Abstract
Proposals for quantum computing using rotational states of polar molecules as qubits have previously considered only diatomic molecules. For these the Stark effect is second-order, so a sizable external electric field is required to produce the requisite dipole moments in the laboratory frame. Here we consider use of polar symmetric top molecules. These offer advantages resulting from a first-order Stark effect, which renders the effective dipole moments nearly independent of the field strength. That permits use of much lower external field strengths for addressing sites. Moreover, for a particular choice of qubits, the electric dipole interactions become isomorphous with NMR systems for which many techniques enhancing logic gate operations have been developed. Also inviting is the wider chemical scope, since many symmetric top organic molecules provide options for auxiliary storage qubits in spin and hyperfine structure or in internal rotation states.
Highlights
In principle, a quantum computer can perform a variety of calculations with exponentially fewer steps than a classical computer.1–6 This prospect has fostered many proposals for means to implement a quantum computer.7–17 Using arrays of trapped ultracold polar molecules is considered a promising approach, since it appears feasible to scale up such systems to obtain large networks of coupled qubits.15–29 Molecules offer a variety of long-lived internal states, often including spin or hyperfine structure as well as rotational states
We examined how the external electric field, integral to current designs for quantum computation with polar molecules, affects both the qubit states and the dipole-dipole interaction
As in other work concerned with entanglement of electric dipoles, we considered diatomic or linear molecules, for which the Stark effect is ordinarily second-order
Summary
A quantum computer can perform a variety of calculations with exponentially fewer steps than a classical computer. This prospect has fostered many proposals for means to implement a quantum computer. Using arrays of trapped ultracold polar molecules is considered a promising approach, since it appears feasible to scale up such systems to obtain large networks of coupled qubits. Molecules offer a variety of long-lived internal states, often including spin or hyperfine structure as well as rotational states. The dipole moments available for polar molecules provide a ready means to address and manipulate qubits encoded in rotational states via interaction with external electric fields as well as photons. Ω shift unambiguously, but in view of line broadening expected with a sizable external field, whether that will be feasible remains an open question.29 This question led us to consider polar symmetric top molecules, for which the Stark effect is first-order in most rotational states. The constancy of the symmetric top effective dipole moments makes entanglement properties of electric dipole interactions isomorphous with those for nuclear magnetic resonance systems This suggests that NMR techniques, extensively developed for quantum computation but limited in application by the small size of nuclear spins and scalability prospects, might find congenial applications with qubit systems composed of polar symmetric top molecules
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