Furthermore, investigators can expand the quantum gate operations to large numbers of qubits by connecting additional ion emitters by optical fiber and repeating the procedure until more entangled links are established. It should also be possible to use both photon coupling and the motional coupling discussed earlier to connect several small clusters of trapped ions over remote or even global distances. This is exactly the idea behind a “quantum repeater,” in which small quantum computers are networked at periodic distances to maintain a qubit as it travels over hundreds of kilometers. Without such a system the data would usually be lost forever.
The Quantum Future
Scientists are still far from constructing a quantum computer that can take on the daunting challenges—such as factoring very large numbers—that have stymied conventional machines. Still, some features of quantum information processing are already finding uses in the real world. For example, several of the simple logic operations required for two-qubit gates can be employed in atomic clocks, which keep time based on the frequency of the radiation emitted when atoms transition between quantum states. And researchers can apply the techniques for entangling trapped ions to increase the sensitivity of measurements in spectroscopy, the analysis of the light emitted by excited atoms.
The field of quantum information science promises to radically change the rules of computing. Collections of trapped ions are at the forefront of this effort because they offer a level of isolation from the environment that is currently unmatched in most other physical systems. At the same time, through the use of lasers, researchers can readily prepare and measure entangled quantum superpositions devised with small numbers of ions. In the coming years, we look forward to a new generation of trapped-ion chips that may pave the way for quantum computers with much larger numbers of qubits. Then scientists may finally realize their dream of creating a quantum machine that can tackle Herculean tasks once thought to be impossible.