The standard process for the production of strongly squeezed states of light is degenerate optical parametric amplification (OPA) below threshold in nonlinear dielectric media such as LiNbO3 or periodically poled potassium titanyl phosphate (KTP). Here, we present a graphical description of squeezed-light generation via OPA, visualizing the interaction between the nonlinear dielectric polarization of the medium and the electromagnetic quantum field. We explicitly focus on the transfer from the field's ground state to a squeezed vacuum state and from a coherent state to a bright squeezed state by the medium's second-order nonlinearity, respectively. Our pictures illustrate the phase-dependent amplification and deamplification of quantum uncertainties and give the phase relations between all propagating electromagnetic fields as well as the internally induced dielectric polarizations. The graphical description can also be used to describe the generation of nonclassical states of light via higher-order effects of the nonlinear dielectric polarization such as four-wave mixing and the optical Kerr effect.
The standard process for the production of strongly squeezed states of light is degenerate optical parametric amplification (OPA) below threshold in nonlinear dielectric media such as LiNbO3 or periodically poled potassium titanyl phosphate (KTP). Here, we present a graphical description of squeezed-light generation via OPA, visualizing the interaction between the nonlinear dielectric polarization of the medium and the electromagnetic quantum field. We explicitly focus on the transfer from the field's ground state to a squeezed vacuum state and from a coherent state to a bright squeezed state by the medium's second-order nonlinearity, respectively. Our pictures illustrate the phase-dependent amplification and deamplification of quantum uncertainties and give the phase relations between all propagating electromagnetic fields as well as the internally induced dielectric polarizations. The graphical description can also be used to describe the generation of nonclassical states of light via higher-order effects of the nonlinear dielectric polarization such as four-wave mixing and the optical Kerr effect.
The standard process for the production of strongly squeezed states of light is optical parametric amplification (OPA) below threshold in dielectric media such as LiNbO3 or periodically poled KTP. Here, we present a graphical description of squeezed light generation via OPA. It visualizes the interaction between the nonlinear dielectric polarization of the medium and the electromagnetic quantum field. We explicitly focus on the transfer from the field's ground state to a squeezed vacuum state and from a coherent state to a bright squeezed state by the medium's secondorder nonlinearity, respectively. Our pictures visualize the phase dependent amplification and deamplification of quantum uncertainties and give the phase relations between all propagating electro-magnetic fields as well as the internally induced dielectric polarizations. The graphical description can also be used to describe the generation of nonclassical states of light via higherorder effects of the non-linear dielectric polarization such as four-wave mixing and the optical Kerr effect.
The standard process for the production of strongly squeezed states of light is degenerate optical parametric amplification (OPA) below threshold in nonlinear dielectric media such as lithium niobate or periodically poled potassium titanyl phosphate.This work presents the generation of the most strongly squeezed states of light so far, as well as the first graphical description of squeezed-light generation via OPA.The newly developed graphical description visualizes the interaction between the nonlinear dielectric polarization of the medium and the electromagnetic quantum field.It explicitly focuses on the transition from the field's ground state to a squeezed vacuum state, and from a coherent state to a bright squeezed state by the medium's second-order nonlinearity.The pictures visualize the phase-dependent amplification and deamplification of quantum uncertainties, and give the phase relations between all propagating electromagnetic fields, as well as the internally induced dielectric polarizations.The graphical description can also be used to describe the generation of nonclassical states of light via higher-order effects of the nonlinear dielectric polarization, such as four-wave mixing, and the optical Kerr effect.By superposing strongly squeezed states of light, strongly entangled states can be produced.This work measured states such as those discussed in 1935 in the famous gedanken experiment by Einstein, Podolsky and Rosen (EPR) and introduced by Schrödinger in terms of entanglement and steering.The source of entanglement in this work was composed of a half-monolithic, optically nonlinear cavity providing 11,3 dB squeezing and a monolithic, optically nonlinear cavity providing 12,7 dB squeezing.The latter value is the highest noise suppression up to now.This source of entanglement achieved a sixfold increase of the observed EPR-steering effect with regard to previous experiments, as quantified by the Reid criterion.It achieved an unprecedentedly low conditional variance product of about 0,04 < 1, where 1 is the upper bound below which steering is demonstrated.The steering effect was observed on an unconditional two-mode-squeezed entangled state that contained a total vacuum state contribution of less than 8 %, including detection imperfections.Together with the achieved high interference contrast between the entangled state and a bright coherent laser field, this state is compatible with efficient applications in high-power laser interferometers and fiber-based networks for entanglement distribution.
