Entanglement of polar molecules in pendular states
Abstract
In proposals for quantum computers using arrays of trapped ultracold polar molecules as qubits, a strong external field with appreciable gradient is imposed in order to prevent quenching of the dipole moments by rotation and to distinguish among the qubit sites. That field induces the molecular dipoles to undergo pendular oscillations, which markedly affect the qubit states and the dipoledipole interaction. We evaluate entanglement of the pendular qubit states for two linear dipoles, characterized by pairwise concurrence, as a function of the molecular dipole moment and rotational constant, strengths of the external field and the dipoledipole coupling, and ambient temperature. We also evaluate a key frequency shift, △ω, produced by the dipoledipole interaction. Under conditions envisioned for the proposed quantum computers, both the concurrence and △ω become very small for the ground eigenstate. In principle, such weak entanglement can be sufficient for operation of logic gates, provided the resolution is high enough to detect the △ω shift unambiguously. In practice, however, for many candidate polar molecules it appears a challenging task to attain adequate resolution. Simple approximate formulas fitted to our numerical results are provided from which the concurrence and △ω shift can be obtained in terms of unitless reduced variables.
 Publication:

Journal of Chemical Physics
 Pub Date:
 March 2011
 DOI:
 10.1063/1.3567486
 arXiv:
 arXiv:1102.5772
 Bibcode:
 2011JChPh.134l4107W
 Keywords:

 molecular moments;
 quantum entanglement;
 quantum gates;
 rotational states;
 03.67.Lx;
 03.67.Mn;
 33.15.Kr;
 33.15.Mt;
 03.67.Bg;
 Quantum computation;
 Entanglement production characterization and manipulation;
 Electric and magnetic moments polarizability and magnetic susceptibility;
 Rotation vibration and vibrationrotation constants;
 Entanglement production and manipulation;
 Quantum Physics
 EPrint:
 Will be available in Journal of chemical physics