In order to optimize quantum information processing in individual traps such as optical lattices, we propose a combined atom-molecule system. In particular, gates, initialization, and readout are suggested, using two atoms of different species---one atom carrying the qubit and the other enabling interaction. We describe in some detail the implementation of a two-qubit phase gate in which a pair of atoms is transferred into the ground rovibrational state of a polar molecule with a large dipole moment, thus allowing molecules in adjacent sites to interact via their dipole-dipole interaction. We also discuss how the reverse process could be used as a nondestructive readout tool.
In order to optimize quantum information processing in individual traps such as optical lattices, we propose a combined atom-molecule system. In particular, gates, initialization, and readout are suggested, using two atoms of different species---one atom carrying the qubit and the other enabling interaction. We describe in some detail the implementation of a two-qubit phase gate in which a pair of atoms is transferred into the ground rovibrational state of a polar molecule with a large dipole moment, thus allowing molecules in adjacent sites to interact via their dipole-dipole interaction. We also discuss how the reverse process could be used as a nondestructive readout tool.
We show that an array of polar molecules interacting with Rydberg atoms is a promising hybrid system for scalable quantum computation.Quantum information is stored in long-lived hyperfine or rotational states of molecules, which interact indirectly through resonant dipole-dipole interactions with Rydberg atoms.A two-qubit gate based on this interaction has a duration of 1 μs and an achievable fidelity of 99.9%.The gate has little sensitivity to the motional states of the particles-the molecules can be in thermal states, the atoms do not need to be trapped during Rydberg excitation, the gate does not heat the molecules, and heating of the atoms has a negligible effect.Within a large, static array, the gate can be applied to arbitrary pairs of molecules separated by tens of micrometres, making the scheme highly scalable.The molecule-atom interaction can also be used for rapid qubit initialization and efficient, nondestructive qubit readout, without driving any molecular transitions.Single-qubit gates are driven using microwave pulses alone, exploiting the strong electric dipole transitions between rotational states.Thus, all operations required for large-scale quantum computation can be done without moving the molecules or exciting them out of their ground electronic states.
We analyze a recently proposed physical implementation of a quantum computer based on polar molecules with ``switchable'' dipoles, i.e., dipole moments that can be switched ``on'' and ``off''. Conditional dipole-dipole interaction is an efficient tool for realizing two-qubit quantum gates necessary to construct universal gates. A set of general requirements for a molecular system is presented, which would provide an optimal combination of quantum gate times, coherence times, number of operations, high gate accuracy, and experimental feasibility. We proceed with an analysis of a two-qubit phase gate realization based on switchable dipole-dipole interactions between polar molecules in an optical lattice architecture. We consider one of the schemes proposed in our previous work [Phys. Rev. A 74, 050301(R) (2006)], using specific molecules, such as CO and NF. We suggest suitable electronic states and transitions, and investigate requirements for the laser pulses driving them. Finally, we analyze possible sources of decoherence and list practical difficulties of the scheme.
Arrays of trapped neutral atoms and polar molecules have separately emerged as powerful and complementary platforms for quantum science. Neutral atoms enable fast, programmable interactions through excitation to Rydberg states, whereas polar molecules possess long-lived rotational states that are attractive for quantum memories and qudits. Combining these platforms would create new possibilities, but requires a coherent interface between individual atoms and molecules, which so far has not been realised. Here, we establish such an interface between a single neutral atom and a single polar molecule. By tuning atomic and molecular transitions into resonance, we realise strong state-dependent dipolar interactions at micrometre separations in an optical tweezer platform with single-particle control. We exploit this interface to perform quantum operations between the two particles, demonstrating atom-mediated readout of a molecular qubit, coherent spin exchange, and entanglement using a blockade-based controlled-NOT operation. These results establish a new hybrid quantum platform at the intersection of atomic and molecular physics, in which long-lived molecular quantum information can be rapidly mapped onto an atom for readout or onward coherent transfer. The platform provides a route to hybrid quantum processors utilising atom-mediated readout and entanglement of molecular qubits, mixed-species quantum simulators of dipolar systems, and macroscopic entangled molecular states for quantum-enhanced metrology and precision sensing.
We study the possibility to use interaction between a polar molecule in the ground electronic and vibrational state and a Rydberg atom to construct two-qubit gates between molecular qubits and to coherently control molecular states. A polar molecule within the electron orbit in a Rydberg atom can either shift the Rydberg state, or form a Rydberg molecule. Both the atomic shift and the Rydberg molecule states depend on the initial internal state of the polar molecule, resulting in molecular state dependent van der Waals or dipole-dipole interaction between Rydberg atoms. Rydberg atoms mediated interaction between polar molecules can be enhanced up to 10(3) times. We describe how the coupling between a polar molecule and a Rydberg atom can be applied to coherently control molecular states, and specifically, to individually address molecules in an optical lattice, and to non-destructively readout molecular qubits.
"We analyze recently proposed physical implementations of a quantum computer based on polar molecules with switchable dipoles. Switch- able dipole-dipole interaction is an efficient tool for realization of two-qubit quantum gates, necessary to construct a universal set of gates. We specifically study a phase gate realization based on switchable dipole-dipole interactions between polar molecules in an optical lattice architecture. We consider one possible realization of the phase gate using a specific molecule, such as 13 CO."
Polar molecules, with their rich internal structure, offer immense potential for fundamental physics, quantum technology, and controlled chemistry. However, their utilization is currently limited because of slow and imperfect state detection and weak dipolar interaction, limiting fast and large-scale entanglement generation. We propose and analyze a scheme for quantum logic control and measurement-based state preparation in a hybrid platform of polar molecules and neutral atoms. The method leverages fast, high-fidelity atom-molecule gates and high-fidelity atomic ancilla measurements to overcome the common challenges in molecule-only platforms, while preserving their diverse structural advantages. The proposed atom-molecule controlled-phase gate is based on resonant dipole-dipole exchange between a molecular rotational transition and an atomic Rydberg transition, rendering it three orders of magnitude faster than any direct molecule-molecule entangling gate. We further study several applications of our scheme including the preparation of molecular GHZ states for quantum enhanced precision measurements, the preparation of exotic molecular qudit states with topological order, and measurement-altered criticality. Our scheme is applicable to any polar molecule. It expands the paradigm of quantum logic control and paves the way to large-scale molecular entangled states. More generally, it highlights a concrete hybrid quantum system in which each qubit is utilized in an optimal way and where the measurement-based approach can yield a significant advantage in near-term devices.