"Coupled quantized harmonic oscillators" by Kenton Brown

In theory, quantum computers can solve certain problems much more efficiently than classical computers. This possibility has motivated experimental efforts to construct devices that manipulate quantum bits (qubits) in a variety of physical systems. One such system is composed of atomic ions confined by electric fields in a rf Paul trap. The motions of such ions can be modeled to a very good approximation as harmonic oscillators, and with suitable laser cooling techniques they can be cooled to the harmonic oscillator ground state. When trapped within the same potential minimum, ions interact strongly via the Coulomb force, thereby enabling multiple-qubit quantum gates that are routinely used in ion trap quantum information experiments. However, a similar interaction between ions held in separate trapping potentials (where the force is much weaker) has not been observed until now. I will discuss an experiment demonstrating coupling, at the quantum level, between two ions trapped in separate potential minima. The ions are confined to independent regions above a microfabricated, surface-electrode trap held at 4.2 K by a helium bath cryostat. This represents the first observation of coupling between quantized harmonic oscillators held in separate locations. Such an interaction may prove useful for quantum information processing, simulations, and metrology. The experiment also represents a first step toward hybrid quantum systems, such as coupling a trapped ion to a quantized mechanical oscillator. If time permits, I will also present very recent results verifying the exquisite level of control we have over single-qubit gates in this system.