Abstract
We present a systematic approach to implementation of basic quantum logic gates operating on polar molecules in pendular states as qubits for a quantum computer. A static electric field prevents quenching of the dipole moments by rotation, thereby creating the pendular states; also, the field gradient enables distinguishing among qubit sites. Multi-target optimal control theory is used as a means of optimizing the initial-to-target transition probability via a laser field. We give detailed calculations for the SrO molecule, a favorite candidate for proposed quantum computers. Our simulation results indicate that NOT, Hadamard and CNOT gates can be realized with high fidelity, as high as 0.985, for such pendular qubit states.
Highlights
Quantum computers take direct advantage of superposition and entanglement to perform computations
We focused on entanglement and on consequences of using a strong external electric field with appreciable gradient, required to prevent quenching of the dipole moments by rotation and to enable addressing individual qubit sites
Under conditions deemed amenable for proposed quantum computers, we found that both the concurrence and a key frequency shift, ω, that has a major role in logic gates, become very small for the ground eigenstate
Summary
Quantum computers take direct advantage of superposition and entanglement to perform computations. DeMille has detailed a prototype design for quantum computation using ultracold polar molecules, trapped in a one-dimensional optical lattice, partially oriented in an external electric field, and coupled by the dipole-dipole interaction. This offers a promising platform for quantum computing because scale-up appears feasible to obtain large networks of coupled qubits.. We apply the multi-target optical control theory (MTOCT) to design laser pulses that enable resolving and inducing transitions between specified states of the qubit system This approach has been previously employed to study optimal control for elements of quantum computation in molecular systems, using as qubits vibrational or rotational states.. III, we present simulation results using MTOCT to obtain optimized laser pulses for realizing NOT, Hadamard, and CNOT logic gates; those gates with the addition of the phase gate π /8 provide the basis for universal quantum computation. Section IV discusses strategies to contend with cases in which the ω shift is zero or becomes too small to resolve
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