A Stern–Gerlach experiment for slow light

P. L. Knight

Leon Karpa, Martin Weitz

Electromagnetically induced transparency allows for light transmission through dense atomic media by means of quantum interference of absorption amplitudes. Media exhibiting electromagnetically induced transparency have interesting properties, such as very slow group velocities. Associated with the slow light propagation are quasiparticles, so-called dark polaritons, which are mixtures of a photonic and an atomic contribution. Here, we demonstrate that these excitations behave as particles with a nonzero magnetic moment, which is in clear contrast to the properties of a free photon. It is found that circularily polarized light passing through a rubidium gas cell under the conditions of electromagnetically induced transparency is deflected by a small magnetic field gradient. The deflection angle is proportional to the propagation time of an optical pulse through the cell. The observed beam deflection can be understood by assuming that dark state polaritons have an effective magnetic moment. This is attributed to the spin wave contribution that develops upon entry of light into the medium. Our experiment can be described in terms of a Stern-Gerlach experiment for the dark polaritons.

M. Sağlam, Ziya Saglam

We have calculated the expectation values of the spin and the intrinsic magnetic moment of the gamma photons created as a result of the electron-positron annihilation. We show that, depending on its helicity a gamma photon propagating in z direction with an angular frequency carries a magnetic moment of along the propagation direction. Here the (+) and (-) signs stand for the right hand and left circular helicity respectively. e argue that in a Stern-Gerlach experiment (SGE) the magnetic moment is an important property but not the spin of the particles. Because of these two symmetric values of the magnetic moment, we expect a splitting of the gamma photon beam into two symmetric sub beams in a (SGE). We believe that the present result will be helpful for understanding the recent attempts on the (SGE) with slow light and the behavior of the dark polaritons and also the atomic spinor polaritons.

H. Schmidt‐Böcking, Lothar Ph. H. Schmidt, Hans Jürgen Lüdde +3 more

Joseph March Brom, Frank Rioux

Lecture demonstrations involving polarization of light are presented and discussed from the quantum theoretical point of view. The demonstrations clearly show that only two base states are required to describe the quantum state of a photon and they illustrate an optical analog of the Stern—Gerlach experiment that involved electrons.