* Astronomy

Who knew it would take nearly a century to create the Bohr atom?

The first successful model of the hydrogen atom was proposed by Danish physicist Niels Bohr almost a century ago and comprised an electron in classical circular "planet-like" orbit about the nucleus. With the advent of quantum mechanics it was realised that the position of an electron could not be precisely specified but rather it must be viewed as being distributed within the atom. However, for sufficiently large systems this microscopic quantum world should transition into the macroscopic classical world. Scientists at Rice University have taken advantage of this to produce the closest analogy yet achieved to the Bohr model of the atom. This has been accomplished by manipulating atoms in highly excited Rydberg states using a carefully-tailored series of short electric field pulses. In Rydberg atoms one electron is excited to a high-lying state and is well removed from the nucleus. Indeed, such atoms are the true giants of the atomic world. Those investigated at Rice have diameters approaching a millimetre and, if opaque, would be visible to the naked eye. Starting with laser-excited quasi-one-dimensional Rydberg atoms the researchers have been able using electric field pulses to transfer the electron from its initial highly-elliptical orbit into a near circular orbit while at the same time localizing the electron within this orbit. Measurements show that the electron remains localized for several orbits and behaves much as a classical particle. This creation of the Bohr atom illustrates the power of atomic engineering using pulsed electric fields and has potential applications in studies of classical and quantum chaos, of information storage and processing in atoms, and of ultrafast laser-matter interactions.

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