F. Yamaguchi

All-Silicon Quantum Computer

A solid-state implementation of a quantum computer composed entirely of silicon is proposed. Qubits are 29Si nuclear spins arranged as chains in a 28Si (spin-0) matrix with Larmor frequencies separated by a large magnetic field gradient. No impurity dopants or electrical contacts are needed. Initialization is accomplished by optical pumping, algorithmic cooling, and pseudo-pure state techniques. Magnetic resonance force microscopy is used for ensemble measurement.

Hybrid quantum repeater using bright coherent light.

We describe a quantum repeater protocol for long-distance quantum communication. In this scheme, entanglement is created between qubits at intermediate stations of the channel by using a weak dispersive light-matter interaction and distributing the outgoing bright coherent-light pulses among the stations. Noisy entangled pairs of electronic spin are then prepared with high success probability via homodyne detection and postselection. The local gates for entanglement purification and swapping are deterministic and measurement-free, based upon the same coherent-light resources and weak interactions as for the initial entanglement distribution. Finally, the entanglement is stored in a nuclear-spin-based quantum memory. With our system, qubit-communication rates approaching 100 Hz over 1280 km with fidelities near 99% are possible for reasonable local gate errors.

Efficient implementation of selective recoupling in heteronuclear spin systems using hadamard matrices

We present an efficient scheme which couples any designated pair of spins in heteronuclear spin systems. The scheme is based on the existence of Hadamard matrices. For a system of

Electron entanglement via a quantum dot.

n

Crystal lattice quantum computer

spins with pairwise coupling, the scheme concatenates

Quantum search with two-atom collisions in cavity QED

cn

Quantum error correction via robust probe modes

intervals of system evolution and uses at most

Even-odd conductance oscillation in atomic wires

c n^2

Efficiency of free-energy calculations of spin lattices by spectral quantum algorithms

pulses where

Decoherence in crystal lattice quantum computation

c \approx 1