NIST demonstrates quantum-mechanically-entangled, spin-squeezed states. (News Briefs).

By applying coherent laser beams to trapped ions, NIST staff in Boulder have generated quantum-mechanically-entangled, spin-squeezed states, and, for the first time, shown that such states can be used to increase measurement precision beyond that which is possible without the use of entanglement. The results of these studies have recently been reported in Physical Review Letters. As a demonstration, the NIST researchers produced spin-squeezed states of two beryllium atomic ions and showed that when the spins are rotated in a magnetic field, the uncertainty in determining the rotation angle is smaller than can possibly be obtained if the atoms are not entangled. Such techniques are an integral part of the emerging fields of quantum logic and quantum information, but can also be used to improve sensitivity in spectroscopy and reduce noise in atomic clocks.

Although spectroscopic precision can be improved without the need for entanglement by increasing the number of atoms observed, in atomic clocks based on ions, however, the quest for accuracy requires the use of only a small number of ions. With a potential relative uncertainty of [10.sup.-18], these techniques should find application in the development of new optical ion clocks. CONTACT: Dave Wineland, [phone]; [e-mail].