105,188 research outputs found
Universal quantum computation with electronic qubits in decoherence-free subspace
We investigate how to carry out universal quantum computation
deterministically with free electrons in decoherence-free subspace by using
polarizing beam splitters, charge detectors, and single-spin rotations. Quantum
information in our case is encoded in spin degrees of freedom of the
electron-pairs which construct a decoherence-free subspace. We design building
blocks for two noncommutable single-logic-qubit gates and a logic controlled
phase gate, based on which a universal and scalable quantum information
processing robust to dephasing is available in a deterministic way.Comment: 14 pages, 3 figure
Simple Realization Of The Fredkin Gate Using A Series Of Two-body Operators
The Fredkin three-bit gate is universal for computational logic, and is
reversible. Classically, it is impossible to do universal computation using
reversible two-bit gates only. Here we construct the Fredkin gate using a
combination of six two-body reversible (quantum) operators.Comment: Revtex 3.0, 7 pages, 3 figures appended at the end, please refer to
the comment lines at the beginning of the manuscript for reasons of
replacemen
Universal Fault-Tolerant Computation on Decoherence-Free Subspaces
A general scheme to perform universal quantum computation within
decoherence-free subspaces (DFSs) of a system's Hilbert space is presented.
This scheme leads to the first fault-tolerant realization of universal quantum
computation on DFSs with the properties that (i) only one- and two-qubit
interactions are required, and (ii) the system remains within the DFS
throughout the entire implementation of a quantum gate. We show explicitly how
to perform universal computation on clusters of the four-qubit DFS encoding one
logical qubit each under "collective decoherence" (qubit-permutation-invariant
system-bath coupling). Our results have immediate relevance to a number of
solid-state quantum computer implementations, in particular those in which
quantum logic is implemented through exchange interactions, such as the
recently proposed spin-spin coupled GaAs quantum dot arrays and the Si:P
nuclear spin arrays.Comment: 5 pages, no figures. Many small changes and clarifications. Expanded
discussion of relevance to solid-state implementations. This version to
appear in Phys. Rev. Let
Randomized benchmarking in measurement-based quantum computing
Randomized benchmarking is routinely used as an efficient method for
characterizing the performance of sets of elementary logic gates in small
quantum devices. In the measurement-based model of quantum computation, logic
gates are implemented via single-site measurements on a fixed universal
resource state. Here we adapt the randomized benchmarking protocol for a single
qubit to a linear cluster state computation, which provides partial, yet
efficient characterization of the noise associated with the target gate set.
Applying randomized benchmarking to measurement-based quantum computation
exhibits an interesting interplay between the inherent randomness associated
with logic gates in the measurement-based model and the random gate sequences
used in benchmarking. We consider two different approaches: the first makes use
of the standard single-qubit Clifford group, while the second uses recently
introduced (non-Clifford) measurement-based 2-designs, which harness inherent
randomness to implement gate sequences.Comment: 10 pages, 4 figures, comments welcome; v2 published versio
Robust Ising Gates for Practical Quantum Computation
I describe the use of techniques based on composite rotations to combat
systematic errors in controlled phase gates, which form the basis of two qubit
quantum logic gates. Although developed and described within the context of
Nuclear Magnetic Resonanace (NMR) quantum computing these sequences should be
applicable to any implementation of quantum computation based on Ising
couplings. In combination with existing single qubit gates this provides a
universal set of robust quantum logic gates.Comment: 3 Pages RevTex4 including 2 figures. Will submit to PR
A Theory of Computation Based on Quantum Logic (I)
The (meta)logic underlying classical theory of computation is Boolean
(two-valued) logic. Quantum logic was proposed by Birkhoff and von Neumann as a
logic of quantum mechanics more than sixty years ago. The major difference
between Boolean logic and quantum logic is that the latter does not enjoy
distributivity in general. The rapid development of quantum computation in
recent years stimulates us to establish a theory of computation based on
quantum logic. The present paper is the first step toward such a new theory and
it focuses on the simplest models of computation, namely finite automata. It is
found that the universal validity of many properties of automata depend heavily
upon the distributivity of the underlying logic. This indicates that these
properties does not universally hold in the realm of quantum logic. On the
other hand, we show that a local validity of them can be recovered by imposing
a certain commutativity to the (atomic) statements about the automata under
consideration. This reveals an essential difference between the classical
theory of computation and the computation theory based on quantum logic
Quantum Computation with Diatomic Bits in Optical Lattices
We propose a scheme for scalable and universal quantum computation using
diatomic bits with conditional dipole-dipole interaction, trapped within an
optical lattice. The qubit states are encoded by the scattering state and the
bound heteronuclear molecular state of two ultracold atoms per site. The
conditional dipole-dipole interaction appears between neighboring bits when
they both occupy the molecular state. The realization of a universal set of
quantum logic gates, which is composed of single-bit operations and a two-bit
controlled-NOT gate, is presented. The readout method is also discussed.Comment: 5 pages, 1 eps figure, accepted for publication in Phys. Rev.
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