Direct observation of a single proton in a Penning trap

Experiments are performed on a single proton stored in§ a Penning trap aiming at the determination of the g-factor.§ The eigenmotion of an isolated, free proton could be detected§ electronically via coupling to a resonance circuit, which§ represents a non-destructive measurement. The free cyclotron§ frequency emerging from the measured eigenfre-quencies is one§ of two frequencies required for a direct determination of the§ magnetic moment. Design, developing, and commissioning of the§ experimental setup have been accomplished leading to a§ measuring accuracy of 10-7. The technical challenges for the§ determination of the second (Larmor) frequency arising from§ the smallness of the magnetic moment were mastered. Since the§ spin state required for this measurement is an internal§ degree of freedom, it can only be accessed through a coupling§ of the magnetic moment to the eigenmotion. A novel, hybrid§ Penning trap is presented, which im-prints the spin§ information onto the eigenmotion, thus, realizing a quantum§ jump spectrometer. Therewith, the frequency shift of the two§ spin states resulting from the magnetic coupling reaches for§ the first time an electronically detectable range.