Spin Quantum Computer Research Articles

All-optical electron spin quantum computer with ancilla bits for operations in each coupled-dot cell

A quantum cellular network with a qubit and ancilla bits in each cell is proposed. The whole circuit works only with the help of external optical pulse sequences. In the operation, some of the ancilla bits are activated, and autonomous single- and two-qubit operations are made. In the sleep mode of a cell, the decoherence of the qubit is negligibly small. Since only two cells at most are active at once, the coherence can be maintained for a sufficiently long time for practical purposes. A device structure using a quantum dot array with possible operation and measurement schemes is also proposed.

An insider's guide to quantum causal histories

A review is given of recent work aimed at constructing a quantum theory of cosmology in which all observables refer to information measurable by observers inside the universe. At the classical level the algebra of observables should be modified to take into account the fact that observers can only give truth values to observables that have to do with their backwards light cone. The resulting algebra is a Heyting rather than a Boolean algebra. The complement is non-trivial and contains information about horizons and topology change. Representation of such observables quantum mechanically requires a many-Hilbert space formalism, in which different observers make measurements in different Hilbert spaces. I describe such a formalism, called “quantum causal histories”; examples include causally evolving spin networks and quantum computers.

Nonresonant effects in the implementation of the quantum Shor algorithm

We simulate Shor's algorithm using the Ising spin quantum computer. The influence of nonresonant effects is analyzed in detail. It is shown that the method developed earlier in our papers successfully suppresses nonresonant effects even for relatively large values of the Rabi frequency.

Solid-state quantum computation—a new direction for nanotechnology

We review current proposals for six types of solid-state quantum computers. We discuss the general requirements for solid-state quantum computers and describe proposals which employ superconducting junctions, electron orbitals in quantum dots, electron spin resonance, nuclear spins of impurity atoms, and nuclear spins in a crystal lattice. We also describe our proposed nuclear spin quantum computer based on magnetic resonance force microscopy. Finally, we describe our numerical method for modeling quantum transformations with a large number (up to 1000) of qubits.

Theory of spin coherence in semiconductor heterostructures

Consideration of the spin degrees of freedom of the carriers in semiconductor heterostructures creates interesting possibilities for spin optoelectronics, magnetoelectronics and quantum computing. This theory paper attempts to explain in simple terms the concepts of optical and spin coherence, how they can be observed, simple deductions of the spin dynamics in magnetic fields, exciton interaction effects, exciton exchange effects and the spin transport across semiconductor–metal interface.

A silicon-based nuclear spin quantum computer

Quantum computers promise to exceed the computational efficiency of ordinary classical machines because quantum algorithms allow the execution of certain tasks in fewer steps. But practical implementation of these machines poses a formidable challenge. Here I present a scheme for implementing a quantum-mechanical computer. Information is encoded onto the nuclear spins of donor atoms in doped silicon electronic devices. Logical operations on individual spins are performed using externally applied electric fields, and spin measurements are made using currents of spin-polarized electrons. The realization of such a computer is dependent on future refinements of conventional silicon electronics.

Error correction for a spin quantum computer

The problems of error correction in a spin quantum computer are discussed. For digital processing in the Ising and Heisenberg chains driven by a resonant electromagnetic field, the simple schemes are suggested which provide correction of errors caused by imperfect \ensuremath{\pi} pulses, and prevent the most significant errors caused by the nonresonant action of \ensuremath{\pi} pulses. The probability of error caused by the Heisenberg interaction during the action of \ensuremath{\pi} pulses is estimated. For quantum computations in spin systems a principal opportunity to correct the phase errors, based on Steane's three quantum-bits scheme, is described.