Ultrafast Gates in Atomic Qubits PFC experimentalists in

Ultrafast Gates in Atomic Qubits PFC experimentalists in the Trapped Ion Quantum Information group have performed a gate that flips the state of a single atomic qubit in less than 50 picoseconds. The time to perform this same operation with continuous wave (CW) lasers, a standard for these types of atomic systems, is typically over 10, 000 times slower. In conventional computers a bit can be in the state 0 or 1, but not both simultaneously. By contrast, a quantum bit, or qubit, can reside in a combination of the two states. Qubits can made from any quantum system having two energy levels. In this experiment, the qubit is a laser cooled, singly ionized Ytterbium atom having two ground state electronic levels labeled [1] and [0], or up and down. The state of this system can be controllably manipulated with lasers or microwave radiation. The researchers drive qubit rotations using a highly energetic single pulse or by optically dividing the pulse into two counterpropagating pulses. The gate, whether performed with CW or pulsed lasers, is a process that requires two photons. Here, the key technology is an ultraviolet laser that emits a pulse of light that is 10 picosecond long every 8 nanoseconds. Within each individual pulse there are photons that have the frequency separation required (12. 6 GHz) to coherently manipulate the qubit. An ion has internal energy levels that can serve as a qubit. The qubit begins in the down state ([0]). By absorbing and emitting photons from a single pulse (shown below) the qubit can be flipped to the up ([1]) state. 12. 6 GHz The pulse can be optically shaped to make any combination or superposition of the two qubit states: [1] and [0]. "Ultrafast Gates for Single Atomic Qubits, " W. C. Campbell, J. Mizrahi, Q. Quraishi, C. Senko, D. Hayes, D. Hucul, D. N. Matsukevich, P. Maunz, and C. Monroe, Phys. Rev. Lett. 105, 090502 (2010).