The Photon-subtracted Manipulation Of A Class Of Superbunching Light Field Quantum States

A key requirement of many quantum protocols is to use specific light quantum states as information processing resources,so it is of essential importance to study various quantum states of light fields.Quantum states can be divided into Gaussian states and non-Gaussian states.Although the feasibility of experimental production of the Gaussian state has made Gaussian quantum information processing a great success and it is used in many tasks,when limited to the Gaussian state,various important quantum-enhanced information processing protocols cannot be implemented,such as quantum error correction,quantum-enhanced sensing,and optimal cloning of coherent states,etc.Therefore,for experimental quantum optics,the preparation of high-quality non-Gaussian quantum states is of great significance.A relatively simple method to introduce non-Gaussianity is to utilize detection-induced,usually probabilistic,methods such as photon number subtraction,which has been shown to enhance entanglement and fidelity of teleportation.In this work,we firstly construct a photon-subtracted squeezed coherent state by repeatedly operating the photon annihilation operator on squeezed coherent state for m times,and theoretically derive the normalized constant and the second-order correlation function of this state.Furthermore,the relationship between the second-order correlation function and the squeezing factor,the number of subtracted photons and the coherent component of this state by numerical simulation is obtained.Then the conclusions are extended to the photon-subtracted squeezed vacuum state,which is the main concern of this paper.The single-mode squeezed vacuum state is a typical superbunching light field quantum state,but after subtracting a certain number of photons,the superbunching effect of the squeezed vacuum state can only maintain when subtracting the even number of photons and squeezing factor r is small.Interestingly,when the number of subtracted photons is odd and squeezing factor r is small,the light field exhibits antibunching effect,which is a non-classical property of light.On the basis of obtaining the theoretical second-order correlation function of the photon-subtracted squeezed vacuum state,we theoretically provide an experimental scheme that can generate the above-mentioned light field in laboratory and take measurements by HBT apparatus to get the second-order correlation function of the prepared light field.In the first step,the nonlinear crystal with second-order nonlinear polarizability ?² is pumped through the degenerate parametric amplification process to prepare the superbunching optical field manipulated in this paper—the squeezed vacuum state.And the second-order correlation function is obtained by numerical simulation.Compared with its theoretical value,it is concluded that the maximum theoretical squeezing parameter of the squeezed vacuum state prepared by this strategy can reach 1.7.In the second step,inputting the squeezed vacuum state prepared in the first step,we prepare the photon-subtracted squeezed vacuum state through the lossless beam splitter and the photon number resolving detector.Then we obtain the relationship between the second-order correlation function and the mean photon number and photon number fluctuation of the prepared light field state and the number of photons detected in the output reference channel,the transmittance(or reflectivity)of the beam splitter used for condition measurement,and the squeezing parameters.Finally,we take measurement to obtain the second-order correlation function of the light field state prepared in the second step based on the HBT apparatus.Compared with the second-order correlation function of the light field state prepared in the second step through the definition calculation to obtain,it is necessary to take into account at least the influence of factors such as background noise,the number of subtracted photon,squeezing parameters and efficiency of detection system on the measurement results of the second-order correlation function of the light field.We hope that the work in this article can provide some theoretical guidance for related experimenters.