extreme sensitive and high resolution measurement based on quantum mechanical principles such as quantum entanglement and squeezing, which can potentially revolutionize modern technology for defense and national security. Squeezed light plays a fundamental role in quantum metrology due to its reduced noise properties. Recently, it was used to increase the sensitivity of the LIGO interferometer to measure gravitational waves and provide new ways to observe the universe. Additionally, a quantum advantage has also been demonstrated in other optical devices such as plasmonic sensors and quantum imaging. However, there are still many challenges and opportunities for squeezed light to be adopted to current sensors and other systems. Therefore, the focus of this dissertation is to extend the applicability of squeezed light to atomic sensors and enable a control of quantum noise. To extend the applicability of squeezed light to atomic systems, it must have a frequency close to or on atomic resonance and a narrow linewidth to obtain an efficient interaction with atomic ensembles. Therefore, there is substantial interest in generating narrowband squeezed light on atomic resonance. The successful demonstration of atomic resonance squeezed light and the effective control of the noise properties of squeezed light can enable improved sensitivity of atomic-based sensors and deterministic transfer of the quantum correlation between two distant atomic ensembles. In the first part of the dissertation, we present three different approaches to generate two-mode atomic resonant squeezed light with a four-wave mixing (FWM) processes in hot $^{85}$Rb. First, we take advantage of the proximity of the energy levels in the D1 line of $^{85}$Rb and $^{87}$Rb to demonstrate the generation of resonant squeezed light with a non-degenerate FWM in which one mode is on resonance with the D1 $F=2$ to $F^\prime=2$ transition and the other mode is on resonance with the $F=1$ to $F^\prime=1$ transition in the D1 line of $^{87}$Rb. For this configuration, we obtain an intensity difference squeezing level of $-3.9$~dB. Moreover, the intensity difference squeezing increases to $-6.3$~dB and $-6.2$~dB when only one of the modes of the squeezed state is resonant with the D1 $F=2$ to $F^\prime=2$ or $F=1$ to $F^\prime=1$ transition of $^{87}$Rb, respectively. Another approach used to generate resonant squeezed light is via the coupling with additional pump beam to enhance the atomic processes. We apply an optical beam to transfer population between the ground states, dress the atomic system, or saturate the transition to enhance FWM process. We measure $-0.8$~dB of intensity difference squeezing when both probe and conjugate are simultaneously on resonance with the D1 $F=3$ to $F^\prime=3$ transition of $^{85}$Rb and $-1$~dB of intensity difference squeezing when the probe is resonant with the D2 $F=2$ to $F^\prime=3$ transition of $^{87}$Rb. While the first two approaches generate resonant squeezed light for certain transitions, there are still many transitions that we cannot reach with our techniques. To overcome this limitation, we dress the atomic state via an external DC electric field to increase the frequency tunability of the two-mode squeezed light. We design a vacuum chamber with parallel plates to apply large electric fields of up to $110$~kV/cm to the atomic vapor source. Our work increases the frequency tunability of the squeezed light to $600$~MHz, demonstrating the generation of squeezed light resonant with the D1 $F=3$ to $F^\prime=3$ transition of $^{85}$Rb. In the second part of the dissertation, we discuss two different methods of controlling the properties of two-mode squeezed light to generate single-mode squeezed light and multipartite entangled light. We obtained a single-mode squeezed state with a squeezing level of $-2.9$~dB by transferring the intensity quantum correlations present in the twin beams to a single beam using a feedforward technique. In the last chapter, we introduce a novel scheme to generate scalable genuine multipartite entanglement. We show configurations of the proposed scheme that can generate genuine quadpartite, hexapartite, and octapartite entanglement, which we verify through a violation of the positive partial transpose (PPT) criterion. The generation of resonant squeezed light using atomic ensembles overcomes several experimental difficulties associated with other sources and make it possible to study the interaction between atoms and quantum states of light. Thus, our work will be a building block for quantum metrology based on squeezed light, particularly important for atomic sensing and quantum information science