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Register a new userRole of the phase-matching condition in non-degenerate four-wave mixing in hot vapors for the generation of squeezed states of light
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Non-degenerate forward four-wave mixing in hot atomic vapors has been shown to produce strong quantum correlations between twin beams of light [McCormick et al, Opt. Lett. 32, 178 (2007)], in a configuration which minimizes losses by absorption. In this paper, we look at the role of the phase-matching condition in the trade-off that occurs between the efficiency of the nonlinear process and the absorption of the twin beams. To this effect, we develop a semi-classical model by deriving the atomic susceptibilities in the relevant double-lambda configuration and by solving the classical propagation of the twin-beam fields for parameters close to those found in typical experiments. These theoretical results are confirmed by a simple experimental study of the nonlinear gain experienced by the twin beams as a function of the phase mismatch. The model shows that the amount of phase mismatch is key to the realization of the physical conditions in which the absorption of the twin beams is minimized while the cross-coupling between the twin beams is maintained at the level required for the generation of strong quantum correlations. The optimum is reached when the four-wave mixing process is not fully phase matched.
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We report the generation of a squeezed vacuum state of light whose noise ellipse rotates as a function of the detection frequency. The squeezed state is generated via a four-wave mixing process in a vapor of 85Rb. We observe that rotation varies with experimental parameters such as pump power and laser detunings. We use a theoretical model based on the Heisenberg-Langevin formalism to describe this effect. Our model can be used to investigate the parameter space and to tailor the ellipse rotation in order to obtain an optimum squeezing angle, for example, for coupling to an interferometer whose optimal noise quadrature varies with frequency.
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 $-2.9pm0.1$ dB when it is tuned off-resonance and a level of $-2.0pm 0.1$ dB when it is tuned on resonance with the D1 $F=2$ to $F=2$ transition of $^{87}$Rb.
Entangled multi-spatial-mode fields have interesting applications in quantum information, such as parallel quantum information protocols, quantum computing, and quantum imaging. We study the use of a nondegenerate four-wave mixing process in rubidium vapor at 795 nm to demonstrate generation of quantum-entangled images. Owing to the lack of an optical resonator cavity, the four-wave mixing scheme generates inherently multi-spatial-mode output fields. We have verified the presence of entanglement between the multi-mode beams by analyzing the amplitude difference and the phase sum noise using a dual homodyne detection scheme, measuring more than 4 dB of squeezing in both cases. This paper will discuss the quantum properties of amplifiers based on four-wave-mixing, along with the multi mode properties of such devices.
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.
We have built a compact light source for bright squeezed twin-beams at 795,nm based on four-wave-mixing in atomic $^{85}$Rb vapor. With a total optical power of 400,mW derived from a free running diode laser and a tapered amplifier to pump the four-wave-mixing process, we achieve 2.1,dB intensity difference squeezing of the twin beams below the standard quantum limit, without accounting for losses. Squeezed twin beams generated by the type of source presented here could be used as reference for the precise calibration of photodetectors. Transferring the quantum correlations from the light to atoms in order to generate correlated atom beams is another interesting prospect. In this work we investigate the dispersion that is generated by the employed four-wave-mixing process with respect to bandwidth and dependence on probe detuning. We are currently using this squeezed light source to test the transfer of spatial information and quantum correlations through media of anomalous dispersion.
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