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Quantum-optical state engineering up to the two-photon level


The ability to prepare arbitrary quantum states within a certain Hilbert space is the holy grail of quantum information technology. It is particularly important for light, as this is the only physical system that can communicate quantum information over long distances. We propose and experimentally verify a scheme to produce arbitrary single-mode states of a travelling light field up to the two-photon level. The desired state is remotely prepared in the signal channel of spontaneous parametric down-conversion by means of conditional measurements on the idler channel. The measurement consists of bringing the idler field into interference with two ancilla coherent states, followed by two single-photon detectors, which, in coincidence, herald the preparation event. By varying the amplitudes and phases of the ancillae, we can prepare any arbitrary superposition of zero-, one- and two-photon states.

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Figure 1: Scheme to produce arbitrary quantum-optical states at the two photon level.
Figure 2: Various superpositions of photon number states.
Figure 3: Reconstructed superpositions of states |0〉, |1〉 and |2〉, corrected for detection efficiency.


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This work was supported by Natural Sciences and Engineering Research Council of Canada, iCORE, Canada Foundation for Innovation, Alberta Ingenuity Fund, QuantumWorks, and Canadian Institute for Advanced Research. We thank S. Huisman and M. Lobino for assistance.

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All authors contributed to the concept and design of the experiment. E.B., N.J. and A.M. implemented the experiment and acquired the data. E.B., N.J. and A.I.L. analysed the data and wrote the paper.

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Correspondence to A. I. Lvovsky.

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The authors declare no competing financial interests.

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Bimbard, E., Jain, N., MacRae, A. et al. Quantum-optical state engineering up to the two-photon level. Nature Photon 4, 243–247 (2010).

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