Spatial squeezing in bright twin beams generated with four-wave mixing: constraints on characterization with an EMCCD camera

TL;DR

This paper systematically investigates the factors affecting the measurement of spatial quantum noise reduction in bright twin beams generated via four-wave mixing, emphasizing the importance of acquisition speed to overcome technical noise.

Contribution

It provides a detailed analysis of the limiting factors in measuring spatial squeezing with EMCCD cameras in bright quantum states, highlighting critical parameters for optimal results.

Findings

High photon flux achieved with four-wave mixing in atomic vapor.

Fast image acquisition is crucial to suppress classical noise.

Identification of key parameters influencing spatial squeezing measurement.

Abstract

The observation of spatial quantum noise reduction, or spatial squeezing, with a large number of photons can lead to a significant advantage in quantum imaging and quantum metrology due to the scaling of the signal-to-noise ratio with the number of photons. Here we present a systematic study of the limiting factors that play a role on the measurement of spatial squeezing with an electron-multiplying charge coupled device (EMCCD) camera in the limit of bright quantum states of light generated with a four-wave mixing process in an atomic vapor cell. We detect a total number of photons per beam of the order 10$^8$ in 1 $\mu$s pulses, which corresponds to a photon flux per beam of the order of 10$^{14}$ photons per second. We then investigate the role of different parameters, such as cell temperature, pump power, laser detunings, scattered pump background noise, and timing sequences for the image acquisition with the EMCCD camera, on the level of spatial squeezing. We identify critical parameters to obtain an optimum squeezing level and demonstrate that for bright beams it is essential to acquire images at a rate fast enough to overcome the effect of classical technical noise.