Generation of Dicke States with Phonon-Mediated Multi-level Stimulated Raman Adiabatic Passage

We generate half-excited symmetric Dicke states of two and four ions. We use multi-level stimulated Raman adiabatic passage (STIRAP) whose intermediate states are phonon Fock states. This process corresponds to the spin squeezing operation and half-excited Dicke states are generated during multi-level STIRAP. This method does not require local access for each ion or the preparation of phonon Fock states. Furthermore, it is robust since it is an adiabatic process. We evaluate the Dicke state using a witness operator and determine the upper and lower bounds of the fidelity without using full quantum tomography.Comment: 5pages, 4 figure

Quantum State Engineering using Single Nuclear Spin Qubit of Optically Manipulated Ytterbium Atom

A single Yb atom is loaded into a high-finesse optical cavity with a moving lattice, and its nuclear spin state is manipulated using a nuclear magnetic resonance technique. A highly reliable quantum state control with fidelity and purity greater than 0.98 and 0.96, respectively, is confirmed by the full quantum state tomography; a projective measurement with high speed (500us) and high efficiency (0.98) is accomplished using the cavity QED technique. Because a hyperfine coupling is induced only when the projective measurement is operational, the long coherence times (T_1 = 0.49 s and T_2 = 0.10 s) are maintained. Our technique can be applied for implementing a scalable one-way quantum computation with a cluster state in an optical lattice.Comment: 4 figure

Generation of a decoherence-free entangled state using a radio frequency dressed state

We propose the generation of entangled states with trapped calcium ions using a combination of an rf dressed state and a spin dependent force. Using this method, a decoherence-free entangled state of rf qubits can be directly generated and ideally its fidelity is close to unity. We demonstrate an rf entangled state with a fidelity of 0.68, which has a coherence time of more than 200 ms by virtue of the fact that it is an eigenstate with energy gaps between adjacent levels.Using the same technique, we also produce a qutrit-qutrit entangled state with a fidelity of 0.77, which exceeds the threshold value for separability of 2/3.Comment: 4 figure

Quantum magnonics: magnon meets superconducting qubit

The techniques of microwave quantum optics are applied to collective spin excitations in a macroscopic sphere of ferromagnetic insulator. We demonstrate, in the single-magnon limit, strong coupling between a magnetostatic mode in the sphere and a microwave cavity mode. Moreover, we introduce a superconducting qubit in the cavity and couple the qubit with the magnon excitation via the virtual photon excitation. We observe the magnon-vacuum-induced Rabi splitting. The hybrid quantum system enables generation and characterization of non-classical quantum states of magnons.Comment: 10 pages, 6 figure