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Experimental realization of sub-shot-noise quantum imaging

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The properties of quantum states have led to the development of new technologies, ranging from quantum information to quantum metrology1,2,3,4,5,6,7,8,9,10,11,12. A recent field of research to emerge is quantum imaging, which aims to overcome the limits of classical imaging by making use of the spatial properties of quantum states of light13,14,15,16,17,18 . In particular, quantum correlations between twin beams represent a fundamental resource for these studies19,20,21,22,23,24,25,26,27,28,29,30,31,32. One of the most interesting proposed schemes takes advantage of the spatial quantum correlations between parametric down-conversion light beams to realize sub-shot-noise imaging of weak absorbing objects14, leading ideally to noise-free imaging. Here, we present the first experimental realization of this scheme, showing its potential to achieve a larger signal-to-noise ratio than classical imaging methods. This work represents the starting point for this quantum technology, which we anticipate will have applications when there is a requirement for low-photon-flux illumination (for example for use with biological samples).

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Figure 1: Experimental imaging of a π-shaped titanium deposition with α(x) = 0.5 when σ = 0.35.
Figure 2: Experimental set-up.
Figure 3: Degree of correlation.
Figure 4: Ratio R between the signal-to-noise ratio in quantum imaging, and differential (dcl) and direct (cl) classical imaging.

Change history

  • 08 March 2010

    In the version of this Letter originally published online, the signal-to-noise ratio equation was incorrect. The correct equation should have had an underbar to indicate temporal averaging. The error has been corrected for all versions of the Letter.


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This work has been supported by Compagnia di San Paolo, by PRIN 2007FYETBY (CCQOTS) and by Regione Piemonte (E14). The authors thank E. Monticone and C. Portesi for the thin film deposition representing the weak absorbing object, A. Meda and P. Cadinu for help with data analysis and A. Gatti, E. Brambilla, L. Caspani and L. Lugiato for theoretical support.

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Experimental work and data analysis were predominantly carried out by I.R.B., who also largely contributed to project planning with G.B. and M.G. I.R.B. wrote the paper, together with G.B. and M.G., who supervised the project and equipped the laboratory (M.G. leads the Quantum Optics group).

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Correspondence to I. Ruo Berchera.

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The authors declare no competing financial interests.

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Brida, G., Genovese, M. & Ruo Berchera, I. Experimental realization of sub-shot-noise quantum imaging. Nature Photon 4, 227–230 (2010).

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