Population Redistribution of Rydberg Atoms
Rydberg atoms (atoms with highly excited valence electrons or equivalently atoms whose outer electrons have extremely large orbits on the order of the size of a human hair) are currently being studied extensively in the context of quantum computing as well as an intermediary in the production of ground state anti-hydrogen for a precision comparison with hydrogen as a test of fundamental physics [Ref. 1]. In both of these contexts, control over the internal states of the Rydberg atom are essential. Typical atomic physics techniques involve the use of lasers and microwaves to control the time evolution of atoms. However Rydberg atoms can be in thousands of different states each requiring a laser with a slightly different frequency for control. This is clearly infeasible in most experiments and thus a different technique is required to allow for control of these atoms.
Up to 10% of the initial Rydberg atom population is transferred to a less excited state
Half-cycle pulses are ideal for controlling internal atomic states in a state independent manner. Their short temporal length relative to the orbit period of an electron in a Rydberg orbital (approximately 20 ps for principle quantum numbers around 50) allows them to effectively "kick" the electron transferring or removing momentum from it and thus changing its quantum state. This is a non-resonant interaction with the primary requirement being the length of the pulse is much shorter than the orbital period and thus works for any states with principal quantum number greater than about 30. Theoretical calculations have suggested that their is a slight preference towards de-excitation for most atomic states but by changing the pulse timing one can specifically choose to excite or de-excite atoms [Ref. 2].
Our lab has shown that it is possible to drive over 10% of an initial population of atoms in a state with principle quantum number of 40 down to a state with quantum number less than 34. This corresponds to a factor of 2 reduction in radiative lifetime of these atoms which if applied to anti-hydrogen atoms could dramatically increase the number of atoms being trapped in the ground state prior to hitting a trap wall and annihilating.
Rubidium atoms are trapped, excited to a Rydberg level, exposed to half-cycle pulses, and then the resulting population changes are detected within the vacuum system shown above.
References
- G. Gabrielse et al., Phys. Rev. Lett. 89, 233401 (2002)
- S. X. Hu and L. A. Collins, Phys. Rev. A 69, 041402 (2004) and T. Kopyciuk and R. Parzynski, Phys. Rev. A 75, 055402 (2007)
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