Abstract
We propose and implement a quantum procedure for enhancing the sensitivity with which one can determine the phase shift experienced by a weak light beam possessing thermal statistics in passing through an interferometer. Our procedure entails subtracting exactly one (which can be generalized to m) photons from the light field exiting an interferometer containing a phase-shifting element in one of its arms. As a consequence of the process of photon subtraction, and somewhat surprisingly, the mean photon number and signal-to-noise ratio of the resulting light field are thereby increased, leading to enhanced interferometry. This method can be used to increase measurement sensitivity in a variety of practical applications, including that of forming the image of an object illuminated only by weak thermal light.
Highlights
Interferometry is the technique of choice for many of the most sensitive physical measurements to date [1]
Our results show that the signalto-noise ratio (SNR) of the interferometric signal can be enhanced by using photon subtraction
We have proposed and realized a procedure based on photon subtraction for increasing the SNR with which one can measure the phase shift induced on a thermal light field with occupation number of fewer than four photons
Summary
Interferometry is the technique of choice for many of the most sensitive physical measurements to date [1]. For a fixed source of illumination, this approach can be realized only at the expense of increasing the measurement time In this communication, we seek alternative methods of enhancing the SNR for a given value of average photon number. In contrast with the conventional approach of utilizing quantum states as the input to the interferometer, we propose to implement photon subtraction on the light exiting the interferometer Such a subtraction scheme leads to an enhancement in both the magnitude of the signal and the SNR, and we demonstrate this in a scenario where the average number of photons in the interferometer is fewer than four photons
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