The desired interference required for quantum computing may be modified by wave-function oscillations for the implementation of quantum algorithms [Phys. Rev. Lett. 84, 1615 (2000)]. To diminish such a detrimental effect, we propose a scheme with trapped ion pairs as qubits and apply the scheme to the Grover search. It will be shown that our scheme cannot only carry out a full Grover search, but can also meet the requirement for scalable hot-ion quantum computing. Moreover, the ion-pair qubits in our scheme are more robust against decoherence and the dissipation caused by the environment than single-particle qubits proposed before.
The superpositional wave function oscillations for finite-time implementation of quantum algorithms modifies the desired interference required for quantum computing. We propose a scheme with trapped ultracold ion-pairs being qubits to diminish the detrimental effect of the wave function oscillations, and apply the scheme to the two-qubit Grover's search. It can be also found that the qubits in our scheme are more robust against the decoherence caused by the environment, and the model is scalable.
Over the past decade, the field of trapped ion quantum computing has emerged as one of the leaders in quantum information processing due the level of manipulation available and the long coherence times possible in the system. As this thesis will demonstrate, all of the necessary building blocks for a quantum computer have been exhibited in ion traps and small scale quantum algorithms have been implemented. In this trapped ion system, quantum bits consist of the first order magnetic field insensitive ground state hyperfine levels of
111Cd
+. The qubits are manipulated via resonant and off-resonant coherent laser interactions. We experimentally realize Grover's quantum search algorithm over a 4 element database with n=2 trapped
111Cd
+ ion qubits. One of the four states is marked, and with a single query it is recovered, on average, with 60% probability. This exceeds the performance of any possible classical search, which can only succeed with 50% probability following a single query. The algorithm consists of two Molmer-Sorensen entangling gates, that utilize bichromatic stimulated Raman transitions to create a spin dependent force, paired with several single-qubit rotations and near-perfect qubit measurements. The spectral arrangement of the Raman beams is tailored to suppress phase noise accumulation between gates. This suppression is critical for reliably performing consecutive operations during the algorithm. Additionally, this thesis discusses the possibility of combining trapped ions with trapped neutral atoms for the purpose studying ultra-cold charge exchange interactions. It may be possible to conceal quantum information, initially prepared in an ionic qubit, inside a pure nuclear spin qubit for the purpose of transportation and storage. As a first step, we present the laser-cooling and confinement of Cd atoms in a magneto-optical trap, and characterize the loading process from the background Cd vapor. The trapping laser drives the
1S0~
rightarrow~
1P1 transition at 229 nm in this two valence electron atom and also photoionizes atoms directly from the
1P1 state. This photoionization dominates other loss mechanisms and allows a direct measurement of the photoionization cross section.