Weak-value amplification of the nonlinear effect of a single photon

In quantum mechanics, the concept of weak measurements allows for the description of a quantum system both in terms of the initial preparation and the final state (post-selection)1. This paradigm has been extensively studied theoretically and experimentally, but almost all of weak-measurement experiments carried out to date can be understood in terms of the classical (electromagnetic wave) theory of optics.

Here, we present a quantum version in which the measurement apparatus deterministically entangles two distinct optical beams. We show that a single photon, when properly post-selected, can have an effect equal to that of eight photons: that is, in a system where a single photon has been calibrated to write a nonlinear phase shift of φo on a probe beam, we measure phase shifts as large as 8φo for appropriately post-selected single photons.

This opens up a new regime for the study of entanglement of optical beams, as well as further investigations of the power of weak-value amplification for the measurement of small quantities.

The article was published in: Nature Physics 13: 540.

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This work was supported (in part) by the Fetzer Franklin Fund of the John E. Fetzer Memorial Trust.