Strong optomechanical coupling at room temperature by coherent scattering

Quantum control of a system requires the manipulation of quantum states faster than any decoherence rate. For mesoscopic systems, this has so far only been reached by few cryogenic systems. An important milestone towards quantum control is the so-called strong coupling regime, which in cavity optomechanics corresponds to an optomechanical coupling strength larger than cavity decay rate and mechanical damping. Here, we demonstrate the strong coupling regime at room temperature between a levitated silica particle and a high finesse optical cavity. Normal mode splitting is achieved by employing coherent scattering, instead of directly driving the cavity. The coupling strength achieved here approaches three times the cavity linewidth, crossing deep into the strong coupling regime. Entering the strong coupling regime is an essential step towards quantum control with mesoscopic objects at room temperature.

Generation of W states via Lyapunov control by combination of quantum Zeno dynamics

We propose a scheme to create a 4-atom W state by Lyapunov control with the help of quantum Zeno effect. The effective Hamiltonian to describe quantum Zeno dynamics can be obtained in an invariant Zeno subspace and the 4-atom W state can be achieved through modulating the system parameters. Numerical simulation shows that the present scheme is robust against both cavity decay and the atom spontaneous emission. Furthermore, we present a proposal for W state conversion by the same principle, which provides theoretically a novel way for multi-qubits entanglement preparation.

Implementation of a quantum $\sqrt{\rm_{swap}}$ gate for two distant atoms trapped in separate cavities

We present a scheme to implement a quantum [Formula: see text] gate for two-atom trapped in distant cavities connected via an optical fiber. In the whole process, the atomic system, the cavity modes and the fiber are not excited ensuring that the operation is insensitive to atomic spontaneous emission, cavity decay and the fiber loss. This scheme is significant for distributed and scalable quantum computation.

Unconventional geometric phase gates for two distant atoms trapped in spatially separate cavities

In this paper, we propose a scheme for implementing an unconventional two-qubit geometric phase gate for two distant atoms trapped in cavities connected by an optical fiber. During the gate operation, the atoms are still in the ground states, while the cavity modes and fiber mode are displaced along a circle in the phase space. In this way, the system can acquire different geometric phases conditional upon the atomic states. We find that the operation of the geometric phase gate can be speeded up as the detuning between the cavity field and light fields decreases. Moreover, it is observed that the fidelity for the geometric phase gate is remarkably insensitive to the fluctuation of the detuning parameter. The effects of cavity decay and fiber loss on the gate have also been checked.

One-step implementation of the Fredkin gate via quantum Zeno dynamics

We study one-step implementation of the Fredkin gate in a bi-modal cavity under both resonant and large detuning conditions based on quantum Zeno dynamics, which reduces the complexity of experiment operations. The influence of cavity decay and atomic spontaneous emission is discussed by numerical calculation. The results demonstrate that the fidelity and the success probability are robust against cavity decay in both models and they are also insensitive to atomic spontaneous emission in the large detuning model. In addition, the interaction time is rather short in the resonant model compared to the large detuning model.