Observation of a Topological and Parity-dependent Phase of m=0 Spin States – Niels Bohr Institute - University of Copenhagen

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Niels Bohr Institute > Calendar > 2007 > Observation of a Topol...

Observation of a Topological and Parity-dependent Phase of m=0 Spin States

One of the most astonishing prediction of quantum mechanics is the
pi-phase shift of spin-1/2 particles by 2pi rotations. The phase shift 
can be interpreted by the double-valuedness of the spinor wave function 
under three-dimensional rotations.
 In this talk, we report on an experiment on the non-trivial pi-phase 
shift of a seemingly trivial integer spin. Here, a Ramsey interrogation 
scheme was used to measure the phase shift of laser-cooled 87^Rb 
clock-transition pseudospins arising as a result of a reversal of a bias 
magnetic field during the interrogation. While no phase shift occurred 
when the reversal was sudden, the Ramsey fringes were shifted by a 
factor of pi when the reversal was adiabatic. We thus verified the 
prediction that the spin states |F,m=0> acquire a purely topological and 
parity-dependent phase factor of (-1)^{F} as a result of the reversal of 
the bias magnetic field.