Generation and manipulation of continuous variable quantum states are the building blocks of quantum communication, quantum key distribution and quantum networks. According to the second-order nonlinear process of the periodically-poled potassium titanyl phosphate (PPKTP) crystal, we design a semi-monolithic optical parametric amplifier (OPA) cavity to generate the bright squeezed light at a wavelength of 1064 nm. With the injection of a seed beam, the squeezed state generated by the OPA has a coherent amplitude, so called bright squeezed state. The squeezing level is directly observed to be –11.6 dB when the pump power is 310 mW at an analysis frequency of 3 MHz. However, with the increase of the pump power, the purity of the squeezed state gets lower and lower due to the increased influence of the anti-squeezing quadrature component on the squeezed quadrature component in the detection process. To obtain a higher purity of the squeezed state for achieving linear optical manipulation and quantum tomography, we choose the pump power of 50 mW, the squeezing level decreases to –6 dB, and the purity of the squeezed state is 98.5% in this case. An electro-optic modulator is adopted to realize the liner manipulation of the squeezed light in the phase space. During the measurement of the bright squeezed state, all the data are taken on condition that the length of the OPA cavity and relative phase between the seed beam and the pump beam are locked by a locking loop. The direct current (DC) signal of the balanced homodyne detection (BHD) is used to accurately determine the phase corresponding to the time domain signal of the squeezed state, while the alternate current (AC) signal of the BHD is mixed with the signal generated by the function generator, after passing through a low-pass filter and a high-pass filter, the signal is then amplified by using a low-noise amplifier. A high-performance oscilloscope is finally used to simultaneously collect the signals, thus obtaining the quantum noise signal of the bright squeezed light after linear manipulation. Together with the maximum likelihood estimation algorithm, the quantum tomography, the density matrix and the Wigner function of the bright squeezed light are obtained, that is, all the information such as the photon number distribution of the quantum state is determined. Multiple iterations are taken in the maximum likelihood estimation algorithm process to eliminate the influence of the low quantum efficiency on the detection system, so that the density matrix is fitted well with the theoretical results.
The influence of quantum fluctuations of the electromagnetic field on the propagation of a polarized light wave in a nonlinear dielectric is investigated. It is shown that in some cases the fluctuations couple to the optical nonlinearities of the medium and make its refractive index dependent on the polarization of the propagating wave. As a consequence, two light waves propagating in the same direction but with different polarizations will have different speeds, so there will be a Kerr-effect birefringence induced by quantum fluctuations. We consider the case of the electromagnetic field in a squeezed vacuum state, where there are regions where the mean squared electric field can be negative and the birefringence effect has the opposite sign to the Kerr effect in classical physics. We give some estimates for the magnitude of these effects, and discuss their possible observability.
The minimum resolvable signal in optical metrology and sensing applications is usually limited by the so-called standard quantum limit. One way to improve the signal-to-noise ratio is to use squeezed states of light. Squeezed light can be generated using different types of nonlinear interactions either in solid-state nonlinear crystals or in atomic systems. One way to generate squeezed light is to use a phase sensitive amplifier that will amplify one quadrature of the considered mode and deamplify the other one. We have recently shown that metastable helium vapor at room temperature can exhibit strong four-wave mixing effects and behave like a perfect phase sensitive amplifier when it is prepared in coherent population trapping situation. In this talk, we will present the application of this phase sensitive amplification to the generation of squeezed vacuum states of light and detail the performances and limitations of the system