21 research outputs found
Quantum entanglement and information processing via excitons in optically-driven quantum dots
We show how optically-driven coupled quantum dots can be used to prepare
maximally entangled Bell and Greenberger-Horne-Zeilinger states. Manipulation
of the strength and duration of the selective light-pulses needed for producing
these highly entangled states provides us with crucial elements for the
processing of solid-state based quantum information. Theoretical predictions
suggest that several hundred single quantum bit rotations and Controlled-Not
gates could be performed before decoherence of the excitonic states takes
place.Comment: 3 separate PostScript Figures + 7 pages. Typos corrected. Minor
changes added. This updated version is to appear in PR
Physical Optimization of Quantum Error Correction Circuits
Quantum error correcting codes have been developed to protect a quantum
computer from decoherence due to a noisy environment. In this paper, we present
two methods for optimizing the physical implementation of such error correction
schemes. First, we discuss an optimal quantum circuit implementation of the
smallest error-correcting code (the three bit code). Quantum circuits are
physically implemented by serial pulses, i.e. by switching on and off external
parameters in the Hamiltonian one after another. In contrast to this, we
introduce a new parallel switching method that allows faster gate operation by
switching all external parameters simultaneously. These two methods are applied
to electron spins in coupled quantum dots subject to a Heisenberg coupling
H=J(t) S_1*S_2 which can generate the universal quantum gate
`square-root-of-swap'. Using parallel pulses, the encoding for three-bit
quantum error correction in a Heisenberg system can be accelerated by a factor
of about two. We point out that parallel switching has potential applications
for arbitrary quantum computer architectures.Comment: 13 pages, 6 figure
Experimental Implementation of the Quantum Random-Walk Algorithm
The quantum random walk is a possible approach to construct new quantum
algorithms. Several groups have investigated the quantum random walk and
experimental schemes were proposed. In this paper we present the experimental
implementation of the quantum random walk algorithm on a nuclear magnetic
resonance quantum computer. We observe that the quantum walk is in sharp
contrast to its classical counterpart. In particular, the properties of the
quantum walk strongly depends on the quantum entanglement.Comment: 5 pages, 4 figures, published versio