Observation of spatial quantum correlations in the macroscopic regime

Abstract

Spatial quantum correlations in the transverse degree of freedom promise to enhance optical resolution, image detection, and quantum communications through parallel quantum information encoding. In particular, the ability to observe these spatial quantum correlations in a single shot will enable such enhancements in applications that require real time imaging, such as particle tracking and in-situ imaging of atomic systems. Here, we report on measurements in the far-field that show spatial quantum correlations in single images of bright twin-beams with 10 8 photons in a 1 µs pulse using an electron-multiplying charge-coupled device camera. A four-wave mixing process in hot rubidium atoms is used to generate narrowband-bright pulsed twin-beams of light. Owing to momentum conservation in this process, the twin-beams are momentum correlated, which leads to spatial quantum correlations in the far field. We show around 2 dB of spatial quantum noise reduction with respect to the shot noise limit. The spatial squeezing is present over a large range of total number of photons in the pulsed twin-beams.PACS numbers: 42.50. Dv, 42.50.Ar, Under certain conditions, the quantum fluctuations in beams of light can be reduced below the shot noise limit (SNL) not only in the temporal domain, but also in the transverse spatial degree of freedom [1]. To date, most of the attention has focused on the study of quantum noise reduction, or squeezing, in the temporal domain [2][3][4][5][6][7][8][9][10][11][12]. Nevertheless, many areas in quantum optics, specifically quantum metrology and quantum imaging, could greatly benefit from the study of the quantum correlations directly in the spatial domain [13][14][15]. This would make it possible to take advantage of the spatial quantum properties of light, such as spatial squeezing, for enhanced spatial resolution and sub shot noise imaging [14].With this in mind, a few groups have recently experimentally demonstrated sub-shot noise spatial correlations using an electron-multiplying charge-coupled device (EMCCD) camera in photon pairs generated through spontaneous parametric down conversion (SPDC) [16][17][18]. As a proof of principle of a potential application of spatial quantum correlations in quantum imaging, Brida et al.[19] imaged a weak absorbing object with significantly higher signal-to-noise ratio than what is possible with classical light. However, the intensity levels were limited by the source and are orders of magnitude lower than what is used in standard imaging techniques. While these initial experiments provided an indication that spatial quantum correlations can lead to significant enhancements, many applications in quantum imaging and quantum metrology require real time imaging and, as such, require the ability to observe the spatial quantum correlations in a single shot with a controllable and macroscopic number of photons. In addition, the use of such a large number of photons can lead to a more sig- * ashok@ou.edu † marino@ou.edu nificant sensitivity enhancement due to t...

Twin-beam intensity-difference squeezing below 10 Hz

“…Very recently Ma et al [17] reported such squeezing down to frequencies below 700 Hz. In the context of imaging, Kumar et al [27] performed intensity-differencing on an EM-CCD camera using a 4WM source similar to ours and were able to obtain a subtraction noise level 2 dB below shot noise. In those experiments two frames are taken in rapid succession for each of the twin images and are subtracted.…”

A gain series method for accurate EMCCD calibration

“…The defining feature of the EMCCD—the amplification of small numbers of photoelectrons above electronic noise—maintains the linear relationship between signal level and the incident photon flux. Accurate characterization of the amplification process and the conversion to digital units are necessary for comparing intensity levels among pixels 10 , 11 , such as when fitting point-spread functions for super-resolution localization microscopy 2 or when comparing intensity differences across regions of the sensor for quantum correlation detection 12 , 13 .…”

A Gain-series Method for Accurate EMCCD Calibration

“…The defining feature of the EMCCD-the amplification of small numbers of photoelectrons above electronic noise-maintains the linear relationship between signal level and the incident photon flux. Accurate characterization of the amplification process and the conversion to digital units is necessary for comparing intensity levels among pixels 10,11 , such as when fitting point-spread functions for super-resolution localization microscopy 2 or when comparing intensity differences across regions of the sensor for quantum correlation detection 12,13 .…”